Wet field early spring

If the pattern continues with cooler temperatures and moisture, there may be problems with disease later in the growing season. Pythium is a major concern for soybeans.

PEORIA, Ill. — For many farmers, June was characterized with late planting and replant in rained-out areas. Now, the wet weather may call for more scouting for potential disease issues.

“This year, if the pattern continues with cooler temperatures and moisture, there may be problems with disease later in the growing season,” Kevin Scholl, Syngenta agronomist, said in June. “There is a lot of disease inoculant out in the field.”

Some farmers are going to use a combination of fungicides, whether there is visible disease or not, for crop enhancement, he said.

“If disease is there it’s a no brainer,” Scholl said of using fungicides.

It’s a matter of economics. Growers make the decision whether to use fungicides based on return on investment, considering the yield gain compared to the cost of the product and applications, Scholl said.

Some of the diseases farmers may expect this year are grey leaf spot and northern corn leaf blight.

“Both can be devastating to corn,” Scholl said, and both are regulars to this area.

New last year as a significant yield robber in the northern tiers of Illinois was tar spot in corn, he said. Several universities and businesses are studying this disease to help farmers find strategies to fight it.

“Seed companies are just getting started” developing resistant varieties, he said.

In soybeans, frogeye leaf spot — which traditionally shows up in southern areas — is moving farther north every year. Ohio State University Extension has reported yield reductions due to this disease, traditionally found in warm, humid environments in the southern United States.

Other annual soybean enemies here are brown spot (septoria leaf spot) and in northern Illinois, white mold, Scholl said.

When the ground is cool and wet at planting, the new soybean crop is susceptible to Pythium, said Jason Carr, Bayer Crop Science ag technology development representative.

Pythium generally will be found in low-lying areas of fields or any location with overly saturated soils.

“It can cause seed rot and pre- or post-emergence damping off (plant death),” Carr said.

The roots of a Pythium-infected plant will rot, and the seedling can be pulled from the ground with little resistance.

“Pythium can start to take hold half an hour after planting. You can still be in the field planting,” said Travis Palmquist of West Central Distributors at a Leaders in Farming Technology conference at the University of Illinois June 26. He emphasized the importance of scouting early.

Fusarium also infects soybeans in waterlogged and chilly soils, especially seedlings and young plant.

“Fusarium causes poor emergence, reduced emergence, damping off or stunted seedlings. The roots of young infected plants will exhibit brown discoloration,” Carr said.

It can also show up later in the growing season, leading the more mature infected plants to have poorly developed, discolored roots and reduced nodulation, he said.

Phytophthora is another disease that can start early in the soybean season. It annually accounts for about 50 million bushels of yield loss in the United States, Carr said.

Phytophthora damage to seedlings looks like other seedling diseases and generally occurs in poorly drained or low-lying areas of fields. In contrast to Pythium, Phytophthora prefers slightly warmer soils. For this disease, there is some good genetic resistance and seed treatments available, unlike with Pythium, but fungicides can also be used for control, Carr said.

If the disease impact is early and the existing stand is poor — less than 100,000 plants per acre — it might be worth considering replanting, Carr said.

“If the infection is not severe enough to warrant replanting, an R3 fungicide application may protect a weakened field’s ability to produce an acceptable yield,” he said.

The key is to reduce the plant’s stress. If wet weather is followed by dry weather and irrigation is an option, it should be used, Carr said.

Plants are like people, they are pretty good at fighting off disease when they are healthy.

“It’s tougher under stress,” he said.

Phyllis Coulter is Northern Illinois field editor, writing for Illinois Farmer Today, Iowa Farmer Today and Missouri Farmer Today.