Crops Bulletin

August 16, 2013  
 Issue 11   


Prepared by

Paul Kassel

Extension Field Agronomist



Serving Clay, Buena Vista, Dickinson, Emmet, Hancock, Kossuth, Palo Alto, Pocahontas, Sac and Winnebago Counties



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Treat Aphids or Take the Insurance? Yield expectations from the late planted soybean crop can be expected to yield - at best - 40 bu/a (June 20 ) to 30 bu/a (July 1). Stated another way, soybeans decline in yield 0.5 bu/a for every day planting is delayed in June.


It is difficult to predict the level of damage that soybean aphids may cause. Yield loss from aphids will be more prevalent if dry weather prevails. Likewise, moderate conditions may minimize yield loss.


The June planted soybeans - currently late R3 stage - will be susceptible to aphid damage through the month of August and into very early September,


Decisions on aphid treatment include yield potential, insurance coverage, good farming practices, the outlook for dry weather and total treatment costs.


Pre-Harvest Intervals(PHI): The PHI for most soybean aphid products is workable with a reasonable harvest date. Asana, Baythroid, Hero and Tundra are 21 days or less. Lorsban/chlorpyrifos products are 28 days. Warrior II/generic Warrior is 30 days.  


Expected Maturity of the June Planted Soybean Crop: The delayed planting will hasten relative maturity. The soybean crop will lose about one day of growing season for every two days of planting delay. Soybean planted June 20 will mature - weather permitting - about October 15. May 20 planted soybean would be expected to mature October 1 - with all other factors the same.


Corn Aphids: Corn aphids infestations can develop quickly. Use these guidelines for treatment decisions on corn aphids: there are 80 percent of the plants infested with aphids, most of the ears have aphids and there are aphids on the ear leaf and above. Dry weather may increase the odds of aphid damage to corn yields. Corn at the dent stage may not benefit from treatment.


Corn Rootworm Adult Control: Erin Hodgson has an excellent article on the management of corn rootworm adults. Fields that have 1 to 2 beetles per plant and will be corn next year may benefit from an insecticide treatment. Corn rootworm pressure can be reduced in the next year's corn crop, but crop scouting is fairly involved.

Prepared by Paul Kassel, Extension Field Agronomist

Phone: (712) 262-2264, Email: