Dry soils, poor emergence may require replanting of wheat
Wheat emergence has been very slow this year in some areas of Kansas because of dry soil conditions, said Jim Shroyer, K-State Research and Extension crop production specialist.
If wheat stands in a field are spotty, it may be necessary to replant some or all of it, depending on the cause of the poor emergence, he said.
"Replanting an entire field is expensive and time-consuming, so producers have to make this decision carefully. Even just spot planting a few bare areas can be time-consuming. Still, replanting any area that truly needs it can pay off," Shroyer said.
Generally, if the average number of plants in an area is about 50 percent or more of normal, the recommendation is to keep the stand, the K-State agronomist said. With less than 40 percent of normal, the recommendation is to replant the field, or portion of the field, he added.
There are two major concerns to consider other than yield potential in deciding whether to replant: the susceptibility of the ground to wind erosion and the potential for weed and grass infestations, he said.
"Where stands are less than 40 percent of normal, these become major concerns, even if yield potential is not a concern. In fact, research in western Kansas indicates that 260,000 to 320,000 plants per acre, or about six to seven plants per foot of row, can produce within 90 percent of expected yields--especially if the plants are able to tiller well and the stand is uniform. But if the soil is blowing or weeds and grass infestations become severe, the stand should probably have been replanted and thickened," he explained.
When replanting into a thin stand, producers should run the drill at a 45 degree angle to the original stand if possible to minimize damage to the existing stand, he said.
If the replanting is done in November or later, producers should use seeding rates of 60 to 75 pounds per acre in western Kansas and 75 to 90 pounds per acre in central Kansas when re-seeding into thin stands that are about 30 to 40 percent of normal, Shroyer said.
Where there was no emergence in all or parts of the field, producers should use a slightly higher seeding rate than used initially--90 pounds per acre in western Kansas and 120 pounds in eastern and central Kansas when planting in November or later, he added.
Seeding rates on non-irrigated fields should not be higher than 90 pounds per acre in western Kansas or 120 pounds per acre in central and eastern Kansas, he added. Under irrigation, seeding rates should never be higher than 150 pounds per acre.
Before replanting, producers should dig through the soil crust to determine why the seed did not emerge, Shroyer said. The most common causes of emergence problems are dry soils, crusting, poor quality seed, seedling rot diseases and wireworms.
"If dry soils are the cause of the problem, which is the most likely situation this year, you should dig up some seed and check its condition. If the seeds are still hard and viable, or have just a very short stub of coleoptile emerging from the seed, there is no need to replant. Just leave the field alone and wait for rain," he explained.
"But if the seed has partially germinated and the coleoptile stalled out before emerging, it's unlikely that seed is still viable and replanting is advisable."
Where crusting is the cause of the emergence problem, producers also should do some digging to evaluate the condition of the seeds or seedlings he added.
"If the seed is still viable, it could still emerge if conditions improve. For example, sometimes a light rain on crusted soil will soften the crust so seedlings can emerge. Otherwise, a rotary hoe will break up the crust, allowing them to emerge," he said.
If the coleoptiles have become bent or crinkled due to the crusting, however, they will most likely have reached their full length already and will not be able to elongate any further to emerge through the soil surface if conditions improve, Shroyer said. In that case, replanting will be necessary.
Finally, if there has been adequate moisture and no crusting, but little or no emergence, poor quality seed, seedling rot diseases, or soil insects are possible causes of the problem, Shroyer said. In this case, the field will need to be replanted with good quality, treated seed, he said.