Getting good stand establishment of wheat is the first hurdle for producers as they begin the new season. If the wheat doesn’t emerge, or emerges in a spotty pattern, producers will have to diagnose the problem quickly and decide whether it would be best to wait a little longer or replant the field. Poor emergence can be caused by a number of problems, such as deep planting, a plugged drill, poor seed quality, seed dormancy, dry soil, soil crusting, and false wireworms. Take time to examine the evidence. Look for field patterns. Closer examination of the situation will help determine the causes of poor stands.
The ideal soil temperature for germination of wheat seed is between 54 and 77 degrees. This year, temperatures have been mild for the most part, conducive for good germination if there are no other problems. Topsoil moisture is better in most of the state this year than it has been for the past two or three years. As a result, there shouldn’t be too many germination and emergence problems caused by dry soils.
Some fields have been crusted by heavy rains after planting, which can prevent the coleoptile from breaking through the soil surface. If the wheat hasn’t emerged in a timely manner and you’ve had a heavy rain after the wheat was planted, dig up some seed and look for crinkled coleoptiles. If this is the case, you can try to break up the crust with a light tillage or hope for a gentle rain. But if the coleoptile stays underground for more than a week or so and hasn’t been able to break through the soil surface, it will start losing viability. At that point, the producer will need to consider replanting.
If soil temperatures are ideal, the topsoil is not unusually dry, and there has been no crusting, the most likely causes of poor stands would be deep planting, a plugged drill, poor seed quality, unusually long seed dormancy, diseases, or insects.
Deep planting, deeper than the coleoptile’s ability to elongate, can slow emergence or cause stand establishment problems. Varieties differ in their coleoptile lengths, but for the most part wheat should be planted about 1.5 inches deep. Most varieties can emerge at slightly deeper depths if the soil is not too restrictive and temperatures are in the ideal range. But if wheat is planted deeper than 2.5 inches, it is possible the wheat cannot emerge. Once the coleoptile grows as long as it can, which is determined by the variety and soil temperature conditions (coleoptile length is shorter at both lower and higher temperatures than the ideal range), the first true leaf will emerge below ground. Under normal conditions, this happens above ground. If the coleoptile is still under the soil surface when it stops growing and the first true leaf has to start growing in the soil, it is very unlikely to be able to force its way through the soil and emerge. What you’ll see when digging up the seed is an intact coleoptile alongside a short first leaf that is scrunched up or crinkled. If this is the case, it’s very unlikely the wheat will make a stand wherever the seed was planted too deeply and replanting will be necessary.
Another possibility is that the seed has poor quality. As long as the seed was tested for germination by a licensed laboratory and had an acceptable germination rate, seed quality should not be a problem. If germination testing on the seed lot was not done by a laboratory, poor seed quality could be a problem if other potential problems have been ruled out. At times, wheat doesn’t germinate simply because the seed has an unusually long seed dormancy requirement. This is hard to identify in the field, and can cause producers to replant when it’s not necessary. There are variety differences in seed dormancy, although this hasn’t been tested recently. And even within the same variety, some seed will have longer dormancy than others depending on the conditions in which it was produced. If a seed lot has unusually long seed dormancy, it should eventually germinate and emerge just fine.
Finally, false wireworms can be the cause of poor emergence. False wireworms are soil-inhabiting, yellowish to orange-colored worms up to 11/2 inches long. A pair of short antennae is clearly visible on the front of the head and the head region does not appear flattened when viewed from the side. They commonly follow the drill row in dry soils, feeding on the seeds prior to germination.
For more information, see K-State’s publication S-84, “Diagnosing Wheat Production Problems” at: http://www.ksre.ksu.edu/bookstore/pubs/s84.pdf
Jim Shroyer, Crop Production Specialist
jshroyer@ksu.edu
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