Soybean Harvest Aids

Soybean harvest has begun in several places around the state. According to the USDA Agricultural Statistics Service in Mississippi, 34% of the soybean acreage is dropping leaves and 9% has been harvested. Yield reports at this point are optimistic in a lot of cases. As a large portion of Mississippi’s soybean acreage is approaching maturity, some may be considering harvest aid management options.

Several calls have come in over the last week regarding fields that have pods which are nearly ready for harvest, but green leaves and/or stems are still present within the field. This is a situation where intensive monitoring can be a benefit. It is easy to drive by a field and notice the color change and defoliation of the soybean plants. However, if pods are reaching maturity but the plants themselves are still green in color, yield loss can occur due to reduced harvest efficiency or delays in harvest. Keep in mind also that indeterminate varieties may have mature pods in the lower portion of the plant but the vegetation may still have a lot of green color present as the pods in the upper plant are trying to finish making. Applying a harvest aid too soon can reduce overall yield as some of the pods may not be fully mature. On the other hand, waiting too long to apply a harvest aid can also reduce yields if shattering occurs in some of the more mature pods. There are several methods to use when making the decision of when to apply a harvest aid in soybean. For example, you may be able to evaluate the percentage of leaves that have dropped in order to make this decision. However, using leaf color/defoliation may not be the best method for determining harvest aid timing in all instances. The most accurate method to determine soybean maturity is through pod color. Once the majority of the soybean crop has reached the R7 growth stage, where at least 50% of the pods have begun to turn yellow in color, it is safe to apply a harvest aid. Also, keep in mind that each of the products available for use as a harvest aid in soybean has a specific preharvest interval that may influence the timing of an application. If the decision to utilize a harvest aid is made, then be prepared to harvest as soon as this interval has passed.

Another situation where harvest aids may be considered would be fields where inadequate canopy closure allowed weeds to germinate prior to soybean maturity. If weed populations are at a high enough level, problems such as increased seed moisture, seed damage, excess foreign material, or decreased harvest efficiency may occur. If the weeds that are present are relatively small and have not produced seed that can contaminate the harvested crop, then it is likely that a harvest aid is not needed.

A higher application volume is generally recommended when making a harvest aid application in soybean as coverage is a key factor with harvest aid applications. The following products are labeled for use as a harvest aid in soybean:

carfentrazone at 0.016 – 0.023 lb ai/acre

Carfentrazone (Aim 2EC) is a product that could be used in situations where excessive weed pressure may cause harvest problems. Generally speaking, this product will be better on vines (morningglory, redvine, etc.) than on other weeds. Aim 2EC is labeled in soybean and will not likely have significant effect as a desiccant for the crop. A nonionic surfactant (0.25% V/V) or crop oil concentrate (1% V/V) should be included. Keep in mind that there is a 3 day preharvest interval if this product is used as a harvest aid.

paraquat at 0.125 – 0.25 lb ai/acre

Paraquat (Gramoxone SL 2.0, Firestorm, etc.) would be the primary choice in situations where green leaves/stems are present. The preferred application rate is 0.25 lb ai/acre. Again, a nonionic surfactant (0.25% V/V) or crop oil concentrate (1% V/V) should be included. For paraquat, a 15 day preharvest interval is required.

sodium chlorate 3 – 6 lb ai/acre

Sodium chlorate will provide desiccation of weeds and soybean. However, the level of activity from this application will depend on environmental conditions at the time of application. In situations where excessive grass pressure is present, a tank-mix of paraquat at 0.25 lb ai/acre + sodium chlorate at 3 – 4  lb ai/acre may help to dry the grassy weeds down to prepare for harvest. This tank-mix combination may also help dry down “green beans.” However, one thing to keep in mind is that since sodium chlorate is a true desiccant, which physically draws moisture out of plant tissues and seed, there is an increased potential for soybean to shatter prior to or during harvest. Sodium chlorate has a 7 to 10 day preharvest interval.

More specific information about the products for use as harvest aids in soybean can be found in the 2012 Weed Control Guidelines for Mississippi publication available at http://msucares.com/pubs/publications/p1532.pdf.