Soybean Aphid Update February 2004

Soybean Aphid Biology Aphid colonization occurs earliest near wooded, protected areas; along streams, especially when buckthorn is present. Soybean aphids reproduce the fastest at 82º F – populations double every 1.5 days. Reproduction is slower at higher or lower temperatures. Lady beetles, minute pirate bugs and parasitic wasps are natural enemies and are significant in lighter infestations. Beneficials exhibit a “lag” behind aphid development and can not slow a rapidly increasing aphid population. Soybean aphids lay their eggs on the overwintering host plant, buckthorn. Crimson clover, red clover, and scarlet runner beans are alternate hosts if soybeans are not present in the spring. Heavy rainfall helps reduce numbers, however, information is largely anecdotal. Ground application of insecticides may provide slightly better effectiveness than air application, but the difference is not significant research indicates a loss of 0.5 – 0.6 bu/acre for each day that treatment is delayed beyond the Economic Injury Level. The greatest yield advantages came to those fields treated early rather than late.

Variety Trial Roundup Ready Beans 1000 – 1500 aphids per soybean plant sprayed by ground ~R3 stage, Aug 12, pint Lorsban 4E/acre 14.7 bu/acre yield improvement 2003 Soybean Aphid Treatment Map Northern Iowa Area Community College - Kevin Muhlenbruch, CPAg

Review of Soybean Growth Stages R1 Beginning bloom (open flower at any node) R2Full bloom (open flower at one of two uppermost nodes on main stem) R3Beginning pod (pod 3/16 inch long) R4Full pod (pod ¾ inch long) R5Beginning seed (seed 1/8 inch long) R6Full seed (green seed that fills pod cavity)

Soybean Aphid Management Recommendations for 2004 Scout fields in July to mid-August during late vegetative stage through seed set (R1 – R5). Potential for damage is not as well understood at later growth stages (R3-R5) but yield advantages have been documented at these later growth stages. A scouting-based Economic Threshold has been established which signals the need for insecticide application when 25 aphids per leaflet are found on late vegetative – early reproductive soybeans. –250 aphids per plant at R1 – R2 –1,000 aphids per plant at R3 –1,500 aphids per plant at R4 – R5

Aphids averaged 1085 per plant prior to treatment. 5.34” of rainfall in the seven days following application reduced aphid populations by 80 – 90% in all treatments. This is the “crash” that can result from heavy rainfall. This trial utilized the high end of the rate range of all products tested. “Lorsban produced sig. better control than Warrior or Mustang Max,” Ron Hines, Sr. Researcher

Treated August 7 at R2 A “medium” level of rates were tested here. “Furadan and Lorsban provided the best control throughout the sampling period. The pyrethroids, while providing control, did not achieve the level of SA reduction provided by the other materials …. The only plots relatively clean of honeydew and sooty mold were the Furadan and Lorsban treatments” Ronald Hammond, Ohio Agricultural Research & Development Center.

Quick Knockdown and Residual At 21 days after treatment, there was no statistically significant difference between the esfenvalerate and lambda cyhalothrin nor between the methomyl and untreated treatments. Chlorpyrifos, at both the 0.5 #/A and the 1.0 #/ac rate, demonstrated the greatest residual of all products tested. esfenvalerate– Asana 0.03 #ai/ac = 6 oz/ac #ai/ac = 7 oz/ac 0.04 #ai/ac = 8 oz/ac methomyl - Lannate 0.45 #ai/ac = 0.5 #/ac chlorpyrifos – Nufos, Lorsban 0.5 #ai/ac = 1 pt/ac 1.0 #ai/ac = 2 pt/ac lambda-cyhalothrin – Warrior 0.25 #ai/ac = 3.2 oz/ac* * equivalent to 3.2 oz/ac (0.125 #ai/ac) gamma-cyhalothrin - Proaxis

Application made between R1 and R2 on Aug 14. “Pounce and the low rate of Baythroid were not significantly different than the untreated control and technically not different from the other insecticides as well, however … the low rate of Baythroid and Pounce probably had the greatest chance for resurgence … since each left a significant proportion of the original population in the field,” Tom Clark, Dept of Entomology.

**** LOG SCALE **** Treated July 31 at R2, >500 aphids per plant Lorsban provided statistically superior control over all treatments at 4 DAT. Lorsban and Warrior provided statistically superior control over all other treatments at the one and two week intervals after application.

Foliar applied insecticide control (product performance) for Soybean aphid. Randall Reinhart farm, Nicollet County, MN (2003). B. Potter, U of M Treatments applied July 18 to R2 soybeans. “The 1 pint rate of Lorsban and the 2.0 and 3.2 oz rates of Warrior provided significantly better knockdown than other products,” Bruce Potter, SWROC, U of MN Lorsban-4E was numerically superior to all treatments at 4 DAT; Lorsban-4E and Warrior were statistically superior to all other treatments at that same timing.

Treatment on August 7/8, stage unknown Insecticide treatments provided 4.3 to 7 bushel yield increase over untreated.

Mustang 2.25 oz/acre 1.6 oz/acre 2.56 oz/acre 2.56 oz/acre 1.0 pt/acre Lorsban-4E can have a shorter depressive effect on some beneficial insects

Soybean Aphid Control with Lorsban*-4E insecticide Lorsban-4E is the industry standard for aphid control in many crops Lorsban-4E provides fast, complete knockdown of aphid populations Roughly 2.5 million acres of soybean aphids were treated with Lorsban-4E in 2003 by ground or air Results were excellent with either application method The ability to tank-mix with glyphosate makes Lorsban-4E extremely versatile In addition to aphids, Lorsban-4E also controls bean leaf beetles, grasshoppers, corn rootworm beetle adults and even spider mites in soybeans Rapid knockdown contact activity is enhanced by fuming activity of Lorsban-4E. This fuming activity explains the quick kill and greater effective coverage; in some cases Lorsban-4E vapors move laterally short distances thus eliminating aphids on foliage not directly sprayed. This movement needs to be taken into consideration when setting up insecticide strip plots. In the few instances where very small double crop soybeans are treated, residuality of Lorsban-4E may be compromised due to this fuming action if there is very little foliage to adhere to. In addition, late planted soybeans are the most attractive for aphid re-infestation.