Abstract. 2010 Report Weed Research in Mint Principal Researchers. Rick Boydston, Weed Scientist, USDA-ARS, Prosser, WA Ray Baker, Research Technologist III, Washington State University, Prosser, WA Statement of purpose. This research develops new knowledge on weed control methods in peppermint and spearmint, including information on the selectivity and efficacy of new herbicides and how to integrate these herbicides into weed management programs for mint. Summary of objectives. 1. Identify and evaluate new herbicides for use in mint crops including dormant herbicide applications and broadleaf weed control in double cut mint. 2. Evaluate the effect of deficit irrigation on herbicide performance and weed seed longevity in soil in peppermint. 3. Determine the extent of herbicide resistant weeds in mint and determine their response to mint herbicides. Actions taken. 1. A field trial was conducted to determine response of native spearmint to five dormant applied preemergence herbicides. Two field trials were conducted in peppermint and native spearmint to determine response of pigweed and mint to herbicides applied soon after the first cutting. A field trial was conducted to determine the response of peppermint to aminocyclopyrachlor applied to dormant peppermint. 2. Three herbicides were evaluated and weed seed packets placed and recovered in line source deficit irrigation field trials in peppermint. 3. Growers, dealers, and chemical industry reps were contacted to determine mint fields with herbicide resistant weeds. Weed seed of eight weed species was collected from over 40 fields throughout Washington State. Results. 1. Indaziflam and pyroxasulfone caused minor injury when applied to dormant mint. Saflufenacil injured mint slightly more, but mint regrew normally. Weed control varied among herbicides. Sulfentrazone controlled redroot pigweed in the regrowth of double cut mint when applied after the first harvest and without injuring mint. Aminocyclopyrachlor applied alone in tank mix combinations at two doses in fall and spring to dormant peppermint killed peppermint. 2. Terbacil and flumioxazin controlled grass weeds best over all irrigation levels in peppermint. Flumioxazin controlled broadleaf weeds the most consistently. Irrigation level had little impact on longevity of weed seed in the soil. 3. Weed seed will be cleaned and tested for resistance to common mint herbicides in greenhouse dose response trials.
2010 Mint Weed Research Report Rick Boydston, USDA-ARS, Weed Scientist, Prosser, WA. Ray Baker, Washington State University, Res. Tech. III, Prosser, WA. Statement of Research. Weeds lower mint oil yield and quality and controlling weeds is a major production cost for growers. The goal of this research is to develop improved weed control methods in spearmint and peppermint and to identify promising new herbicides for use in mint production. Ongoing research will lead to development of new weed control techniques and contribute to the registration of new herbicides in mint that will improve weed control, decrease crop injury, decrease cost of production, decrease harm to the environment, and slow the development of herbicide resistant weeds. Few researchers in the United States conduct studies on weed control in spearmint and peppermint and this research will significantly add to the current body of knowledge on control of weeds in mint. This research has increased our knowledge of peppermint, spearmint, and weed response to various herbicides. The research identified several control options for broadleaf weed control in double cut mint that often escape current standard herbicide treatments and identified three new herbicides that may be useful for weed control in mint. Materials and Methods. Most field trials were conducted at the Prosser Irrigated Agriculture Research and Extension Center (IAREC) on a Warden sandy loam soil (1% O.M., ph 7.9) (peppermint) or Warden silt loam soil (1.2% O.M., ph 6.6) (native spearmint) and were sprinkler irrigated. Trials were randomized complete block (RCB) designs with treatments replicated 3 or 4 times. In most instances plot size was 10 by 20 feet. All herbicides were applied in 25 gpa water volume with a bike CO 2 sprayer equipped with six, 8002XR flat fan nozzles. Peppermint and spearmint response to herbicides was visually estimated and recorded at various times throughout the growing season. Weed control was visually estimated in most trials when weed infestations were great enough and uniform enough to adequately evaluate. Weed density was also determined in some trials by counting weeds in a known area within each plot. In trials that mint hay and oil yield were determined, a 40 inch by 20-foot swath of mint was cut using a sickle bar mower. Mint fresh hay was weighed, and three 7 lb subsamples were taken from each plot and air dried in burlap bags. Oil was steam-distilled from air-dried hay using the standardized mini-stills at IAREC. Research Project Goals and Objectives 1. Identify and evaluate new herbicides for use in mint crops including dormant herbicide applications and broadleaf weed control in double cut mint. 2. Evaluate the effect of deficit irrigation on herbicide performance and weed seed longevity in soil in peppermint. 3. Determine the extent of herbicide resistant weeds in mint and determine their response to mint herbicides.
1. Identify and evaluate new herbicides that control weeds selectively in spearmint and peppermint. Trial 1. Three experimental herbicides were tested in native spearmint. Herbicides were applied February 25, 2010, with a CO 2 bike sprayer delivering 25 gpa. Treatments were replicated four times in a randomized complete block design. Treatments included KIH- 485 (pyroxasulfone) at 0.19 lb ai/a, indaziflam at 0.0652 lb ai/a, and saflufenacil at 0.044 lb ai/a. Indaziflam is a new herbicide from Bayer being registered on turf, tree, and vine crops. Saflufenacil, a BASF product, is labeled in corn and expanding labels in other crops. Pyroxasulfone is an experimental herbicide that controls a similar weed spectrum as Outlook (dimethenamid-p) and Dual Magnum (s-metolachlor) herbicides. Control treatments of labeled herbicides, Goal (oxyfluorfen) at 0.38 lb ai/a and Sinbar (terbacil) at 0.5 lb ai/a, were also included. Crop injury was visually rated in early April and May and weed control was rated May 11, 2010. Native spearmint was harvested July 6, 2010 with a sickle bar mower (40 inch swath) and hay was weighed. A 21 subsample of hay was dried and steam distilled using the standardized mini-stills at IAREC, Prosser. Saflufenacil (BAS800) controlled kochia 93%, but did not control tall