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Issue No. 15/July 1, 2005

Rootworms South of I-70, and Assessing Rootworm Larval Injury
Corn growers in at least the couple of tiers of counties south of I-70 should examine their cornfields for rootworm larval injury.

Rootworm Adults and Silk Clipping
Rootworm adults are clipping silks on plants in fields in which stand development has been uneven, as a direct result of our weather this spring. Consequently, rootworm adults are “ganging up” on the plants that are tasseling and silking early, and much of the rest of the field has not begun to flower.

Japanese Beetle Invasion
Deciding if and when to spray for Japanese beetles can be extremely difficult. Hindering management decisions this year and causing even more anxiety are the drought conditions.

Twospotted Spider Mite Infestations in Soybeans Intensify as Drought Conditions Persist
Observations of spider mite infestations in soybeans are common across many areas of the state. The current threshold is to consider a rescue treatment when 20% to 25% of soybean leaves are discolored before pod set. After pod set occurs, a rescue treatment should be considered when 10% to 15% of the leaves are discolored.

Update--Soybean Aphids
The high temperatures seem to have suppressed development of soybean aphid colonies. But keep scouting to avoid surprises.

Still Waiting for Rain
The most recent corn crop condition report shows an Illinois corn crop in serious decline. The concern that soybean won’t fill its canopy very well in wide rows will continue to increase as long as it stays dry. The winter wheat story is a fairly positive one this year.

Regional Reports
Reports are provided this issue for northern, southern, and west-central Illinois.