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Fight the Blight

July 28, 2012
By: Jen Russell, AgWeb.com Managing Editor google + 
seedlingblights 5356762 LGPT
If you think seedling blight has struck your field, dig up a few plants. In corn, look for rotted seeds, a brown mesocotyl and mushy, underdeveloped roots.  

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When temperatures warmed up and fields looked ready for planting early this spring, it seemed too good to be true. Unfortunately for some farmers, it was.

After several weeks of ideal planting weather, the temperatures cooled and the rain started. With the cooler, wet weather came another problem: seedling blight.

"We had corn and soybean fields that needed to be replanted due to poor emergence," says Carl Bradley, plant pathologist at the University of Illinois. "It’s kind of hard to believe it now, with the hot, dry weather we’ve been having."

Reports of seedling blight sprung up throughout the Corn Belt, from Ohio to Minnesota to Nebraska. Blight can affect both corn and soybean fields, as well as some other crops such as rice and canola.

Bradley says those farmers who planted early in his state were the ones hit with blight the hardest. He says seedling blight generally occurs during cool, wet weather, so fields that are planted early are usually the ones at greatest risk.

However, Anne Dorrance, plant pathologist at The Ohio State University, cautions that soil temperature shouldn’t be given too much consideration, as different plant pathogens prefer different temperatures.

"Really, it just needs to be wet," she says.

In some fields hit with blight, the plants never really recover, and they might be less resilient to future damage from weather or pests.

"The weather that follows planting drives everything else," Bradley says. "Some plants may grow out of it, but in many plants the roots have been injured. Those that don’t have good root development suffer the most."

Kiersten Wise, plant pathologist at Purdue University, says fields in southern Indiana also experienced emergence problems, and some of those plants have been struggling since.

"We had lots of corn that went in early when we had those perfect conditions," she says. Then the rain struck and so did blight.

"We’ve been very dry since, so those plants that might not have had good root development to begin with have not been able to recover," she says.

Dorrance adds that seedling blight can be exacerbated by more than just the weather. Crop rotation and possible fungicide resistance also play a role.

"Corn and soybeans have lost their rotation in Ohio," she explains. "We also have no-till fields with high levels of inoculum built up in the top 4" of soil. So we’re just in a little bit of hurt."

Hard to identify. Seedling blight is caused by pathogens that reside in the soil. Typically, the young plants either fail to emerge or they emerge and then die, also known as damping off.

If you notice poor emergence in your fields, "Go dig up some seeds and see if they are rotted or not," Bradley urges.

A distinguishing factor of seedling disease is a brown or discolored mesocotyl, the tubelike tissue between the seed and the base of the stem. If the seed has already sprouted, look for rotted roots.

"The roots will often be mushy, and sometimes even slough off in your hand," Wise adds.

Seedling disease is caused by a wide variety of pathogens—fusarium, pythium, phytophthora and rhizoctonia are the most common ones—and there are different species of each pathogen, which can make seedling blight tricky for farmers to identify as well as manage.

"For instance, we have more than 30 species of pythium here in Ohio," Dorrance says.

Researchers are working to pinpoint all of the pathogens that cause seedling blight so that the most effective seed treatments can be developed.

If you suspect seedling blight is causing problems in your fields, Bradley suggests, send samples to a diagnostic lab so you know which pathogen is to blame.

"Unfortunately, there is no in-season rescue," he says, "but it’s still important to know what’s in your field."

Knowing whether you have a problem field is a good first step to preventing future seedling disease from occurring. There are also several other agronomic practices to use to prevent disease:

 

  • Crop rotation. Rotating your fields will help prevent pathogens from lingering in the soil from year to year, as well as prevent fungicide buildup that could cause future resistance issues.

  • Improve drainage. Seedling blight usually develops in wet soils, so try to keep your fields dry. "Keep in mind that many of these fungi are water molds," Dorrance says. These pathogens often need only a 24- to 48-hour window to infect seeds. "If you can do anything to improve drainage, do it," Dorrance says. "The shorter the infection period, the less chance you’ll have of disease developing."

  • Delay planting. Since planting is time- and weather- sensitive, Bradley says, this isn’t always a viable option. But waiting until soils are warm and dry can be helpful, especially if you know you have a problem field.

  • Look for resilient varieties. "I strongly think resistance plays a role in seedling blight development," Dorrance says. "So work with your seed company to find good, strong varieties." Bradley adds that in soybeans, selecting the right variety can be a challenge since numerous varieties don’t have ratings for blight.

  • Plant treated seed. "If you’re going to push planting dates, look at seed treatments," Bradley encourages. Seed treatments can help protect those early planted crops, especially since the weather can drastically change in early spring.

Be on the Lookout

As with many diseases, the likelihood of seedling blight depends on the weather. Since it’s difficult to predict weather patterns from year to year, it’s hard to know whether seedling blight will develop in your fields. If cold, wet weather follows early corn planting, be on the lookout for seedling blight. 

Description: Seedlings exhibit slow emergence, stunting, wilting, yellowing and postemergence damping off. Look for rotted seeds, red or yellow leaf discoloration, rotted roots with brown or gray lesions, dead leaf tips and leaf spots on seedlings.
 
Timing/conditions: Seed rots occur early in the season; seedling blights in early to midseason.

Contributing factors: Cool, wet, compacted soil and any conditions unfavorable for seedling growth.

Management practices: Plant high-quality seed into dry, warm soil, and use fungicide seed treatments in problem fields.

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FEATURED IN: Farm Journal - Seed Guide 2012
RELATED TOPICS: Corn, Soybeans, Agronomy, Crops, Management, Seed

 
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