Hurricane Francine Caps Off Rainy Period, Causes Seed Damage in Louisiana Soybean

David Moseley, LSU AgCenter Soybean Specialist

Many areas of Louisiana received several consecutive days of rain between August 28 to September 12 (Table 1). The rainy period was capped off with Hurricane Francine on September 11. The continuous precipitation caused weather damage in soybean plants that were mature or near maturity.

Fields planted on or before April 16 at the Dean Lee Research and Extension Center were harvested by August 28 and had good yield and quality. In addition, fields planted on May 6 or later did not show weather damage on September 12. In this case, fields planted from approximately April 16 to May 6 (35% of the statewide crop) have the largest percent chance of weather damage from the extended rainy period (Figures 1 – 7).

The USDA-NASS reported 40% of the Louisiana soybean crop was harvested by September 8, 2024. At this time, the crop condition was rated as 82% good to excellent (Figure 1). However, 28% and 19% of the crop was dropping leaves and mature, respectively, and not yet harvested. These plants would be the most sensitive to continuous rain events.

With this set of data and observations, it is difficult to determine how much weather damage was caused statewide by the rain events. It appears approximately 20-30% of the crop was in a sensitive growth stage from August 28 to September 12. However, at times, the rain fell in isolated areas and would not have caused as much damage in some areas as others.

Table 1. Rain totals in different regions across the state according to the Louisiana Agriclimatic Information System

Figure 1. The USDA-NASS reported 40% of the Louisiana soybean crop was harvested by September 8. However, harvest progress slowed down in places beginning on August 28 due to rain events. 35% of the crop was planted between April 16 and May 6 and may be the most sensitive plants to the continuous rain events between August 28 and September 12.

Figure 2. Soybean seeds from a March 28th planting date. On September 12, the seed from all maturity group 4 plants and most of the maturity group 5 plants were rotten (left). The timely harvest date for these plants was August 26. The seed from a late maturing group 5 plant was still green and had good quality (right).

Figure 3. Soybean plants from a March 28 planting date at the Dean Lee Research and Extension Center. On September 12, the seeds from all maturity group 4 plants and most of the maturity group 5 plants were rotten (left). The pods and seed from a late maturing group 5 plant was still green and had good quality (right).

Figure 4. Soybean plants from an April 19 planting date at the Dean Lee Research and Extension Center. These plants were beginning to mature in mid-August and matured in late August or early September during the days of continuous rain events. On September 12, the seed from all maturity group 4 plants and most of the maturity group 5 plants had some degree of weather damage.

Figure 5. Soybean plants from an April 19 planting date at the Dean Lee Research and Extension Center. On September 12, the pods and seeds from a late maturing group 5 plant were still green with no damage.

Figure 6. Soybean plants from a May 9 planting date at the Dean Lee Research and Extension Center. On September 12, the pods and seeds from two MG 4.2 plants were at different growth stages but had little to no weather damage.

Figure 7. Soybean plants from a May 21 planting date at the Dean Lee Research and Extension Center. On September 12, the pods and seeds from a MG 4.1 (left) and MG 4.3 (right) variety were at different growth stages but had little to no weather damage.

Watch for Redbanded Stinkbugs When Desiccating Soybean Plants

The LSU AgCenter has developed a video on soybean desiccation and redbanded stinkbugs.

As the soybean harvest season continues it is important to evaluate the redbanded stinkbug population. If the population is at the threshold, a treatment may be needed even though it is time to desiccate the soybean plants.

Preparing Cotton for Harvest Following Wet Weather

Shelly Pate Kerns, LSU AgCenter Corn, Cotton, and Grain Sorghum Specialist

For many cotton growers, hurricane/tropical storm Francine has thrown a wrench in cotton defoliation and harvest plans. Prior to Francine, there were many reports of cotton lodging, or “laying over”. This was most likely due to the fruit shed event Louisiana experienced in August. After shedding fruit in the lower canopy, cotton plants became heavier further up the canopy as bolls continued to develop and mature. As the bolls grew, the plant became heavier. The rains that we received in the last week of August and first week of September added moisture and weight to the lint. As we approached the first week of September, many farmers were ready to start making defoliation decisions. However, Francine delayed the application of these chemicals and further contributed to cotton lodging. Additionally, prolonged wet periods in combination with lodged cotton can play a role in making defoliation decisions. The longer that cotton remains lodged in contact with moist soil or neighboring plant material, the more at risk the plant is to develop boll rot and regrowth from buds that were previously shaded by neighboring plants.

