Source: Emerson Nafziger, University of Illinois
With the great start to row crop planting in Illinois this spring, the less-than-great condition of the wheat crop has not gotten much attention. But with 69 percent of the state's wheat crop rated fair or worse, the 2010 crop not only occupies the smallest acreage we have had since records began in 1866, but it is also one of the worst-looking crops in decades. While there are some good wheat fields in Illinois (2 percent of the crop is rated excellent, but that's only 7,000 acres), there are some very poor-looking fields. It is time to examine, for the last time, whether they are worth keeping.
It is possible that some producers have waited to let the crop grow more before harvesting it as forage or to let it serve as a cover crop with more tonnage of killed material, with soybeans to be planted in May. Our concern about the crop's being late to head out was unfounded; the latest report indicates that 12 percent of the crop was headed on May 2, which is only slightly behind normal. Still, if the plan is to let a marginal wheat crop go to maturity and then to plant double-crop soybeans, you need to consider the risk of trading good row crop planting conditions now for very late planting of a second crop under uncertain conditions in mid- to late June.
Robert Bellm visited some wheat fields in southwestern Illinois this week and sent photographs of several fields. One field that he said "looked good from the road if you drive fast" is shown here.
If we use the rule of thumb that one head per square foot will produce a bushel per acre, and even increase that some based on the fact that thin stands can produce larger heads, it is still clear that the best we could hope for in this field might be 35 to 40 bushels per acre. Wheat prices, responding to the good crop taking shape in other parts of the world, have not been sending a strong signal to keep marginal fields of soft red winter wheat. The color of this crop indicates that it might have been fertilized with spring nitrogen, though thin stands are able to take up more nitrogen per plant than thicker stands, so plants could be this shade of green from residual N only. If it did get top-dressed N, then destroying the wheat and planting corn in this field would almost certainly have been preferable to harvesting wheat and planting soybeans after that. Planting soybeans into a killed wheat crop is also a possibility, but N released when wheat plants break down won't do the soybean crop much good, even if there is some benefit to having "cover crop" residue present.
Actively growing wheat should be relatively easy to kill with herbicides at this stage, and thin stands are easier to plant back into than thicker stands. Be sure to watch closely for insect larvae (e.g., armyworm) that can hatch on wheat plants, then move over to a newly planted crop once the wheat starts to die. There are also some concerns about allelopathy when a new crop is planted into fresh crop residue. Even though an allelopathic effect often can't be measured, and crops planted in this way often do very well, it makes sense to move the residue off the planted row so that anything leaching out of it doesn't get directly to the newly planted seed. It may be difficult for trash movers to push aside all of the crop residue, especially if the wheat crop roots haven't died yet. The goal is to get seed placed in soil and covered without having crop residue pushed into the seed furrow or present next to planted seed. Tillage might be an option, but tillage can also incorporate residue in a way that both interferes with planting and leaves residue near the seed. It may in some cases be necessary to let the killed crop dry up for a few more days, if that's the only way to get good placement of seed of the replacement crop.