Weed Control in Peppermint

Transcription

1 OREGON MINT COMMISSION Spring 2011 Weed Control in Peppermint Barbara Hinds-Cook, Carol Mallory-Smith, Andrew Hulting, Daniel Curtis and Bill Brewster Department of Crop and Soil Science, Oregon State University, Corvallis Five studies were conducted in western Oregon by the OSU Weed Science Program in Results from these studies are discussed below. For more detailed information regarding currently labeled herbicide applications, weed control efficacy and crop rotation restrictions associated with herbicide applications always refer to specific herbicide labels, the Weed Management in Mint Extension Publication (EM8774, Revised 2008, edu/catalog/index.php) and to the Mint Chapter in the 2011 Pacific Northwest Weed Management Handbook ( pnw/weeds). Summer Annual Broadleaf Weed Control in Baby Peppermint Two experimental herbicides, saflufenacil (Sharpen) and pyroxasulfone (KIH-485), were applied early post-emergence to the peppermint and pre-emergence to the weeds. Saflufenacil is a burndown product with limited soil residual properties, while pyroxasulfone has pre-emergence activity. Post-emergence applications of ethofumesate (Nortron), MCPB (Thistrol), MCPB + bentazon (Basagran) and MCPB + carfentrazone (Aim) were also evaluated on actively growing peppermint for crop safety. MCPB may broaden the weed control spectrum of herbicides such as bentazon and carfentrazone in non-dormant peppermint. Saflufenacil was applied at two rates in January to evaluate rates for residual control of summer annual broadleaf weeds. Pyroxasulfone also was applied at two rates to evaluate potential use rates. The MCPB applied alone and the MCPB tank mix combinations were applied in May to actively growing peppermint and post-emergence to the weeds. Visual evaluations of crop injury and weed efficacy were conducted and the peppermint was hand harvested August Table 1. Summer Annual Broadleaf Weed Control in Baby Peppermint Black Common Annual Peppermint nightshade groundsel sowthistle Peppermint Rating Date 6/8/10 5/11/10 5/11/10 5/11/10 8/23/10 9/8/10 Rating Type Injury Control Control Control Fresh wt Oil yield Treatment Rate Appl lb ai/a code % lb/2 yd 2 lb/a check saflufenacil A saflufenacil A pyroxasulfone B pyroxasulfone B MCPB 0.5 C 0 * * * MCPB C 0 * * * bentazon 0.75 MCPB C 10 * * * carfentrazone ethofumesate 1.5 C 0 * * * LSD (P=0.05) ns ns CV A - Applied January 26, 2010; 5% emerged peppermint B - Applied March 4, 2010; 20% emerged peppermint C - Applied May 18, 2010; 10 inch peppermint *Post-emergence treatments not rated for weed control efficacy 1 (continued on page 2)

2 Table 2. Comparison of Pyroxasulfone and Terbacil for Weed Control in Dormant Established Peppermint Annual Sharppoint Common Purslane Peppermint Willowherb sowthistle fluvellin groundsel speedwell Peppermint Rating Date /11/ /1/2010 7/19/2010 Rating Type Injury Fresh wt Oil yield Treatment Rate Appl code lb ai/a % % Control lb/ 2 yd 2 lb/a check b terbacil WP 0.8 A a terbacil WDG 0.8 A ab pyroxasulfone A bc pyroxasulfone A c 10.6 LSD (P=0.05) 2.4 ns CV Means followed by the same letter do not significantly differ (P=.05, Duncan s New MRT) A - Applied March 4, 2010; peppermint emerged 10% 23, 2010 (Table 1). It was not possible to evaluate weed control efficacy for the post-emergence applications as the plots were accidentally hand weeded by a farm crew. The biomass of two square yards of each plot was weighted, air dried and distilled. MCPB + carfentrazone was the only treatment which caused injury (10 percent) to the peppermint. There was no statistical difference in yield between treatments. Comparison of Pyroxasulfone and Terbacil for Weed Control in Dormant Established Peppermint Terbacil (Sinbar) WDG (a new formulation), terbacil WP (the older standard formulation) and two rates of pyroxasulfone were applied early post-emergence to the peppermint for control of summer annual broadleaf weeds. Clethodim (Select) was applied over the study area on April 12, 2010 to reduce competition from the seedling grass weeds. There were no differences between the newer and older formulations of terbacil for crop safety or weed control (Table 2). Two rates of pyroxasulfone were evaluated and both rates caused five percent injury to the crop. Except for common groundsel, weed control was similar with all of the treatments. Terbacil provided no control of the common groundsel at this site while both rates of pyroxasulfone provided control. Peppermint was hand harvested July 1, The biomass of two square yards of each plot was weighed, air dried and distilled. The study was established in a field that had roots dug out of it so the mint stand was thin resulting in low overall yields. Pyroxasulfone, Carfentrazone and MCPB Based Tank Mix Combinations for Summer Annual Broadleaf Weed Control MCPB broadens the weed control spectrum of herbicides such as bentazon (Basagran) and bromoxynil (Buctril, etc.) in nondormant mint. Our preliminary research indicates MCPB-based tank mix treatments and MCPB applied alone are safe on nondormant peppermint. A study was established in a commercial field of established peppermint with a history of pigweed populations to evaluate efficacy on summer annual broadleaf weeds of MCPB tank mix combinations. The study was in a competitive peppermint stand and no weeds emerged in the study area, therefore, only crop injury ratings were taken. All of the treatments were applied postemergence to the peppermint. Pyroxasulfone was applied in April post-emergence to the peppermint and pre-emergence to weeds. Carfentrazone was applied in May and June to evaluate potential use timings. MCPB and MCPB based tank mix combinations were applied in June. Visual evaluations of crop injury were conducted and the mint was hand harvested in August. The biomass of two square yards of each plot was weighed, air dried and distilled. The earlier timing of the carfentrazone caused more visible injury (20 percent) two weeks after treatment than the later timing which caused 10 percent injury one week after treatment (Table 3). The peppermint did recover from the injury. All of the MCPB treatments caused some injury to the peppermint due to the late timing of the application. The MCPB + carfentrazone was the most injurious of all of the MCPB combinations. There were differences in fresh weight yields, but not in the oil yields. Summer Annual Weed Control with Peppermint Herbicides Registered herbicides and herbicides with potential for use in peppermint were compared for their effectiveness on the summer annual weed species. Pigweed and common groundsel seeds were broadcast into the study area followed by application of five preemergence herbicides at various rates, which were incorporated later the same day by a rain event. Natural background populations of sharppoint fluvellin and prickly lettuce were present in the 2

