By Jim Shroyer
Kansas State

Wheat emergence has been very slow this year in some areas of Kansas because of dry soil conditions. If wheat stands in a field are spotty, it may be necessary to replant some or all of the field, depending on the cause of the poor emergence.

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. Nevertheless, replanting any area that truly needs it can pay off.

Stand count determination

The first step is to determine how much below normal the stand count is. To do this, you first have to determine what is normal. This can apply to the entire field or just certain spots that are bare.

If you use a drill with 12-inch row spacings, plants at a 60-pounds-per-acre seeding rate with a variety that has 15,000 seeds per pound, and expects a germination and emergence rate of 75 to 80 percent, there should be 675,000 to 720,000 plants per acre. This amounts to about 15.5 to 16.5 plants per foot of row.

If you planted 60 pounds of seed per acre using 7.5-inch rows, and a germination rate of 75 to 80 percent, that would be about 9 plants per foot or row.

The next step is to determine the average number of plants per foot of row that is present by taking numerous plant counts across the field. This assumes the stand is more or less uniform throughout the field, with no large gaps.

Generally, if the average number of plants is about 50 percent or more of normal, the recommendation is to keep the stand. With less than 40 percent of normal, the recommendation is to replant the field. With a stand that is between 40 and 50 percent of normal, the decision is more difficult.

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. 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.

Where the stand is 30 to 40 percent of normal, the yield potential will have been reduced enough that replanting will usually pay off. If possible, replanting should be done at a 45 degree angle to the original stand to minimize damage to the existing stand.

Seeding rates when re-seeding

Until the end of October, producers could cross-drill at the rate of 30-40 pounds per acre in western Kansas and 40-60 pounds per acre in central and eastern Kansas, using a double-disc opener drill if at all possible to minimize damage to the existing stand. If the replanting is done in November or later, increase the seeding rates to 60-75 pounds per acre in western Kansas and 75-90 pounds per acre in central Kansas. If stands are less than 30 percent of normal, increase the seeding rates just mentioned by 20-30 pounds per acre. If a hoe drill is used, the seeding rate should be higher than if a disc drill is used because the hoe drill will destroy much of the original stand. With a hoe drill, add about 20-30 pounds per acre to the seeding rates mentioned above.

Where there was no emergence in all or parts of the field, producers would have to use a slightly higher seeding rate than used initially -- 75 to 90 pounds per acre in western Kansas and 100 to 120 pounds in eastern and central Kansas, using the higher end of those ranges when planting in November or later.

Seeding rates on non-irrigated fields should not be higher than 90 lbs/acre in western Kansas or 120 lbs/acre in central and eastern Kansas. Under irrigation, seeding rates should never be higher than 150 lbs/acre.

Causes of poor emergence

Before replanting, producers should dig through the soil crust to determine why the seed did not emerge. The most common 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, replanting will do no good unless the seed has partially germinated and stalled out before emerging. If the seed are still hard and viable, or have a very short coleoptile emerging from the seed, the best advice is to leave the field alone and wait for rain.

Where crusting has occurred, producers should determine whether the seeds or seedlings are still viable or the coleoptiles have become bent or crinkled due to the crusting. 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.

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. In this case, the field will need to be replanted with good quality, treated seed.

-- Jim Shroyer, Crop Production Specialist

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