Weed Science Research and Extension

Our research program over the past few years has concentrated on how to best use herbicides that are currently labeled in sugarcane. In this article I would like to update you on the label changes for DuPont K-4 that will affect how it can be used this year.

Our research last year addressed crop response to DuPont K-4 applied overtop at 4 lb product per acre in March, April, and May. This was done to try to relate temperature effects and sugarcane size on potential crop injury. Research also addressed split applications of DuPont K-4 at the full rate in the spring followed by the full rate at layby. This herbicide along with others used in the industry was also evaluated for use both at planting and in fallow programs. Results of research conducted here in the LSU AgCenter and by Dr. Ed Richard with USDA contributed to changes in the DuPont K-4 label for this year. Provided below is a table showing the current recommendations for use of DuPont K-4 at planting, in spring, at layby, and in fallow. Please note the rate restrictions and also the application timing restrictions based on temperature and crop size.

Application Timing	Rate of Formulated Material for 1 Acre Broadcast	Weeds Controlled	Remarks
At Planting Preemergence Application	DuPont K-4 60DG 3.75 – 4.0 lb	Seedling johnsongrass, itchgrass, browntop panicum, and other annual warm and cool season grass and broadleaf weeds	Use of the higher rate can provide bermudagrass suppression/control when applied prior to bermudagrass emergence and following a good fallow program.
Spring Preemergence Application	DuPont K-4 60DG 3.75 – 4.0 lb	Seedling johnsongrass, itchgrass, browntop panicum, and other annual grass and broadleaf weeds	Can provide suppression of bermudagrass at the higher rate if applied prior to bermudagrass emergence from the winter dormant period. Can be applied overtop of sugarcane until daily maximum temperatures for the week preceding application average 80 degrees F or greater. Can be applied with Prowl/Pendimax.
Layby Preemergence Application	DuPont K-4 60DG 2.0 – 3.0 lb	Broadleaf weeds and some annual grasses	Apply as a directed treatment when sugarcane is 30 inches or taller. Injury can occur if herbicide contacts newly emerging sugarcane leaves. If DuPont K-4 was applied in the spring do not apply more than 2 lb/A at layby. Allow 8 weeks between spring and layby applications. Addition of Prowl/Pendimax or Sencor will improve weed control. Add nonionic surfactant or crop oil concentrate if weeds are present.
Fallow Preemergence Application	DuPont K-4 60DG 3.75 – 4.0 lb	Seedling johnsongrass, itchgrass, browntop panicum, and other annual grass and broadleaf weeds	Can provide suppression/control of bermudagrass. Apply to a clean seedbed at least 60 days prior to planting. Can be reapplied at planting but no more than 11.25 lbs can be applied per acre per year.

As a reminder, in the sugarcane weed control guide provided through the LSU AgCenter herbicide rates represent the amount of formulated material needed for one acre on a broadcast basis. To calculate the band rate, use the following formula:

This calculation will provide the correct band rate for any formulation, liquid or dry.

1) If daily maximum temperatures for the week preceding application average 80 degrees F or greater do not apply DuPont K-4 overtop of sugarcane.

2) If DuPont K-4 is applied in spring at the full label rate (4 lb product per acre broadcast or the proportional equivalent band rate) then no more than 2 lb product per acre should be applied at layby.

3) There needs to be an 8 week period between herbicide application in the spring and at layby.

4) When DuPont K-4 is applied at layby sugarcane should be 30 inches or taller and the herbicide should be directed underneath the crop to avoid contact with newly emerging leaves.

Good weed control can be obtained with K-4 at the 4 lb product rate but when the rate is reduced weed control is decreased. If the rate of DuPont K-4 applied at layby is reduced then addition of another herbicide such as Prowl/Pendimax or Sencor will improve weed control.

Dr. Jim Griffin is with the LSU AgCenter in the Department of Agronomy and Environmental Management and has research and extension responsibilities in the area of sugarcane weed management.