3 study area, so control ratings were taken for these two weed species as well. Two rates of pyroxasulfone and three rates of ethofumesate were compared to two rates of each of the formulations of terbacil, the older WP formulation and the new WDG formulation, pendimethalin (Prowl H 2 O) and trifluralin (Treflan) for weed control efficacy. Terbacil treatments provided good control of all of the weed species except for the common groundsel (Table 4). As the rate of terbacil increased the percent weed control increased. A high rate of pyroxasulfone provided the best control of the weed species except sharppoint fluvellin. The high rate of pyroxasulfone provided 87 percent control of sharppoint fluvellin eight weeks after application, but by August it was no longer controlling Table 3. Pyroxasulfone, Carfentrazone and MCPB Tank Mix Combinations for Summer Annual Broadleaf Control Peppermint Rating Type Injury Fresh wt Oil yield Rating Date 5/17/2010 6/22/2010 7/7/2010 8/25/ /5/2010 Treatment Rate Appl % lb/2 yd 2 lb/a lb ai/a code check b pyroxasulfone A ab carfentrazone B a carfentrazone C ab MCPB 0.5 C a MCPB C a carfentrazone MCPB C a bromoxynil 0.25 MCPB C ab bentazon 0.75 LSD (P=0.05) ns 22 CV Means followed by the same letter do not significantly differ (p = 0.05, Duncan s New MRT) A - Applied April 21, 2010; 3 inch peppermint B - Applied May 13, 2010; 8 inch peppermint C - Applied June 14, 2010; 20 inch peppermint Table 4. Evaluation of Summer Annual Weed Control with Peppermint Herbicides Common Sharppoint Prickly Common Sharppoint Prickly Pigweed groundsel fluvellin lettuce Pigweed groundsel fluvellin lettuce Rating Date /19/ /9/ Treatment Rate Appl lb ai/a code % Control check terbacil WP 0.5 A terbacil WP 1.0 A terbacil WDG 5.0 A terbacil WDG 1.0 A pyroxasulfone A pyroxasulfone A ethofumesate 0.5 A ethofumesate 1.0 A ethofumesate 1.5 A pendimethalin 0.95 A trifluralin A A - Applied May 25, 2010; pre-emergence 3 (continued on page 4)

4 Table 5. Evaluation of Herbicides for Crop Safety and Pigweed Control in Double Cut Peppermint Peppermint Pigweed Peppermint Pigweed Peppermint Rating Date 8/16/2010 8/16/2010 8/30/2010 8/30/2010 9/7/ /5/2010 Rating Type Injury Control Injury Control Fresh wt Oil yield Application Treatment Rate code lb ai/a % lb/2 yd 2 lb/a check a 34 pyroxasulfone 0.09 A a 44 pyroxasulfone A ab 40 flufenacet-metribuzin A ab 33 terbacil WP 1.2 A ab 37 terbacil WDG 1.2 A ab 35 saflufenacil A ab 35 diuron 0.8 A a 43 oxyfluorfen 0.5 A ab 33 ethofumesate 1.5 A a 40 carfentrazone B b 28 LSD (P=0.05) CV Means followed by the same letter do not significantly differ (p=0.05, Duncan s New MRT) A - Applied July 13, 2010; preemergence B - Applied August 9, 2010; 8 inch ns this species. Pyroxasulfone was the only treatment that provided some control of the common groundsel. The high rate of the two formulations of terbacil, both rates of pyroxasulfone and a high rate of ethofumesate provided at least 95 percent control of pigweed. Trifluralin and pendimethalin controlled pigweed immediately following application, but failed to control later emerging pigweed over the duration of the study. Neither trifluralin nor pendimethalin controlled the other weed species present in this trial. Evaluation of Herbicides for Crop Safety and Pigweed Control in Double Cut Peppermint A study was established in a cooperating grower s field that had been swathed July 1 and chopped and removed July 7. On July 13 the pre-emergence herbicides, pyroxasulfone, flufenacet-metribuzin (Axiom), the two formulations of terbacil, saflufenacil, diuron (Karmex), oxyfluorfen (Goal) and ethofumesate, were applied and the study area irrigated. Twenty seven days later carfentrazone was applied to actively growing peppermint and pigweed. Carfentrazone injured the peppermint and initially injured the pigweed (Table 5). The carfentrazone treatment resulted in 20 percent injury seven days after treatment. The injury declined to 10 percent at 21 days after treatment. The carfentrazone treatment provided 80 percent control of the pigweed seven days after treatment, but by 21 days after treatment the pigweed had regrown resulting in zero percent control. Pyroxasulfone, terbacil, diuron and ethofumesate all provided at least 95 percent control of the pigweed with no injury to the peppermint. The peppermint was hand harvested September 7, The biomass of two square yards of each plot was weighed, air dried and distilled. There were differences in fresh weight yields but no differences in the oil yields Herbicide Evaluation Summary Pyroxasulfone has good crop safety on dormant and double cut peppermint and is effective on a wide range of grass and broadleaf species. This compound appears to have potential as a peppermint herbicide and we will continue to experiment with it under a variety of use scenarios to further refine application dates and rates. Saflufenacil is safe on dormant and double cut peppermint, but had poor activity on weeds at the rates we applied in We will continue to experiment with this herbicide and explore higher application rates to maximize soil residual activity in peppermint production scenarios. Carfentrazone will injure peppermint when applied late post-emergence, however, the peppermint recovers. Carfentrazone applied early and to small weeds, similar to the current use pattern of paraquat in peppermint, may be the best use scenario for this herbicide. Ethofumesate has a unique weed control spectrum and is safe on actively growing peppermint. We will continue to characterize this weed control spectrum to determine if this compound has a fit in peppermint production and adds value in terms of weed control for peppermint growers. There were no differences in weed control efficacy between the terbacil formulations used in

