University of California Cooperative Extension, Solano and Yolo County U.C. and U.S.D.A. cooperating. Fruit & Nut Notes

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1 University of California Cooperative Extension, Solano and Yolo County U.C. and U.S.D.A. cooperating Fruit & Nut Notes Serving Solano & Yolo Counties! July Issue 21 SACRAMENTO VALLEY ALMOND NEWS Biofix for Almond Worm Pests Melanie Covert and Joe Connell, Farm Advisor Intern and Farm Advisor, Butte County A biofix for each species marks the point in time when you catch the first moth or trap the first eggs. This date is used as the starting point for running degree day models for each of our almond pests. These insect phenology models and degree day calculations can improve spray timing when pressure is great enough to suggest that sprays are needed or predict when pest pressure may increase as harvest approaches. Biofix dates vary with location and the environment so it s best to monitor traps in your orchard and calculate spray timing from your own biofix if you wish to use this information most effectively. Degree Day (DD) calculations. Upper and lower temperature thresholds vary for each insect species. Inexpensive temperature sensors can be purchased that directly output DD accumulations and local weather information. Or, DD calculations can be made easily from the biofix in your orchard using the Degree Day calculator on the UCIPM web site at under Agriculture and floriculture (Pest Management Guidelines). In This Issue: Biofix for almond worm pests Delivering a clean crop Almond blow-over problems Verticillium wilt in almonds Soil testing-part 2 Spider mite control at hull split Several methods for controlling pocket gophers Navel orangeworm (NOW). So far this year we have seen very few NOW eggs on traps in the orchards we re trapping. Strong storms and good sanitation helped to destroy mummy nuts and reduce overwintering larvae. The NOW biofix was April 23 in the Orland orchard we re watching. Using this date and projecting ahead, the second generation NOW egg laying should begin around July 15 and third generation eggs should arrive around August 19. Worm pressure increases as additional generations arrive. NOW produce large amounts of frass and webbing as they feed on the kernel and worm damage increases the potential for aflatoxin contamination. An early Nonpareil harvest before August 19 th will avoid third generation egg laying and minimize NOW crop damage. Late harvesting soft shell varieties such as Livingston, Monterey, and Winters are more vulnerable if harvest is delayed. Peach twig borer (PTB). We caught our first PTB moths in our pheromone traps in Durham on April 22 this year. The DD model indicates second generation larvae should hatch and begin feeding around July If hullsplit occurs earlier or simultaneously, nuts Submitted By Carolyn DeBuse Orchard Systems Farm Advisor Direct Cell cjdebuse@ucdavis.edu UCCE Solano County 501 Texas Street, First Floor Fairfield, CA Fax cesolano.ucdavis.edu UCCE Yolo County 70 Cottonwood Street Woodland, CA Fax ceyolo.udavis.edu Fruit & Nut Notes July 2010

2 Biofix for almond worm pests continued.. could be vulnerable. If this generation emerges prior to hullsplit, larvae will feed mainly on shoots. PTB can be identified in shoot strikes as brown banded larvae and their nut damage is surface feeding on the kernel without any webbing present. The third generation of PTB larvae should hatch around August and could put pressure on later splitting soft shelled pollenizers. Oriental fruit moth (OFM). OFM is rarely a pest of almond kernels but can often be found feeding in the soft tissue of newly splitting hulls. The third generation is projected to emerge and start feeding around July 17 th to 26 th. Watch for them in hulls that are splitting at that time. OFM larvae are cream or pinkish colored while PTB larvae are brown banded. Summary. A timely harvest, especially near other NOW hosts such as pistachios and pomegranates, minimizes exposure to NOW feeding. PTB damage predisposes nuts to NOW infestation, so good PTB management is an essential part of effective NOW management. Second generation PTB, NOW, and third generation OFM will be at a stage to potentially feed on split nuts toward mid to late July. If hullsplit is late due to the cool spring and you feel you have worm pressure, a spray timed at 1% hullsplit on sound nuts should line up pretty well with worm pests toward late July. Remember, a timely and rapid harvest is the best way to avoid significant worm damage. Get the crop off the tree and into the huller while the sun shines! Worm pest Generation length, DD May spray timing DD after Biofix PTB NOW Varies: 1056 on mummy nuts, 723 on new crop nuts OFM Later generation insect activity, DD after Biofix Biofix, start of 1 st generation /22 (1 st moths, Butte Co.) /23 (1 st eggs, Glenn Co.) /15 (1 st moths, Tehama Co.) 1 st Gen insect activity 5/31-6/5 shoot strikes 5/7 egg hatch on mummies 5/1-5/7 shoot strikes Biofix, Start of 2 nd Gen 6/30 2 nd moth flight 7/15 egg laying on mummies, OR, on new crop after hullsplit 5/30-6/3 2 nd moth flight 2 nd Gen insect activity Projected 7/16-7/20 Shoot strikes, or, nut feeding if after hullsplit Projected 7/20 egg hatch Shoot strikes 6/15-6/22 Projected Biofix for 3 rd Gen 8/10 3 rd moth flight 8/19 egg laying if moth developed on new crop 7/4-7/10 3 rd moth flight Projected 3 rd Gen insect activity 8/22-8/26 nut feeding or shoot strikes 8/24 egg hatch, nut feeding 7/17-7/26 shoot strikes, or, hull/nut feeding Fruit & Nut Notes 2 July 2010