hedge mustard and annual grasses well (Table 1). Injury to native spearmint with saflufenacil was variable in 2010 trial and averaged 33% on May 12, 2010 (Table 1). Only minor peppermint and native spearmint injury was observed in 2009 studies. Hay and oil yields were extremely variable and not statistically different among herbicide treatments, but saflufenacil plots tended to average lower hay and oil yield (Table 2). Low oil yields in saflufenacil plots may partially be attributed to poor control of tall hedge mustard and grass weeds. Indaziflam applied at 0.065 lb ai/a suppressed tall hedge mustard 54% and suppressed kochia 49%. Indaziflam controlled grass weeds 97% (Table 1). Unlike results in 2009, indaziflam did not injure native spearmint significantly in 2010 (Table 1). The indaziflam label lists pigweed, henbit, Russian thistle, and horseweed as controlled (susceptible) weeds. Native spearmint was not injured by indaziflam treatment in 2010 and produced hay and oil yields equal to Sinbar controls (Table 2). Mint was visually injured by indaziflam in 2009, but produced normal oil yields. Pyroxasulfone (KIH-485) only suppressed tall hedge mustard 64%, but controlled annual grass weeds 100% and kochia 98% (Table 1). Only minor mint injury was observed with dormant applications of pyroxasulfone, similar to 2009 results. Hay and oil yields were variable and not statistically different among herbicide treatments, but pyroxasulfone treated plots tended to average somewhat lower hay yields (Table 2). Oxyfluorfen did not control kochia or tall hedge mustard well when applied preemergence, but controlled annual grasses in the first cutting (Table 1). Mint was not significantly injured by oxyfluorfen. Terbacil controlled tall hedge mustard and grass weeds well, but kochia control was poor (Table 1). Native spearmint hay and oil yield
were variable due to uneven crop stands and were not affected by herbicide treatments (Table 2). Table 1. Native spearmint injury and weed control following dormant herbicide treatments applied February 25, 2010 near Prosser, WA. Crop / Weed Native Native Tall hedge spearmint spearmint mustard Kochia Grass Rating Date 4-9-10 5-12-10 5-11-10 5-11-10 5-11-10 Rating Type Injury Injury Control Control Control Trt Treatment name Rate (lb ai/a) 1 Indaziflam 0.0652 5 a 0 a 54 abc 49 ab 97 a 2 Saflufenacil (BAS800) 0.044 3 a 33 a 6 cd 93 a 50 a 3 Pyroxasulfone (KIH 485) 0.19 0 a 5 a 64 ab 98 a 100 a 4 Oxyfluorfen (Goal 2XL) 0.375 5 a 0 a 36 bcd 21 bc 100 a 5 Terbacil (Sinbar) 0.5 0 a 8 a 100 a 64 ab 100 a 6Nontreated 0a 0a 0d 0c 0a Means within a column followed by the same letter are not significantly different according to Duncan s New Multiple Range Test at P = 0.05. Table 2. Native spearmint hay and oil yield following dormant herbicide treatments applied February 25, 2010 near Prosser, WA. Trt Treatment name Rate (lb ai/a) Hay Yield Ton/Acre Oil Yield Lb/Acre 1 Indaziflam 0.0652 9. 8 a 31.6 a 2 Saflufenacil (BAS800) 0.044 6.9 a 16.3 a 3 Pyroxasulfone (KIH 485) 0.19 6.7 a 21.9 a 4 Oxyfluorfen (Goal 2XL) 0.375 7.9 a 22.3 a 5 Terbacil (Sinbar) 0.5 9.8 a 32.2 a 6 Nontreated 7.0 a 18.4 a Means within a column followed by the same letter are not significantly different according to Duncan s New Multiple Range Test at P = 0.05.
Trial 2. Peppermint tolerance to aminocyclopyrachlor (MAT28), a pyrimidine herbicide (same herbicide class as clopyralid), was evaluated in a field trial. Peppermint was injured by aminocyclopyrachlor in earlier trials by Oregon State University when applied to nondormant mint. These trials evaluated peppermint tolerance to aminocyclopyrachlor applied to dormant mint Nov. 24, 2009 and Feb. 23, 2010. The trial was located at the WSU headquarters research station near Prosser, WA. Aminocyclopyrachlor (MAT28) was tested at 0.0625 and 0.125 lb ai/a and was applied alone or in combination with terbacil or flumioxazin. MCPB at 0.38 and 0.5 lb ae/a was also included as a fall application November 24, 2009. Treatment 14 also tested a fall treatment of paraquat applied November 24, 2009 with aminocyclopyrachlor applied the following day, November 25, 2009 to determine if burning the peppermint foliage back with paraquat would reduced the foliar uptake of aminocyclopyrachlor and safen the mint to the herbicide. All treatments containing aminocyclopyrachlor (MAT28) totally killed peppermint regardless of rate or timing of application and there was no regrowth of peppermint in the spring (Table 1). MCBP (Thistrol) at 0.38 or 0.5 lb ai/a applied in November did not injure peppermint. Fall applied MCPB (0.38 to 0.5 lb ae/a) did not control tall hedge mustard, flixweed, or henbit, but suppressed prickly lettuce about 75% and controlled common dandelion 95% or more (Tables 2 & 3). All aminocyclopyrachlor treatments controlled prickly lettuce, common dandelion, kochia, and henbit nearly 100% (Tables 2 & 3). Aminocyclopyrachlor did not control the two mustard species, tall hedge mustard and flixweed well (Table 3). Terbacil applied alone in November controlled all weeds well except prickly lettuce and kochia (Table 1). Terbacil plus paraquat applied in February controlled all weeds well except common dandelion (Tables 2 & 3). Aminocyclopyrachlor injured peppermint too greatly be considered a potential herbicide for use in peppermint.
Table 1. Peppermint injury following fourteen herbicide treatments applied November 24, 2009 (A), November 25, 2009 (B), or February 23, 2010 (C) near Prosser, WA. Crop Name Peppermint Peppermint Rating Date 3-24-10 5-12-10 Rating Type Injury Injury Rating Unit % % Trt Treatment name Rate (lb ai/a) Timing 1 Aminocyclopyrachlor 0.063 A 100 a 100 a 2 Aminocyclopyrachlor 0.125 A 100 a 100 a 3 Aminocyclopyrachlor 0.063 A 100 a 100 a 3 4 0 c 0 b 5 Aminocyclopyrachlor 0.063 A 100 a 100 a 5 Flumioxazin (Chateau) 0.125 A 6 MCPB (Thistrol) 0.38 A 0 c 0 b 6 R-11 NIS 0.25% A 7 MCPB (Thistrol) 0.5 A 0 c 0 b 7 R-11 NIS 0.25% A 8 Aminocyclopyrachlor 0.063 C 100 a 100 a 8 R-11 NIS 0.25 C 9 Aminocyclopyrachlor 0.125 C 100 a 100 a 9 R-11 NIS 0.25% C 10 Aminocyclopyrachlor 0.063 C 100 a 100 a 10 Terbacil (Sinbar) 0.5 C 10 Paraquat (Gramoxone) 0.5 C 10 R-11 NIS 0.25% C 11 Terbacil (Sinbar) 0.5 C 6 b 0 b 11 Paraquat (Gramoxone) 0.5 C 11 R-11 NIS 0.25% C 12 Aminocyclopyrachlor 0.063 C 100 a 100 a 12 Flumioxazin (Chateau) 0.125 C 12 Paraquat (Gramoxone) 0.5 C 12 R-11 NIS 0.25% C 13 Nontreated Check 0 c 0 b 14 Paraquat (Gramoxone) 0.5 A 100 a 100 a 14 R-11 NIS 0.25% A 14 Aminocyclopyrachlor 0.125 B Means within a column followed by the same letter are not significantly different according to Duncan s New Multiple Range Test at P = 0.05.
