Volume 63 Number 15 Date 08/16/2018
SOYBEAN APHID - Surveys indicate that populations remain below the established 250 aphid-per-plant treatment threshold in the majority of Wisconsin soybean fields. Densities have increased noticeably since late July, though in most instances, levels field-wide have not reached the point where control is required. The statewide average count at 172 sites surveyed from July 23-August 16 was only eight aphids per plant, with moderate averages of 100-230 aphids per plant found at only 2% of sites. Average counts above the 250 aphid-per-plant economic threshold have not been recorded in any soybean field surveyed by DATCP this season.
GREEN CLOVERWORM - Larvae of various sizes continue to cause light defoliation of soybeans in the southern and west-central counties. The damage observed in the past week was minor at less than 5-10%. This sporadic soybean pest is highly susceptible to parasitism and disease, and is usually controlled without insecticide use.
JAPANESE BEETLE - This beetle remains common in soybeans over much of the state. Although many fields have an abundance of beetles and varying levels of perimeter defoliation, the degree of injury is generally not severe enough to justify treatment. Economic defoliation above the 20% threshold for soybeans in the seed-filling stages has not been observed in any of the 172 fields surveyed in the past three weeks.
TWO-SPOTTED SPIDER MITE - Development and reproduction have been favored by this month's predominantly dry weather pattern. Surveys have found evidence of mites in soybeans in scattered areas of the state, and infestations could persist for throughout August in drier locations. Continued surveillance of soybeans is suggested for another two weeks. As is the case with the soybean aphid, treatment of this pest is not beneficial after the R5 to R5.5 or full pod growth stages.
-- Krista Hamilton, DATCP Entomologist