3 Delivering a Clean Crop Franz Niederholzer, UC Farm Advisor, Sutter/Yuba Counties Producing a clean almond crop provides short and long-term benefits. Low reject levels -- usually due to low levels of worm and/or ant damage -- mean better grower returns. Damaged nuts have no value in the market and some processors pay premiums for nuts below a certain percent damage. Low navel orange worm (NOW) damage also reduces the chance of aflatoxin contamination of nuts. Concerns about a high rate of aflatoxin detection in pistachio nuts from Iran caused the European Union to briefly ban imports of Iranian pistachios. Europe consumes roughly 30% of California almonds so attention to NOW control will help reduce the risk of aflatoxin and will help maintain the excellent reputation of California almonds in the world market. In Sutter and Yuba Counties, and perhaps other regions of the Sacramento Valley, the Nonpareil (NP) crop is generally down in 2010, mostly due to poor pollination weather this spring. In light crop years, % NOW damage can be higher since fewer nuts are available to dilute NOW egg laying activity. A light NP crop often results in large nuts with poorer shell seal, which can mean easier nut access for NOW larvae. Wes Asai, former UC farm advisor and now a private consultant wrote a great article on this topic at: What does all this mean to growers and PCAs in 2010? The following is a quick review of practices to consider to help deliver a clean crop. Track NOW populations in your orchard. Use weekly egg trap counts to track moth flight development and determine when Nonpareil harvest should begin to avoid damage from the 3 rd NOW generation. The graph in Figure 1 is an example of early harvest timed to minimize NOW damage. Harvest soft shell varieties ASAP. Nonpareil should be ready for harvest when % of the nuts at eye level are split (see photo). Test shake a few trees to make sure the orchard is ready to go. If at least 95% of the nuts come off, the orchard is ready to harvest. Be careful with harvest timing. Premature harvest can reduce nut meat quality due to embedded shells. Early harvest is key to a clean crop. Hull split sprays only control 40-60% of NOW larvae, so early harvest is vital to obtain the lowest reject levels especially in a light crop year. If needed, apply a hull split spray for NOW control once hull split has begun on sound nuts and eggs are being laid on split nuts or egg traps. If sound nuts are splitting, but eggs aren t being laid, wait to spray until you see eggs. If egg laying starts before hull split, wait until hull split starts before spraying. Hull split begins in tree tops on the southwest side. Check nuts in that part of the canopy on 5-6 trees per block to monitor for the beginning of hull split. Excellent spray coverage is essential for effective NOW control with a hull split spray. Peach twig borer (PTB) can be partially controlled with a hull split spray as well. With an early harvest, nuts will dry more rapidly on the ground than in the trees. However, don t trade NOW damage for ant damage. Make sure ants are controlled when protein eating ants are present. Ant bait should go down at least 4 weeks before predicted harvest. Prompt pick up of dry nuts will help reduce ant damage. Nuts are ready for pickup when hulls on 8 out of 10 harvested nuts snap instead of bend when bent back between thumb and index finger. Combining an early harvest with a well timed hullsplit spray, if needed, should result in a cleaner crop with better returns to the Figure 1 grower. Fruit & Nut Notes 3 July 2010

