July 16, 2008
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.
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.
Beetles are back with a vengeance this year, eating most everything, including
soybeans. The hotspots are similar to past years, being especially bad in
fields within 20 miles or so of
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.
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
X.B. Yang, ISU Extension Plant Pathologist, addresses soybean fungicide application issues at http://www.extension.iastate.edu/CropNews/2008/0708xbyang.htm.
Asian Soybean Rust
Scouting for soybean
rust continues in sentinel plots in
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.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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