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 effectiveness of novaluron (Rimon 0.83 EC), acetamiprid (Assail 70 WP) or flonicamid (Beleaf 50 SG) in pairs of sequential tank applications for control of lygus bugs during bloom in alfalfa seed, as compared to a grower standard sequential application of dibrom (Dibrom 8 Emulsive) and metasystox-R (MSR Spray Concentrate). Under the low lygus pressure experienced in 2009 (5 to 10 lygus per sweep), sequential applications of novaluron, flonicamid, or acetamiprid (all six, two-pair combinations were tested) performed as well as the grower standard. Flonicamid provided better control of spotted alfalfa aphid than all other treatment combinations, but treatments did not differ in the control of pea aphids and blue alfalfa aphid, but again populations of all aphid species were low in 2009. Bee reproduction rates were compared in plots treated with novaluron (Rimon 0.83 EC) at the high labeled rate (12 oz/acre) in two early bloom applications compared to that of plots receiving a standard pesticide regime not including novaluron. Plots were individual pairs (replicates) of grower fields. Alfalfa leafcutting bee release rates, shelters, shelter placement and field management were as similar as possible. X-ray analyses of bee cells from novaluron-treated and untreated plots indicated that, although mean number of bee cells did not differ in plots treated with novaluron and plots treated with a grower standard insecticide, the number of pollen balls was higher in plots treated with novaluron. The percentage of pollen balls also was higher, and the percentage of live larvae lower, in novaluron-treated fields. Pollen balls averaged about 20% more in plots treated with novaluron compared to plots treated with a grower standard insecticide. Dissection of pollen balls revealed that plots treated with novaluron had a significantly lower percentage of live eggs compared to plots treated with a grower standard insecticide. Trends were similar for samples collected at two week intervals, and samples collected only once at the end of the bloom period. The negative impact of novaluron on percent pollen balls and percent live larvae, however, was greater in sequentially collected samples. This may indicate a diminishing impact of novaluron on alfalfa leafcutting bees during the later bloom period. ADODR monitoring is done via e-mails, phone calls, and discussions at professional meetings.