4 Almond Tree Blow-Over Problems Bill Krueger, UC Farm Advisor, Glenn County Periodically almond trees fall over. Heavy tree losses are usually associated with fall, winter, or spring storms with associated high winds and saturated soil conditions. To a lesser degree, tree failure can occur throughout the year. In March of 1995, a storm brought 6 inches of rain and wind gusts up to 100 mph to the Sacramento Valley and resulted in an estimated loss of 15,000 acres of almonds worth $210 million. More recently, storms with wind gusts in up to 70 mph in December 2002 and January 2008 resulted in tree losses greater than 30% in some orchards. When trees fall, their failure can usually be classified as windthrows or wood decay related. Windthrow is when trees with sound healthy roots are uprooted as a result of strong winds and wet soil conditions. Wood decay related failures are the result of infection from wood decay fungi, which consume the lignin in the cell walls of the heartwood. Eventually these trees fall, often in wind storms or when the trees are heavily loaded with crop. Wood decay fungi are secondary pathogens and are not capable of penetrating intact plant membranes and must rely on some type of injury to gain access. Survey work conducted by Joe Connell, Butte County Farm Advisor, and Dr. Jim Adaskaveg, UC Riverside Plant Pathologist following the March 1995 storm revealed the following. Generally, as trees age, tree losses increase. Windthrow was an important factor in young orchards (Fig.1) and as orchards matured wood decay became more dominant. Wood decay accounted for approximately 90 % of the tree loss in mature orchards. On Lovell peach, of 394 downed trees evaluated, 81% had crown gall and 77% had wood decay. Crown galls function as sites of entry for wood decay fungi. Almond on Lovell Peach % Tree Losses to Wood Decay and Windthrow Orchard Age - Years Generally almonds on Marianna 2624 rootstock suffered lower losses than Lovell peach rooted trees. The exceptions included orchards in flooded areas with softened soil and unpruned orchards with dense canopies. Generally plum rooted orchards had less crown gall and wood decay. Suggestions for reducing tree losses from blow-over: Windthrow At Planting Use rootstock less prone to windthrow. There is currently much interest in the Krymsk 86 rootstock in the Sacramento Valley partly because it is believed to be better anchored. Anchorage only affects windthrow which is primarily a young tree problem. This is a new rootstock and there are still many unknowns. Unless Krymsk 86 is more resistant to crown gall and wood rots, blow-overs as the orchard ages may still be an ongoing problem. More information on rootstocks will follow in future editions of this newsletter. Fruit & Nut Notes 4 July 2010

5 Almond tree blow-over problems continued.. Orient strong roots in the direction of prevailing winds. Avoid planting on high berms perpendicular to prevailing winds. Pay attention to the orientation of irrigation wetting patterns particularly with regard to prevailing winds to ensure root distribution which favors anchorage. Planting depth. On well-drained soil, it may be possible to plant plum rooted trees deeper than they were in the nursery. In addition to reducing the number of root suckers, this may also provide for better anchorage. Avoid heading trees too high. Canopies on high-headed trees will have greater leverage and trees are at greater risk. Post plant Prune by thinning out the tallest limbs to even up variety related tree height differences and allow wind to blow through the tree more readily. Taller trees will catch more wind and are at greater risk. Pruning by topping does not appear to provide the needed relief. Avoid irrigation prior to predicted strong winds. Apply zinc sulfate foliar fertilization in the fall which can promote early leaf fall and/or or pruning prior to leaf fall prior to reduce wind resistance prior to fall and winter storms. Wood Decay Prevent crown gall. Buy trees from a nursery with a good crown gall prevention program. Treat new trees prior to planting to prevent/reduce infection. Avoid injuring crowns and roots while doing orchard maintenance to decrease the chance of crown gall infection. Avoid any practices which may injure trunks or roots and create an opening for wood decay fungi. Verticillium Wilt in Almonds Carolyn DeBuse- Farm advisor Solano and Yolo Counties Verticillium wilt can be seen in many young almond orchards this year. The cool wet spring has increased the disease s incidence. The symptoms show up in orchards in the late spring when the weather changes from cool to hot. The most visual symptom is dry yellow/brown leaves still hanging from one or two scaffolds of a young tree. At first look this disease gives the appearance of killing the trees but few trees are actually killed. The collapsed scaffolds often leaf out later in the year with the only loss being the tender tips of scaffolds that are too desiccated to regrow. It has been shown that affected trees can have reduced yields in subsequent years mainly due to smaller tree size. Disease development Verticillium wilt (also known as blackheart) is caused by the fungus Verticillium dahliae. This soil borne fungus can be found in bare soil as microsclerotia or in plant debris that remains in the field. Microsclerotia are hard coated compacted fragments of fungus that can withstand harsh environmental conditions staying quiescent in the soil for years until roots of a host plant are in the vicinity. When a host plant is near, the fungus infects the roots