By Larry Steckel
Aerial seeding cover crop questions have been numerous this month. Indeed, the wet month of August does greatly increase the probability that aerial seeding will be successful as we enter September. This was the case last year where aerial seeding cover crops into standing crops in September was quite successful for many. Often these early cover crops helped provide good control of marestail and in some cases helped suppress Palmer amaranth this spring.
The specific questions arise on what cover species should be seeded and at what rate. To answer these questions one needs to know what crop is intended in these fields next year. If the intended crop is corn or cotton then a legume cover such as vetch, crimson clover or Austrian winter pea would be good candidates. Of the three legume species, the winter pea is the least forgiving for late planting. As a result, it responds better to being seeded earlier than vetch or clover.
If the crop is cotton or soybean and the main reason for the cover is weed suppression and possibly spring sand-blasting protection, then wheat or cereal rye are probably the best candidates. If cereal rye or wheat are the crops of choice then August or even September is too early to seed.
The main reason for this is that if a lot of acres of wheat or cereal rye are seeded in September we could develop a real issue with Hessian fly in our cash wheat crop. Plant scientist Neal Stewart has informed me that Hessian fly can go through a generation in 11 days in a September seeding of cover crop wheat or cereal rye.
As far as seeding rates by air one typically wants to go with the high end of the recommended rate. That would be 1 1/2 to 2 bushels per acre for wheat and cereal rye. For the legumes, seeding rates of 25 pounds per acre for crimson clover, 30 pounds per acre for vetch, and 60 pounds per acre for Austrian winter pea are adequate rates.
Finally there have been questions on whether cotton defoliant will harm a newly emerged cover crop. Typically cotton defoliants do not reach the lower cotton canopy, let alone the soil, and have not been a problem harming newly emerged covers. The only time to be cautious with cotton defoliant would be on a sequential application to remove the lower canopy. If that is the case, stay away from defoliants like Def, Aim or ET on the legume covers. However, we would expect Aim and ET to be relatively safe on the cereal covers.