Soybean aphid densities were very low throughout Illinois in 2010. In fact, suction trap counts in September and October of last year were exceptionally low, Gray says. These sub-economic adult densities led to very few eggs on its overwintering host, buckthorn.
"I anticipate a very weak flight of aphids to soybean fields this spring," he says. "The late planting of soybeans will further contribute to a downward spiral of aphid densities early in the season. If the summer of 2011 is mild, aphid densities could certainly rebound by late season. The reproductive power of this insect is impressive. A hot summer may result in another "no-show" for this insect."
White grubs and wireworms
In general, delays in corn planting negatively affect densities of these soil insect pests. If planting has occurred and seedlings are subjected to prolonged periods of cool and wet soil conditions, increased levels of root injury by white grubs and feeding on below-ground portions of the stem may occur by wireworms.
"As soil temperatures increase, wireworm larvae typically begin to move deeper into the soil profile and away from the seed zone", Gray explains. "Corn that is planted later in the month into soils that are becoming progressively warmer may not experience as much wireworm injury."
Annual white grubs, such as Japanese beetle grubs, typically complete pupation by late May and early June. Consequently, their potential to injure late-planted corn is greatly diminished the further planting is delayed in May. However, true white grubs have a three-year life cycle and may injure corn root systems all summer long the second year of their life cycle. Accurate identification of grub species is key to their effective management, Gray says.
Corn earworms, corn leaf aphids, and fall armyworms
Many insects migrate into the Midwest each year. However, it's a bit too early to determine how the planting may affect densities of corn earworms, corn leaf aphids, and fall armyworms, according to Gray.
"Corn may reach the pollination period at a later date in July this season, typically a period of the summer more prone to hot and dry conditions," he concludes. "These insects may reach economic densities on corn plants growing under more stressful conditions this year. Time will tell."
For more information on late planting and insect pests, read the May 12 edition of The Bulletin online at http://bulletin.ipm.illinois.edu/.