July 10, 2008

 

HAY

Potato Leafhoppers

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.

 

 

Leaf Diseases

 

 

 

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.

 

 

 

 

CORN

 

Corn Borers

 

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

 

As 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 Muscatine County through Scott County and into Clinton County in 2006.  The Illinois and Indiana experience with this pest is that it starts out very spotty, so a cart blanc use of rootworm management in first year corn is not yet warranted.  Rather, soybean fields that will be planted to corn in 2009 should be monitored for western corn rootworm adult activity beginning in the last week of July and continuing through the first three weeks of August using the Trece Pherocon AM yellow sticky traps.  Follow the protocol developed by the University of Illinois, which can be found at http://www.ipm.uiuc.edu/fieldcrops/insects/western_corn_rootworm/wcr.pdf.  The traps can be ordered from:

 

Great Lakes IPM
10220 Church Road NE
Vestaburg, Michigan 48891
e-mail: glipm@nethawk.com

http://www.greatlakesipm.com/

 

Gemplers,
100 Countryside Drive
PO Box 270

Belleville, Wisconsin 53508
http://www.gemplers.com

Fungicides

 

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.

 

 

SOYBEAN

 

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.

 

When 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.

 If the symptoms appear after a field is sprayed and there is a sprayer pattern to the symptoms, the possibility of sprayer contamination with dicamba (Banvel, Clarity, Northstar, Distinct, Status) or another growth regulator herbicide should be investigated. However, we do occasionally see these symptoms in the absence of a growth regulator herbicide. Occasionally additives, such as ammonium sulfate (AMS), 28% Nitrogen solution, or surfactants can cause these symptoms. I have also seen symptoms not show up until 2 or more weeks after the field is sprayed. If dicamba was the source of the problem, symptoms should show up within a day or two.

In some cases the entire field showed the problem before anything was sprayed on the field or in neighboring fields. Sometimes the symptoms are uniform across the entire field and sometimes certain parts of the field are worse than others, but there is no drift pattern. I see this most often when the soybeans go through a growth spurt when temperatures are high after some cool weather or after a heavy rainfall. Apparently under these conditions, the balance of naturally occurring hormones in the plant is disrupted, resulting in symptoms characteristic of growth regulator herbicide damage. Usually the soybeans recover from this condition with little to no effect on the final yield. See the July 19, 1999 ICM Newsletter for more information (http://www.ipm.iastate.edu/ipm/icm/1999/7-19-1999/malsoy.html).

 

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.

 

Fungicides

 

X.B. Yang, ISU Extension Plant Pathologist, addresses soybean fungicide application issues at http://www.extension.iastate.edu/CropNews/2008/0708xbyang.htm.