July 13, 2005
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
levels of corn rootworm beetles, occasionally combined with grasshoppers and
Japanese Beetles, are resulting in considerable clipping of corn silks.
If silks are clipped to within less than 1/2 inch of the husk, the injury may
prevent successful pollination. Once pollination has occurred, silk
clipping will have no consequence. If an insecticidal treatment is
needed, labelled products for corn rootworm beetles
in corn include Ambush 25W, Asana XL, Lorsban 4E,
Mustang, Mustang MAX, Penncap-M, Pounce 3.2EC, Sevin XLR+, and Warrior. Purdue has a good reference
on silking and silk clipping at http://www.agry.purdue.edu/ext/corn/news/articles.03/Silks-0716.html.
Potassium Deficiency Symptoms
Blight / Top Dieback / Potassium Deficiency has again
begun to show up in some soybean fields. The new leaves
exhibit yellowing along the margins, often followed by necrosis of the tissues.
The debate about the relationship of disease and potassium in this phenomenon
continues, but higher levels of potassium often lessen the severity of this
phenomenon. Likewise, genetics and disease levels make a difference; be
sure to check plants for signs of root rots and soybean cyst nematode (See the
item below.). Also, poor rooting and/or root function due to soils being
compacted, too loose, and/or too dry can promote these symptoms. For more
details, see the pages
172 173 of the September 13, 1999 Integrated
Crop Management Newsletter.
Two Spotted Spidermites
As the dry weather continues, the instances of two-spotted spidermites damaging soybean are increasing. 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. Organophosphates (Dimethoate 400 or Lorsban 4E) are the most effective products for this pest. Dimethoate 400 will have less residual activity and is less effective against soybean aphids, so using this product may kill the predators and allow any soybean aphid population to increase more rapidly. Likewise, other products labelled for soybean aphid have little activity on spidermites but may again kill predators, allowing the spidermite population to increase more rapidly. Bottom line: Before making an insecticide treatment, be sure to take a complete inventory of insect pests and spidermites before making a final product selection.
aphids are now being found in eastern
Bean Leaf Beetle
Bean Leaf Beetle numbers in some fields suggest that numbers will become high enough during the second generation (early August) to warrant an insecticide application. Remember, there is a strategy for using first generation numbers to predict the need for an second-generation spray, allowing that application to be made before the second generation causes significant damage. For more information on that strategy see http://www.extension.iastate.edu/Pages/eccrops/blb3.html or pages 90 - 91 of the July 12, 2004 ICM Newsletter. Before making an insecticidal application for soybean aphid, be sure to also check for two spotted spidermites; see the item above.
Soybean Cyst Nematode
While scouting any soybean fields where the presence of soybean cyst nematode is not known, be sure to carefully dig up a few plants, gently shake off any soil, and examine the roots for the presence of soybean cyst nematode. For more on soybean cyst nematode, see pages 115 - 116 of the June 30, 1997 ICM Newsletter or http://www.ipm.iastate.edu/ipm/icm/1997/6-30-1997/scoutSCN.html, IPM-47s "Scouting for Soybean Cyst Nematode http://www.extension.iastate.edu/Publications/IPM47S.pdf, and Pm-879 "Soybean Cyst Nematode" http://www.extension.iastate.edu/Publications/PM879.pdf.
Asian Soybean Rust
The first observation of
soybean rust in soybeans planted this year was made recently in southern
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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