Research and IPM

Almond Production in California: A Study of Pest Management Practices, Issues, and Concerns

By Sonja Brodt¹, Frank Zalom², Rose Krebill-Prather³, Walt Bentley¹, Carolyn Pickel¹, Joseph Connell⁴, and Larry Wilhoit⁵
(2/9/04)

A recent survey conducted by the University of California Integrated Pest Management Program (UC IPM) suggests a reduction in use of organophosphate sprays by almond growers in California’s three major production regions, the Central and South San Joaquin Valley, the North San Joaquin Valley, and the Sacramento Valley. The survey, conducted in 2000, asked growers to report on practices they used during the 1999 growing season. Results presented here focus primarily on growers reporting more than 20 bearing acres.

Sixty-six percent of responding growers reported spraying during the 1998-99 dormant season. These figures are lower than the 93 percent who reported using dormant sprays in a 1986 survey of all almond growers conducted by UC researchers (Figure 1). Approximately half of growers responding in both years considered peach twig borer (one of the main targets for dormant sprays) to be a problem that required control to prevent economic damage in their orchards. San Jose scale, another target of dormant sprays, was considered a problem by 21 percent of growers in the 2000 survey (The 1986 survey did not ask about San Jose scale problems.)

Furthermore, approximately one-third of growers who reported using dormant insecticide sprays in 1999 also reported applying oil alone during the dormant season, suggesting that some growers use different applications on different orchard blocks (either insecticide and oil, or oil alone), or that they considered the oil alone to be a "dormant insecticide."

Changes in dormant spray use to some extent reflect the history of UC pest management recommendations regarding dormant sprays. In the 1970’s and 1980’s, UC recommended the use of dormant sprays to control peach twig borer, San Jose scale, and the eggs of both brown almond mite and European red mite. Spraying during the dormant season reduces overwintering populations of these pests during vulnerable periods of their lifecycles while reducing exposure of biological control agents and nontarget organisms as well as workers who might be in orchards during the growing season. Dormant sprays can also effectively reduce or eliminate the need for multiple insecticide applications for the target pests during the growing season. However, water quality concerns arose during the early 1990’s when it was discovered that organophosphate runoff from agricultural and urban areas during the rainy season was entering waterways and posing a potential risk to aquatic invertebrates. Subsequently, UC research and extension recommendations emphasized monitoring for the key pests before applying dormant sprays and also focused on alternatives to dormant sprays, including spraying only an oil during the dormant season and then using Bt sprays during bloom.

The decline in use of dormant sprays may be an indication of the success of UC’s research and extension efforts to help the industry respond to important environmental concerns with acceptable alternatives while maintaining quality almond production.

Furthermore, the decline in dormant sprays has not led to a corresponding increase in in-season sprays of organophosphate insecticides. Survey data show that use of May sprays of organophosphates has also decreased since 1986, from 78 percent to 22 percent, as has the use of hull-split sprays, from 82 percent to 58 percent (Figure 1).

Figure 1. Percent of Surveyed Growers Applying Organophosphate
Insecticides in 1986 and 1999 (1986 sample includes all farm sizes;
1999 sample includes only farm sizes >20 acres).

Survey results suggest that by 1999 many almond growers were using reduced-risk alternatives to organophosphate sprays. Figure 2 illustrates that almost one-third of growers surveyed in 2000 applied dormant oil with no insecticides to kill overwintering scale and mite eggs. In addition, 41 percent applied the microbial pesticides Bt or spinosad to control peach twig borer, while 8 percent reported using pheromone mating disruption.

Figure 2. Percent of Surveyed Growers (acreage >20) Who
Applied Alternatives to Organophosphate Sprays for Control
of Peach Twig Borer and San Jose Scale in 1999.

Careful pest monitoring forms the backbone of any IPM program. And indeed, the vast majority of growers responding in 2000 reported monitoring peach twig borer and navel orangeworm in 1999, 84 percent and 82 percent respectively. Sixty-six percent responding growers also reported monitoring San Jose scale. For peach twig borer, nearly two-thirds of all responding growers reported sampling blossom and shoot strikes (64 percent), while just over half monitor emergence from hibernacula at limb crotches where the larvae overwinter (55 percent) and/or use pheromone traps (56 percent). Monitoring emergence from hibernacula can be especially useful for timing Bt bloom sprays. Two-thirds of responding growers who reported using dormant sprays also reported monitoring hibernacula. Of the one-third who did not monitor hibernacula, about half also reported not having sampled blossom and shoot strikes the previous year, suggesting that some growers apply dormant sprays prophylactically rather than using monitoring to determine if there is a need to control peach twig borer. In some cases, however, it is also possible that the grower's PCA may have been performing this monitoring without the grower's knowledge.

San Jose scale can be monitored during the dormant season by checking for infested spurs, and by placing double-sided sticky tape or pheromone sticky traps in the orchard. Survey results in 2000 showed that 43% of growers checked for infested spurs in 1999, while only 19% monitored by placing double-sided sticky tape and only 14% used pheromone sticky traps. Furthermore, almost half of those reporting use of dormant sprays reported not monitoring for scale. Most of these growers who did not monitor, however, also reported that they did not consider scale to be a problem that year (66 percent).

Navel orangeworm is monitored by counting the number of mummy nuts remaining in trees, which is best done in February. If there are two or fewer nuts per tree at this time, an in-season treatment for navel orangeworm will probably not be needed. Only about half of growers responding in 2000 reported that they had counted mummy nuts (54 percent). Navel orangeworm can also be monitored near or after harvest by examining for eggs or larvae in nuts. In the 2000 survey 62 percent of growers indicated they monitored navel orangeworm in this way. Monitoring at this time, however, only informs the grower whether a problem has already occurred, and does not give much scope for prevention and treatment during the current season. A more effective method of in-season monitoring is to place baited egg traps in the spring, so that if in-season sprays are needed, they can be optimally timed to coincide with egg laying in May or with hull split. In the 2000 survey, 47 percent of responding growers indicated they do place baited egg traps in the spring. And among those growers who did apply insecticides at hull split, 58 percent reported using egg traps to monitor navel orangeworm.

Declines in organophosphate use by surveyed growers in the three major almond producing regions of California suggests encouraging trends within the industry to reduce negative environmental impacts of pest control practices. The findings also show that a proportion of growers are successfully using various monitoring techniques to decide on the need to apply an insecticide for key insect pests and/or are using available alternative techniques for their control, thus attesting to the efficacy of these practices. The survey results also suggest, however, that more growers could benefit from the use of monitoring as a key component of pest management decision making and could make greater use of alternative techniques for the control of key insect pests.

Acknowledgements

The survey was conducted by the UC IPM Program in support of the Almond Pest Management Alliance. In addition to the authors, Pete Goodell (UC IPM Program), Chris Heintz (Almond Board of California), Marsha Gibb (Community Alliance with Family Farmers), and Gene Beach (Almond Hullers and Processors Association) participated in developing the survey and their contribution to the effort is gratefully acknowledged.

¹ University of California Statewide Integrated Pest Management Program
² Department of Entomology, University of California, Davis
³ Social and Economic Sciences Research Center, Washington State University
⁴ University of California Cooperative Extension, Butte County
⁵ California Department of Pesticide Regulation

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