5 Evaluation of Biological Control Agents for Verticillium Wilt in Peppermint Bo Ming Wu, Rhonda Simmons, Richard Affeldt, Oregon State University Jim Cloud, Cloud Farms, Culver, Oregon Results from the 2009 field trials showed that Headline, Proline and Quadris exhibited limited efficacy on Verticillium wilt. Peppermint has a long window of susceptibility to infection by Verticillium and there are few economic ways to apply chemical to rhizosphere for established peppermint but it may be unrealistic to find new chemicals for protection of peppermint roots for such a long period. On the other hand, because peppermint is a perennial crop, if a biological control agent (BCA) can survive through the winter, effects of one application could potentially last for multiple years. This could potentially make BCAs a more favorable management practice against Verticillium wilt in peppermint. Some biological control agents have shown promising results in controlling Verticillium wilt in a variety of crops and Serratia plymuthica based RhizoStar and vesicular arbuscular mycorrhizal (VAM) fungi are promising commercially available products for which efficacy against Verticillium wilt has been reported. Our objectives were to evaluate the efficacy of these BCA treatments to control Verticillium wilt or mitigate its impacts on peppermint and to determine the effects of BCAs on growth of peppermint. An experiment was conducted in 2010 at COARC in Madras to evaluate biological control agents for controlling Verticillium wilt in peppermint. RhizoStar obtained from E-nema GmbH, and MycoApply Liquid Endo containing four species of endomycorrhizae and a customized powdery product containing nine species of endomycorrhizae provided by Mycorrhizal Application, Inc. were used in the experiment. On May 24, Verticillium free Black Mitcham seedlings provided by Pioneer West, Inc. were transplanted into four-gallon pots, buried in a plot without a history of Verticillium and eight treatments were included: 1. Non-inoculated soil and no treatment; 2. Inoculated soil and no treatment; 3. Inoculated soil and spraying seedling roots with MycoApply Liquid Endo at planting; 4. Inoculated soil and drenching with MycoApply Liquid Endo ten days after transplanting; 5. Inoculated soil and spraying roots with customized ninespecies VAM fungi at planting; 6. Inoculated soil and drenching with nine-species VAM fungi ten days after transplanting; 7. Inoculated soil and dipping seedling roots in RhizoStar at planting; 8. Inoculated soil and dipping seedling roots in RhizoStar and spraying Headline at planting. For inoculation, microsclerotia of Verticillium dahliae were reproduced in laboratory, dried and mixed into soil to achieve one microsclerotium per gram soil. The soil with microsclerotia was filled into a four-gallon pot and peppermint seedlings were transplanted into the soil and subject to appropriate treatments. For non-inoculated control, clean soil without contamination by V. dahliae was used. The RhizoStar dipping treatment was done via dipping the seedling roots in the RhizoStar suspension (diluted with 1:1 H 2 O) prior to planting for 30 minutes. Spraying of Headline and mycorrhizal fungi was done after placing a seedling into each pot and the roots of the seedlings were covered with soil immediately after spray. Headline was diluted with (1:200) H 2 O and sprayed onto roots and surrounding soil at 20 ml/pot. MycoApply Liquid Endo (1/2 dilution with H 2 O) and water suspension of the nine-species powder (16 g/l) were sprayed at 20 ml/pot. Soil drenching was done ten days after transplanting. MycoApply Liquid Endo (1/8 dilution with H 2 O) and water suspension of the nine-species powder (4 g/l) were drenched at 100 ml/pot. The pots were buried into a Verticillium free field plot at COARC, Madras, Oregon. The eight treatments were arranged according to a randomized complete block design with ten replicates (pots). The pots were fertilized, irrigated and weeded as needed. The weather in the early spring was mostly rainy and cold at Madras. The peppermint seedlings grew slowly until the end of June. The plants had very limited growth until July 21, Due to the limited growth of plants, no root samples were taken for examining the colonization by mycorrhizal fungi until harvest. Prior to harvest on August 30, 2010, severity of Verticillium (continued on page 6) 5

