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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 planted prior to late-September 2017 have poor stands (Figure 1). The poor emergence tends to be spotty, often with lower areas in the field exhibiting the worst stand establishment. These low-lying areas are typically not as well-drained as other areas in the field, which contributes to the poor emergence. The main reason for reduced emergence in the 2017-18 cropping season is the excessive rainfall during the first half of October, which may have led to poor soil aeration and seedling death. Also, some fields have been crusted by heavy rains after planting, which can prevent the coleoptile from breaking through the soil surface. If the coleoptile stays below the soil surface 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 areas 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.


While the example shown on Figure 1 occurred in Saline County, it is typical of many wheat fields across the state. Reports of poor wheat emergence due to excessive moisture occurred as far west as Rooks and Phillips counties. Where stands are too thin, producers will have to decide whether to replant.

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

  1. Stand uniformity
     

As shown in Figure 1, easily recognizable patterns occur in the field based on soil water drainage and water accumulation when excessively moist soils are the cause for 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 consider replanting top-priority for large areas with poor emergence once conditions allow for field work. If the 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.

  

  1. Percent stand compared to the goal
     

In areas that already emerged despite the excessive moisture, stands might also be sub-optimal and thinner than desired. 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, 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 a 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

 

  1. Replanting date and seeding rate
     

As of late October, most of the state is past the optimum sowing date, with maybe 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 10-15% for every week past the optimum sowing date.

In parts of the field 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 as is the case for many fields, producers should replant immediately to avoid 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.

  1. 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. 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 stage 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 made between risking some herbicide injury to more developed plants versus those that emerged late in uneven wheat fields.

  1. 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 that date. Figure 2 shows 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 the 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 coverage of 1% 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 2.


Figure 2. 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