and grows in the xylem (water conducting tissue) of the plant. The xylem becomes plugged with the fungus making it nonfunctional for water transport causing the plant to wilt. Cool wet springs are favorable for the growth of the fungus promoting the development of the disease. The fungus s growth is slowed or terminated by the hot dry summer conditions allowing the affected scaffolds to recover. In following years, re-infection can occur from new root infections or surviving fungus within the tree s roots and wood. Many plants are hosts for verticillium including all of the Prunus tree species, many row crops commonly grown in California (tomatoes, melons, potatoes, safflower, strawberry, eggplant, cotton) and many weed species (nightshade, groundsel, lambsquarters, dandelion, pigweed). Verticillium microsclerotia numbers can increase up to 60 per gram of soil where host plants have been grown. Yet, the disease can be a problem in new orchards planted where only 2-3 microsclerotia per gram of soil are found. The majority of the microsclerotia are found in the top layer of soil. Fruit & Nut Notes 5 July 2010

6 Verticillium wilt in almonds continued.. Diagnosing the disease Almonds are most susceptible to the disease from 1-5 years of age with most of the disease showing in the 2 nd to 4 th years. The following symptoms will help diagnose the disease. Flagging or wilting of one or two whole scaffolds often starting at the top of the scaffold and progressing downward. The rest of the tree may remain healthy. (photo 1) Leaves turn yellow/brown and adhere to the affected branches. Some leaf drop occurs lower on the scaffold. Scaffold shoot tips desiccate creating a shepherd s hook appearance. Cutting into the wood or making a cut across the wood will show a darkening and streaking of the xylem tissue. (photo 2 & 3) What to do after Verticillium strikes When you find verticillium affected trees the current recommendation is to be patient and not prune prematurely. The summer heat will slow the growth of the fungus and allow the tree to push new growth from the surviving tissue. I have already seen early infections this year begin to re-leaf. Do not prune out dead wood until you can tell how much of the tree will have made a full recovery. Often you ll find that only the tips of affected scaffolds have died. In 1 st and 2 nd leaf orchards, in extreme cases some trees may die and will need to be replaced. How to avoid or minimize the disease Avoid planting new orchards following cultivation of susceptible host crops or weed infestations. Don t intercrop with verticillium susceptible hosts in new orchards. Take soil samples from the top 12 inches to determine amount of microsclerotia present before planting. If verticillium is a risk, in the year(s) prior to planting reduce the microsclerotia survival by flooding during the heat of summer, solarization using clear plastic tarps, fumigation with chloropicrin or a combination that contains chloropicrin, or grow a non-host cover crop like sudan grass. Use the verticillium tolerant Marianna 2624 rootstock if you are planting compatible almond varieties. Nonpareil is not compatible. M2624 comes with other negative issues such as suckering and possibly Union Mild Etch problems so all risks need to be considered in choosing this rootstock. If the orchard is already planted, black plastic mulch the first year can reduce infection or the use of a non-host cover crop (grasses) has been reported to help. Photo 2&3. Xylem darkening in verticillium affected almond tree. (C.DeBuse) Photo 1. Verticillium wilt in a young almond tree. (C.DeBuse) Fruit & Nut Notes 6 July 2010

7 Part 1 of this series (April 2010) emphasized that soil testing is complementary to plant tissue testing and not a substitute in orchard management. Considerations to ensure soil testing provides representative and useful information and interpretation of two common soil test parameters: 1) Saturation Percentage (SP); and 2) ph were also discussed. This article will focus on the nutrients nitrogen (N), phosphorus (P), and potassium (K). Nitrogen Nitrogen occurs in soils as organic and inorganic forms and soil testing may be performed to measure levels of either. Nitrate nitrogen (NO 3 -N) is most commonly measured in standard soil tests because it is the primary form of nitrogen available to trees and, therefore, an indicator of nitrogen soil fertility. However, soil concentrations of NO 3 -N depend upon the biological activity and may fluctuate with changes in soil temperature, soil moisture, and other conditions. Nitrate is also easily leached with rainfall or irrigation so current soil tests may not reflect future levels of nitrogen soil fertility. Table 1 provides guidelines for evaluating NO 3 -N soil fertility levels. Table 1. Guidelines for interpreting nitrate nitrogen (NO 3 -N) levels in soil test results. 