Table 2. Prickly lettuce, common dandelion, and kochia control following fourteen herbicide treatments applied November 24, 2009 (A), November 25, 2009 (B), or February 23, 2010 (C) near Prosser, WA. Pest Name Prickly Common lettuce dandelion Kochia Rating Date 3-24-10 3-24-10 5-12-10 Rating Type Control Control Control Rating Unit % % % Trt Treatment Name Rate (lb ai/a) Timing 1 Aminocyclopyrachlor 0.063 A 100 a 100 a 99 a 2 Aminocyclopyrachlor 0.125 A 100 a 100 a 100 a 3 Aminocyclopyrachlor 0.063 A 100 a 100 a 100 a 3 4 27 c 100 a 7 b 5 Aminocyclopyrachlor 0.063 A 100 a 100 a 100 a 5 Flumioxazin (Chateau) 0.125 A 6 MCPB (Thistrol) 0.38 A 72 b 100 a 0 b 6 R-11 NIS 0.25 % A 7 MCPB (Thistrol) 0.5 A 78 ab 95 a 0 b 7 R-11 NIS 0.25% A 8 Aminocyclopyrachlor 0.063 C 100 a 100 a 100 a 8 R-11 NIS 0.25% C 9 Aminocyclopyrachlor 0.125 C 100 a 99 a 100 a 9 R-11 NIS 0.25% C 10 Aminocyclopyrachlor 0.063 C 100 a 100 a 100 a 10 Terbacil (Sinbar) 0.5 C 10 Paraquat (Gramoxone) 0.5 C 10 R-11 NIS 0.25% C 11 Terbacil (Sinbar) 0.5 C 100 a 83 b 100 a 11 Paraquat (Gramoxone) 0.5 C 11 R-11 NIS 0.25% C 12 Aminocyclopyrachlor 0.063 C 100 a 98 a 100 a 12 Flumioxazin (Chateau) 0.125 C 12 Paraquat (Gramoxone) 0.5 C 12 R-11 NIS 0.25% C 13 Nontreated Check 0 d 0 c 0 b 14 Paraquat (Gramoxone) 0.5 A 100 a 100 a 100 a 14 R-11 NIS 0.25% A 14 Aminocyclopyrachlor 0.125 B Means within a column followed by the same letter are not significantly different according to Duncan s New Multiple Range Test at P = 0.05.
Table 3. Tall hedge mustard, flixweed, and henbit control following fourteen herbicide treatments applied November 24, 2009 (A), November 25, 2009 (B), or February 23, 2010 (C) near Prosser, WA. Pest Name Tall hedge mustard Flixweed Henbit Rating Date 5-12-10 5-12-10 5-12-10 Rating Type Control Control Control Rating Unit % % % Trt Treatment Name Rate (lb ai/a) Appl 1 Aminocyclopyrachlor 0.063 A 0 d 40 ab 85 b 2 Aminocyclopyrachlor 0.125 A 13 cd 30 ab 100 a 3 Aminocyclopyrachlor 0.063 A 100 a 100 a 100 a 3 4 100 a 100 a 99 a 5 Aminocyclopyrachlor 0.063 A 42 bcd 100 a 100 a 5 Flumioxazin (Chateau) 0.125 A 6 MCPB (Thistrol) 0.38 A 10 cd 23 ab 0 c 6 R-11 NIS 0.25% A 7 MCPB (Thistrol) 0.5 A 49 bc 0 b 0 c 7 R-11 NIS 0.25% A 8 Aminocyclopyrachlor 0.063 C 7 d 60 ab 100 a 8 R-11 NIS 0.25% C 9 Aminocyclopyrachlor 0.125 C 2 d 90 a 100 a 9 R-11 NIS 0.25% C 10 Aminocyclopyrachlor 0.063 C 100 a 100 a 100 a 10 Terbacil (Sinbar) 0.5 C 10 Paraquat (Gramoxone) 0.5 C 10 R-11 NIS 0.25% C 11 Terbacil (Sinbar) 0.5 C 100 a 100 a 100 a 11 Paraquat (Gramoxone) 0.5 C 11 R-11 NIS 0.25% C 12 Aminocyclopyrachlor 0.063 C 75 ab 100 a 100 a 12 Flumioxazin (Chateau) 0.125 C 12 Paraquat (Gramoxone) 0.5 C 12 R-11 NIS 0.25% C 13 Nontreated Check 0 d 0 b 0 c 14 Paraquat (Gramoxone) 0.5 A 0 d 0 b 100 a 14 R-11 NIS 0.25% A 14 Aminocyclopyrachlor 0.125 B Means within a column followed by the same letter are not significantly different according to Duncan s New Multiple Range Test at P = 0.05.
Trials 3 and 4. Sulfentrazone (Spartan) is labeled for use in dormant mint. Sulfentrazone applied POST to mint injures any emerged mint when used at labeled rates. Mint is commonly cut twice in the long growing season in the Columbia Basin of eastern Washington. Herbicides applied to dormant mint in February or early March have usually dissipated by mid- summer and broadleaf weeds, such as pigweed, often emerge and compete with mint in late summer following the first mint harvest. In 2002, 2007, 2008, and 2009 research, sulfentrazone applied at 0.063 to 0.13 lb ai/a immediately after the first cutting of peppermint (but prior to any regrowth) controlled pigweed with little or no injury to peppermint regrowth. Sulfentrazone could also be useful to improve control of Sinbar resistant weed biotypes. These studies were conducted to further evaluate crop safety and efficacy of sulfentrazone and saflufenacil in both peppermint and spearmint when applied after the first harvest and prior to mint regrowth and irrigation. In 2010 trials, sulfentrazone was included as a dormant application in February to selected treatments followed by a second application of sulfentrazone after the first mint harvest. In other treatments, sulfentrazone was only applied after the first harvest of mint, which followed a terbacil plus pendimethalin treatment that was applied in February when mint was dormant. All dormant treatments of sulfentrazone (0.19 lb ai/a), pendimethalin (1.5 lb ai/a), and terbacil (0.5 lb ai/a) were applied to peppermint and native spearmint February 25, 2010. Both trials were conducted on Warden sandy loam soil with 0.7% O.M. at the WSU-Roza research station. Herbicides were applied with a small plot CO 2 sprayer. Treatments were replicated four times in a randomized complete block design and a nontreated check was included. All plots were 10 by 20 feet. Weed control and crop injury were evaluated periodically after each herbicide application. Native spearmint was first harvested July 8, 2010 and peppermint July 22, 2010. Cool weather in May and June delayed the first harvest of both crops. Pigweed seed was applied to the peppermint study to supplement the native population. Some pigweed and common lambsquarters had emerged in the native spearmint trial prior to the first harvest and were cut off with the mint during harvest. Treatments of sulfentrazone or saflufenacil (BAS800 or Kixor) were applied July16, 2010 to native spearmint and July 28, 2010 to peppermint following the first harvest and prior to mint regrowth and prior to an irrigation. Terbacil and bentazon were applied early POST to native spearmint July 28, 2010 and to peppermint August 16, 2010 when pigweed was beginning to emerge and less than 1 inch tall and mint regrowth was 2 inches or less. Weed control and mint injury were rated on a scale of 0=no injury to 100=dead, at various times following the herbicide application. The second harvest of native spearmint was September 13, 2010 and peppermint was harvested the second time on October 11, 2010. Mint hay yield was determined by harvesting a 40 inch swath by 20 feet from the center of each plot and weighing. Hay was then dried from each plot and steam distilled to determine oil yield. Data was subjected to ANOVA and treatment means were separated by using Duncan s multiple range test at the 5% probability level.