6 wilt was determined for each plant using the following scale (see Figure 1 for photo samples): 0 = no disease 1 = minor symptom on a few leaves 2 = symptoms on majority of leaves, minor dwarf 3 = significant dwarf, yellowing, wilt and defoliation 3.5 = some shoots with severity 3, and some shoots died 4 = the whole plant died The plant height was measured for each pot and then all the above ground parts were cut off and the fresh plant weight was determined at harvest on August 31. Two stems were randomly selected, surface sterilized with 0.5 percent bleach and rinsed twice in sterilized H 2 O. Five 1-2 mm dissects from each stem (apart from each other along the stem) were plated onto NP- 10 medium. The plates were examined for colonization of V. dahliae after ten days of incubation at room temperature (about 68 o F). On September 1 about 40 percent of roots were dug out from each pot. The root samples were cleaned, surface sterilized and rinsed in sterilized H 2 O. Five fine pieces from each of two randomly selected roots were plated onto NP-10 medium and the colonization of V. dahliae was determined as the above. The remaining roots were filled in a tea bag and subject to cleaning with 10 percent KOH at 149 o F for five hours, rinsing with H 2 O three times and one percent HCl for 30 minutes and staining in trypan blue (0.05 percent w/v in lactoglycerol) at 149 o F for one hour. The samples were then kept at room temperature until microscopy examination for colonization by mycorrhizal fungi. Results and Discussion In general, the inoculation of V. dahliae was successful; the average wilt incidence reached 66 percent at harvest for all different treatments with inoculated soil while nine out of ten of the non-inoculated plants remained symptomless. It was interesting to note that the symptoms of wilt only become visible approaching the end of season when the plants started to flower. There were only three out of 70 total inoculated plants that exhibited wilt symptoms by August 6, but this number increased quickly, reached 19 on August 16 and 46 prior to harvest on August 31. The results of the 2010 experiment showed that Verticillium wilt significantly affected the growth of peppermint plants. The wilt severity scales used in disease reading well-represented the impacts of the disease on the growth of peppermint plants. The higher the severity, the lower the fresh plant weight (Figure 2). The plant height and fresh weight were also closely correlated with each other (Figure 3). The disease severity was lower and the fresh weight greater for treatments six and eight (average 1.25 and 1.30) than other treatments (Figure 4). The disease incidence was mostly 60 percent or higher for inoculated treatments with the exception of treatment eight (dipping the roots in RhizoStar and spraying with Headline at transplanting) (Table 1). The difference was not statistically significant because of the small number of plants used in the experiment. While the previous year s experimental design allowed us to compare multiple treatments and manipulate inoculum level accurately with limited cost, it offered us less power to differentiate treatment effects. It is required to evaluate RhizoStar + Headline again in a field trial at an increased scale to confirm its effect in reducing wilt incidence and severity. The plating tests revealed that disease reading (incidence and severity) and colonization of stem by V. dahliae matched very well (Table 2 and Figure 5). There were only four out of 46 symptomatic peppermint plants that tested negative (Table 2). However, the colonization of roots showed more mismatches with disease readings. Among the 46 symptomatic plants, only 22 plant roots were colonized by V. dahliae (Table 2). Microscopic examination Table 1. Average plant height, fresh weight, wilt severity and incidence for potted peppermint plants subjected to different treatments Treatment Height Fresh weight Wilt severity Wilt incidence % % % % % % % % Table 2. Colonization of stems and roots by Verticillium dahliae for peppermint plants classified into symptomatic and symptomless groups Category Number of plants Stem colonization Root colonization Symptomatic Symptomless

7 Figure 1. Photo examples of peppermint plants with different wilt severity scales. From left to right and top to bottom were scaled as 0, 1.0, 2.0, 3.0, 3.5 and Figure 3. The relationship between the plant height and fresh weight of potted peppermint at harvest. Figure 2. The relationship between wilt severity reading and fresh plant weight at harvest Fresh weight (g) Fresh plant weight (g) Severity reading Plant height (inch) (continued on page 8) 77

8 of stained roots has not given any sign of colonization of root by mycorrhizal fungi. Five root samples were sent to Mycorrhizal Applications, Inc. for confirming the finding. The results also showed low colonization by mycorrhizal fungi even when the roots were cleared and stained over a prolonged period of time. In addition, the little effects of mycorrhizal fungi products on wilt incidence, wilt severity and plant fresh weight might have been caused by low colonization of root by mycorrhizal fungi. This was likely due to the low post-treatment soil temperature. A study on effects of root zone temperature demonstrated that colonization of sorghum roots by mycorrhizal fungus, Glomus intraradices was significantly reduced at 59 o F compared with at 73.4 o F and almost completely inhibited at 50 o F. It is necessary to optimize the application techniques and timing for mycorrhizal fungi products for future studies. Figure 4. Average severity of Verticillium wilt and fresh plant weight of potted peppermint subject to different treatments. The 8 treatments were: 1) Uninoculated control; 2) Inoculated control; 3) Inoculated soil and spraying roots with MycoApply Liquid Endo; 4) Inoculated soil and soil drenching with MycoApply Liquid Endo; 5) Inoculated soil and spraying roots with customized 9-species VAM fungi; 6) Inoculated soil and soil drenching with customized 9-species VAM fungi; 7) Inoculated soil and dipping roots in RhizoStar ; 8) Inoculated soil, dipping root stock in RhizoStar and spraying with Headline Fresh Plant Weight (g) Severity Rank Treatment Treatment Figure 5. Relationship between colonization of peppermint stems by Verticillium dahliae and incidence of wilt symptom/severity. Symptom Stem Colonization 100% 100% 80% 80% Incidence 60% 40% Stem Colonization 60% 40% 20% 20% 0% Treatment 0% Severity Scale 8