1 Some laboratories report NO 3 -N as lbs/ac rather than as a concentration (ppm). A soil bulk density is assumed in this calculation so the NO 3 -N fertility levels should be considered an estimate rather than an absolute level. Ammonium nitrogen (NH 4 -N) is also a plant available form of nitrogen in orchard soils and it can be determined with soil testing upon request. In general, NH 4 -N is not determined and reported with a standard soil test. Ammonium nitrogen does not usually accumulate in soil because soil temperature and moisture conditions that are suitable for tree growth are also ideal for conversion of NH 4 -N to NO 3 -N. Ammonium nitrogen concentrations of 2-10 ppm are common. Levels above 10 ppm NH 4 -N may occur in cold, wet soils or in soils irrigated with a water supply that is high in ammonium nitrogen. Total nitrogen which is a measure of all organic and inorganic forms of nitrogen in soil can be determined with soil testing. However, it is not included in standard soil testing. Phosphorus Understanding and Applying Information From a Soil Test - Part 2 Allan Fulton, Farm Advisor, Tehama, Glenn, Colusa, and Shasta Counties Fertility Level ppm lbs/acre 1 Low <10 <36 Medium High Excessive >30 >108 Soil tests are performed to determine the concentrations of plant available phosphorus in soil. The Bray P1 Test is used for neutral and acid soils (ph 7.0 and lower) and the Olsen sodium bicarbonate test is used primarily for alkaline soils (ph>7.0) but can be used on soils with ph >6.5. These phosphorus soil tests measure ortho-phosphate (PO 4 -P) and provide an index of the phosphorus availability. Table 2 provides guidelines for evaluating phosphorus soil fertility. Table 2. Guidelines for interpreting phosphorus (PO 4 ) levels in soil test results. Fertility Level Bray P1 method PO 4 Concentration (ppm) Low <20 <10 Medium High Excessive >100 >40 Olsen method PO 4 Concentration (ppm) Fruit & Nut Notes 7 July 2010

8 Soil test-part 2 continued.. Depending on soil ph, the availability of phosphorus to trees is influenced by two processes in the soil: 1) specific adsorption to iron and aluminum minerals; and 2) the precipitation or dissolution of calcium phosphate compounds. Both the Bray and Olsen methods of analyzing phosphorus fertility recognize these processes by providing an index of the phosphorus availability. However, neither method simulates the exact soil reactions that occur so the soil test values cannot be used to calculate available phosphorus in absolute terms as lbs P 2 O 5 /acre. If soil test levels are reported in units expressed as lbs/acre rather than concentration, they should also be viewed as estimates or relative indicators. Lastly, phosphorus deficiency has not been common in California orchards, so if soil tests suggest low phosphorus fertility the possibility of a deficiency should be confirmed with plant tissue testing. Potassium Potassium undergoes exchange reactions with other cations in the soil such as calcium, magnesium, sodium, and hydrogen and this affects the plant available potassium. Therefore, an ammonium acetate extraction method is the most common method to model these soil reactions and analyze for potassium fertility. Less commonly, a sodium bicarbonate extraction method may be used to analyze potassium fertility. When the sodium bicarbonate method is used the soil test results might indicate slightly lower values. Table 3 provides guidelines to interpret potassium soil test results. Table 3. Guidelines for interpreting potassium (K) soil test results using the ammonium acetate method. Fertility Level Very Low < 75 Low Medium High Very High > 800 Extractable K (ppm) Orchards growing on soils with extractable potassium concentrations less than 150 ppm in the root zone are most likely to respond to potassium fertilization. Soils with extractable potassium levels between 150 and 250 ppm are not as likely to respond as lower levels but they could be signaling a decline in fertility and a trend toward future deficiencies. Combining soil and plant tissue testing is preferred to monitor trends in potassium nutrition and guide management. Pacific Spider Mite Control at Hull Split in Almonds David Haviland, Entomology Farm Advisor, UC Cooperative Extension, Kern Co. Hull split is one of the most critical decision-making periods of the year for PCAs that manage spider mites in almonds. At this time, hot weather, dusty conditions, tree stress due to crop load, and reduced irrigation can all cause significant outbreaks of spider mites. Hull split is also often the last opportunity to utilize miticides in a spray program due to PHIs, as well as an opportunity to get a free ride through the field with a navel orangeworm spray. There are many new miticides available for mite control. However, not all fields require hull split miticide sprays. In many cases, beneficials are sufficient to keep spider mite populations in check. Deciding if a treatment is needed Monitoring and treatment guidelines can be found within the University of California Pest Management Guidelines for Almonds ( Treatment decisions are made based on the percentage of leaves with mites present on them. If no predators are present, treatments should be made if about 25% of the leaves have mites on them. If predators are present, treatments can be held off until about 50% of the leaves are infested. As with any monitoring program the sampling accuracy increases as the number of trees sampled and number of areas in the field sampled increase. The UC guidelines take this into account. Fruit & Nut Notes 8 July 2010

