Crop Scene Investigation - 20 Solved: What teamed up to damage Matthew's corn?
Wednesday, November 4, 2009
by DEAN SHANTZ
There were definitely a few issues with this corn field. You're right if you guessed that nitrogen deficiency, soil compaction and/or slug feeding contributed to Matthew's problem.
It made sense that the outside 12 rows looked better than the rest of the field when I learned that Matthew had opened up the outer part of the field last fall for early corn silage harvest. This meant very little trash was left on the soil surface in this area.
The poorer corn had considerably more trash, which meant cooler soil temperatures contributed to slower plant emergence. Corn stalks and other residue require nitrogen to decompose, and this may come at the expense of the growing crop if not accounted for in the nitrogen application. How much extra nitrogen should Matthew have used to account for the trash? The amount is debatable. The best bet is to trust your experience combined with the Ontario agriculture ministry's nitrogen calculator.
Compaction problems throughout the field, created by a heavy fall application of manure under relatively wet soil conditions, also contributed to non-uniform plant growth.
Matthew could have applied less manure in the fall, or used a spring application to reduce or avoid compaction issues. With a spring application, he would have also had more nitrogen available for crop growth and decomposition of trash. With a fall application, there is no crop to utilize the nitrogen and, as a result, half may be lost through leaching during the winter. The trade-off, however, is increased workload in the spring.
Finally, slugs were at work in this field as well. They feed mainly at night and hide in the soil or under trash and debris during the day. Slug feeding causes the leaves to have a ragged, shredded appearance, and all slugs leave a trail of slime wherever they move. The trail has a silvery, shiny appearance when dried, a telltale sign of the presence of slugs nearby.
Slugs typically damage the leaves of young corn plants in no-till fields during periods of cool, wet weather in May and June. Although feeding may be extensive, younger corn plants seldom die because the growing point usually escapes damage.
Active plant growth is one of the best ways for a crop to deal with slug damage, which is why Matthew's good corn exhibited fewer signs of the pest. At this time, there is no known practical or economical method of slug control registered for use in field corn.
I estimated Mathew's yield may be down as much as eight to 10 per cent due to uneven emergence. Of course, the combine tells the real story at harvest time. While there was nothing Matthew could do to correct the situation for this season, we looked ahead to next year and discussed Best Management Practices for optimum nitrogen levels and reducing compaction.
Congratulations to Dave Schill, Earlton, who wins a weather station for his correct answer. BF