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Soybean varieties to fit your fields

In real estate, there’s a saying that the three most important factors are location, location and location. Many farmers paraphrase that when selecting seed, saying the three most important factors are yield, yield and yield.

As farmers finalize their seed selection, they may want to check for unbiased yield data from Iowa State University and other universities in the upper Midwest.

Once your list of high-yielding varieties has been assembled, you should begin to narrow the list based on other characteristics, such as disease resistance. Soybean cyst nematode and soybean sudden death syndrome are two potential yield robbers that should be high on the list of pests and diseases to consider.

SDS was widespread and severe in Iowa in 2010, sometimes causing significant yield losses in areas previously thought to be free of SDS. The vast majority of 2010 soybean fields will be planted to soybean again in 2012. As SDS survives in the soil, including on corn residue, there will be high levels of SDS inoculum in many fields that will be planted to soybean in 2012, suggesting that SDS resistance should be a consideration for those fields.

Put the odds in your favor

Weather is the major driver that determines if a field containing SDS inoculum will display SDS symptoms. While genetic resistance to SDS is not complete, planting bean varieties with good SDS ratings is the most important way farmers can minimize chances that SDS will be an issue in 2012.

SCN has been confirmed in 98 Iowa counties, and there is a positive correlation between SCN presence and the expression of SDS symptoms. Therefore, SCN resistance is also an important genetic consideration. Fortunately, there is a tendency for varieties with good SDS ratings to also be SCN-resistant. In addition, if a field has a history of phytopthora root rot, brown stem rot or white mold, you should also be looking for resistance or tolerance to those diseases. And farmers with calcareous soils need to remember iron deficiency chlorosis resistance.

Most farmers have noticed that SDS tends to be the worst in wet, compacted areas, so improving drainage and relieving compaction will help minimize SDS. Areas that are tilled tend to have fewer SDS problems, although it isn’t entirely clear why, and it is also unclear if the tillage benefits will be observed in fields that have been in long-term no-till. We do know tillage spreads around the inoculum.

What about planting date?

Later-planted soybeans tend to have less SDS, most likely because soils are warmer at planting time. But later-planted soybeans also tend to have lower yields, so planting late just because of a potential SDS infestation is not advised.

Palle Pedersen, former ISU Extension soybean specialist, says, “Plant early and manage SDS using the other techniques.” But he would also advise growers to rank their fields in order, beginning with the fields with the fewest SDS problems and ending with the fields having the most SDS problems, and then plant, without delay, the fields in that order.

The result is that the worst SDS fields are planted later than the others.

Farmers should select bean varieties with high yield potential that are resistant to SDS and SCN. If the field has a phytopthora root rot, white mold, brown stem rot or iron deficiency chlorosis history, seek varieties with genetic resistance to those conditions. Manage water and compaction issues in the soil. Do not intentionally delay planting, but do rank fields in order from those with the fewest SDS problems to those with the most SDS problems, and then plant the fields in that order.

Schmitt is ISU Extension field crop agronomist in southeast Iowa.

New research

Studies by X.B. Yang and Leonor Leandro at ISU suggest most infections resulting in leaf symptoms occur at or shortly after planting and are favored by cool, wet soil conditions at that time.

Their work also suggests warm and wet conditions during grain fill promote SDS leaf symptoms. So the “perfect storm” is cool, wet conditions at or immediately after planting followed by warm and wet conditions during grain fill, which is what much of Iowa experienced in 2010.

This article published in the January, 2012 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.