Peppermint results. Sulfentrazone applied at 0.063, 0.09, or 0.125 lb ai/a before peppermint began to regrow did not injure or delay peppermint regrowth whether following a dormant application of sulfentrazone (0.19 lb ai/a) in February or following a dormant application of pendimethalin plus terbacil (1.5 + 0.5 lb ai/a) in February (Table 1). Saflufenacil applied at 0.044 lb ai/a before peppermint began to regrow also did not injure or delay peppermint regrowth, but the higher rate of saflufenacil at 0.066 lb ai/a slightly injured peppermint in late August and early September (Table 1). Terbacil and bentazon applied early POST when peppermint had 1.5 inches of new growth slightly injured peppermint (chlorosis) 7 to 9% at 3 DAT, but peppermint soon recovered (Table 1). Nontreated checks averaged 34 pigweed plants per plot. Pigweed was controlled 98 to 100% with all sulfentrazone treatments (Table 2). Some pigweed escapes occurred following the lower rate of 0.044 lb ai/a saflufenacil, whereas the higher rate of saflufenacil (0.066 lb ai/a) completely controlled pigweed (Table 2). An early POST application of terbacil also completely controlled pigweed in this trial, but has not consistently controlled pigweed in previous trials, possibly due to terbacil resistant pigweed populations. Bentazon applied POST controlled pigweed 95% which was greater than control obtained in most previous studies (Table 2). Peppermint hay yield only averaged 2.8 tons fresh wt. hay/acre and oil yield averaged 15.5 lbs/acre (Table 6) partially due to the late first and second harvest. Peppermint hay and oil yields were variable and not significantly different among herbicide treatments (Table 6). Native spearmint results. Sulfentrazone applied at rates from 0.063 to 0.13 lb ai/a following the first harvest caused minor (3 to 8%) at 11 DAT and at later dates no significant injury was present on native spearmint regrowth (Table 3). Saflufenacil at 0.044 lb ai/a caused minor injury (7.7%) to regrowth of native spearmint at 11 DAT and saflufenacil at 0.066 injured native spearmint 12% that tended to persist into early September (Table 3). Terbacil and bentazon applied POST caused some minor chlorosis to native spearmint at 5 DAT, but injury did not persist beyond mid August (Table 3). The pigweed population consisted of a mix of plants that had been cut off during the first harvest and seedlings emerging from seed. All rates of sulfentrazone controlled pigweed 93% or more except the lowest rate of sulfentrazone (0.063 lb ai/a) that followed terbacil and pendimethalin, which controlled pigweed about 83% (Table 4). Saflufenacil failed to control established pigweed that was cut off during the first harvest and some new seedlings emerging from seed regardless of rate (Table 4). Bentazon and terbacil applied POST partially controlled pigweed from 68 to 73% (Table 4). Common lambsquarters also consisted of a mix of older plants that had been cut off during the first harvest and new seedlings emerging from seed. Common lambsquarters
was completely controlled in plots that received a dormant application of sulfentrazone in February followed by a sulfentrazone application after the first cutting (Table 5). Sulfentrazone at 0.13 lb ai/a following a dormant application of terbacil plus pendimethalin also controlled common lambsquarters completely (Table 5). The low rate of sulfentrazone (0.063 lb ai/a) partially controlled common lambsquarters 88% when following a dormant application of terbacil plus pendimethalin (Table 5). Saflufenacil failed to control common lambsquarters when applied after the first mint harvest regardless of rate (Table 5). Bentazon and terbacil applied POST controlled common lambsquarters 100 and 95%, respectively (Table 5). Native spearmint hay yield averaged 4.3 tons fresh wt. hay/acre and oil yield averaged 21.6 lbs/acre (Table 6). Native spearmint hay and oil yields were variable and not significantly different among herbicide treatments (Table 6).
Table 1. Peppermint injury following ten herbicide treatments applied: A = February 25, 2010; B = July 28, 2010; and C = August 16, 2010. Crop Name Peppermint Peppermint Peppermint Peppermint Peppermint Rating Date 4/9/2010 8/9/2010 8/19/2010 8/26/2010 9/10/2010 Rating Type Injury Injury Injury Injury Injury Trt Treatment name Rate (lb ai/a) Timing 1 Sulfentrazone (Spartan) 0.1875 A 0.0 a 0.0 a 0.0 c 0.0 a 0.0 a Sulfentrazone (Spartan) 0.0625 B 2 Sulfentrazone (Spartan) 0.1875 A 0.0 a 0.0 a 0.0 c 0.0 a 0.0 a Sulfentrazone (Spartan) 0.09 B 3 Sulfentrazone (Spartan) 0.1875 A 0.0 a 0.0 a 0.0 c 0.0 a 0.0 a Sulfentrazone (Spartan) 0.125 B 4 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 0.0 a 0.0 c 0.0 a 0.0 a Sulfentrazone (Spartan) 0.0625 B 5 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 0.0 a 0.0 c 0.0 a 0.0 a Sulfentrazone (Spartan) 0.125 B 6 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 0.0 a 0.0 c 0.0 a 0.0 a Saflufenacil (BAS800) 0.044 B 7 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 0.0 a 0.0 c 1.0 a 2.7 a Saflufenacil (BAS800) 0.066 B 8 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 0.0 a 8.7 a 1.7 a 0.0 a Terbacil (Sinbar) 0.5 C COC 1 % C 9 Pendimethalin (Prowl H2O) 1.5 A 5.0 a 0.0 a 7.0 b 1.0 a 0.0 a Bentazon (Basagran) 1 C COC 1% C 10 Pendimethalin (Prowl H2O) 1.5 A 6.7 a 0.0 a 0.0 c 0.0 a 0.0 a Means within a column followed by the same letter are not significantly different according to Duncan s New Multiple Range Test at P = 0.05.
