Replanting Decisions For Winter Wheat

By Romulo Lollato

Wheat and Forages Specialist

Wheat stands may be thin this year, for a variety of reasons. For example, some regions of southwest Kansas have been without substantial precipitation for more than a month, which may result in uneven wheat emergence and sub-optimal stand establishment (Figure 1). Where stands are too thin, producers will have to decide whether to replant.



Figure 1. Contrasting wheat emergence near Belleville during the 2015-16 growing season. Photo by Romulo Lollato, K-State Research and Extension.

 
The most probable cause for uneven wheat emergence during this fall in southwest Kansas is dry soils. However, poor seed quality may also play a role in poor wheat emergence, especially when using saved seed, or brown bagged seed, which might be common this growing season due to the low commodity prices. Soil crusting, seedling rot diseases, soil insects, or low soil pH, may also be causes of poor emergence. For more details on these, please read the accompanying article in this issue of the Agronomy eUpdate “Most likely causes of poor wheat emergence.”

If dry soils are the cause of the problem, replanting will not bring many benefits unless the seed has partially germinated and perished before emerging. It is very important to dig into the soil and evaluate the seed to determine the cause of poor emergence. Wheat seeds may still be germinating and emergence may occur in the next few days, depending on temperatures. Thus, if seed are still hard and viable, or if germination started to occur recently and there are very short coleoptile emerging from the seed (Figure 2), the best advice is to leave the field alone.

Figure 2. Wheat seed with elongating coleoptile visible below ground. This particular field, close to Belleville, got approximately an inch of rain in the week prior to taking this photograph and some seed had just begun germinating. Photo by Romulo Lollato, K-State Research and Extension.

 Considerations when deciding whether to replant wheat fields are i) percent stand compared to the target stand, ii) replanting date, iii) stand uniformity, and iv) weed control.

    Percent stand compared to the goal

In order to check how far actual stands are from the target stand, counting the number of emerged plants per row foot and comparing to the values on Table 1 should give a good estimate. Table 1 shows the number of target plants per row foot depending on seeding rate, seed size, and row spacing, and considering 80% emergence. If seed size is not known, 14,000 to 16,000 seeds per pound can be used for most wheat varieties in Kansas, except those with rather large or small kernels.

Table 1. Target plants per row foot (80% emergence) based on seeding rate, seed size, and row spacing.

Seeding rate

To determine the average number of plants per foot of row, several random plant counts across the field should be taken, given a more or less uniform emergence throughout the field. If the average number of plants is about 50 percent or more of normal and the stand is evenly distributed, the recommendation is to keep the stand. Wheat’s tillering ability can greatly compensate for poor stand provided soil fertility is adequate and the weather is favorable. With less than 40 percent of normal stand, the recommendation is to replant the field. If possible, replanting should be done at a 45 degree angle to the original stand to minimize damage to the existing stand.

Replanting date and seeding rate

As of early October, there is still time to hit the optimum planting date window for most of Kansas with the exception of some areas in the northwest portion of the state. If there are signs that the field will not achieve about 50% stand, it will not emerge evenly, or that the seedlings have perished after planting, producers still have time to take the decision of replanting until the middle to end of October without compromising the yield potential. Producers can 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 these seeding rates by 20-30 pounds per acre.

Weed control

A thin wheat stand can increase the potential for weed and grass infestations. If these concerns become severe, the wheat stand should probably be replanted or thickened. Uneven wheat stands can also influence herbicide timing due to different staging of the crop within the same field. Figures 1 and 2 exemplify a field where parts of the field will begin tillering at the same time other parts are still emerging. Herbicides such as 2,4-D and dicamba have very specific application guidelines, and attention must be paid to the herbicide label to avoid injury to the wheat crop.

Paying attention to wheat leaf staging when controlling weeds can help minimize the consequences of applying these herbicides outside the labeled recommendations. Potential problems due to improper application timing include trapped heads, missing florets, or twisted awns. More developed plants during the fall often hold the best yield potential; thus, this factor might be considered if a decision needs to be taken between risking some herbicide injury to more developed plants versus those that emerged late in uneven wheat fields.

Source:ksu.edu