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K-State Agronomy eUpdates

Department of Agronomy

Kansas State University

1712 Claflin Rd.

2004 Throckmorton PSC

Manhatan, KS 66506

785-532-6101

agronomy@ksu.edu

Extension Agronomy

Replanting decisions for winter wheat


Many Kansas wheat fields that have already been planted might end up with poor stands due to the prolonged wet and cool period observed in the first few weeks of October. These cool and damp conditions can influence seed viability and have delayed emergence in many fields. Unfortunately, there is not much that can be done at this time.  Right now, the best thing we can do is wait to see what proportion of the plants emerge, and critically evaluate whether the plant population is sufficient to meet our yield goals. Below, we outline some steps to assess the need for replanting in the near future.


Figure 1. Slow and scattered wheat emergence in a field planted October 2, 2018 near Belleville, Republic Co., Kansas. Photo taken October 18, 2018 by Andrew Esser, K-State Research and Extension.


In many cases, the emergence is “spotty” with lower areas in the field presenting worst stand establishment (Fig. 2). These low-lying areas are typically not as well drained as other areas in the field. These areas can become saturated quickly resulting in a low oxygen soil environment that suppresses seed germination and seedling growth. In other fields, the upper portions of the soil were hardened by heavy rains. This “soil crusting” can prevent the coleoptile from breaking through the soil surface. If the coleoptile has not been able to break through to the soil surface within 7-10 days, the health of the young plants will decline rapidly. At that point, the producer will need to consider replanting.


Figure 2. 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, Extension Agent for the Central Kansas District.


Factors to consider when making replant decisions in wheat include: stand uniformity, actual stand compared to the target stand, replanting date, weed control, and insurance cutoff date.

  • Stand uniformity. As shown in Figure 2, easily recognizable patterns occur in the field based on soil water drainage and accumulation when excessively moist soils cause poor wheat emergence. 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. Producers should have as top-priority replanting those large areas with poor emergence once conditions for fieldwork allow. If stand is patchy in areas that already emerged, producers should also consider replanting at lower seeding rates to bring final population closer to the desired stand, as discussed below.
     
  • Actual stand compared to the target stand. In areas that already emerged despite the excessive moisture, stands might also be suboptimal and thinner than desired. In these situations, it is often helpful to compare the actual stand with what desired plant populations was to meet our yield goals. Table 1 shows the number of target plants per row foot depending on seeding rate, seed size (provided with certified seed), 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 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 approximately 900,000 emerged plants per acre are 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 is past the optimum sowing date, maybe with the exception of south-central Kansas. For portions of the field with no stand established, where 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. Producers should consider replanting if a fields with: partial stand (50% or less of target stand), highly variable stands, or large areas that have failed. 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 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. Treating the seed with a fungicide can help ensure viability in wet soil environments and reduce the risk of additional problems with stand establishment this season.
     
  • Weed control. A thin wheat stand can increase the potential for weed infestations. This was clearly a problem for many fields during the 2017-18 growing season. Therefore, we need to acknowledge that weed control needs to be part of the decision to replant of thicken wheat stands. Moreover, uneven wheat stands can also influence herbicide timing because parts of the field are at development stages. Herbicides such as 2,4-D and dicamba can cause serious crop injury when misapplied.  Potential problems due to improper application timing include trapped heads, missing florets, or twisted awns. Accounting for this variability in growth stage within a field can lower the risk of crop injury and loss of yield.
     
  • Insurance cut off dates. Finally, some producers might also consider insurance cut off dates.  Figure 3 shows the 2018 crop year final plant dates for wheat. 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 of 1% coverage per day until the end of the late-planting period. For wheat, late-planting period often occurs about 15 days after the final plant date shown in Figure 3.
     

Figure 3. USDA 2018 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