Table 2. Pigweed control in peppermint following ten herbicide treatments applied: A = February 25, 2010; B = July 28, 2010; and C = August 16, 2010. Pest Name Redroot pigweed Redroot pigweed Redroot pigweed Crop Name Rating Date 8/19/2010 8/26/2010 9/10/2010 Rating Type Control Control Control Trt Treatment name Rate (lb ai/a) Timing 1 Sulfentrazone (Spartan) 0.1875 A 100.0 a 100.0 a 100.0 a Sulfentrazone (Spartan) 0.0625 B 2 Sulfentrazone (Spartan) 0.1875 A 100.0 a 100.0 a 100.0 a Sulfentrazone (Spartan) 0.09 B 3 Sulfentrazone (Spartan) 0.1875 A 100.0 a 100.0 a 100.0 a Sulfentrazone (Spartan) 0.125 B 4 Pendimethalin (Prowl H2O) 1.5 A 100.0 a 96.3 ab 98.0 ab Sulfentrazone (Spartan) 0.0625 B 5 Pendimethalin (Prowl H2O) 1.5 A 100.0 a 100.0 a 100.0 a Sulfentrazone (Spartan) 0.125 B 6 Pendimethalin (Prowl H2O) 1.5 A 100.0 a 88.3 b 85.0 b Saflufenacil (BAS800) 0.044 B 7 Pendimethalin (Prowl H2O) 1.5 A 100.0 a 100.0 a 100.0 a Saflufenacil (BAS800) 0.066 B 8 Pendimethalin (Prowl H2O) 1.5 A 18.3 b 100.0 a 100.0 a Terbacil (Sinbar) 0.5 C COC 1% C 9 Pendimethalin (Prowl H2O) 1.5 A 16.7 b 95.0 ab 95.0 ab Bentazon (Basagran) 1 C COC 1% C 10 Pendimethalin (Prowl H2O) 1.5 A 0.0 c 0.0 c 0.0 c Means within a column followed by the same letter are not significantly different according to Duncan s New Multiple Range Test at P = 0.05.
Table 3. Peppermint hay and oil yield of second harvest on October 11, 2010 following ten herbicide treatments applied: A = February 25, 2010; B = July 28, 2010; and C = August 16, 2010. Rating Date 10-11-2010 10-11-2010 Rating Type Hay Yield Oil Yield Rating Unit Ton/Acre Lb/Acre Trt Treatment Rate (lb ai/a) Timing 1 Sulfentrazone (Spartan) 0.1875 A 3.17 a 15.97 a 1 Sulfentrazone (Spartan) 0.0625 B 2 Sulfentrazone (Spartan) 0.1875 A 2.83 a 17.23 a 2 Sulfentrazone (Spartan) 0.09 B 3 Sulfentrazone (Spartan) 0.1875 A 3.03 a 15.93 a 3 Sulfentrazone (Spartan) 0.125 B 4 Pendimethalin (Prowl H2O) 1.5 A 2.40 a 13.73 a 4 4 Sulfentrazone (Spartan) 0.0625 B 5 Pendimethalin (Prowl H2O) 1.5 A 3.30 a 17.27 a 5 5 Sulfentrazone (Spartan) 0.125 B 6 Pendimethalin (Prowl H2O) 1.5 A 3.07 a 27.43 a 6 6 Saflufenacil (BAS800) 0.044 B 7 Pendimethalin (Prowl H2O) 1.5 A 2.17 a 16.40 a 7 7 Saflufenacil (BAS800) 0.066 B 8 Pendimethalin (Prowl H2O) 1.5 A 2.67 a 13.30 a 8 8 Terbacil (Sinbar) 0.5 C 8COC 1% C 9 Pendimethalin (Prowl H2O) 1.5 A 2.43 a 17.70 a 9 9 Bentazon (Basagran) 1 C 9COC 1% C 10 Pendimethalin (Prowl H2O) 1.5 A 2.50 a 11.97 a 10 Means within a column followed by the same letter are not significantly different according to Fisher s protected Least Significant Different Test at P = 0.05.
Table 4. Native spearmint injury following ten herbicide treatments applied: A = February 25, 2010; B = July 16, 2010; and C = July 28, 2010. Crop Name Spearmint Spearmint Spearmint Spearmint Spearmint Rating Date 4/9/2010 7/27/2010 8/2/2010 8/19/2010 9/10/2010 Rating Type Injury Injury Injury Injury Injury Trt Treatment name Rate Timing (lb ai/a) 1 Sulfentrazone (Spartan) 0.1875 A 0.0 a 2.7 bc 2.0 bc 1.0 b 0.0 b Sulfentrazone (Spartan) 0.0625 B 2 Sulfentrazone (Spartan) 0.1875 A 0.0 a 6.3 abc 2.7 bc 0.0 b 0.0 b Sulfentrazone (Spartan) 0.09 B 3 Sulfentrazone (Spartan) 0.1875 A 0.0 a 4.0 bc 1.0 bc 1.7 ab 1.7 ab Sulfentrazone (Spartan) 0.125 B 4 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 6.0 abc 0.7 bc 0.7 b 0.0 b Sulfentrazone (Spartan) 0.0625 B 5 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 8.3 ab 2.7 bc 2.0 ab 0.0 b Sulfentrazone (Spartan) 0.125 B 6 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 7.7 ab 0.0 c 1.0 b 3.3 ab Saflufenacil (BAS800) 0.044 B 7 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 12.3 a 5.0 b 4.7 a 5.0 a Saflufenacil (BAS800) 0.066 B 8 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 0.0 c 10.0 a 1.0 b 0.0 b Terbacil (Sinbar) 0.5 C COC 1% C 9 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 0.0 c 2.7 bc 1.0 b 0.0 b Bentazon (Basagran) 1 C COC 1% C 10 Pendimethalin (Prowl H2O) 1.5 A 0.0 a 0.0 c 0.0 c 0.0 b 0.0 b Means within a column followed by the same letter are not significantly different according to Duncan s New Multiple Range Test at P = 0.05.
Table 5. Pigweed control in Native spearmint following ten herbicide treatments applied: A = February 25, 2010; B = July 16, 2010; and C = July 28, 2010. Pest Name Redroot Redroot Redroot Redroot pigweed pigweed pigweed pigweed Rating Date 7/27/2010 8/2/2010 8/19/2010 9/10/2010 Rating Type Control Control Control Control Trt Treatment name Rate Timing (lb ai/a) 1 Sulfentrazone (Spartan) 0.1875 A 98.3 a 100.0 a 93.3 ab 95.0 a Sulfentrazone (Spartan) 0.0625 B 2 Sulfentrazone (Spartan) 0.1875 A 100.0 a 100.0 a 96.7 a 96.7 a Sulfentrazone (Spartan) 0.09 B 3 Sulfentrazone (Spartan) 0.1875 A 98.3 a 95.0 a 94.3 ab 96.7 a Sulfentrazone (Spartan) 0.125 B 4 Pendimethalin (Prowl H2O) 1.5 A 65.0 b 81.7 b 83.3 bc 86.7 ab Sulfentrazone (Spartan) 0.0625 B 5 Pendimethalin (Prowl H2O) 1.5 A 90.0 a 95.3 a 96.0 a 96.7 a Sulfentrazone (Spartan) 0.125 B 6 Pendimethalin (Prowl H2O) 1.5 A 22.5 c 0.0 c 0.0 d 0.0 c Saflufenacil (BAS800) 0.044 B 7 Pendimethalin (Prowl H2O) 1.5 A 25.0 c 3.3 c 0.0 d 0.0 c Saflufenacil (BAS800) 0.066 B 8 Pendimethalin (Prowl H2O) 1.5 A 0.0 d 86.0 b 81.7 c 73.3 b Terbacil (Sinbar) 0.5 C COC 1% C 9 Pendimethalin (Prowl H2O) 1.5 A 0.0 d 78.3 b 75.0 c 68.3 b Bentazon (Basagran) 1 C COC 1% C 10 Pendimethalin (Prowl H2O) 1.5 A 0.0 d 0.0 c 0.0 d 0.0 c Means within a column followed by the same letter are not significantly different according to Duncan s New Multiple Range Test at P = 0.05.
