Applying Harvest Aids in Louisiana Soybean

David Moseley, Stephenson, Daniel O., Brown, Sebe, Miller, Donnie K.

Daniel Stephenson, Donnie Miller, Sebe Brown, and David Moseley, LSU AgCenter Scientist

Use of a herbicide as a desiccant in soybean has become popular to potentially improve harvest efficiency in Louisiana. Herbicides such as paraquat, Aim, Sharpen, and sodium chlorate are labeled for use in soybean as a desiccant, but paraquat is the most widely used. The paraquat label states at least 65% of pods should be mature (Figure 1) or moisture content should be 30% or less for indeterminate soybean varieties; and at least 50% of the leaves should have dropped and remaining leaves should be yellow for determinate varieties. Table 1 gives the harvest aid application timing label requirements for the labeled products in soybean.


Figure 1. Soybean plants where approximately 65% of the pods have turned their mature color.

In instances with excessive morningglory pressure, growers might consider co-applying Aim or Sharpen with paraquat to improve desiccation of vines. If weedy grass is problematic, co-applying paraquat and sodium chlorate can improve desiccation.

Paraquat, Aim, Sharpen, and sodium chlorate labels are very specific as to when they can be applied to soybean as a harvest aid. Soybean is essentially fully mature, at least R7.5 or later, when these herbicides can be legally applied as a desiccant.

What if a herbicide desiccant is applied earlier than labeled in soybean? Research was conducted in Louisiana to evaluate this question and indicated that harvest seed quality and yield was not affected by harvest aid application if the application was made after the plant reached physiological maturity (Boudreaux and Griffin 2011; Weed Technology vol. 25:38-43). Physiological maturity is when the seed have separated from the white membrane inside the pod and seed margins are prominently defined (Figure 2), which occurs at the growth stage 6.5 (R6.5 and approximately 50% moisture). Data indicate that maturity group IV soybean yield was reduced by 15.4% when paraquat was applied to soybean at seed moisture of 60%, which is prior to R6.5 (Figure 2). For maturity group V and VI varieties, harvest aid application prior to R6.5 or 40% seed moisture resulted in yield loss of 15.6 and 4%, respectively. Any use of a harvest aid prior to the seed reaching physiological maturity will result in a loss in yield. This research highlighted that soybean yield can be reduced if paraquat is applied prior to physiological maturity. Growers are cautioned that application of paraquat, Aim, Sharpen, or sodium chlorate that does not follow product labeling with respect to harvest aid timing to the crop is illegal. These products are labeled specifically for weed desiccation, not soybean desiccation.

Seed progression with R65 descriptionpng

Figure 2. Soybean seed within pods showing, from left to right, youngest to oldest. The pod where the white membrane has detached with clear seed margins would be considered at R6.5 growth stage.

Plant appearance at growth stage R6.5 will vary by variety so determination should be based on the uppermost four nodes across the field and specifically whether seed have separated from the white membrane. For indeterminate type soybean varieties, when the last pods could be considered at the R6.5 reproductive stage, the plant may already be at the R7 reproductive stage with at least one mature pod (Figure 3).


Figure 3. Soybean plants between the R6.5 to R8 reproductive growth stages.

Paraquat, Aim, Sharpen, and sodium chlorate are contact herbicides, thus good coverage is essential. Also, environmental conditions following application can greatly affect efficacy. Paraquat label states that it is rain fast in 15 to 30 minutes after application. Defol 5 label (sodium chlorate) states that applications should not be made if rainfall is anticipated within 24 hours, and as stated on the label, defoliation will be best on sunny, hot, and humid days. The longer it remains on the plant the better it will perform.

Producers must also consider the required preharvest interval (PHI) associated with each product. When using multiple products, the longest PHI must be adhered to. Labeled rates and comments are presented in Table 1 which was adapted from the 2021 Louisiana Suggested Chemical Weed Control Guide.

Redbanded Stink Bug Considerations

Across the state, redbanded stink bug (RBSB) numbers are increasing as the growing season progresses. LSU AgCenter entomologists recommend the control of threshold populations of RBSB until the soybean are out of the field. This means that the inclusion of an insecticide for the control of RBSB with a harvest aid application could be necessary (sodium chlorate cannot be tank-mixed with any insecticide). It is important to keep in mind however, the restrictions placed upon many of the products at this point in the season. These restrictions may include total active ingredient restrictions and PHIs. Acephate, a common recommendation for RBSB control, can only be applied up to 2 lb ai per acre per year in Louisiana. Other insecticides also have increased PHI such as the pre-mix product Endigo, with a PHI of 30 days. It is important to read all label materials prior to any use of labeled product. When label restrictions prevent the inclusion of an insecticide with the harvest aid application, growers should not delay the harvest of soybean so that the seed can be removed from the field as quick as the label allows.

Table 1. Herbicides labeled for use as a desiccant in soybean.

Active Ingredient and Rate

Formulated Product and Rate

Weeds Controlled

Remarks and Precautions

carfentrazone @ 0.016-0.023 lb/A

Aim 2EC @ 1-1.5 oz/A;

Add 1% v/v COC

Better on morningglories than pigweed, sicklepod, etc.

Apply after crop has matured and grain has begun to dry down. More effective on annual vines. Do not apply within 3 days of harvest. Apply in 10 gal. by ground, 5 gal. by air.

saflufenacil @ 0.022-0.045 lb/A

Sharpen @ 1 - 2 oz/A;

Add 1% v/v MSO + 8.5 lb/100 gal AMS

Morningglories and other broadleaf weeds

Apply once soybean has reached physiological maturity (all pods and seeds have no green color). Indeterminate varieties: 65% brown pods, more than 70% leaf drop, 30% or less seed moisture. Determinate varieties: more than 50% leaf drop and remaining leaves are yellowing. Preharvest interval is 3 days.

paraquat @ 0.13 - 0.25 lb/A

paraquat (2 lb/gal formulation) @ 8-16 oz/A;

paraquat (3 lb/gal formulation) @ 5.4-10.7 oz/A;

Add 0.25% v/v NIS; see label

Desiccation of weeds and soybeans only

Indeterminate varieties: 65% of pods are mature or moisture content is 30% or less. Determinate varieties: 50% leaf drop and remaining leaves are yellow. Some drought stressed weeds will not be desiccated. Do not graze or harvest for hay. Apply in 20 gal. by ground or 5 gal. by air. Preharvest interval is 15 days. Immature soybeans will be injured.

sodium chlorate @ 6 lb/A

6 lb/gal formulation @ 1 gal/A;

5 lb/gal formulation @ 1.2 gal/A;

3 lb/gal formulation @ 2 gal/A

Desiccation only. Level of weed control is affected by environmental conditions.

Apply 7-10 days before harvest. Apply in 20 gal. by ground, 5 gal. by air. Check label for environmental conditions most favorable for desiccation. Apply under high temperatures and humidity.

8/16/2021 1:49:18 PM
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