The planting conditions across the state have been varied since late March. The south has been a little dry and the north has been too wet to plant in several places. The 2020 growing season has started with two tornadoes and heavy rains across central and north Louisiana. The weather has been cool since Easter weekend which could slow emergence and vegetative growth.

According to the USDA, 33% of the soybean crop had been planted by April 26 with 18% emerged. This progress is ahead of last year and even with the five-year average. Reports from southern parishes indicate the soybean planting is almost complete in the sugarcane production areas. Besides the sugarcane production areas, the progress has been reported to be between 8% - 30% complete with plants progressing up to the V2-V3 vegetative growth stage.

There have been a few issues with soybean fields at the Dean Lee Research Station and across the state.

Poor soybean stand

The first planting of a date of planting trial at the Dean Lee Research Station was on March 19, 2020. Three inches of rain fell during the next three days. The planting rate was 137,500 seeds/acre, but only 46% survived with a final stand of 63,300 plants/acre. An article, “Considerations for replanting soybean,” in the Volume 10, Issue 3 – April of the Louisiana Crops Newsletter, suggest stand counts below 70,000 to 75,000 plants/acre may result in lower yields. However, the cost of replanting versus the potential profit should still be considered before replanting. An article covering the economics of replanting soybean will be submitted for the May issue of the Louisiana Crops Newsletter. Soybean plants do have an ability to compensate for gaps up to a certain point. At Dean Lee, a series of pictures are tracking the growth and development of soybean plants as they compensate for various spacing.

Figure 1: Soybean plant at approximately the V3 growth stage with a 3-inch spacing. The planting date was on March 19, 2020 and the picture was taken on April 17, 2020.

Figure 2: Soybean plant at approximately the V5 growth stage with an initial 3-inch spacing. The vegetative growth has almost filled the open space. The V5 growth stage picture was taken on April 30, 2020.

Figure 3: Soybean plant at approximately V2 growth stage with a 6-inch spacing. The planting date was on March 19, 2020 and the picture was taken on April 17, 2020.

Figure 4: The soybean plant with a 6-inch spacing was behind the other plants on April 17, 2020. On April 30, 2020, the plant had almost filled the open space on one side.

A field was planted to soybean at the Dean Lee Research Center on April 22, 2020. Severe weather, including a tornado and approximately 2-3 inches of rain, came through the same day. The seedlings emerged eight days later on April 30, 2020. A pre-emergent program, including flumioxazin, was applied after planting. I walked this field with Dr. Stephenson, discussing the symptoms, the pre-emergent treatment, and the amount of precipitation since planting. The discussing led to diagnosing the symptoms of the cotyledons to be from flumioxazin pre-emerge herbicide. However, the plants are expected to grow out of the damage. A good indication of this prognosis is the minimum damage to the unifoliate leaves growing from the epicotyl.

Figure 5: A soybean seedling at the VC growth stage on May 1, 2020. The cotyledons show symptoms suggesting damage from flumioxazin pre-emerge herbicide. The unifoliate leaves appear to have only minimum damage.

Figure 6: Soybean seedlings at the VC growth stage on May 4, 2020. The seedlings show symptoms suggesting damage from flumioxazin pre-emerge herbicide. The unifoliate leaves appear to have only minimum damage, and the first trifoliate leaves appear healthy.

Lower stand counts have been reported in areas of north Louisiana, possibly due to poor seed-to-soil contact. The seeds were drilled in a no-till production system with a terminated cover crop. The planting equipment must be able to properly cut the residue, allowing a good seeding depth and seed-to-soil contact.

This week looks to be warm with a small chance of precipitation. It should be a great week to plant soybean.

Figure 7: Preparing a field at the Dean Lee Research Center on May 4, 2020 for the 2020 Official Variety Trial.