9 Mites at hull split continued.. PCAs should also take into account additional information such as drought stress to the trees and mite history within the block. At hull split it is also wise to adapt the thresholds a little to consider that hull split may be the last opportunity to get into the field and spray before harvest begins. Choosing a miticide There are several miticides to choose from at hull split. The most commonly used include Envidor, Fujimite, Acramite, Zeal, and Omite. Each of these products can do well at hull split, depending on what you want to accomplish. It is also important to remember that 415 Oil is, by itself, a miticide. Use rates of 1% by volume with other miticides or insecticides will assist in mite control. Use rates of 2% can be very effective at suppressing mite populations while maintaining biological control organisms. In three years of UC trials in Kern County, Fujimite and Envidor provided the best overall control at hull split (Table 1). Plots treated with these products either did not, or rarely had mite populations return to pretreatment levels for the duration of the trial. Pros and cons are that Fujimite acts very quickly and has long residual, but is highly toxic to predatory mites. Envidor has long residual and is safer on predatory mites, but takes longer to work. Acramite and Zeal also provided excellent knockdown of mites for a period of three to four weeks. Both products work quickly and are safe to predatory insects, though Zeal is highly toxic to predatory mites. Omite also continues to be an option, though its use decreases each year due to the availability of the reduced-risk miticides that were previously described. Table 1. Affects of hull-split sprays on residual control of spider mites in large scale field trials in Kern County, Treatment 1 Days after treatment to return to an average of 1 mite per leaf Days after treatment to return to an average of 2 mites per leaf Fujimite Envidor Acramite Zeal Kanemite 10 NT NT % Oil NT NT Most treatments were made with the addition of 1% 415 oil at a water volume of 200 GPA. 2 Not evaluated in that year. A Comparison of Several Methods for Controlling Pocket Gophers Roger A. Baldwin, UC Wildlife Pest Management Advisor, Kearney Agricultural Center Pocket gophers (Thomomys spp.) cause extensive damage to many crops throughout California. Many tools are available for controlling gophers including trapping, fumigation with aluminum phosphide, poison baits, and the use of a gas explosive device. Trapping gophers has been a common method for controlling gophers for many years. However, a new trap called the Gophinator (Trapline Products, Menlo Park, CA) is now available that may increase efficiency of trapping. Additionally, combining aluminum phosphide fumigation with trapping may increase effectiveness, as gophers will occasionally spring traps without getting captured. In these situations, gophers often become trap shy and are much more difficult to capture. Treating these tunnel systems with aluminum phosphide shortly after trapping could remove these individuals from the population thereby increasing gopher control in vineyards. Poison baiting with strychnine, zinc phosphide, and anticoagulant baits (e.g., chlorophacinone and diphacinone) has often been used to control gophers. Efficacy of these treatments has varied widely, although strychnine baits reportedly are most effective. Gas explosive devices have been used to control a number of burrowing animals, although no scientific Fruit & Nut Notes 9 July 2010

