Winter Wheat Update

DR. Emerson Nafziger and Giovani Preza Fontes

URBANA, ILLINOIS

Illinois producers planted 650,000 acres of winter wheat in the fall of 2021 and harvested 560,000 acres in 2022, with an average yield of 79 bushels per acre. Boosted by high world wheat prices, high wheat and good doublecrop soybean yields, and dry fall weather, planted acreage for 2023 rose to 880,000 acres. That’s 45 percent higher than the average of the past ten years, and the highest planted wheat acreage in Illinois since 2008. Crop condition ratings on March 26 were good, with 68 percent rated good or excellent, and 33 percent fair.

Weather and the crop to date

The Illinois wheat crop was planted at about the normal time last fall, with 50% planted by October 17. Temperatures were normal in November and December, except for the blast of cold around Christmas, with lows averaging in single digits, and little or no snow cover. This killed off some leaf area, but most plants survived. Temperatures were 5 to 6 degrees above normal in both January and February, which allowed plants to green up some in southern Illinois growing areas. Temperatures in March returned to near normal, with some cold mornings. Warmer weather will help speed growth as we move into April.

Much of Illinois south of I-70 received 5 to 7 inches of rain in March, which will likely bring standing water problems, including possible loss of stand, in some areas. That, and modest growth rates in March, may limit tiller formation in some fields. Wheat plant produce more tillers than heads, so that’s not a major concern, but a sudden return to warm temperatures can cause stems to begin elongating, which normally brings an end to tiller formation. Monitor this by looking at the amount of ground cover as upright growth begins—if it’s complete or nearly complete, then there’s not much concern. But if a strip of soil is visible between rows, tiller numbers may be inadequate for highest yield. As a rough estimate, each productive tiller (head) per square foot translates to a yield of about one bushel per acre. Head size will adjust to some extent for higher or lower head numbers, but having fewer than 50 or so heads per square foot may limit yields.

Nitrogen

Many Illinois wheat fields have already had nitrogen applied, though some fields in central or northern Illinois, and where it’s been wet in southern Illinois, may still need topdressing. Rapid growth and setting of yield potential haven’t yet begun, so not having N applied hasn’t lowered yield yet. While N is often applied while the crop is still dormant, there is little evidence that such early application helps more tillers to form or stimulates greenup; early growth is limited by soil and air temperatures, and by the amount of leaf area, not by availability of N. Agronomically, applying N after the crop greens up is a sound practice. Logistically, however, fields are often wet at greenup, so many producers apply when field conditions allow, often in February or early March, including when soil is frozen. Applying N on frozen soil isn’t ideal due to possible runoff with rains after application, but may be a better choice than applying when soil is wet, or than long delays due to wet weather after crop growth begins.

The form of N used to topdress wheat was historically ammonium nitrate. After availability of AN declined, urea became the most common source. Now, many producers apply UAN with streamer bars. This method provides a uniform application, and with little leaf area contacted by UAN, typically results in little or no leaf injury.

We suggest higher N rates for wheat in southern Illinois than in central and northern Illinois, based partly on the fact that soils with less organic matter provide less mineralized N. Wheat in southern Illinois also takes up N over a shorter period of time than in central and northern Illinois, so more N needs to be available in the soil early, before mineralization kicks in. We suggest basing N rates on the price of N relative to the price of wheat. With July wheat currently at about $7.00 per bushel and N (as UAN) at about $0.70/lb (one bushel will “buy” 10 lb of N), suggested N rates are about 75 lb N/acre in northern Illinois, 100 lb in central Illinois, and 125 lb in southern Illinois.

Some question whether these rates of N are adequate, and suggest applying more N where we expect higher yields, or applying enough N to cause the crop to lodge some. Such higher rates may be part of a “high-management” approach that includes foliar fungicide and perhaps plant growth regulators to shorten stems to prevent lodging. We have not found this approach to be consistently profitable. Current varieties have been bred to produce maximum yields at N rates lower than those needed to cause lodging. High N rates can increase foliar disease severity, and can contribute to grain quality problems under some conditions. Higher N rates typically increase grain protein, which is an advantage when producing hard (bread) wheat, but not with soft wheat, which is mostly what Illinois growers produce.

Spring growth

As we watch the Illinois wheat crop over the next month, keep in mind that, although we like the crop to grow fast and the canopy to have good, green color, yield prospects are more closely tied to weather conditions in May and early June than to how good the crop looks in April. Periods of dry weather during and after flowering are favorable for wheat, and wet weather can be problematic, both because it tends to increase foliar disease development (and to make fungicide application more difficult), and also because wheat grain fills quickly, and does this best when there is a lot of sunlight with moderate temperatures after flowering. ∆