Soybeans Overcoming Diseases, Other Issues

August 30, 2004

COLUMBUS, Ohio — Ohio's soybean crop is holding its own despite getting slammed with diseases and the onset of cooler-than-normal August temperatures, which could delay the grain-filling process.

 

Ohio State University Extension specialists and researchers can only speculate what kind of impacts these issues will have on yields, but for the time being the crop is healthier than what growers faced last year.

"The crop is in better shape now than last year at this time. I'm hoping for a 40-42 bushel-per-acre crop as compared to the 37-38 bushels per acre we got last year," said Jim Beuerlein, an OSU Extension agronomist. "It should be emphasized that we still have lots of disease."

Anne Dorrance, an Ohio State plant pathologist with the Ohio Agricultural Research and Development Center in Wooster, Ohio, said that growers are faced with just about every problem that can inflict soybeans: Phytophthora, powdery mildew, brown spot, sudden death syndrome (SDS), soybean cyst nematode (SCN), Sclerotinia, Phomopsis — even diseases that are uncommon in Ohio.

"We are finding downy mildew, which hasn't been a problem since 1997. We've run across sunburned leaves," said Dorrance. "We are even finding frog eye, especially in the southern part of the state. Although at very low levels, it is unusual for this foliar disease to be found in Ohio."

Because of the diseases, large pockets of soybean plants are beginning to die off, especially in areas where fields are impacted by more than one pathogen. For example, the combination of SDS and SCN is becoming a deadly mix in some areas.

"SDS alone does not greatly impact yield. SCN, on the other hand, can cause losses of 5-10 bushels without growers ever seeing any above-ground symptoms," said Dorrance. "But if you put the two together, you can get much earlier development of foliar symptoms, which is what growers are seeing right now."

Ohio State specialists agree that lack of crop rotation, combined with wet, humid conditions earlier in the season, created the perfect environment for disease development.

"We are not doing a good job of rotating crops. Lack of rotation promotes all diseases," said Beuerlein. "For each year you have the same crop in the ground, most diseases increase from five- to 10-fold just from disease load. For every year you take that crop out of the field, you'll cut that disease load in half. Growers need to get out of continuous beans for several years to drop those disease loads."

In addition to disease pressures, the recent onset of cool temperatures may pose some problems for the soybean crop.

"The cool weather is slowing things down," said Beuerlein. "As of mid-August most of our crop is in the grain filling stage. Lower than normal day and night temperatures reduce the photosynthesis rate and also the respiration rate, so there may be a small reduction in the net accumulation of dry matter, and that loss could be offset with a one- to two-day delay in maturity."

On the upside, cooler temperatures reduce water demands on the crop, relieving stress on the crop.

"Cooler temperatures have a positive effect in that they reduce the water requirement of the crop so that any drought stress will be delayed," said Beuerlein. "Moisture stress late in the grain fill period hastens maturity and reduces yield as does stress from disease and temperature extremes. Therefore the cooler than normal temperatures of early August could have little or no effect on yield."

Author(s): 
Candace Pollock
Source(s): 
Anne Dorrance, Jim Beuerlein