Desiccation of Kenaf with Roundup

Mark E. Kurtz, Marty J. Fuller, and John G. Black

One method of harvesting kenaf in Mississippi is to mechanically cut the crop using a forage chopper and blowing chopped stalks into a cotton boll buggy for transfer into a module builder for in­field storage. In Mississippi, however, if harvest is delayed past late October, rainy weather often makes

harvesting difficult if not impossible. To build a kenaf module, stalk moisture must be less than 30% or the module will go through a heat generated by microbial action. To avoid these problems, kenaf moisture must be reduced below 30% and harvested before late October.

In 1990 and 1991, Roundup was evaluated as a preharvest aid in kenaf at 4.5 kg ai/ha after kenaf had bloomed. In 1992, Roundup was evaluated at 6.4 lb/A at three timings; prior to first bloom (FB) August 24,1992, 2 weeks after FB (September 9), and 6 weeks after FB (October 6). In 1993, Roundup was evaluated

at 6.4 and 3.2 lb ai/A at three timings prior to first bloom (September 2, 20, and October 4,1993). In 1993, kenaf did not bloom before the third application.

In 1990, 1991, and 1992, Agri­Dex (0.625% v/v was added to all treatments. In 1993, X­77 was added at 1.0% v/v. In 1990, chemicals were applied with a hand­held CO2­charged sprayer delivering 20 gpa. All other treatments were applied with a tractor­mounted compressed air system at 10 gpa.

In 1990 and 1991, Roundup failed to desiccate kenaf stalks at 1, 2, or 3 weeks after treatment (WAT). At 3 WAT, kenaf stalk moisture was higher in the Roundup treatment than in the untreated. In 1992, kenaf stalk moisture was reduced to 16% 3 WAT when Roundup was applied prior to FB. Kenaf stalk moisture

was reduced to 31% and 19% with Roundup applied 2 weeks after FB by 4 and 5 WAT, respectively. Stalk moisture was not reduced at the latest timing. In 1993, when Roundup was applied at the first timing, kenaf stalk moisture was reduced to 18% and 27% with the high and low rate, respectively, by 3 WAT. With the

second timing, it took 4 WAT to reduce stalk moisture to 27% and 42% with the high and low rates, respectively; and like 1992, the third timing did not reduce stalk moisture.

These data suggest that timing of Roundup application is very important and the rate of Roundup can be reduced to 3.2 lb ai/A and effectively desiccate kenaf below 30% stalk moisture in 3 weeks, if the chemical is applied prior to first bloom. Additional research is required to elucidate the effects of air

temperature at time of application and flowering on kenaf stalk desiccation.

Economic Analysis

Desiccation of the kenaf crop offers the opportunity of a more timely fall harvest when field conditions are generally suitable in late October and early November. From the middle of November through February, field conditions, or days suitable for field work, are limited to approximately one day per week on

sandy soils in the Mississippi Delta. This time period provides little opportunity for harvesting, which can lead to kenaf harvesting activities in March and April. The March/April time frame can prove to be disadvantageous because this is a period when farmers would prefer to be focusing on soil preparation practices for the upcoming crop. If kenaf harvest is taking place during this time, delays or late planting of the crop following the kenaf are possible. This would especially be true if the kenaf was followed by cotton, kenaf, milo, or corn.

An economic analysis was conducted to evaluate the effects of alternative desiccation dates on the net returns of kenaf production versus a frost­killed scenario. The data in Table 1 display the assumptions employed.

For the assumptions employed in this paper, it appears that a significant cost premium is attached to desiccation, especially the early date (September 2). For the September 2 date, a farmer will experience approximately $139 in yield loss and chemical cost, assuming a $55 per ton value for the kenaf. For the

September 20 date, the cost premium is approximately $77, utilizing the same assumptions.

A further point that must be noted is the economic feasibility of the desiccation scenarios. For the yields assumed in this work, kenaf production would not be economically feasible if desiccation were employed. However, if yields can be increased to about 5 tons per acre in the September time frame,

desiccation could be a feasible alternative. This may be possible with an earlier planting date or better growing conditions.

In summary, it appears that the chemical cost and yield loss associated with desiccation is a high price to pay in order to accomplish a fall harvest of kenaf in the Mississippi Delta. Farmers who are growing kenaf will have to carefully formulate a farm plan that incorporates a late harvest of frost­killed kenaf in conjunction with a crop that is planted later, such as soybeans, or evaluate the potential farm program impacts of using this land as idle acres for the following year. As future research developments occur in the plant breeding and agronomic

areas, which might increase early yields, the potential of desiccation may be worthwhile.

Table 1. Assumptions used to project net returns from kenaf desiccated at different dates versus frost­killed kenaf. 

 Desiccation Date Sep. 2 Sep. 20 Frost killed


 Potential Harvest Date1Sep. 23 Oct. 27 Dec. 10

 Days Suitable for2

 Harvest Prior to Nov. 30  42.65 15.55   0

 Direct Cost of Production3($) 166 166 133

 Yield (tons/acre)   3.06   4.20  5.0

 Returns over Direct Costs ($)  2.19  65.10 141.80

1-Date at which crop moisture is less than 30 percent.

2-From "Days Suitable for Field Work" ­ Mississippi River Delta Cotton Area:, D.A.E. Research Report No. 384, Louisiana State University.

3-From "Mississippi State Budget Generator", Direct costs are included through the harvesting phase; does not include module tarp or transport.

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Mark E. Kurtz is a Plant Physiologist, Delta Branch Experiment Station, Stoneville, MS. Marty J. Fuller is a Professor and Agricultural Economist and John G. Black is a Research Assistant I, Department of Agricultural Economics, Mississippi State

University.