April 28, 2004

Soybeans

Some farmers have started planting soybeans in the area and others will be starting soon. A few things to keep in mind this spring

Soybean Seed Size Smaller This Year

Last year's August drought has caused much of the soybean seed supply to have smaller than usual seed size. Its important to adjust planter's and drill's accordingly so we are not wasting seed and money. Most research has shown that soybean plant populations between 125,000 and 225,000 yield the same. High populations can make soybeans more susceptible to lodging and to white mold. To achieve a planting population of about 150,000 to 160,000 seeds per acre, shoot for

2 seeds per foot of row in 7" rows

3 seeds per foot of row in 10" rows

4.5 seeds per foot of row in 15" rows

6 seeds per foot of row in 20" rows

9 seeds per foot of row in 30" rows

11 seeds per foot of row in 36" or 38" rows

Smaller seed may also not have the ability to emerge from quite as deep. The ideal planting depth is usually about 1-1.5 inches for soybeans. For more information see the March 22, 2004 ICM Newsletter at http//www.ipm.iastate.edu/ipm/icm/2004/3-22-2004/smallsoy.html

Gaucho Labeled for Seed Treatment

Gaucho received an emergency (section 18) exemption this February to be used as a seed treatment for soybeans to aid in the control of bean leaf beetles and soybean aphids. Up to 455,000 seed units are allowed to be treated up to May 15 in Iowa. Although the label includes commercial soybean production, most of the Gaucho is likely to be used in seed fields and for food-grade soybeans, where seed quality concerns are greater. Gaucho has been shown to control early season bean leaf beetles, which should reduce the incidence of bean pod mottle virus. It also has some effectiveness against soybean aphids, especially when planting is delayed. For more information see the February 23, 2004 ICM Newsletter at http//www.ipm.iastate.edu/ipm/icm/2004/2-23-2004/gaucho.html.

Planting Dates

Soybean planting dates have been pushed earlier over the past few years. Although optimum planting dates for soybeans are similar to corn, soybean yields do not drop off as rapidly as corn yields do if planting is delayed beyond mid-May. Early soybean planting has been partially responsible for increased problems with bean leaf beetles and soybean sudden death. Bean leaf beetles may not be a widespread problem this year, but they will likely be a greater problem in the first bean fields to emerge in the neighborhood. Planting date studies done across Iowa from 1995-97 showed that soybeans planted in mid-May yield about the same as those planted in late April, so there is no reason to rush to get beans planted. For more information, see the April 19, 2004 ICM Newsletter at http//www.ipm.iastate.edu/ipm/icm/2004/4-19-2004/soyplantdate.html.

Stalk Borers Begin to Hatch

Stalk borers have begun to hatch along Highway 34 (Burlington - Mount Pleasant area), and the hatch will move north.  In areas of fields with high grassy weed or giant ragweed pressure in 2003, spraying an insecticide just prior to egg hatch is one strategy to consider if corn will be planted this year.  Stalk borers begin to hatch at 575 Growing degree days base 41 and hatch is complete at 750 GDD Base 41.

Following are GDD Base 41 accumulations as of the end of the respective day.

DATE           BURLINGTON      CEDAR RAPIDS   DAVENPORT       DUBUQUE

April 20                 568                        457                           491.5                        375

April 21                 582                        466                           500                           383

April 22                 592                        474.5                        507.5                        391.5

April 23                604.5                      486.5                        519                           402

April 24                618.5                      494.5                        527.5                       409.5

April 25                628.5                      502.5                        536.5                       415.5

April 26                640                         511.5                         546                           422.5

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