Flooded fields, replanting considerations for Ark. soybeans

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click image to zoom Due to the excessive and record-breaking rainfall that occurred early Sunday morning, many fields in an area covering Prairie, Woodruff, Jackson, Monroe, St. Francis, and Cross Counties have been flooded or are still under water.

Currently, we are estimating that 100,000 acres of soybeans will need to be replanted, with many more soybean fields receiving some yield damage due to saturated soil conditions. Due to many of the ditches and rivers being at capacity, many of these fields will remain flooded for several more days.

click image to zoom Many of the fields that I was able to look at since Monday had soybeans ranging from just emerging to V6. At these early growth stages, soybean plants cannot survive being totally submerged much longer than 24 hours with the hot, sunny weather that we have had since Sunday.

Historically, we have said that planting after June 15 results in a 1 to 2 percent yield loss per day, with the yield loss potential increasing to 2 to 3 percent per day after July 1, and not recommending planting after July 15. However, some new research conducted by Dr. Larry Purcell indicates that this may not be the case. This research will be discussed in more detail below.

For soybean growers that are considering replanting, there are several items that need to be addressed.

Late Season Replant Considerations:

  1. How long was a field flooded? - Those fields that were only submerged less than 24 hour should be evaluated. If new growth is observed three to four days after the flood water has receded, then these fields may not need to be replanted. Any field submerged more than 24 hours will likely need to be replanted.
  2. Removal of “old” soybean stands - Many of these flooded fields will possibly need to be reworked prior to replanting. This should remove any surviving soybean plants and any weeds that have emerge after the waters recede. For fields that will not be reworked, consider herbicide options to remove remaining soybean plants and any emerging weeds.
  3. Weed control - Our recommendations would be to plant a Liberty Link soybean variety. Growers will have more weed control options with the Liberty Link system than with Roundup Ready or conventional systems. Growers should also take into consideration what herbicides and rates have been applied to these fields so far this year. Be sure to not apply rates over the labeled amounts for the season. Also, be sure to look at the Plant-Back Intervals for the herbicides to be used. These can be found in here. Many of the common soybean herbicides have as much as a 10 month plant-back to other commodities, and 10 months from July 15 would be May 15 of the following year.
  4. Maturity group - Below are Dr. Larry Purcell’s comments on a research project evaluating soybean maturity groups by planting dates. For the past two years, his research indicates that late-MG IV varieties had the highest yield potential planted in July than the other maturity groups evaluated.

A large soybean project funded jointly by the United Soybean Board and the MidSouth Soybean Board was conducted at eight locations in the US Midsouth in 2012 and 10 locations in 2013, with four planting dates at each location, and 16 soybean cultivars from MG 3 to 6. The MG 4 cultivars had the highest yields, or were not significantly different from the highest yield, in 100% of the environments studied in both early- and late-planting. When considering only locations in east-Arkansas and nearby experimental sites (Rohwer and Keiser, AR, Stoneville, MS; Portageville, MO, and Milan, TN) results indicate that average soybean yields were highest with MG 4 soybean cultivars (70 bu ac-1) with plantings from June 1to June 15. For plantings from June 15 to June 30, average yields were nearly identical (50 to 51 bu ac-1) for MG 4, 5, and 6 cultivars. Finally, with plantings in July, average yields were highest with MG 4 soybeans (50 bu ac-1).

click image to zoom Figure 1 shows the average yield over all 18 environments for MG 3 through 6 cultivars for early and late planting dates. The asterisks above the data points indicate that the early-planting dates were significantly greater than the late planting dates. The solid symbols, within the early or late planting dates, indicate that the average MG yields were not different from the yield of the MG with the greatest yield.

click image to zoom click image to zoom







5. Seeding rate - Our recommendations for Full-Season soybean production ranges from 110,000 – 185,000 seed/ac. For late plantings, we recommend increasing your normal seeding rate by 10 – 15%. The reason for this increased seeding rate is to obtain quicker canopy closure and increase the number of nodes per acre since the number of nodes per plant will be reduced due to shortened growing season.

6. Row spacing - At this point in the planting window, our recommendations would be to plant on narrow rows less than 20 inches. Narrow rows will increase the likelihood of canopy closure. Complete canopy closure will decrease weed competition, increase irrigation efficiency, increase light interception, and possibly decrease late-season insect problems.

7. Late season pest concerns - Scout, Scout, Scout and Scout. When considering an extremely late replant of soybeans, growers should budget in at least 1-2 applications of an insecticide and a fungicide. With the tremendous numbers of soybean insects we are currently expecting in the state, these late-planted fields will more than likely need insecticides applications.

8. Average frost date - For the area affected by the flooding, the average frost date is November 1. Planted in mid-July, mid-MG IV and early-MG V’s soybean varieties will require 110 to 115 days to reach R8. These late plantings will be reaching maturity very close to the average frost date.

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