No. 13/June 23, 2000

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IN THIS ISSUE:
Grape Colaspis Story Changes Chapters
Many people throughout central Illinois will remember 2000 as yet another year when grape colaspis larvae caused economic damage to corn. We still know very little about the biology and behavior of these insects, and management options are few and far between. We would like to keep track of when grape colaspis adults move into soybeans. If you find grape colaspis adults on yellow sticky traps, in sweep nets, or simply by observation, please let us know.

Corn Rootworm Adults Are Emerging
Rootworm development this year is a bit ahead of schedule, so it's not too soon to start watching for both northern and western corn rootworm adults throughout the state. The article discusses two reasons to scout for rootworm adults in corn: to watch for silk-clipping injury that interferes with pollination and to assess the potential for injury in corn in 2001.

Evaluating Corn Roots for Rootworm Damage
From mid-June through early July, many growers, dealers, consultants, and seed and pesticide company representatives spend some time roaming through cornfields, digging up root systems, and looking for corn rootworm larvae and signs of their feeding injury. Appropriate interpretation of what you find is important.

The article presents the best procedure for sampling for rootworm larvae and assessing root damage. We think it is more prudent to assess performance of an insecticide by evaluating the amount of damage to the root system.

The article also addresses "rescue" treatments for cornfields with rootworm larvae and rootworm damage.

Status of European Corn Borers
The amount of injury being caused by corn borers in southeastern counties this year is greater than the amount of injury being caused in northwestern Illinois. It is usually the other way around, although the presence of southwestern corn borers in southern Illinois changes things a bit. As it stands right now, we probably will not experience many problems with first-generation European corn borers this year. Nevertheless, when adults that will lay eggs for the second generation begin emerging in July, we'll keep you apprised.

Spider Mites in Soybeans in Some Dry Areas of the State
For those of us in areas of the state that have been inundated with rain, talk about twospotted spider mites in soybeans seems silly. However, in the dry areas in western Illinois, spider mites have begun to make their presence known.

Management of twospotted spider mites in soybeans depends greatly on vigilance. At the first sign of injury caused by spider mites, you should examine the injured area to look for the mites. If you find spider mites only in field edges, spot treatments to prevent additional damage and to halt their movement may be justified. However, you should make certain that spider mites are not present throughout the field.

Soybean Leaf Cupping/Puckering
While the 2000 growing season has been relatively favorable for soybean development and has also allowed for timely applications of postemergence herbicides, the leaf-puckering phenomenon has again appeared. This article presents several theories that have been put forward by weed scientists across several states in the north central region, including the following:

1. Somehow, the plants have been exposed to a growth regulator herbicide. 2. The soybean plant is expressing a physiological response to somewhat adverse growing conditions. 3. The response is induced by a postemergence herbicide application.

Note that it is very unlikely that only one of these possibilities will explain the cause of puckered soybeans in all instances.

The available literature tends to suggest that this type of injury does not always necessarily result in soybean yield loss, but several factors are involved in determining if yield loss will occur, such as soybean variety, time of exposure, and dosage.

Maximum Weed Sizes for Post-emergence Soybean Broadleaf Herbicides
Surplus rainfall, hot temperatures, and some delayed soybean planting have all combined to create significant broadleaf weed problems in many soybean fields. One "good" point with respect to past and current environmental conditions is that the weeds have not been under moisture stress conditions and are relatively "soft." This may translate into better activity from many post-emergence broadleaf herbicides. Unfortunately, the soybeans are also "soft," which increases the likelihood for crop response following the postemergence herbicide application.

The article includes a table that contains maximum broadleaf weed sizes as indicated on several postemergence soybean herbicide labels.

Postemergence Soybean Herbicide Injury: Is There a Yield Penalty?
Postemergence herbicide applications for weed control in soybeans are nearly completed in some areas of Illinois. Depending on the herbicide applied, some of these recently treated soybean fields are easily identified from a "windshield survey"; due to the large amount of soybean injury. The Soybean Research and Development Council worked in conjunction with the University of Illinois, Southern Illinois University, and Iowa State University to conduct research trials on evaluating the effect of postemergence herbicides on soybean yield. The article answers these questions:

What type of soybean injury was experienced?
Did injury reduce soybean yield?
What is the bottom line?

According to the study, injury from postemergence herbicides is not a good predictor of soybean yield loss.

Wheat Crop "Season Finale"
Wheat headed about a week to 10 days early in most areas, and with the warm temperatures in the past month, it has also filled grain and ripened earlier than usual. Nearly all of the wheat in the southern half of the state has reached physiological maturity, and the main problem now is wet soils that both keep the grain above ideal harvest moistures and also keep combines out of the field.

As all wheat producers know from painful experience, harvest delays due to wet weather usually decrease the quality of wheat. On the other hand, remember that wheat grain can lose moisture very fast (up to five or six points per day), and so the time gained by harvesting at high moisture may be minimal.

Corn Keeps Up the Pace
At its current rate of development, I expect most of the corn planted in April in central Illinois to reach tasseling by late June and early July. Records for early development are being broken this year. The corn crop in southern and northern Illinois is somewhat behind in development, due both to later planting and to cooler temperatures in the northern areas.

Regional Reports
Extension center educators, unit educators, and unit assistants in northern, west-central, east-central, and southern Illinois prepare regional reports to provide more localized insight into pest situations and crop conditions in Illinois. The reports will keep you up to date on situations in field and forage crops as they develop throughout the season.

This week's issue includes reports from northern Illinois and west-central Illinois.



The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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