No. 1/March 19, 1998
Assessing Cold Weather Damage on Wheat
The "great so far" season for winter wheat in Illinois came to an end on March11 and 12 when temperatures dipped into single digits over most of the state.Temperatures had been high enough to allow some growth of the crop most of thewinter. Fortunately, temperatures in the week before the cold snap had cooledsomewhat, and growth had slowed. This effect likely helped to decrease thedamage from the cold.
Many of the Extension field staff have reported how the cold temperaturesaffected the crop. In general, damage does not appear to be quite as severe ashad been feared. In the northern half of the state, growth had been slowenough to prevent much injury. Snow cover also helped through the central partof the state. The growth stage is reported to be about Feekes 4 (beginning ofupright growth) in most of northern and central Illinois. One thing wascertain even before the cold weather: The crop has had plenty of temperatureslow enough to assure that it will produce heads. Growers need not worry thatthey'll have "only straw" to harvest.
The injury picture is not as clear in southern Illinois. Some of the wheat,especially that planted too early--well before the fly-free date--was ingrowth stage 6, with the growing point (head at the top of the stem) elongatedan inch or more above the soil surface. Freezing temperatures can directlydamage the head as it pushes upward. Fortunately, leaves above the growingpoint and warm soil below both provide protection against the cold. That waslikely a major factor in the wheat's having escaped direct injury to thegrowing point.
Even though the growing point appears to have escaped serious freeze injury,there is likely a considerable amount of leaf injury in many fields,especially those where plants were large. The full extent of this injury willnot be known for several days, but loss of half the leaf area may be possible.This injury is not a disaster; but even the upper two leaves, which were stillcontained in the surrounding leaf sheaths during the freeze, might havesuffered. Having the upper two leaves intact and healthy is crucial for goodyields, so the appearance of new leaves, and assessment of overall leaf canopycover, will help to predict how well the crop might yield. Given the lack ofgreen leaf area, there will be a period of very slow growth as new leavesemerge over the next weeks.
Although watching the crop is about all that can be done, there are stillfields where nitrogen (N) has not yet been applied. Waiting to see whatcondition the crop is in before investing in N might make sense in fields withsmaller plants. In fields with larger plants, especially in areas where soilshave been wet, further delays might result in N deficiency. There are reports,however, that considerable damage was done during the cold weather, as N wasapplied in fields that were not frozen. It takes more than two nights of lowtemperatures to freeze soils that are protected by a blanket of wheat leaves.
Emerson Nafziger (firstname.lastname@example.org), Crop Sciences, (217)333-4424