Table 6. Common lambsquarters control in Native spearmint following ten herbicide treatments applied: A = February 25, 2010; B = July 16, 2010; and C = July 28, 2010. Pest Name Common Common Common Common lambsquarters lambsquarters lambsquarters lambsquarters Rating Date 7/27/2010 8/2/2010 8/19/2010 9/10/2010 Rating Type Control Control Control Control Trt Treatment name Rate Timing (lb ai/a) 1 Sulfentrazone (Spartan) 0.1875 A 100.0 a 100.0 a 100.0 a 100.0 a Sulfentrazone (Spartan) 0.0625 B 2 Sulfentrazone (Spartan) 0.1875 A 100.0 a 100.0 a 100.0 a 100.0 a Sulfentrazone (Spartan) 0.09 B 3 Sulfentrazone (Spartan) 0.1875 A 100.0 a 100.0 a 100.0 a 100.0 a Sulfentrazone (Spartan) 0.125 B 4 Pendimethalin (Prowl H2O) 1.5 A 52.5 b 65.0 b 87.5 b 87.5 b Sulfentrazone (Spartan) 0.0625 B 5 Pendimethalin (Prowl H2O) 1.5 A 90.0 a 100.0 a 100.0 a 100.0 a Sulfentrazone (Spartan) 0.125 B 6 Pendimethalin (Prowl H2O) 1.5 A 20.0 cd 0.0 c 0.0 c 0.0 c Saflufenacil (BAS800) 0.044 B 7 Pendimethalin (Prowl H2O) 1.5 A 25.0 c 0.0 c 0.0 c 0.0 c Saflufenacil (BAS800) 0.066 B 8 Pendimethalin (Prowl H2O) 1.5 A 0.0 d 96.5 a 100.0 a 100.0 a Terbacil (Sinbar) 0.5 C COC 1% C 9 Pendimethalin (Prowl H2O) 1.5 A 0.0 d 97.3 a 97.3 a 95.0 ab Bentazon (Basagran) 1 C COC 1% C 10 Pendimethalin (Prowl H2O) 1.5 A 0.0 d 0.0 c 0.0 c 0.0 c Means within a column followed by the same letter are not significantly different according to Duncan s New Multiple Range Test at P = 0.05.
Table 7. Native spearmint hay and oil yield of second harvest on September 12, 2010 following ten herbicide treatments applied: A = February 25, 2010; B = July 16, 2010; and C = July 28, 2010. Spearmint Spearmint Rating Date 9/13/2010 9/13/2010 Rating Type Oil Yield Hay Yield Trt Treatment name Rate Timing (lb ai/a) Lbs/a Ton fresh/a 1 Sulfentrazone (Spartan) 0.1875 A 18.13 a 3.57 a Sulfentrazone (Spartan) 0.0625 B 2 Sulfentrazone (Spartan) 0.1875 A 20.37 a 3.60 a Sulfentrazone (Spartan) 0.09 B 3 Sulfentrazone (Spartan) 0.1875 A 15.50 a 3.30 a Sulfentrazone (Spartan) 0.125 B 4 Pendimethalin (Prowl H2O) 1.5 A 30.97 a 5.90 a Sulfentrazone (Spartan) 0.0625 B 5 Pendimethalin (Prowl H2O) 1.5 A 22.13 a 4.47 a Sulfentrazone (Spartan) 0.125 B 6 Pendimethalin (Prowl H2O) 1.5 A 19.03 a 4.07 a Saflufenacil (BAS800) 0.044 B 7 Pendimethalin (Prowl H2O) 1.5 A 18.60 a 3.60 a Saflufenacil (BAS800) 0.066 B 8 Pendimethalin (Prowl H2O) 1.5 A 28.33 a 5.60 a Terbacil (Sinbar) 0.5 C COC 1% C 9 Pendimethalin (Prowl H2O) 1.5 A 23.50 a 4.63 a Bentazon (Basagran) 1 C COC 1% C 10 Pendimethalin (Prowl H2O) 1.5 A 19.47 a 4.17 a Means within a column followed by the same letter are not significantly different according to Fisher s protected Least Significant Different Test at P = 0.05.
Trial 5. Control of white campion (white cockle) with saflufenacil (BAS800, Kixor) applied at 0.033 and 0.044 lb ai/a, flumioxazin (Chateau) at 0.125 lb ai/a, and asulam (Asulox) at 1.7 and 2.5 lb ai/a were tested in greenhouse trials. White campion seed collected from Moses Lake, WA was planted in 4 inch pots filled with sandy loam soil. Seedlings were thinned to three plants per pot soon after emergence. When white campion plants were 5 cm and 10 cm tall, herbicides were applied with a single nozzle bench sprayer calibrated to deliver 25 gpa. Methylated seed oil (MSO) was added at 1% spray volume to saflufenacil treatments. Crop oil concentrate (COC) was added at 1% spray volume to flumioxazin treatments and R-11 nonionic surfactant was added at 0.25% spray volume to asulam treatments. Each treatment was replicated 5 times in a completely randomized design. White campion injury was rated at 7 and 21 days after herbicide application. Saflufenacil completely controlled white campion at both rates and timings tested by 3 weeks after treatment. Flumioxazin completely controlled white campion when applied at the younger stage of application, but when applied at the more advanced stage of growth, some plants recovered. Asulam suppressed growth of white campion, but did not control white campion at either rate or stage of growth tested. Complete results will be presented in the 2011 report. Greenhouse trials will be repeated in early 2011. A field trial was initiated in October, 2010 near Post Falls, ID. 2. Evaluate the effect of deficit irrigation on herbicide performance and weed seed longevity in soil in peppermint. These studies were conducted in cooperation with Drs. T. Peters and D. Walsh. Herbicides [flumioxazin, sulfentrazone, or terbacil tank mixes with paraquat, and paraquat alone (untreated control)] were applied in February 23, 2010 to peppermint irrigated with a line source irrigation system that provided a range of irrigation levels across all herbicide treatments. This was the second year of these irrigation and herbicide treatments in peppermint. The line source irrigation treatments were imposed in April when irrigation water was available and the entire study was brought to field capacity after the first harvest of mint in July in an attempt to prevent death of peppermint in the extreme deficit irrigation plots. After irrigating the entire field, the line source irrigation treatments were then imposed for the remainder of the season. Dr. T. Peters report has details of irrigation levels in both studies. The number of weeds emerged in each plot were counted (by species) June 10 and September 21, 2010 to determine the impact of irrigation level and herbicide treatment on weed population density. Peppermint was harvested July 27 and October 18, 2010. Weed seed longevity in three irrigation treatments was evaluated by burying weed seed in nylon mesh packets on February 17, 2009 in native spearmint and December 15, 2008 and November 3, 2009 in peppermint. One hundred seed each of redroot pigweed and prickly lettuce, and fifty seed of Western salsify were buried in nylon mesh packets placed 2 cm deep each of three irrigation treatments (100% ET replacement, 60% ET replacement, and dry). Each weed species and irrigation treatment was replicated 4
