Issue No. 2, Article 8/April 9, 2010
Looking at the Wheat Crop
The spring so far has been reasonably good for bringing the wheat crop along, but many questions remain about the potential for many fields to produce high yields. After what was the worst fall for planting wheat in at least three decades, and a reduction of about 60% in acres planted from the previous year, wheat prices remain low enough that we need to assess the crop carefully to see if it's worth keeping. Crop insurance considerations also are in play for many producers.
The wheat crop in Illinois is currently rated at 9% very poor, 21% poor, 23% fair, 28% good, and 1% excellent. In contrast, the early April rating for the crop in 2009, which was perhaps a little above average, was 3% poor, 23% fair, 64% good, and 10% excellent. Having less than a third of the crop rated as good or better is very likely to mean that some of the current crop will not (and should not) be kept to harvest.
The first things to evaluate in a struggling wheat field are the stand and stand uniformity. This evaluation requires that stand counts be made in enough areas of the field to provide a good picture of both numbers of plants and variability. Low, drowned-out areas will be a factor in many fields, and decisions will have to be made about whether to keep the field based on the extent and distribution of such areas. If drowned-out areas are large but the rest of the crop is good, it may work well to plant another crop in the low areas. The fill-in crop would likely be soybean, but it could be oats in northern Illinois, though it's already time to plant oats and these areas are probably still wet. Keeping weeds down will be helpful, even if these areas remain without a crop until the field is double-cropped in June.
Complicating the stand count this year are the delayed planting and small size of wheat plants coming into the spring. I suggested back in the winter that a crop that had barely emerged before dormancy or would emerge in the spring may need 30 to 35 plants per square foot to compensate for the likely reduction in tillering. This drops to 25 to 30 plants per square foot if plants covered about a third of the ground area at green-up, or 20 to 25 plants if half the ground area was covered at green-up. We have normally suggested keeping stands with counts as low as 15 to 20 plants per square foot, but that works only if plants make normal fall growth and cover two-thirds or more of the ground area by the time they green up in the spring.
It's the tiller count that is really needed to assess yield potential. At this point in the season it should be possible, at least in the southern half of the state, to get an idea of how many tillers might form and to use that information to make decisions about keeping a stand. Our normal rule of thumb is that one head per square foot means about one bushel per acre. So if we set 50 bushels per acre as the threshold to keep a stand, you will need about 50 heads to form per square foot. It takes a tiller to make a head, of course, but not all tillers form heads. It's difficult to predict which tillers will form heads until into jointing (Feekes 7), or when plants are about 8 inches tall. By then you can start to see which tillers are growing vigorously enough to win the race and form heads. Before then, you can only guess at likely head numbers. Assume that the small tillers hidden beneath the rest of the plant are not likely to form heads. More tillers form on plants in low stands, but not always enough to compensate for low plant numbers.
The length of the tillering period, which lasts up to the start of jointing, varies with temperatures; above-normal temperatures like we've had the past week improve crop color and growth, but they can also hasten the end of tiller formation and result in lower head numbers. The expected return to more normal temperatures this week may give a small boost to tiller and head formation, but we can expect jointing to begin within the next week or 10 days in southern Illinois, and we should be able to assess yield potential more fully after that.
Late planting and cool March weather mean that most of the crop is well behind normal in development now. This means that heading is likely to be late and harvest is likely to be later than normal. The only way this may not happen is if temperatures average well above normal from now into June. Because wheat is a cool-season crop, above-normal temperatures may well reduce yield, especially if rainfall is normal or above normal. But if temperatures stay normal, the delay in harvest will result in a delay in double-crop planting. This may be a factor in the decision to keep a marginal stand, especially if double-crop is necessary to make the system profitable. Most double-crop in 2009 was planted as early as full-season soybeans, but we hope that will not be the case in 2010.--Emerson Nafziger