9 In Crop Use of Telone II for the Management of Verticillium Wilt and Nematodes Impacting Mint Philip Hamm and Russ Ingham, Oregon State University and Jordan Eggers, Hermiston Agricultural Research & Extension Center This work was initiated to investigate the use of Telone II for the control/management of two related diseases impacting peppermint, root-lesion nematodes (Pratylenchus penetrans and P. neglectus) and Verticillium wilt (Verticillium dahliae). The novelty of this project involved the application of Telone II after root stocks had been transplanted and established in a field. A grower-initiated demonstration in 2008 showed that in-crop use of Telone II at 15 and 20 gallons/acre (gpa), when fall applied after rhizomes were dormant, appeared to provide significant increase in plant growth. No determinations were made as to the reason for the growth response, although a possible cause may have been reduced pressure from nematodes, Verticillium or both. Anticipated benefits of this project would be the identification of a product that can be used in established mint fields to control one or two serious diseases of mint that generally require crop rotation/removal (Verticillium wilt) or the repeated in-season use of Vydate to control nematodes. Currently there is no control of Verticillium wilt after planting. A one-year-old commercial field that had a high root-lesion nematode population (determined by survey sampling prior to plot establishment) was selected for this research. Two sites (wedges) were established in the field in the fall of 2009, each containing four treatments (Telone II [0 (shanks run through plots), 15 and 20 gpa] and an undisturbed control) with four replications. Treatments were applied October 21, Plots were 50 feet long by the width of the fumigator width (17 feet). A noble blade with nozzles appropriately placed was used for Telone II applications at a 14 inch depth. One of the two wedges (Wedge #8) had an additional treatment of Mocap applied at four quarts/acre and watered in October 27-28, Soil and root samples were taken prior to application (October 21, 2009), post fumigation (March 19, 2010), and after the second cutting (October 17, 2010) to assay population of Verticillium (soil only) and plant-pathogenic nematodes (soil and roots). Yield was determined by hand harvesting on July 17 and September 17, Two 4 x 30 strips were cut from each replication at each site and total fresh hay weights were determined in the field. Pre-fumigation levels of Verticillium dahliae were low in Post-fumigation samples indicated that the level of Verticillium dahliae increased following fall fumigation (Table 1). While not significantly different, post-fumigation levels of V. dahliae tended to be higher where shanked applications of Telone II had been applied. Harvest V. dahliae levels were not significantly different among the treatments of either wedge, although V. dahliae levels in the Telone-treated plots in wedge #5 stayed relatively the same from post-fumigation to harvest while the V. dahliae levels in the other treatments decreased slightly. (continued on page 10) Table 1. Effect of treatments on soil populations of Verticillium (CFU/g dry soil) and mint yield (lb hay/240 sq. ft.). Wedge 1 Treatment Pre-Fumigation V. dahliae (CFU/g dry soil) 2 Post Fumigation V. dahliae (CFU/g dry soil) 3 Harvest V. dahliae (CFU/g dry soil) 4 1st Harvest Yield (lbs fresh foliage) 5 2nd Harvest Yield (lbs fresh foliage) 5 5 Non-tilled Control 0.0 a a 8.0 a 63.2 a 34.9 a 5 Shanked Control 0.5 a 23.5 a 5.0 a 43.9 c 19.2 b 5 Telone II 15 gpa (shanked) 0.0 a 29.5 a 30.0 a 43.2 c 19.6 b 5 Telone II 20 gpa (shanked) 0.0 a 27.5 a 27.0 a 37.2 c 17.0 b 5 Non-tilled Control 0.5 a 14.0 a 6.0 a 59.1 a 28.6 a P= P= P= P= P= Non-tilled Control 5.0 a 20.0 a 11.0 a 96.4 a 42.9 a 8 Shanked Control 0.0 a 17.0 a 13.0 a 61.6 b 25.5 a 8 Telone II 15 gpa (shanked) 10.0 a 48.5 a 19.0 a 59.7 b 32.4 a 8 Telone II 20 gpa (shanked) 1.0 a 45.0 a 7.0 a 58.1 b 27.8 a 8 Mocap 4 quarts/a (sprayed/watered in) 1.5 a 25.5 a 5.0 a a 43.9 a P= P= P= P<.0001 P= Two areas within the field were used, wedge 5 and wedge 8. The plots in wedge 8 also included the Mocap treatment. 2 Values are the numbers of Colony Forming Units (CFU)/gram of dry soil. Soil samples were taken in the fall before fumigation. 3 Values are the numbers of CFU/gram of dry soil. Soil samples were taken in the spring as mint was beginning to grow. 4 Values are the numbers of CFU/gram of dry soil. Soil samples were taken in the fall right after the second hand harvest. 5 The lbs of mint foliage obtained from the first and second cuttings, harvested just days before the commercial harvest. 6 Numbers in the same column followed by the same letters are not significantly different by the P level indicated. 9

