As wheat growers evaluate their wheat stand, some may be considering replanting fields yet this fall. In some cases, the emergence might be spotty, with lower areas in the field presenting the worst stand establishment (Figure 1). These low-lying areas are typically not as well-drained, which creates conditions that cause the poor emergence. Other fields might have experienced heavy rains after planting, causing soil crusting and prevented the coleoptile from breaking through the soil surface. If the coleoptile stays underground for more than a week or so, it will start losing viability. At that point, the producer will need to consider replanting.
Figure 1. Poor wheat emergence in lower portions of a wheat field in Saline County, Kansas. Higher areas, as seen in the back of the photo, tend to have good emergence and stand establishment. Photo taken mid-October 2017 by Tom Maxwell, KSRE Agent for the Central Kansas District.
When deciding whether to replant wheat fields it is helpful to consider these factors: i) stand uniformity, ii) percent stand compared to the target stand, iii) replanting date, iv) weed control, and v) insurance cutoff date.
Stand uniformity
As shown in Figure 1, poor wheat emergence caused by poor soil water drainage often results in recognizable field patterns associated with the excessively moist soils. In this case, stands might be relatively uniform in better-drained areas, but non-existent in poorer-drained areas, leading to a high within-field variability. In this case, replanting large areas with poor emergence should have top-priority once conditions are suitable for fieldwork. If a stand is sparse in areas that already emerged, producers should also consider replanting these areas with lower seeding rates to bring final population closer to the desired stand, as discussed below.
Percent stand compared to the goal
In areas with suboptimal and thinner stands than desired, counting the number of emerged plants per row foot and comparing the observed stand to target populations (Table 1) is a good place to start.
The target number of plants per row foot (Table 1) is influenced by 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. 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.
Recent K-State research indicates that a minimum of approximately 900,000 emerged plants per acre is needed for most varieties to maximize yields under normal fertility conditions in Kansas. Thus, if producers are not aware of their target plants per row foot, the above threshold might be a good goal for central Kansas producers.
Table 1. Target plants per row foot (80% emergence) based on seeding rate, seed size, and row spacing.
|
Seeding rate |
Seed size |
Row spacing (inches) |
||||
|
6 |
7.5 |
8 |
10 |
12 |
||
|
lb/ac |
seeds/lb |
Target plants per row foot (80% emergence) |
||||
|
45 |
12,000 |
5 |
6 |
7 |
8 |
10 |
|
14,000 |
6 |
7 |
8 |
10 |
12 |
|
|
16,000 |
7 |
8 |
9 |
11 |
13 |
|
|
18,000 |
7 |
9 |
10 |
12 |
15 |
|
|
60 |
12,000 |
7 |
8 |
9 |
11 |
13 |
|
14,000 |
8 |
10 |
10 |
13 |
15 |
|
|
16,000 |
9 |
11 |
12 |
15 |
18 |
|
|
18,000 |
10 |
12 |
13 |
17 |
20 |
|
|
75 |
12,000 |
8 |
10 |
11 |
14 |
17 |
|
14,000 |
10 |
12 |
13 |
16 |
19 |
|
|
16,000 |
11 |
14 |
15 |
18 |
22 |
|
|
18,000 |
12 |
15 |
17 |
21 |
25 |
|
|
90 |
12,000 |
10 |
12 |
13 |
17 |
20 |
|
14,000 |
12 |
14 |
15 |
19 |
23 |
|
|
16,000 |
13 |
17 |
18 |
22 |
26 |
|
|
18,000 |
15 |
19 |
20 |
25 |
30 |
|
|
120 |
12,000 |
13 |
17 |
18 |
22 |
26 |
|
14,000 |
15 |
19 |
21 |
26 |
31 |
|
|
16,000 |
18 |
22 |
24 |
29 |
35 |
|
|
18,000 |
20 |
25 |
26 |
33 |
40 |
|
Replanting date and seeding rate
As of late October, most of the state has passed the optimum sowing date, with maybe the exception of south-central or southeast Kansas. For portions of the field with no established stand (the entire stand will need to be replanted), producers should plan to increase their seeding rates by 10-15% for every week past the optimum sowing date.
In areas where a partial stand was achieved but for a total of about 50% stand, or parts of the field that did not emerge evenly, or that the seedlings have perished after planting, producers should make the decision about replanting immediately to avoid further compromising the yield potential.
In portions of the field where stand is below optimum, 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. The higher seeding rates are needed because the cool soil temperatures encountered by late planted wheat will likely slow emergence, favor seedling diseases and reduce the potential for fall tillering. Using a fungicide seed treatment can reduce the potential for seedling disease and help achieve the target populations.
Weed control – Pay attention to application timing
A thin wheat stand can increase the potential for weed and grass infestations. In fields with a history of severe weed problems, the wheat stand should probably be replanted or thickened. Keep in mind that the uneven wheat stands can also influence herbicide timing due to different staging of the crop within the same field. 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.
Insurance cut-off dates
Finally, some producers might also consider insurance cut-off dates, as they need to ensure their crop is planted prior to this date. The 2019 crop year final plant dates for wheat are shown in Figure 2.
For insurance purposes, crops planted before these dates are insured with no reduction in coverage or adjustment to premium. The final plant date is already past for parts of western Kansas, which means that producers replanting after this date will have a reduction in 1% coverage per day until the end of the late-planting period. For wheat, the late-planting period often occurs about 15 days after the final plant date (Figure 2).
Figure 2. USDA 2019 crop year final planting date for wheat. Crops planted before the dates above can be insured with no reduction in coverage or adjustment to premium. The final planting date for wheat is generally 15 days after the dates above, at a reduction in coverage of 1% per day during the period between initial and final plant date.
Romulo Lollato, Wheat and Forages Specialist
lollato@ksu.edu
Erick DeWolf, Extension Wheat Pathologist
dewolf1@ksu.edu
Tags: wheat replanting