Consulting agronomist Bob Streit describes the fungal invasion of many Midwest soybean fields, and suggests some remedial answers for healthier crops in future seasons.
Oct. 31, 2018 By Bob Streit — The latest NASS figures tell that corn harvest still has about 40% left to go. Bean harvest is further along and with the shorter days heavy dews slow progress. In many cases and along the major rivers a lot of water still needs to drain from those fields before they can be harvested. Winds being on the gusty category likely caused more stalks to collapse.
While memories of stalk quality are fresh in growers’ minds, it’s a good time to be looking for answers to causes and how best to make changes for 2019.
There is no one factor that dooms one field to severe problems, though a knowledgeable person could make a checklist that should be quite accurate.
1. High up on the list would be mineral deficiencies of the four major minerals that help fuel the plant’s immune system. A few of the beneficial minerals could be applied this fall.
2. Also, severe moisture stress of either too much or too little water.
3. Next up would be moderate or severe genetic weakness to these diseases.
4. Fourth would be lots of disease inoculum which has overwintered in the plant residue, poised to infect the plants as soon as they germinate. Crop residue needs to be managed this fall, and typically enhanced by the decomposing microbial mixes which seem to be doing the best job.
Selecting the best seed variety is typically done in December or January. Tighter budgets could force many corn growers to seriously consider planting conventional varieties. Should that scare a corn grower? Not that I have seen over the last decade. Growers need to learn which insects pose a threat to their crops, whether they are local in origin or which migrate in, and the timing and method of reproduction.
For the fields with major rutting problems, deep tilling may not help much unless and until the ground dries enough that it shatters with ripping. One other solution could be to plant tillage radish soon after harvest and hope that the seeds germinate quickly enough that the roots grow deep enough to shatter the compaction zone.
Late Season SB Diseases
There were many questions about the black appearance of soybean plants that stood in the fields for three to four weeks after they should have been combined. Several more species of fungus were diagnosed on those black stems and pods.
Early analysis told that Anthracnose, Pod and Stem Blight and Phomopsis were commonly being seen. As the season progressed, Diaporthe, Charcoal rot, Fusarium and Alternaria were added to the list. This year, the added moisture increased the infection rates and delayed harvest, keeping beans standing in the fields longer.
Newer Insect Pests in Soybeans
One insect that I have mentioned before as posing a threat to soybeans in Iowa and having already been found in neighboring states is the Dectes Stem Borer.
In parts of Kentucky, as just south of SE Illinois, this insect appeared in many fields and yield losses in excess of 12 bu. per acre being found. In one field, an extension specialists found that 25% to 50% of the plants had been felled by the tunneling larvae. It has also been found in both Kansas and Illinois. When will it appear in Iowa? Will alert scouts and farmers be able to identify it and figure out the treatment threshold?
Bob Streit is an independent crop consultant and columnist for Farm News. He can be reached at (515) 709-0143 or www.CentralIowaAg.com.