10 Nematode levels in the soil prior to fumigation were high (Table 2). Following fumigation numbers were still high although significant decline occurred more often where Telone II had not been applied. Nematode levels in the roots prior to fumigation were very high as well (Table 2) and samples taken after fumigation revealed no significant reduction in population. Harvest nematode counts in both the soil and roots were not significantly different among the treatments in either wedge. The lack of reduction in the soil populations of Verticillium following fumigation was expected, given the low beginning numbers and the fact that Telone II is not specifically reported to be a fumigant that controls this soil-borne fungus. Previous work with this product with potatoes did not demonstrate a direct reduction of Verticillium, but given the close relationship and synergistic impact between P. penetrans and Verticillium in potatoes, controlling either of these pathogens would potentially help control Verticillium wilt. What was not expected was the much higher levels of Verticillium found following fumigation. Likewise, Telone II is a very effective nematicide. However, in nearly every case, whether looking at soil or root population densities (Table 2), fumigation treatments had little impact on nematode populations. Mocap, when applied in the fall in the one replicated block, was the only treatment that suggested a nearly significant reduction (P<0.06) in nematodes and also had a significantly greater yield of mint (first cutting, Table 1). Verticillium and nematode levels seem to have been favored and yield negatively impacted by ground disturbance during fumigation. Infrared photography showed that stands in the shanked treatments (with or without Telone II) were in poor shape in the spring and never fully recovered from the treatment. The noble blade applicator apparently disrupted the rhizomes enough to harm the plants. Population assessments of Verticillium and the lesion nematodes suggest that each pathogen thrived on the stressed plants and replicated at higher rates. Table 2. The impact of treatments on soil and root populations of root-lesion nematodes (primarily Pratylenchus penetrans). # Pratylenchus per 250 grams of Dry Soil # Pratylenchus per gram of Fresh Mint Roots Wedge 1 Treatment Pre-Fumigation 2 Post Fumigation 3 Harvest 4 Pre-Fumigation Post Fumigation Harvest 5 Non-tilled Control 149 a 5 92 a* 122 a 1939 a 1521 a 1128 a 5 Shanked Control 135 a 66 a* 110 a 1384 a 2747 a 759 a 5 Telone II 15 gpa (shanked) 253 a 102 a 79 a 2219 a 1775 a 562 a 5 Telone II 20 gpa (shanked) 236 a 117 a 53 a 1682 a 1856 a 969 a 5 Non-tilled Control 196 a 87 a* 94 a 2324 a 1509 a 969 a P= P= P= P= P= P= Non-tilled Control 228 a 133 a 249 a 734 a 440 a 2559 a 8 Shanked Control 175 a 197 a 144 a 1564 a 981 a 1507 a 8 Telone II 15 gpa (shanked) 229 a 59 a* 102 a 1161 a 407 a 1164 a 8 Telone II 20 gpa (shanked) 203 a 76 a 136 a 1130 a 516 a 1261 a 8 Mocap 4 quarts/a (sprayed/watered in) 299 a 82 a 264 a 1430 a 280 a* 2012 a P= P= P= P= P=0.954 P= Two areas within the field were used, wedge 5 and wedge 8. The plots in wedge 8 also included the Mocap treatment. 2 Values are the numbers of nematodes in the soil collected prior to fumigation in the fall of Values are the numbers of nematodes in the soil collected in the spring of 2010 as mint was beginning to grow. 4 Values are numbers of nematodes in the soil or roots collected in the fall of 2010 shortly after the second harvest. 5 Numbers in the same column followed by the same letters are not significantly different by the P level indicated. *Significantly lower than the pre-fumigation nematode counts of the same treatment at P<0.06. Integrated Pest Management on Peppermint Computer Program (IPMP) The computer program developed by Ralph Berry and Len Coop from Oregon State contains information about management of insects, weeds, diseases and nematodes on mint. This program is available at and contains links to the newest PNW Insect, Weed and Disease Management Handbooks, which are updated each year and posted on the IPMP site. IPMP has colored photos and information on biology, sampling and daydegree models to help make decisions for control and to help time applications of pesticides, if they are necessary. 10

11 Evaluation of Mycorrhizal Fungus on Peppermint Grown in Northeast Oregon Bryon Quebbeman, Quebbeman s Crop Monitoring, La Grande, Oregon Mycorrhizal fungi can form close associations with plant roots, which can provide benefits to most plants including increased nutrient and water uptake and resistance to diseases. A company called Mycorrhizal Applications, Inc. located in Grants Pass, Oregon is commercially producing this type of mycorrhizal fungus in the spore form. This company has research articles from foreign researchers indicating that mycorrhizal fungus can increase the growth of Mentha arvensis and that it can increase fresh and dry weights of other various plants that are planted into soil infested with Verticillium wilt. This mycorrhizal fungus is reported to be most effective when it is applied directly to the roots or seeds at planting time. It can also be applied to established crops at any time as long as it is washed into the soil. Applying the mycorrhizal fungus spores to an established crop requires more product to be applied and benefits will likely occur more slowly. Objective Compare established mint treated with a product called MycoApply Liquid Endo to untreated mint. Measure any visual growth differences, the dry hay weight and oil yields. Treatments were applied with a C0 2 powered backpack sprayer on two identical experiments April 9, Treatments were replicated eight times in a complete randomized block design. Experiment One was harvested on August 11, while Experiment Two was harvested on August 16. Before the treatments were applied, root samples were taken from each experiment and sent to Mycorrhizal Applications, Inc. for evaluations of pre-treatment levels of mycorrhizal fungus. Post-harvest root samples were also collected and sent to Mycorrhizal Applications, Inc. for evaluation of the colonization of mycorrhizal fungi. Samples were not labeled as treated and untreated, to eliminate biasing of the evaluation. Results No visual differences of any kind were observed through the growing season between the treated and untreated areas. The average oil yields and dry hay weights were numerically lower in the treated plots than in the untreated plots, however, the differences were not significant (Table 1). The results of the pre-treatment sampling of roots for mycorrhizal fungus found no mycorrhizal fungus in either experiment. Mycorrhizal Applications, Inc. reported this as being very unusual to have no naturally occurring Mycorrhizal fungi present. Table 1. Comparison of peppermint oil yields and dry hay weights between mint treated with MycoApply Liquid Endo and untreated mint. Treatment Rate Exp. 1 Exp. 2 Exp. 1 Exp. 2 Oil yields Dry hay weight (lbs/ac) (lbs/sample) Untreated check MycoApply 7 fl Liquid Endo Post-harvest root samples were also taken and sent to Mycorrhizal Applications, Inc. to determine the percent colonization of the mint roots with mycorrhizal fungus. Two samples were taken for each treatment. In both experiments plots that were treated with MycoApply Micronized Liquid Endo had roots that were colonized several times more than the untreated plots (Table 2). However, the results in both experiments are not statistically significant at the P=0.05 level. This lack of statistical significance is likely due to the low number of replications taken when sampling for the fungus. It could be speculated that the mycorrhizal fungus was able to colonize the mint roots during the crop season but there was not time for it to affect the growth or yield of the mint plants. It could also be possible that these mint fields were not significantly stressed in any way so the mycorrhizae was not able to provide any benefits in growth or oil yields. It will be of interest to observe these plots in the future to see if the mycorrhizae provides any benefits to the mint as the stand ages and weakens. Verticillium wilt has been observed in the fields of both experiments, however, no clear wilt strikes were observed within the plot areas of either experiment. It is likely that the Verticillium levels will increase as the stands age. It will be of interest to see if the mycorrhizae treated plots respond positively to resist the effects of Verticillium wilt as the stands age. Conclusions oz/ac P<0.05 NS NS NS NS Sample means were compared with Fisher s Protected LSD (p=0.05). The applications of MycoApply Liquid Endo to established mint had no visual affect on the mint growth, oil yields and dry hay weights. (continued on page 12) 11

