Outlook for short, stressed wheat
Jim Shroyer, K-State Research and ExtensionFigure 1. Wheat only 9 inches tall with flag leaf emerged. Saline County demonstration plots, April 24, 2014. The wheat crop in much of central and western Kansas has many problems this year. It is about two weeks behind normal in development, shorter than normal (on dryland fields at least), has a shortened flag leaf, and/or has a poorly developed root system. In addition, some fields are still under drought stress, have freeze injury, or suffered winterkill damage.
If wheat remains under drought stress and the weather turns unusually hot, producers can expect to see the following symptoms:
- White heads, which can develop very quickly
- Curled and dried up flag leaf
- Sloughed tillers
- Loss of one or more small developing kernels in the spikelet
- Poorly developing kernels
- Chlorotic leaves due to poor root development and nutrient deficiencies
From the boot stage through heading and grain fill is a period of high moisture use, with wheat using about 0.25 to 0.30 inches of moisture per day. If the moisture isn’t available, the wheat will begin to show the symptoms listed above. The combination of dry soils and heat, in particular, will cause heads to turn white rather quickly, almost overnight. Any additional stress, such as diseases or insects, will just add to the stress.
If temperatures are cool to moderate in the coming weeks and rain comes to stressed wheat sometime before the flowering stage, the wheat may be able to recover some yield and test weight potential as long as the flag leaves are still alive. If the plants are under severe stress and shut down while kernels are in the early dough stage, it is unlikely that any subsequent rain will help the kernels complete their fill. This will result in a loss of yield and low test weight regardless of the weather during the remainder of the season. The early dough stage, of course, is at least a month away.
The drought this year has resulted in very short flag leaves in many cases, and reduced the overall photosynthetic potential of the wheat. All of this will have an effect on grain fill, yields, and test weight.
click image to zoomJim Shroyer, K-State Research and ExtensionFigure 2. Wheat that turned blue in part of the field due to drought stress. Drought-stressed wheat is already shorter than normal. In some cases, these plants may eventually recover if they get some rain by the boot or early heading stage – even wheat that turned blue from drought stress. But yield potential will be reduced. In severe cases, however, some of these plants may turn brown and die.
This brings up two main questions:
1. How much yield loss will wheat suffer if it is short and late, with a small flag leaf? At this point in the season, it is impossible to answer that question. It depends on the weather from now through the soft dough stage.
2. How can you go about deciding when it’s time to pull the trigger and destroy the crop to get ready for a follow-up crop of grain sorghum, soybeans, summer annual forage, or sunflowers? That’s another tough question, and involves crop insurance considerations. If the wheat is very short and stands are thin, you can probably make the call any time now, pending approval by your crop insurance representative. If stands are good but the crop is short and late, it’s best to wait until about the soft dough stage. By then you will be able to get kernel counts and make an estimate of grain fill.
If the wheat crop is terminated, producers may be able to plant a follow-up crop. Two of the most commonly planted summer crops after wheat are grain sorghum and soybeans. The crop choice will depend on soil moisture and wheat herbicide carryover considerations -- see eUpdate No. 445, March 14, 2014 at: https://webapp.agron.ksu.edu/agr_social/eu_article.throck?article_id=184
- Needs 21 inches of combined stored soil moisture and available precipitation for a full season hybrid; a little less for a medium maturity hybrid.
- Takes 6.9 inches of combined stored soil moisture and available precipitation to get grain sorghum to the first bushel of yield
- After that, each inch of available precipitation received and utilized will return about 9.4 bushels per acre
- Prefers soil temperatures above 60° F at planting time
- Medium-early hybrids planted the first 10 days of May can reach harvestable maturity in mid to late September
- Planting in June means later October harvest
- Earlier planting = taller plants with more foliage
- The later the planting usually the greater the lodging potential
- Needs/would like about 24 inches of available soil moisture and precipitation.
- Takes 9 inches of combined stored soil moisture and available precipitation to get soybeans to the first bushel of yield.
- After that, each inch of available precipitation received and utilized will return about 4.5 bushels per acre.
- Also prefer soil temps above 60° F at planting time.
- If planting prior to Memorial Day and especially in no-till, use a good seed treatment fungicide.
- Early Group III’s planted in early May should be physiologically mature by September 20-25 and be ready for harvest 10-14 days later.
- Group IV’s planted in early May will normally run about 10-14 days later than the early III’s.
- For every 3 days delay in planting, plan on the crop maturing 1 day later. Example: The same variety planted June 12 will reach physiological and harvest maturity approximately 2 weeks later than if it was planted May 1.