10 Pocket gophers continued.. studies on gophers have been reported. These devices combust a mixture of propane and oxygen within tunnel systems, thereby killing gophers through concussive force while also destroying the burrow system. All of these methods are currently allowable techniques for controlling gophers in California, although the efficacy and efficiency of these approaches, particularly in comparison to one another, remain unclear. To better address these issues, I established a replicated trial at Laguna Ranch, Sebastopol, CA, from 6 April 8 May, 2009, to estimate the efficacy and efficiency of these approaches. Three study blocks were established ranging from acres in size. Plots of all three treatment types (trapping + aluminum phosphide, baiting with strychnine, gas explosive device [Rodenator ]) and a control were established within each block. Based on absolute indices (number of sites with any gopher sign after treatment/number of sites with any gopher sign before treatment), Rodenator control ranged from 0 55%, baiting control ranged from 30 56%, and trapping + fumigation ranged from 74 90%. Relative index values (number of gopher mounds and feeder holes after treatment/number of gopher mounds and feeder holes before treatment) mirrored absolute indices, with substantial reductions in gopher sign for all trapping + fumigation plots (range = 91 96%); only 2 of 3 baiting (range = 22 81%) and Rodenator (range = 0 86%) plots indicated substantially reduced gopher sign. Index values did not differ for control plots for either absolute or relative indices. Therefore, observed differences within and across treatments did not appear to be an artifact of natural variation in gopher populations over the sampling period. The time required to apply each treatment was relatively similar between baiting, trapping, and Rodenator treatments ( seconds); fumigation treatments were substantially longer (260 seconds). Approximate costs per acre for each treatment were $420 for baiting, $396 for the Rodenator, and $252 for trapping + fumigation. Please note these values are higher than what would typically be observed as densities were at the highest levels recorded for gophers (>60 gophers/acre). To be effective, control measures need to result in a minimum of a 70% reduction in plots with gopher activity; values of 80 90% are preferable. Trapping + fumigation met this minimum criterion in all three plots, and met the more rigorous criterion in 2 of 3 plots. Even the one plot that fell short of an 80% reduction in plots with gopher activity yielded a 92% reduction in overall gopher activity. In addition to being more efficacious, trapping + fumigation was also more cost effective. Therefore, trapping + fumigation appears to be an effective method for controlling gophers. Baiting and Rodenator treatments did somewhat reduce gopher activity in most plots, but these levels of control fell well below the minimum threshold for effectiveness (70%). As such, growers may realize short-term benefits from control, but will have to apply equal effort for control the following year. More effective control measures (80 90%) should reduce the cost of control in subsequent years. Although absolute values were lower than desired for baiting and Rodenator treatments, relative index values indicated a substantial reduction in gopher activity for 2 of 3 plots for both baiting and Rodenator treatments. Therefore, an additional round of treatments could have resulted in greater absolute control values, although additional treatments would add additional costs to control efforts. This is of note, as baiting, and in particular, Rodenator, treatments have the potential for slowing reinvasion rates due to the destruction of gopher burrow systems by the Rodenator, and due to residual bait remaining in vacated gopher tunnel systems. However, given that these treatment types were already more costly than trapping + fumigation, a relatively high reduction in reinvasion rates would be required to offset these costs. These reinvasion rates are being assessed, although presently trapping + fumigation appears to be the most effective and efficient method for gopher control. Pocket gopher Fruit & Nut Notes 10 July 2010

11 Yolo County UCCE 70 Cottonwood St.. Woodland, CA, SACRAMENTO VALLEY ALMOND NEWS Fruit & Nut Notes The University of California prohibits discrimination or harassment of any person on the basis of race, color, national origin, religion, sex, gender identity, pregnancy (including childbirth, and medical conditions related to pregnancy or childbirth), physical or mental disability, medical condition (cancer-related or genetic characteristics), ancestry, marital status, age, sexual orientation, citizenship, or status as a covered veteran (covered veterans are special disabled veterans, recently separated veterans, Vietnam era veterans, or any other veterans who served on active duty during a war or in a campaign or expedition for which a campaign badge has been authorized) in any of its programs or activities. University policy is intended to be consistent with the provisions of applicable State and Federal laws. Inquiries regarding the University s nondiscrimination policies may be directed to the Affirmative Action/Staff Personnel Services Director, University of California, Agriculture and Natural Resources, 300 Lakeside Drive, 6 th Floor, Oakland, CA , (510) Cooperative Extension provides reasonable disability accommodation for those who require such assistance. To make sure your request for accommodation, please call at least two weeks prior to the event. Fruit & Nut Notes 11 July 2010