1a. Objectives (from AD-416):
Lygus bugs are key pests in alfalfa seed production systems and control is often hampered by a need to protect alfalfa leafcutting bees, which are released in these fields as pollinators. Until recently, compounds available for lygus bug control in alfalfa seed consisted largely of broad spectrum, organophosphate, carbamate and pyrethroid insecticides. Since 2006, three new, low risk pesticides have received Special Local Needs (24c) registration for lygus bug control in alfalfa seed: novaluron (Rimon 0.83 EC), acetamiprid (Assail 70 WP) and flonicamid (Beleaf 50 SG). These compounds are expected to be safe to non-target insects, including bees. However, there is a need for research evaluating the effectiveness of these compounds when used in rotation during the bloom period. For example, do rotations that use the systemic compounds, (flonicamid or acetamiprid) early in the bloom period followed by a spray of novaluran late in the bloom period, effectively control lygus compared to rotations that use novaluron early and systemic compounds late? There presumably would be an advantage to using the systemic compounds early as plant uptake of these compounds, and therefore effectiveness, should be better early rather than late in plant development. Likewise, the use of the most selective compound, flonicamid, during early bloom may be less disruptive to bee nesting and pollination during this period. These compounds can also be applied as tank mixes. The project will determine the safety of these compounds and application methods to alfalfa leafcutting bees in the field, and as compared to more traditional insecticides.
1b. Approach (from AD-416):
1. Conduct field experiments examining the effectiveness of novaluron (Rimon 0.83 EC), acetamiptrid (Assail 70 WP) and flonicamid (Beleaf 50 SG) for control of lygus bugs in alfalfa seed. One experiment will include all combinations of the compounds used in sequential bloom period applications. A second experiment will compare all tank mix combinations of these compounds during the bloom period in two bloom period applications. An untreated control and standard bloom period applications of Dibrom or MSR will be included in both experiments. The bloom period treatments in both experiments will be bracketed by pre-(Warrior applied 5 to 7 days prior to bee release) and post-bloom (Supracide applied ca. 2 weeks after the final bloom period treatment) clean up sprays. Studies will be conducted on 0.01 acre plots of established alfalfa seed at the Parma R&E Center, Parma, ID. Plots will be arranged in a randomized complete block design with four replications. Foliar broadcast spray applications will be made using a tractor-drawn boom sprayer calibrated to apply 30 gpa at 32 psi using 8002VS flat fan nozzles on 22" spacing. Lygus bug and natural enemy abundance will be estimated at 7, 14, 21, and 28 days after treatment by taking one, 180-degree sweep from each plot on each date. The number of pea aphids + blue alfalfa aphids, and spotted alfalfa aphids will also be recorded. Yield (lbs/acre) and percentage damaged seed will be collected from each plot. All materials will be applied according to label specifications. Data will be analyzed using repeated measures ANOVA. 2. Conduct laboratory and field experiments that determine the response time of alfalfa leafcutting bees (ALCB) combinations of the the three newer insecticides and of each new insecticide tank mixed with abamecktin (Temprano), lambda cyhalothrin (Warrior), bifenthrin (Capture), and dibrom (Dibrom 8E). Other combinations may be evaluated as time allows and as producer input is received. The response time of treatments to alfalfa leafcutting bees (ALCB) and to adult bigeyed bugs, damsel bugs and minute pirate bugs will be determined by exposing insects to field-weathered alfalfa foliage 2h, 8h, 24h, 48h & 96h after application of selected pesticides. Experimental design will be a randomized complete block with 4 replicates. Pesticides will be applied at labeled rates using a CO2-backpack sprayer calibrated to apply 30 gpa at 32 psi using 8002VS flat fan nozzles on 22" spacing. Mortality of insects will be plotted over time.
3. Progress Report:
Field experiments were continued to examine the efficacy of currently labeled and new insecticides against lygus bugs and other pests of alfalfa, and to determine the safety of these to bees. We compared the efficacy of the sulfoxamine insecticide, sulfoxaflor (Transform WG), against lygus bugs and aphids in alfalfa seed with that of two currently labeled insecticides: flonicamid (Beleaf 50SG), an anti-feedant insecticide with good efficacy against lygus bugs and aphids that is considered safe to alfalfa leafcutting bees and most natural enemies, and lambda-cyhalothrin (Warrior II), a pyrethroid with good activity against lygus bugs, fair activity against aphids that is harmful to alfalfa leafcutting bees and most natural enemies. None of the insecticides provided control of adult lygus bugs. This was not unexpected since pesticide impacts on the very mobile adults are difficult to document. All insecticides provided control of small (instars 1-3) and large (instars 4 & 5) lygus nymphs compared to the untreated control. Two, applications of these insecticides spaced 14 days apart provided better lygus and aphid control than a single application. Two applications of sulfoxaflor provided control equal to or better than that provided by two applications of flonicamid or lambda-cyhalothrin. Sulfoxaflor provided better control of pea and blue alfalfa aphids than flonicamid or lambda-cyholothrin and there was a similar, but not quite as strong, trend for spotted alfalfa aphids. Some caution in reference to the flonicamid results is necessary, since flonicamid kills very slowly and high numbers are not necessarily an indication of lack of control. We also continued laboratory experiments to determine the residual time required before sulfoxaflor resudues cause only 25 percent mortality (RT25) for adult alfalfa leafcutting bees. Field collected and apparently healthy alfalfa leafcutting bees were exposed to alfalfa foliage treated with sulfoxaflor (2.25 oz per acre) that had been field-weathered 2h, 8h, 24h, 48h & 96h post-application. In this test mortality of adult bees never exceeded 25 percent (RT25 less than 2hr) indicating that sulfoxaflor likely could be applied during early mornings with little or no harm to bees.