times, except for Western salsify, which was replicated 8 times. Weed seed packets were recovered after 9 and 12 months of burial and weed seed removed and counted. All intact seed was placed on germination paper in Petri dishes in a dark germination cabinet at 60º F (prickly lettuce and salsify) and 95º F (redroot pigweed) for two weeks. Germinated seed was counted and removed every 2 to 3 days. Results. Weed population density data is presented in Tables 1 and 2. The most prevalent weeds were mustards (tall hedge mustard and tumble mustard) at both the June and September sampling dates. In June, other weeds present were common lambsquarters, Russian thistle, kochia, prickly lettuce, and horseweed (marestail). In September, additional weeds included annual grasses (green foxtail, barnyardgrass, and large crabgrass) and redroot pigweed. Weed densities varied by herbicide treatment and/or irrigation treatment and there were only a few instances in which there was a significant herbicide by irrigation treatment interaction on weed density. A. June weed counts. Kochia population density was not significantly affected by herbicide treatment although the lowest numbers of kochia were in flumioxazin and sulfentrazone treated plots across all irrigation levels. Kochia density was greatest in the lowest irrigation treatment, probably a result of less crop competition as the mint grew poorly in those plots and offered little competition with weeds (Table 1). Prickly lettuce population density was not affected by irrigation treatment and all three herbicides reduced prickly lettuce densities compared to the nontreated checks (paraquat without a residual herbicide).tall hedge mustard population density was affected by both irrigation level and herbicide treatment. Lower densities of tall hedge mustard were recorded in plots receiving the least irrigation, possibly due to heavier densities of other weeds (tumble mustard, kochia, Russian thistle, common lambsquarters, and horseweed) in those plots. Terbacil and flumioxazin controlled tall hedge mustard well across all irrigation levels, whereas sulfentrazone did not control tall hedge mustard (Table 1). Tumble mustard population density was impacted by both irrigation level and herbicide treatment and there was a significant herbicide by irrigation treatment interaction. Tumble mustard densities were greatest in the two lower irrigation treatments and terbacil completely controlled tumble mustard across all irrigation levels (Table 1). Flumioxazin partly controlled tumble mustard, whereas sulfentrazone failed to control tumble mustard. Common lambsquarters density was more random and population density was not significantly affected by either herbicide or irrigation level in June, although lowest densities were recorded in sulfentrazone and terbacil treated plots. Russian thistle population density was greatest in the lowest irrigation treatment (Table 1). Terbacil failed to control Russian thistle whereas sulfentrazone completely controlled Russian thistle and flumioxazin was intermediate. Horseweed densities were also higher in the lowest irrigation treatment and terbacil and sulfentrazone controlled horseweed well across all irrigation levels (Table 1). Flumioxazin did not control horseweed. There was a significant herbicide by irrigation level interaction on total weed counts in June. In the untreated check plots, weed numbers were greatest in the plots
receiving the lowest irrigation level probably a result of poor crop competition (Table 1). Similar trends were evident in terbacil and flumioxazin treated plots with the greatest number of escape weeds in the plots receiving low irrigation. A similar number of total weeds were present across all irrigation levels in plots treated with sulfentrazone, but the species composition changed in response to irrigation levels. B. September weed counts. Kochia population density in September was significantly affected by herbicide treatment with the lowest numbers of kochia occurring in flumioxazin and sulfentrazone treated plots across all irrigation levels. Kochia density was greatest in the lowest irrigation treatment, similar to results in June (Table 2). Prickly lettuce population density was not affected by irrigation treatment and all three herbicides reduced prickly lettuce densities compared to the nontreated checks. Tall hedge mustard population density was affected by both irrigation level and herbicide treatment. Unlike spring counts, highest densities of tall hedge mustard were in the two treatments receiving the least irrigation, possibly due to establishment of many new seedlings with little crop competition following the irrigation of all plots (including deficit irrigated plots) after the first cutting (Table 2). Terbacil controlled tall hedge mustard well across all irrigation levels, followed by flumioxazin which partially controlled the weed. Sulfentrazone failed to control tall hedge mustard (Table 2). Russian thistle population density was greatest in the lowest irrigation treatment and greatest in the plots receiving 100% replacement of ET (Table 2). Similar to June results, terbacil failed to control Russian thistle whereas sulfentrazone completely controlled Russian thistle and flumioxazin was intermediate (Table 2). There was a significant herbicide by irrigation level interaction on common lambsquarters population density. In nontreated checks, common lambsquarters density increased as irrigation level decreased. Terbacil and sulfentrazone nearly eliminated lambsquarters across all irrigation levels, whereas flumioxazin partially reduced lambsquarters counts (Table 2). Redroot pigweed was much more prevalent in September than in June as it is a later emerging species requiring warmer soil temperature for germination. Pigweed counts were not significantly impacted by irrigation level, probably a result of irrigating the entire plot area uniformly once after the first peppermint harvest. Terbacil and sulfentrazone applied in February failed to reduce pigweed density in September whereas flumioxazin reduced numbers across all irrigation levels (Table 2). Terbacil is normally somewhat weak on pigweed and there may have been terbacil resistant pigweed present. Sulfentrazone was likely degraded to levels below biological activity needed for pigweed control due to the long period of time between herbicide application in February and pigweed germination in July. Annual grass weeds were also present in all plots after the first cutting and the entire plot area was treated with sethoxydim August 17, 2010 to control grasses. Grass counts in September were similar over all herbicide treatments and counts increased
