|Case Against Preventive Miticide Sprays
Managing Mites in the Almond Orchard
If left untreated, mites can cause severe economic damage in the almond orchard. Mites feed on tree leaves, causing reduced photosynthetic rates, which in turn have an adverse impact on almond production the following year. A classic study by a UC entomologist on the effects of a mite infestation found a 16% reduction in yield, a 25% drop in terminal growth, and a 7% drop in leaf size.
There are several species of mites that can cause damage in almond orchards, including Pacific spider mite, brown mite, two spotted spider mite, strawberry spider mite, European red mite, and citrus red mite.
From May through August, monitor for mites on at least a weekly basis. If the orchard has problem areas such as trees along roads or water-stressed trees, monitor every few days. Before July 1, focus on monitoring hot spots – areas that develop mites first. Once the treatment threshold has been reached in these areas, sample the remainder of the orchard to determine if a spot treatment is sufficient or the entire orchard requires treatment. After July 1, monitor the whole orchard, dividing it into sampling areas that could be treated separately.
Predators are important in managing mites, so consider their presence and relative abundance before treatments are applied. Orchards with high predator to pest mite ratios will not require treatment. Monitor orchards for both predators and spider mites at least once every two weeks from March to early May, and once a week or more after that. When treatments are required, choose selective miticides that have the least negative impact on predators.
New miticide choices
Several new miticides give almond growers an opportunity to obtain season-long control of problem mites without using the same material twice. These new choices will help prevent resistance, which is an emerging issue for the older miticides.
Another advantage of the miticide array available is a reduction of reliance on products which are formulated as emulsifiable concentrates (ECs) and emit volatile organic compounds (VOCs).
Some of the newer materials are slow-acting, but have long residual activity, which makes them good candidates for early-season application, while others have quick knockdown and short residual — useful for late-season applications when necessary.
New chemistries which are slower acting, but with longer residual, include Envidor (spirodiclofen), Onager (hexythiazox), and Zeal (etoxazole).
New chemistries with quick knockdown and shorter residual include Fujimite (fenpyroximate), Kanemite (acedquinocyl), Desperado (pyridaben + sulfur) and the organically approved Ecotrol (botanical oils). Summer oils also work in this manner.
A consideration in choosing a miticide is the effect of each product on the western predatory mite. This beneficial mite can control webspinning spider mites at lower populations.
Using the presence/absence sampling method as detailed at the UC IPM Web site will not only determine the need to treat, but also the contributions of the western predatory mite to managing webspinning mites.
Almond Board of California-supported work at UC Davis is assessing the impact of miticides on this important predator. Laboratory work on the effects of early-season miticides shows Onager does not kill adult predatory mites; however the longer-term impact on predatory mite eggs and female fertility has not been assessed.
Envidor maintains a slightly persistent negative impact lasting 5 to 15 days — while Zeal has the greatest negative effect on predaceous mites — reducing western predatory mite fertility for more than 30 days. For the later season miticides, research shows Kanemite and Acramite have a slightly persistent impact lasting 5 to 15 days.
In contrast, Fujimite has a persistent impact lasting more than 30 days. As noted in the UC IPM guidelines, pyridaben — the active ingredient for both Desperado and Nexter — is not as selective as other miticides. Therefore, it is best not to use it for early season control. Avoid pyrethroid, organophosphate and carbamate insecticides. All can cause upsets of biological control.
Dust reduction techniques benefit the environment and reduce mite flare ups. Avoid creating dusty conditions in the orchard. Dust is not only an air quality issue, it contributes to mite flare-ups.
Expanded Miticide Choices Boost Almond IPM Programs, Western Farm Press
UC IPM Spider Mite Management
UC IPM Mite Management
Seasonal Guide to Environmentally Responsible Pest Management Practices in Almonds