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
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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