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Options for dormant-season pest management in almonds

In an ongoing quest to develop sustainable, economic, reduced-risk options for dormant-season control of peach twig borer (PTB) and other insects and mites, University of California entomologists and farm advisors have developed a substantial body of information related to sampling and treatment thresholds, combinations of products, and application timings and methods to manage these pests in an environmentally sound program. The research, supported since 1998 by the Almond Board of California (ABC), the California Department of Pesticide Regulation and U.S. EPA Region 9, came about primarily because of water quality concerns related to organophosphate pesticides used in dormant sprays. Moreover, this research has led to reduced exposure and risk to wildlife, such as hawks.

Over the years, the findings of this research have been accumulated and made accessible to almond growers through the ABC Almond Industry Conference, the Environmental Committee of the ABC in partnership with the Coalition for Urban and Rural Environmental Stewardship (CURES), and the Almond Pest Management Alliance. The findings are summarized both in the “Seasonal Guide to Environmentally Responsible Pest Mangement Practices in Almonds,” UC Agriculture and Natural Resources Leaflet 21619, and online as the Almond Year-Round IPM Program ( ).

As a result of this research and education, dormant sprays of organophosphates in almonds have been reduced substantially, despite increased acreage since the programs were initiated.

Best management practice options

Studies show there are numerous options to traditional dormant control of peach twig borer, as newly available reduced-risk materials can be applied either in-season and/or in combination with a dormant oil application. Dormant treatment is still best to control San Jose scale, European red mite, and European fruit lecanium. However, UC researchers led by Walt Bentley have developed a dormant spur sampling technique and guidelines to determine when treatment is really necessary.

Peach twig borer alternatives

As part of the dormant-season pest management project, UC investigators Frank Zalom and Franz Niederholzer have evaluated alternative products and application timings for PTB control compared to more traditional diazinon and esfenvalerate (Asana). Several new reduced-risk products were included in delayed-dormant trials in the most recent year of investigation. These products all provided PTB control “at a level similar to that afforded by the pyrethroids and organophosphates, when properly timed,” according to their final report. As well, a number of reduced-risk materials can be applied in season, for instance, timed with pheromone traps in May for effective control.

Another option is earlier applications of traditional pesticides for PTB control to reduce insecticide runoff. In two years of trials as part of the long-term dormant-season pest management project, combinations of esfenvalerate with oil, diazinon with oil, and both products alone at different timings, were show to significantly reduce PTB shoot strikes in all of the treatments at all of the timings compared to the untreated controls. Treatment dates were mid-October, late November, late December and late January. However, the researcher, UC Davis Entomologist Frank Zalom, in collaboration with Farm Advisor Franz Niederholzer, Sutter/Yuba counties, reported that applications made later, on the December and January treatment dates, were more effective than on the earlier treatment dates. They also found that December treatments containing oil accelerated bloom by eight days in the final year of the trials, in contrast to either earlier or delayed-dormant sprays with oil that did not accelerate bloom.

Sampling and treatment decisions for scale/mites

Dormant spur sampling can be used to determine when treatment is necessary to control San Jose scale, European red mite, brown mite and the scale European fruit lecanium. Spurs, the short shoots that contain flower buds, are sampled once a year between mid-November and the end of January.

Treatment thresholds have been established for these pests on the basis of the number of spurs found with live scale or mite eggs. When thresholds are reached, oil or oil plus a reduced-risk pesticide such as an insect growth regulator can be used. Spur sampling and treatment guidelines can be found under the almond Pest Management Guidelines at the UC IPM Web site.

Delayed-dormant is the best timing for oil applications, according to Walt Bentley, IPM entomologist, UC Kearney Ag Center. “Avoid applications close to a fungicide spray that could result in phytoxicity from the oil,” he cautions. He also warns that using the higher rate of oil (6 gallons per acre) to treat San Jose scale may damage trees stressed from drought. However, he notes that “as growers have done post-harvest irrigations, the occurrence of oil damage has dropped dramatically.”

As mentioned above, a dormant treatment decision table and a list of environmentally friendly insecticides are provided in the publication, “Seasonal Guide to Environmentally Responsible Pest Management Practices in Almonds,” created with support by the Almond Pest Management Alliance, and available through UC Agriculture and Natural Resources or at the UC IPM Web site.

Additional dormant-season BMPs to mitigate off-site movement of pesticides are given in a CURES BMP publication. This information is also available at the CURES Web site

Almond growers interested in this and other almond-production topics can learn more at the Almond Board of California-sponsored Almond Industry Conference to be held Dec. 10-11 at the Modesto Centre Plaza, Modesto. Go to for more information.

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