12 Table 2. Comparison of mycorrhizal fungus colonization in established peppermint treated with MycoApply Liquid Endo to untreated mint. Treatment Rate Exp. 1 Exp. 2 Average percent colonization of roots Untreated check MycoApply Liquid Endo 7 fl oz/ac P=0.05 NS NS The pre-treatment sampling indicated that there was little to no native mycorrhizal fungus present. Post-harvest sampling showed that the mycorrhizal fungus colonized the roots more in the treated plots than the untreated plots. Although the differences between the levels of root colonization was not statistically different, it appears that the application of the MycoApply Liquid Endo did make a difference in the amount of root colonization. Continued monitoring should be conducted to determine if MycoApply Micronized Liquid Endo affects the oil yields, mint vigor and disease levels in future years. The Mint Biotechnology Project Progress Toward a Verticillium-Resistant Line With a Peppermint-Like Oil Profile Mark Lange, Washington State University The emphasis of the mint biotechnology project has recently changed in that we are now focusing on the development of a line with peppermint-like oil quality, improved yield and a high degree of Verticillium tolerance. The Croteau laboratory was highly successful in generating a peppermint line with high yield (> 70 percent yield increase over Black Mitcham controls in field trials) and desirable composition (low pulegone and menthofuran concentration under stress). However, a genetic engineering effort to confer Verticillium resistance using an approach used with satisfactory results in other plants did not give rise to appreciable level of tolerance in peppermint. We thus decided to start off with a mint variety that is already tolerant to Verticillium attack and contains essential oil that could be engineered to resemble that of peppermint. The best candidate appeared to be the Erospicata variety developed by Aromatics Inc. in the 1990s. The MIRC ran field trials in 2009/2010 that confirmed the Verticillium tolerance of this line. In our hands the Erospicata variety has consistently yielded at least 60 percent more oil compared to Black Mitcham controls (greenhouse data). The Erospicata oil accumulates high amounts of menthone, which is an important component of peppermint oil, but it lacks menthol, another key constituent of peppermint. Over the last nine months we have worked on a transformation protocol for the Erospicata variety. This was not trivial as spearmint transformation has been very difficult in the past, but we have made considerable progress and we have transferred the first set of test transgenics into the greenhouse. Our project now has two main aims: (1) to identify and characterize promoters (strong on/off switches of genes) that guide the expression of genes to the specialized anatomical structures that carry out the essential oil biosynthesis; and (2) to use these promoters in combination with the menthone:menthol reductase gene (already in hand) to convert a substantial percentage of the menthone to menthol. We have isolated two large promoters from peppermint which are currently being tested for their specificity. This is done by fusing each promoter to a gene encoding a so-called marker gene. The expression of the marker gene (controlled by the peppermint promoter) can be detected because it encodes a marker enzyme that catalyzes a color reaction. When transgenic tissues are exposed to a certain chemical substrate, cells that express the marker enzyme accumulate a blue-colored product, whereas all other cells remain uncolored. We already have promising preliminary data for one of the peppermint promoters (blue staining of oil-synthesizing cells on leaf surfaces), but this needs to be verified in independently generated transgenics. We are currently in the process of generating an analogous promoter-marker gene fusion for the second peppermint promoter. At the same time we have begun work on obtaining a third promoter which will give us a higher chance of finding the appropriate on/off switch for our menthone:menthol reductase gene. We are expecting to have definitive data for one promoter and preliminary data for two additional promoters for the Mint Commission meetings in late fall. On a different token, we have completed a side project to evaluate the possibility of using genetic engineering to add a chemical marker to the oil. We have successfully generated transgenics that reproducibly accumulate (+)-limonene to higher levels than Black Mitcham and spearmint. This would allow us to recognize oil distilled from transgenic plants without significantly affecting overall yield and composition. In summary, we are on schedule for reaching our goal of delivering Erospicata lines with substantially increased menthol amounts by

