July 14, 2006
Western Bean Cutworm
Western bean cutworm
moth flights have been recorded in the area and egg masses are being found on
corn leaves. Scouting for the pest needs to be done now. Check 20
consecutive corn plants in 5 places in the field. Egg masses are usually laid
on the upper surface of the leaf. Individual eggs are about the size of a
pinhead and are white when first laid, but turn tan and then purple before
Hopefully the recent rains will reduce problems with this pest, but some infestations have already been found in the area. Under drought conditions, the two-spotted spider mites can thrive. Insecticide treatments should be considered if spider mite damage is present, mites are still found, and the forecast is for continued dry weather. Initial damage appears as little yellow spots or “stipples” on the leaves and progresses until leaves die and drop. Lorsban and dimethoate are labeled for spider mites. The synthetic pyrethoids are not effective on spider mites and can actually cause spider mite problems by killing the predator mites that keep spider mite populations in check. For more information see the last ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2006/7-10/spidermites.html.
Japanese beetles are
back in the areas that have had problems with the pest in the past, especially
within about 20 miles of
Bean Leaf Beetles
The first generation bean leaf beetles are showing up now. When they first emerge from the soil they are grey in color and have a soft shell. As the shell hardens, they may change to other colors (red, yellow, brown). As this generation populates, we can monitor for threshold levels with a sweep net. It is best to sweep in the afternoon when they tend to be at peak activity. The general threshold for reproductive stage soybeans is 4 to 5 per sweep in row beans and 3 to 4 per sweep in drilled beans. It is usually the second generation that emerges in August that causes the most damage. More detailed threshold information can be found at:
have yet to find a single soybean aphid in fields I’ve been monitoring in the
area. It’s looking like soybean aphids are not likely to be a big problem this
year. Brian Lang is reporting very low numbers in
far soybean rust has been reported in
High numbers of potato leafhoppers can be found in some hay fields. For more information on managing potato leafhopper, see pages 107 - 110 of the June 21, 1999 Iowa State University Integrated Crop Management Newsletter or http://www.extension.iastate.edu/Pages/eccrops/potatoleafhopper.html. Remember, waiting to see hopperburn is waiting too long as substantial losses have already occurred by that time.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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