Several new miticides have come on the market recently, giving almond growers an opportunity to obtain season-long control of problem mites without using the same material twice. This will help maintain efficacy of all miticides.

With the array of miticides now available, it is possible not to spray any one active ingredient more than once per season. This is particularly important because resistance is an emerging issue for the older miticides, such as Omite, Vendex, Apollo, and abamectin, which is sold as Agri-Mek and other trade names. Other miticide active ingredients sold under multiple trade names are pyridaben (Desperado and Nexter) and hexythiazox (Onager and Savey).

Using Desperado and Nexter in the same season, for example, would be using the same active ingredient twice.

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 constituents (VOCs). California pesticide regulators are pushing to reduce emissions from these compounds. One miticide formulated as an EC is abamectin.

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.

Application windows

Ongoing research supported by grants from the Almond Board of California and conducted by David Haviland, Extension entomology advisor, Kern County, is showing which products work best, and at what timing in the southern San Joaquin Valley.

The next question being resolved is to determine the consistency of these products in large-scale research plots over several seasons.

Up until now, the early season “standard” miticide has been abamectin. Haviland found that Envidor, Onager and Zeal also work well when applied in this window. In his large-scale trials last year, application of these products in May resulted in spider mite suppression until hullsplit or after. Mite reduction was comparable to results with abamectin when applied at the same time, making them good alternatives, or products for use in rotation.

At hullsplit Haviland discovered that Envidor and Zeal, as well as several contact materials, are effective. Contact materials include Fujimite, which has consistently had the greatest effectiveness and longest residual in his trials, as well as Kanemite and Desperado that have shorter residuals, but can be used close to harvest. Trials in the south and north also show Acramite has performed during this window and this miticide has been registered for a while.

Mite monitoring

Because the early season miticides are slower acting, they should be applied after sampling indicates pest mites are increasing, but before significant webbing or damage is present. As a group, these miticides generally stop development of juvenile-immature stages — both eggs and nymphs.

Monitoring and sampling guidelines are given at the UC IPM Web site, which calls for weekly monitoring starting in May. Areas of the orchard that may be more susceptible, such as along roads or where deficit-irrigation may have stressed trees, should be monitored more frequently.

When treatment thresholds are reached in these areas, sample the remainder of the orchard to determine if a spot-treatment is adequate, or the entire orchard requires treatment.

After July 1, monitor the whole orchard, dividing it into sections that can be sampled and treated separately. Contact materials, which provide quick knockdown and have varied levels of residual, are most likely to be used effectively during July and August, which is the traditional Omite timing.

Mite predators

Another 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 by Dr. Frank Zalom, entomologist, UC Davis, is assessing the impact of miticides on this important predator.

Zalom's 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, Zalom's work 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.