Farm Talk

August 20, 2013

Disease possibilities in crops increase with rain


CNHI

Parsons, Kansas — Recent rains have created conditions conducive to disease development on corn and soybeans according to Jill Scheidt, an agronomy specialist with University of Missouri Extension in Barton County.

“Rain carries funguses in the air which makes it easier for the funguses to spread.  Diseases like rust, gray leaf spot, northern corn leaf blight, brown spot, crazy top and stalk and ear rots develop best in wet and humid conditions,” said Scheidt. Fungicides that effectively and economically suppress these diseases are most effective if applied while corn is in the vegetative stage, or before silking.  If corn already has silks, plants will not respond as well to a treatment.“It is not economical to apply a fungicide past the tasseling stage,” said Scheidt.

Sudden Death Syndrome or SDS may become a concern with wet conditions after planting and later in the season during bloom.  According to Scheidt, wet conditions early in the season are conducive to the infection of SDS and wet conditions during bloom or late in the season are conducive to symptoms being expressed. “It is difficult to assess yield loss due to SDS. Yield loss is more likely if leaf tissue dies and pods or blooms are aborted rather than seeing severe yellowing between the veins,” said Scheidt. Other foliage diseases that affect soybeans during wet conditions are septoria brown spot, downy mildew and bacterial blight. Young plants that are in flooded or saturated soils have an increased chance of root rot diseases.

Flooding causes problems in corn and soybean plants as well. Saturated soils along with moving water can cause lodging because the roots do not have a solid structure to hold on to in order to stay upright. “The longer an area is flooded, the more damage it will cause,” said Scheidt.

If the weather remains humid after the rains have ceased, it is more likely ear rot on corn will occur. If the humidity is less dense and the air is drier, there is a better chance of not developing diseases. “If a field is underwater and is going to be harvested, it should be harvested as soon as it is ready and the combine settings should be adjusted to allow less trash and sediment to stay in the combine. Unfortunately, there is no fungicide producers can apply to seed after it is harvested and goes into the grain bin to eliminate funguses already present on the seed,” said Scheidt.

Some insect threats have slowed with the increased rain. Grasshoppers, spider mites and thrips are less of a threat in wet conditions.  Pod worm, also known as corn earworm, and bean leaf beetle feeding are not affected by wet conditions and still need to be scouted.  Threshold levels for foliage feeding on soybean are 30 percent defoliation before bloom and 20 percent defoliation during and after bloom. “Now is the time to be scouting regularly for pod feeders such as pod worms. Pod worms are rapid pod feeders and can destroy much of a field in one night; threshold levels for pod worm in soybean are one per foot,” said Scheidt. £