Disease Considerations For 2011 Soybean Variety Selection

Disease Considerations For 2011 Soybean Variety Selection

As farmers plan for 2011 growing season, and decide which soybean varieties to plant, many are making disease management a high priority because of the widespread outbreak of Sudden Death Syndrome in 2010.

As farmers in Iowa plan for the 2011 soybean growing season, many will make disease management a high priority because of the outbreaks of sudden death syndrome in 2010. Some soybean growers will select soybean varieties for the coming season according to what happened during the last season.

"While choosing SDS resistant or tolerant varieties may seem to be a good decision, the risk of white mold should be considered as well, particularly in northern Iowa where white mold was wide spread in 2009," says X.B. Yang, an Iowa State University Extension plant pathologist and soybean disease expert. "It is too early to say what disease may have outbreaks for the coming season."

Yang and his ISU colleague Xun Li offer the following guidelines and advice for farmers to consider when making soybean variety choices for 2011 planting.

What's the risk of white mold occurring in your fields in 2011?

For growers who are in a corn-soybean rotation, soybean fields that had white mold in 2009 still pose a serious risk for having white mold in 2011 production—with the level of occurrence depending on summer weather conditions. The reason is that in a year of normal weather, the corn canopy may provide shaded and cool conditions so that the white mold sclerotia from the previous season may germinate and won't threaten soybean plants in the next season.

However, that was not the case for weather in 2010. In July and August 2010, although the mean temperature was only slightly higher than normal, the night-time temperature was much higher so that diurnal temperature range was small. White mold sclerotia need cool and wet weather (temperature around 65F and good soil moisture) to produce apothecia, the mushroom-like structures of the fungus (see previous article) that produce airborne spores for infection.

The warmer-than-normal summer night temperatures in 2010 gave the white mold sclerotia a very limited time window to produce mushrooms. Northern Iowa field surveys in early July yielded very limited counting of mushroom in corn fields this year, which means a lot of sclerotia will be available for the next season in these fields when soybeans are planted.

What's the risk of sudden death syndrome occurring in 2011?

The widespread occurrence of SDS in the 2010 season suggested that SDS fungus was present in almost every Iowa soybean field. This disease was also prevalent in 2009 although not as severe as in the 2010 growing season. This means that the SDS pathogen is widely present in Iowa and the inoculum is unlikely a limiting factor of the outbreak in Iowa. Therefore, the risk of SDS is equally serious in 2011.

What's the risk of other soybean diseases occurring in 2011?

 

A previous study on climate change and plant disease suggested that a change in the climate would lead to an increase in extreme weather events, which leads to more frequent pest and disease outbreaks because these outbreaks are associated with extreme weather events. Because the type of extreme weather events is unpredictable, next season's weather may favor the occurrence of diseases other than SDS or white mold.

So, diseases that have been a problem on a farm in recent years should not be forgotten. Also, you need to consider that this winter's weather may impact the disease profile of next summer greatly.

In general, both SDS and white mold have built a sufficiently high amount of inoculum in soybean fields in Iowa. Which of these diseases may have greater risk of outbreak will be determined by the weather conditions next summer. "We will have a better clue when spring is approaching, as we did last March when predicting the SDS risk," says Yang.

So, what kind of resistant soybean variety should you select?

"If only one disease is a concern, the answer is simple, select a bean variety resistant to that disease," says Yang. "If both SDS and white mold are major production concerns in a particular field, I would use varieties to manage SDS risk and consider a fungicide to manage white mold risk when its risk becomes more certain. Effective fungicides now are available on the market to control white mold without yield penalty when mold is a threat in summer."

He adds this caution: "Keep in mind that not every soybean variety labeled as resistant to SDS is really resistant. More progress in breeding SDS resistance into soybean varieties is yet to be made. Resistant varieties in the early maturity group soybeans are less reliable than those in later maturity groups."

TAGS: Extension
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