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 conducted to examine the susceptibility of alfalfa leafcutting bees to novaluron (Rimon 0.83 EC) when this pesticide is applied during the early, middle or late period of alfalfa bloom. After each Rimon application, we also evaluated the impact of the length of time bees had access to nesting (full access and access limited by 2 and 4 weeks after spray). Spray timing had no impact on the mean number of alfalfa leafcutting bee larvae that were alive at the end of the season. However, percent of cells with dead eggs or very small larvae was lower, and percent live larvae higher, on unsprayed (control) plots and plots treated with Rimon late in the bloom period than on plots treated in early and mid-bloom periods. These results indicate a diminishing impact of Rimon on alfalfa leafcutting bees when applied during the later bloom period. The effect of predators on lygus bugs and alfalfa aphids was also evaluated. All insects were removed from alfalfa stems, these stems were then placed in sleeve cages. The cages were re-infested with 10 small lygus bug nymphs and 0, 20 or 40 pea aphids. Late instar (older larvae) or adult big eyed bugs or damsel bugs were then added at a rate of 0 predators or two predators (2 big eyed bugs, 2 damsel bugs or 1 big eyed bug plus 1 damsel bug) per cage. Big eyed bugs and damsel bugs reduced lygus bug survival when sleeve cages contained 0 or 20 aphids per cage, but not when cages contained 40 aphids. Aphids had no impact on lygus survival in the absence predators. In other words, when aphid infestations are high, they provide an alternative prey for the predators, and then biological control of lygus is diminished. This study indicates that aphid management (or lack of) may significantly impact biological control of lygus provided by generalist predators. ADODR monitoring is performed through email and phone calls, as well as discussions at professional meetings.