Wet weather hampers wheat management practices

Wheat development may outpace growers’ ability to make timely applications of herbicides, nitrogen and fungicides.

May 8, 2017 - Author: Martin Nagelkirk, Michigan State University Extension

Adverse weather has not favored timely farming operations this spring. Even applying products at the appropriate time to winter wheat has been a struggle in some areas of Michigan. At this point, growers are encouraged to assess the developmental stage of their crop and possibly alter their plans in some cases.

Interestingly, wheat’s rate of development is largely on par with past seasons despite cooler temperatures in recent days. This means that despite wet conditions and cold fronts, most wheat has moved beyond the tillering stages. In the Thumb, the crop has entered the jointing stages exhibiting one or two nodes (growth stages 6 and 7, respectively). In central Michigan, there are likely some fields where the tip of the flag may be visible (growth stage 8), and in the southern tier of counties growers may soon be seeing the flag leaf fully extended (growth stage 9).

Wheat growth stage 7

At growth stage 7, the second node, along with the developing seed head, has extend above the first node. The first node is useful in anticipating the emergence of the flag leaf in that when the leaf (and sheath) emanating from the first node is labeled as “leaf 4,” the flag leaf will almost always be “leaf 1.” Once the flag leaf emerges from the whorl of leaf 2, the plant is considered to be in growth stage 8.

Where applications of various inputs have been delayed, growers are encouraged to assess their crops and consider management options particularly as it relates to herbicide, nitrogen fertilizer and fungicides.

Herbicides

All herbicide labels define when the product can be used to avoid crop injury or residue concerns. These restrictions are noted in the “2017 Weed Control Guide for Field Crops” and summarized in the fact sheet “Weed control in winter wheat: Timing is everything” by Michigan State University Extension weed specialist Christy Sprague. The application window is closed for a number of products already, and by the time fieldwork can commence, wheat development may be beyond the timing allowed for the use of some other popular products.

Nitrogen

Depending on the circumstance and springtime weather patterns, it’s usually preferable to have some nitrogen fertilizer applied by growth stage 6 (first node extends above ground level). In those cases where obstacles prevent any nitrogen applications, grain yields may be reduced by half; therefore, an attempt should be made to apply some of the nutrient even where the crop has reached the boot stage. Under this scenario, the nitrogen rate should be substantially reduced to reflect the crops reduced yield potential. Also, at this stage the nitrogen should be applied as a stream rather than a spray to minimize the amount of burn to the flag leaf. An additional measure to consider is diluting the liquid nitrogen with water.

In wheat fields where only some of the intended nitrogen has been applied, the balance of the nitrogen can still be applied at later jointing stages. In a replicated trial near Sandusky, Michigan, in 2009, a late dose of supplemental nitrogen was applied to wheat that exhibited significant nitrogen deficiency due to an extensive wet spell. Despite yields being better than anticipated in the absence of additional nitrogen (see table), there was an economic response to the use of 30 pounds of nitrogen as 28 percent UAN. Later, at the late boot stage, there was no benefit to applications of 14 or 28 pounds of nitrogen (data not shown).

Supplemental fertilizer N applied to winter wheat during flag leaf emergence

N rate pounds per acre

Grain harvest moisture (%)

Grain yield, 13% M, bushels per acre

Lodging2 0-5

0

20.7

97.4

1.0

301

21.5

105.5

2.4

601

22.3

107.6

3.8

1 Streamer application using TeeJet SJ3-03.
2 Relative rating from 0 to 5 with 0 denoting no lodging.

Fungicides

Growers who opt for applying an early foliar fungicide can still do so. In fact, with the slow development of leaf disease this spring, there is likely an advantage to delaying a fungicide application until the flag leaf stage. Others may elect to forego the first fungicide application and instead simply rely on the normal treatment at heading. However, this needs to be decided field by field based on the susceptibility of the variety being grown and the level of diseases found.

Tags: agriculture, field crops, msu extension, wheat


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