13 Affect of Headline Fungicide on Established Peppermint Oil Yields in Northeast Oregon Bryon Quebbeman, Quebbeman s Crop Monitoring, La Grande, Oregon Past research done in the La Grande, Oregon area has shown positive results of Headline fungicide increasing mint oil yields. In addition, the 2009 research done in the La Grande area indicated that the increase in mint oil yield occurred when the Headline was applied within nine to three weeks before harvest. These yield increases occurred in the absence of any visual disease pressure. This 2010 research duplicates the 2009 research, but only on established mint, to again determine if the application date of the Headline affected the oil yields. These research trials were conducted in the same plots in 2010 as in This allowed us to compare plots that were treated two years in a row (2009 and 2010) to plots that were treated only in The following table (Table 1) shows the date each of the Headline treatments were applied. Treatments one through four were applied to the exact same plots in 2010 as they were in The plot for treatment number five was included in the randomized block design in This treatment number five was not treated with Headline in 2009 but was treated in 2010, so as to provide a comparison of mint treated two consecutive years to mint treated only after one year. Results and Discussion Table 1. Application dates of 12 oz. per acre Headline on two experiments applied on four different dates. Experiment number Trmt. 1 Trmt. 2 Trmt. 3 Trmt. 4 Trmt. 5 Trmt. 6 and field age UTC Exp. 1. Fourth year mint June 14 July 1 July 16 July 31 July Exp. 2. Second year mint June 14 July 1 July 16 July 31 July Table 2. Comparison of peppermint oil yields from Headline applied on different dates. (Experiments One and Two harvested August 16 and 18, 2010 respectively) Experiment One Trmt. Treatments Rate lb Application Mean oil yield # ai/a dates (lbs/a) No powdery mildew or rust was observed on any of the treatments of either experiment throughout the growing season. No differences in bloom or any other visual differences were observed between any of the treatments and/or the untreated checks of either experiment. Objective One: Determine if Headline fungicide increases mint oil yields significantly compared to untreated mint. Experiment Two 1 Headline 12 oz/a 0.2 June c Headline 12 oz/a 0.2 July c Headline 12 oz/a 0.2 July bc Headline 12 oz/a 0.2 July a Headline 12 oz/a 0.2 July c Untreated check ab 106 LSD 9 NS Sample means were compared with Fisher s Protected LSD (p=0.05). Results were mixed in this year with Experiment One having some treatments with significantly higher (P=0.05) oil yields than the untreated check (UTC), while Experiment Two had no Headline treatments with significantly greater oil yields than the UTC (Table 2). In Experiment One, there is a significant increase in dry hay weight of some Headline treatments compared to the UTC (Table 3). The increased dry hay weight appears correlated to the significant oil yield increases of the same treatments. There were no significant differences in dry hay weights in Experiment Two. Objective Two: Determine if the application date of Headline affects the oil yield. Experiment One was the only experiment with any significant differences in yields. Experiment One does show the two earliest applications having significantly greater oil yields than the UTC. The third application date is statistically similar to the UTC while also being statistically similar to the other two earliest Headline treatments (Table 4). The last application date of July 31, is statistically similar to the UTC, and is also numerically lower than the UTC by two pounds per acre. (continued on page 13) 13

14 Table 3. Comparison of dry hay weights of peppermint treated with Headline on different dates. Experiment 1 Experiment 2 Trmt. Treatments Rate lb Application Mean weight of air dry # ai/a dates peppermint hay (lbs/sample) 1 Headline 12 oz/a 0.2 June b Headline 12 oz/a 0.2 July b Headline 12 oz/a 0.2 July ab Headline 12 oz/a 0.2 July a Headline 12 oz/a 0.2 July b Untreated check a 11.0 LSD 0.49 NS Sample means were compared with Fisher s Protected LSD (p=0.05). Table 4. Comparison of oil yields from different application dates of Headline. (Experiments One and Two harvested August 16 and 18, 2010 respectively) Experiment 1 Experiment 2 Trmt. Treatments Rate lb Application Mean oil yield # ai/a dates (lbs/a) 1 Headline 12 oz/a 0.2 June b Headline 12 oz/a 0.2 July b Headline 12 oz/a 0.2 July ab Headline 12 oz/a 0.2 July a Untreated check a 106 LSD 9 NS Sample means were compared with Fisher s Protected LSD (p=0.05). Experiment Two has no significant differences in oil yields but like Experiment One, the lowest oil yield occurred with the latest Headline application of July 31. The three earlier application dates all numerically equaled or exceeded the UTC. In the 2009 experiments the last Headline application date did significantly increase the yield while in the 2010 trial the last application date did not increase the oil yield. One difference between the 2009 and 2010 experiments is that there are approximately three weeks between the last application and harvest in 2009, but only about two weeks between the last application and harvest in It appeared that two weeks was not enough time for the Headline to have a positive effect on the oil yield. It could also be speculated that the unusually late growing season of 2010 may have also impacted the effect of the Headline differently in 2010 than it did in Objective 3: Determine if mint treated in 2009 and 2010 with Headline yields the same as mint treated with Headline only in Experiment One was the only experiment that showed any significant response to the Headline treatments. The comparison between the two treatments show no significant difference between the yields of mint treated two consecutive years to mint treated only one year (Table 5). Analysis of oil from peppermint treated with Headline fungicide. 14