July 22, 2005
Two Spotted Spidermites
Spider Mite problems are increasing in the area with the hot, dry conditions, with many fields being sprayed, especially east of the Cedar Rapids-Iowa City area. Since many are finding some soybean aphids as well, Lorsban has been the main product of choice. Hopefully the humidity that we have had will help to reduce the problems with the pest. For details on scouting for and managing this pest go to http://www.extension.iastate.edu/Pages/eccrops/spidermite.html or pages 148 - 149 of the July 22, 2002 Integrated Crop Management Newsletter. Also see the recent article by Matt O'Neal on spider mites and aphids at http://www.extension.iastate.edu/news/2005/jul/071501.htm.
Soybean aphids can be found
in most fields in the area now, but in most cases the numbers are staying well
below the economic threshold of 250 per plant. This may be due to the heat,
since aphids reproduce most rapidly under cool conditions. We need to continue
watching the fields, since numbers can increase rapidly. For more information
on soybean aphids see http://www.ent.iastate.edu/soybeanaphid/
and the latest ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2005/7-11/aphids.html.
Asian Soybean Rust
There are now 4 states where
Asian Soybean rust has been confirmed this year (
Potato Leafhopper numbers
continue to be high in many fields, so scouting of hay fields continues to be
an important activity. For 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.
A couple of sources for sweep nets are http://www.gemplers.com/a/shop/product.asp?T1=R13101&src=21SM001
Extended Diapause - Rootworm Problems in First Year Corn
A number of producers in
Although the severe drought
conditions in general are to the east of the area I cover, the hot and dry
weather is taking its toll on crops in the area.
Virgil Schmitt, who covers the area in extreme eastern
The days immediately leading up to tasselling through the first few days after pollination are critical to the corn plant. This is the time when the plant is making the final determination of how many kernels it "thinks" it can carry to maturity. The more stressed it is during that time, the shorter will be the ear it will try to keep. Some fields have been showing much more stress than others, depending on location, soils, history, management, genetics, insect injury, etc. The fields showing little stress still have excellent yield potential while the most severely stressed fields will be most valuable as silage.
Green Chop and Silage
Some corn fields are now
being harvested as green chop or silage. Be sure to check the WWW link
above for details; http://corn.agronomy.wisc.edu/WCM/2003/W138.htm
is especially noteworthy. A few key points to remember when green chopping or making silage are:
1. Be sure silage is at the correct moisture content for the storage method you have. The visual queues you usually use may not be accurate with drought-damaged corn.
2. Nitrates are seldom a problem. If they are, it is when the drought-damaged corn silage is harvested within a few days after a significant rainfall. The plant may take in a "big gulp" through the root system and not have the ability to move it into the kernel.
A. If nitrate accumulation does occur, it will be in the bottom 12 - 18 inches, so cutting high will help.
B. Many forage testing laboratories can test for nitrate in forage.
C. After 2 - 3 weeks of fermentation in the ensiling process, the nitrate level dissipates greatly. If you are still concerned, have the fermented product tested for nitrate.
D. Cattle and sheep can tolerate 0.5% nitrate on a dry matter basis.
E. Cattle and sheep can tolerate higher levels if feeding occurs over a period of several hours.
F. Nitrate tolerance is increased if grain is fed.
G. Gradually introduce cattle to suspect forages
over a period of several days.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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