as irrigation rate decreased (Table 2). Less peppermint competition was present in low irrigation treatments to compete with late season grass weeds. In addition, poor grass control is often observed with postemergence graminicides when weeds are water stressed. C. Weed seed recovery and germination. Only one seed packet contained two intact Western salsify seed, whereas the remaining 22 seed packets had no intact salsify seed. The two seed recovered were viable and germinated. Most salsify seeds appeared to have germinated within the nylon mesh packet. Salsify seed has a low level of dormancy and readily germinates when conditions are favorable, thus it tends to be a short-lived seed in the soil. Irrigation level did not significantly impact the number of redroot pigweed seed recovered from seed packets (Table 3). The number of intact redroot pigweed seed recovered was significantly affected by the number of months buried and the mint type (peppermint versus native spearmint). There was also a significant interaction between the mint type and number of months buried on redroot pigweed seed recovered. The number of intact seed recovered tended to be slightly greater from the native spearmint compared to the peppermint, but both were 90% or greater indicating that most redroot pigweed seed did not germinate within the seed packets over the 9 to 12 month period (Table 3). The number of seed recovered was slightly greater at 12 month compared to 9 month burial in the high irrigation treatment in native spearmint and over all irrigation treatments in peppermint (Table 3). We cannot explain this slight increase in seed recovery with the longer time of burial. The percent germination of the recovered redroot pigweed seed was not significantly affected by irrigation level or time of burial. However, mint type (native spearmint versus peppermint) significantly affected the percent germination of the recovered redroot pigweed seed. Percent germination of recovered redroot pigweed seed was much greater (57%) in native spearmint than in peppermint (7%) over all irrigation treatments and time of burial (Table 3). The low germination of seed recovered from the peppermint study could be due to an induced dormancy of the seed or a reduction in seed viability in the peppermint study by some unknown environmental factor. The peppermint study was irrigated to field capacity after the first cutting of mint, whereas irrigation treatments in the native spearmint trial were constant the entire irrigation season, and this may have impacted pigweed seed dormancy. Irrigation treatment did not significantly impact the number of intact prickly lettuce seed recovered from seed packets (Table 4).The number of prickly lettuce seed recovered was significantly affected by the number of months buried and the mint type (peppermint versus native spearmint). There was also a significant interaction between the mint type and number of months buried on total prickly lettuce recovered. The number of prickly lettuce seed recovered tended to be slightly greater from the native spearmint compared to the peppermint indicating that more seed had either germinated or rotted in the peppermint study. The number of seed recovered was greater at 9 month compared to 12 month burial in native spearmint
(Table 4). The number of prickly lettuce seed recovered from the peppermint trial actually increased slightly from 9 months to 12 months at the two higher irrigation levels, whereas recovery declined at 12 months in the deficit irrigation plots (Table 4). Time of burial did not significantly impact the percent germination of recovered prickly lettuce seed. Germination of the recovered prickly lettuce seed was significantly affected by irrigation treatment and mint type, but there was no significant interaction. Percent germination of recovered prickly lettuce seed was greatest in the two higher irrigation treatments compared to the deficit irrigated (dry) treatment in both peppermint and native spearmint studies (Table 4). Perhaps the dry conditions in the severe deficit irrigated plots induced dormancy in prickly lettuce seed or reduced viability of the seed. Percent germination of recovered seed also tended to be greater from the seed packets collected from the native spearmint trial compared to those from the peppermint trial over all irrigation treatments (Table 4). Peppermint hay and oil yield can be found in Dr. T. Peter s deficit irrigation study report. Table 1. Weed counts June 10, 2010 in Peppermint grown under five levels of irrigation following four herbicide treatments applied Feb. 23, 2010. Means within a column followed by the same letter are not significantly different at the P= 0.05 level. Kochia (averaged over all herbicide levels, herbicide not significant) Irrigation level No. /m 2 Deficit irrigation 3.78 a Med dry 0.37 b Medium 0.30 b Medium wet 0.27 b Full irrigation 0.18 b Prickly lettuce (averaged over all irrigation levels, irrigation not significant) Herbicide No./m 2 Untreated 0.203 a Sinbar 0.002 b Chateau 0.041 b Spartan 0.032 b Tall Hedge Mustard Irrigation level No. /m 2 Herbicide No./m 2 Deficit irrigation 0.60 b Untreated 2.21 a Med dry 1.65 a Sinbar 0.04 b Medium 1.61 a Chateau 0.07 b Medium wet 1.16 ab Spartan 2.39 a
Full irrigation 1.66 a Russian Thistle Irrigation level No. /m 2 Herbicide No./m 2 Deficit irrigation 0.27 a Untreated 0.08 b Med dry 0.07 b Sinbar 0.21 a Medium 0.04 b Chateau 0.08 b Medium wet 0.05 b Spartan 0.0 c Full irrigation 0.04 b Horseweed Irrigation level No. /m 2 Herbicide No./m 2 Deficit irrigation 0.62 a Untreated 0.26 ab Med dry 0.20 b Sinbar 0.0 b Medium 0.06 b Chateau 0.49 a Medium wet 0.05 b Spartan 0.03 b Full irrigation 0.03 b Tumble Mustard Herbicide Treatment Irrigation level Untreated Sinbar Chateau Spartan ------------------No/m 2 ------------------- Deficit irrigation 3.09 a 0.0 c 0.27 c 1.93 b Med dry 2.38 ab 0.0 c 0.50 c 1.76 b Medium 0.48 c 0.0 c 0.20 c 0.26 c Medium wet 0.48 c 0.0 c 0.15 c 0.13 c Full irrigation 0.31 c 0.0 c 0.12 c 0.25 c Total Weed Counts in June 2010 Herbicide Treatment Irrigation level Untreated Sinbar Chateau Spartan ------------------No/m 2 ------------------- Deficit irrigation 22.78 a 5.35 b 2.90 b 4.04 b Med dry 6.22 b 1.46 b 2.16 b 4.46 b Medium 3.83 b 1.11 b 1.77 b 3.00 b Medium wet 3.60 b 0.84 b 1.27 b 2.11 b Full irrigation 3.94 b 0.67 b 1.11 b 3.06 b
Table 2. Weed counts Sept. 21, 2010 in Peppermint under five levels of irrigation and following four herbicide treatments applied Feb. 23, 2010. Grass weeds (green foxtail, barnyardgrass, crabgrass) (averaged over all herbicide levels, herbicide not significant) Irrigation level No. /m 2 Deficit irrigation 8.45 a Med dry 4.08 b Medium 0.58 c Medium wet 0.87 c Full irrigation 0.76 c Redroot pigweed (averaged over all irrigation levels, irrigation not significant) Herbicide No./m 2 Untreated 1.29 a Sinbar 1.24 a Chateau 0.25 b Spartan 1.27 a Prickly lettuce (averaged over all irrigation levels, irrigation not significant) Herbicide No./m 2 Untreated 0.184 a Sinbar 0.002 b Chateau 0.023 b Spartan 0.023 b Tall Hedge Mustard Irrigation level No./m 2 Herbicide No./m 2 Deficit irrigation 117.9 a Untreated 141.0 a Med dry 118.8 a Sinbar 13.3 c Medium 73.7 b Chateau 49.6 b Medium wet 37.9 c Spartan 129.5 a Full irrigation 68.6 bc Russian Thistle Irrigation level No./m 2 Herbicide No./m 2 Deficit irrigation 0.28 a Untreated 0.13 ab Med dry 0.11 b Sinbar 0.17 a Medium 0.07 bc Chateau 0.09 b Medium wet 0.02 c Spartan 0.01 c Full irrigation 0.02 c