Some regions in central Kansas had been without substantial precipitation since earlier in the summer, which led to somewhat poor and uneven wheat emergence (Figure 1). Where this scenario holds true, producers will have to decide whether to replant.
Figure 1. Contrasting wheat emergence in north central Kansas, near Belleville. Field planted during the first week of October. Photo taken Oct. 28, 2015 by Romulo Lollato, K-State Research and Extension.
The most probable cause for uneven emergence during this fall is dry soils. However, poor seed quality may also play a role in poor wheat emergence, especially after the last growing season when wheat head scab was a major problem in some areas of Kansas. Soil crusting, seedling rot diseases, or soil insects may also be causes of poor 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 important to dig into the soil and evaluate the seed to determine the cause of poor emergence, especially where there has been some recent rainfall. Wheat that received some of last week’s rain 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 following last week’s rainfall events and there is a 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 field, close to Belleville in north central Kansas, received approximately an inch of rain last week and some seed is now germinating. Photo by Romulo Lollato, K-State Research and Extension.
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.
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 |
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 |
|
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
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 these seeding rates by another 20-30 pounds per acre.
- Stand uniformity
Where there was no emergence in all or parts of the field and large gaps are present, producers would have to use a slightly higher seeding rate than used initially — 60 to 90 pounds per acre in western Kansas and 90 to 120 pounds in eastern and central Kansas. These higher planting rates can help compensate for a late planting, so the higher end of those ranges should be used when planting in November.
- Weed control
A thin wheat stand can increase the potential for weed and grass infestations. If these 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 be beginning to tiller while other parts of the field will still be 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, which can result in trapped heads, missing florets, or twisted awns. More developed plants in the fall often hold the best yield potential. 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.
Romulo Lollato, Wheat and Forages Specialist
lollato@ksu.edu
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