July 10, 2008
High numbers of potato leafhoppers can be found in some hay fields. Be sure to use a sweep net to monitor potato leafhopper numbers and treat if numbers exceed the threshold. 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. Be careful to not confuse leaf diseases with hopperburn.
Many hay fields now have evident leaf diseases, most commonly common leaf spot and lepto leaf spot. Fields in third year alfalfa have greater disease risk than first and second year alfalfa fields because the pathogens build up over time. There are differences in disease tolerance between varieties. Because many of the hay nutrients are in the leaves and because severe leaf disease can cause defoliation, if the disease level is high, early cutting generally is recommended so that defoliation can be avoided. Cutting as early as mid-bud stage may be necessary when the disease is severe.
With the high price of corn, interest in managing the first generation of the European Corn Borer has increased. The current bible for management of this insect is NCR-327 European Corn Borer Ecology and Management, relevant portions of which can be viewed at http://www.mda.state.mn.us/plants/insects/ecb.htm. Jon Tollefson, ISU Extension Entomologist, wrote a summarizing article and created a spreadsheet for calculating thresholds, both of which can be accessed at http://www.extension.iastate.edu/CropNews/2008/0709jtollefson.htm.
Rotation Resistant Western Corn Rootworms
you know, rotation resistant western corn rootworms have been confirmed throughout the
counties I cover, and levels above threshold were confirmed in the area from northeastern
10220 Church Road NE
Vestaburg, Michigan 48891
100 Countryside Drive
PO Box 270
The time is fast approaching when final decisions about applying foliar fungicides to corn will be made. Alison Robertson, ISU Extension Plant Pathologist, wrote an excellent article on the subject, which can be viewed at http://www.extension.iastate.edu/CropNews/2008/0703Robertson.htm.
Cupped Soybean Leaves
I have been getting a number of calls and been in numerous fields related to soybeans that have cupped up or have malformed leaves that look like dicamba or growth regulator herbicide injury.
this problem occurs, the possibility of spray drift needs to be investigated. If an
herbicide has drifted from a nearby corn field or roadside, the symptoms should be
greatest near the source of the drift and gradually diminish with a greater distance from
the source. Also the symptoms should be less near anything that would have obstructed the
drift, such as tall grass or trees. If a drift pattern is not evident, then it is unlikely
to be the reason for the symptoms.
Rhizoctonia Root Rot
Rhizoctonia root rot is reducing stands in many soybean fields. The disease can be identified by the brick-red lesions on the roots; often the roots take on a more definitive color after being exposed to the air for a few minutes. When the lesion is scraped off with a finger nail, the tissue underneath appears normal.
Rhizoctonia root rot is an opportunistic disease, invading plants that are under stress. Once an infection has occurred, there are no management options. In general, plants can out grow root rot problems and symptoms disappear as the season progresses into late July and August. With severe infection, infected plants wilt and die in patches.
X.B. Yang, ISU Extension Plant Pathologist, addresses soybean fungicide application issues at http://www.extension.iastate.edu/CropNews/2008/0708xbyang.htm.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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