The good news is now that Francine has passed, we are forecasted to receive some windows during the 3^rd week of September of dry weather with temperatures higher than they were before the storm. This slight boost in daytime temperatures will be good for defoliant absorption by the plant. Overall, if we have good weather, and therefore get good activity out of our defoliants, it should somewhat help with the lodging we are seeing. This is because cotton harvest aids remove leaves, reduce moisture in the lint and seed, and facilitate drying by increasing air movement within the canopy. I think there is a good opportunity to get most of our cotton defoliated this month. However, for those that had later planted cotton due to the heavy rainfalls in May and June, it is imperative to consider how the weather shift into Fall we will experience later this month/into October will impact the efficacy of your chosen defoliant. Weather and defoliant/desiccant information can be found in the 2024 Mid-South Cotton Defoliation Guide: https://www.mississippi-crops.com/2024/08/21/2024-mid-south-cotton-defoliation-guide/ (Figure 1).

Figure 1. Use pattern and expected activity for defoliants and desiccants as listed in the 2024 Mid-South Cotton Defoliation Guide.

As for making decisions on when to defoliate, there are several methods to determine plant maturity:

Nodes Above White Flower (NAWF) + Degree Day (DD) 60’s: DD60’s are used to calculate heat unit accumulation of the cotton plant. Once the plant reaches cutout (NAWF=5), the plant has ended its boll loading period. Many growers often only use NAWF5 as a measurement of plant maturity, this can lead to a premature defoliation of the plant which can prevent some bolls from maturing (impacting fiber quality and yield). Therefore, when using the NAWF or DD60 method, both should be used together to determine plant maturity. In general, the field should have reached NAWF=5 and have accumulated 850-degree days before defoliation. DD60’s can be calculated using the following equation: DD60 = ((Degrees F Maximum + Degrees F Minimum) / 2) – 60.

Percent Open Boll: Visually inspecting plants for % open boll is another “classic” method of determining when to defoliate. Defoliating plants at 60% open boll is broadly used as the recommendation. However, there are other decisions that factor into this method. For example, defoliating at 60% open boll may lead to premature defoliation if the crop has set its fruit at varying time periods due to insect damage and stress (leading to varying maturity rates of bolls). To ensure that you are getting an accurate percentage of open bolls, it is best to measure 3 feet of row in 10 places in the field, then count open and closed bolls to calculate what percent are open.

Node Above Cracked Boll (NACB): Cotton can be harvested around 4 NACB. To determine NACB, find the uppermost cracked boll and count upwards to the uppermost harvestable boll. Once the uppermost harvestable boll is found, it should be cut into a knife with a knife to determine if the boll is mature. If it is not mature, defoliation should be held off until the plant reaches NACB3.

Sharp Knife Method: Choose the uppermost boll that you think is harvestable (generally 4-5 nodes below the terminal) and cut a cross section. If the bolls is difficult to cut into, lacks “jelly”, and has darkened seed coats, then that bolls is mature.

A Combination of All Methods (Most Recommended): It is best to use a combination of all techniques to determine plant maturity and make defoliation decisions. For example, a field is ready to defoliate when plants have accumulated 850 DD60’s, is at NAWF=5, has approximately >60% bolls open, NACB=4 or 3, and the uppermost harvestable boll is determined to be mature using the sharp knife technique.

Hopefully the application of defoliants will help with lodging in the field. However, if plants are still laying over, it is important to use caution when picking. It is recommended to slow the picker down and accurately adjust the height of the header if you are having trouble picking cleanly. Overall, be mindful of changing weather patterns and field conditions to help you determine when it is best to defoliate and harvest your crop.

LSU AgCenter Specialists