Judging by phone calls this fall, there is now widespread interest in cover crops here in Tennessee. This interest in cover crops really started last year. This was pointed out to me by the couple hundred folks that attended the University of Tennessee grain conference in Dyersburg, Tenn., last February where 50 percent of the attendees in a survey at that conference indicated that they had utilized a cover crop at least to some extent on their farms in 2012.
The utilization ranged from raising cover crops on just a few acres to get a feel for the concept to several thousand acres for folks more versed in cover crop use. There are a number of drivers as to why folks are looking to adapt cover crops to their farming operation. Some of this interest is driven by the Natural Resources Conservation Service, which has a program that can at least offset some cover crop seed cost.
Another big reason is that many farmers have figured that the complete answer to managing herbicide resistant weeds cannot be solved with a spray boom alone and are looking to integrate cultural practices like cover crops into their weed management program.
I have fielded a number of questions on using cover crops to help out on weed control. The most common question is which cover crop or crop mix to use. This question is not a “one answer fits all” situation. It really depends on what crop is to be planted in the spring and also when realistically a field can be sowed with cover crop this fall.
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I really prefer wheat and cereal rye for fields that will be planted to soybeans or cotton as they provide the best weed control of any covers for horseweed in the winter and even can help on Palmer amaranth provided they are seeded early enough to get some size. Moreover, a clethodim product can be used in the burndown to take out any glyphsosate-resistant ryegrass that may find its way into the field without worry of corn re-crop. These grass cover crops are more forgiving for late establishment as they can provide some value planted as late as early November.
Vetch, crimson clover and Austrian winter pea are some of the legume type covers we have evaluated for weed control as well. They really need to be sown before mid-October to provide any horseweed control. They will not help on Palmer amaranth control and in fact, in some of our work, promoted germination of pigweed due to leaving nitrogen in the soil. As a result, I like these legume type crops in a field that will go to corn. Corn can readily use the nitrogen left by the legume and we have more herbicides in corn to deal with Palmer than soybean or cotton. Timing is everything on planting these legume crops, the earlier they are sown the better.
We have had a number of farmers aerial seeding cover crop seed into standing cotton and soybeans in September this year. In wet falls like this year the stand establishment is often quite good. In dry falls, establishment of covers with flown on seed is sketchy at best.
The next question is on tillage turnips. I am not a fan of them from a weed management point of view. First, in the fields I have walked, they do not produce enough cover to prevent horseweed germination. Second, they do not winterkill here in the Mid-South and I have yet to find a consistent herbicide combination that will kill large, well-established tillage turnips in the spring. In fact, tillage seems to be the only way to control tillage turnips.
What about sowing multiple blends of covers? Of the blend covers we have researched, cereal rye or wheat sown with vetch has worked fairly well. The vetch will often climb up the grass crop and produce more residue and the legume can somewhat offset any nitrogen penalty if cotton or corn is to be planted.
If you do not have experience with cover crops, utilizing them for the first time can be a complex issue. There are a sundry of agronomic issues that go into successfully employing them in your weed control program. My advice is start small and get a feel for what works best on your farm, and go from there. In a year or two you should have enough experience with them to be successful. One last point is to make sure to sow the cover into a clean seed bed provided by tillage or Gramoxone.
The integration of cover crops does appear to be worth it from a weed control stand point. Our research consistently shows that they can help provide good control of horseweed and, depending upon the species and planting date, can help provide some Palmer amaranth control.