Charles A. Mullins and Angela Harrison

Azafenidin at the rate of 0.25 lb ai/A, although lower rates could possibly be used, appeared to have considerable potential for use on greens crops (collard, kale, mustard, turnip). Sulfentrazone at 0.1875 to 0.33 lb ai/A did not injure crops, and was effective for weed control. Trifluralin combined with pyridate, clopyralid, or bensulide did not reduce yields of the greens crops, but these treatments were less effective than azafenidin and sulfentrazone for weed control.

Greens crops are grown in large commercial acreage, primarily for processing (freezing) in Tennessee. Excellent weed control is necessary for processing greens since mechanical harvesters are used to cut a wide strip across the field. Fresh market greens are grown in small acreage, primarily for local markets. Weed control with hand labor or mechanical means is expensive, and labeled chemicals are not completely effective for weed control, especially of certain broadleaf weeds and nutsedge. Weed species appear to be influenced considerably by environmental conditions. Several new chemicals were screened in preliminary trials, and showed potential for use on greens crops. An experiment was conducted at the Plateau Experiment Station at Crossville, TN in 2000 to evaluate performance of 11 herbicide treatments compared to a weedy check on greens crops (mustard, turnip, collard, and kale). This trial was supported by the IR-4 program as new technology research.

The site was prepared for planting using conventional tillage in late April. Fertilizer was broadcast at 300 lb/A of 15-15-15 before disking on May 1. PPI herbicides were applied on May 3 and the entire plot was tilled with a tractor mounted rototiller on May 3. Plots were direct seeded with ‘Vates’ collard, ‘Vates’ kale, ‘Southern Giant Curled’ mustard, and ‘Purple Top White Globe’ turnip on May 3. The seed source for all seeds was Seedway. Plot size was 12 ft by 20 ft. One row of each crop (total of 4 rows) was planted in each main herbicide plot. Rows were spaced 30 inches apart, and were 20 ft long. Seeding was with a Plantet Junior planter using specified plates for each crop. Experimental plot design was a split block, but data for each crop were analyzed as a randomized complete block with four replications. Each 12 by 20 ft plot was treated with the selected preplant incorporated (PPI) before planting or preemergence treatment after planting on May 3. Post emergence treatments were applied on May 30. Herbicide treatments were applied in 27 gal of solution/A using a plot sprayer with a 12 ft boom equipped with 8004 flat fan nozzles. Compressed air was the pressure source and application pressure was 40 psi. Weed control treatments, source of herbicides, and herbicide lot numbers are presented in Table 1.

Carbaryl (Sevin XLR) at 1 lb ai/A was applied for insect control on May 17. Esfenvalerate (Asana) at 0.05 lb ai/A was applied for insect control on June 14. Crop stand counts were made on May 22. Crops were harvested and yields were recorded on June 20. Weed ratings were made at harvest. Analysis of variance procedures were used to analyze all data, and mean separation was by Duncan’s multiple range tests at the 0.05 level of probability.

The overall stand of collard and kale was less than desired. The stand of mustard and turnip was excellent. Stand of all crops was reduced by treatments of azafenidin at 0.5 lb ai/A, halosulfuron at 0.024 lb ai/A preemergence, and halosulfuron at 0.016 lb ai/A preemergence followed by halosulfuron at 0.016 lb ai/A post emergence when compared to the untreated check plots (Table 2). Azafenidin at 0.25 lb ai/A tended to reduce stand of collard, kale, and turnip; and reduced stand of mustard significantly. Azafenidin rates could probably be reduced as weed control was complete at the rate of 0.25 lb ai/A. Treatments of metolachlor, clopyralid, and sulfentrazone reduced stand of turnips compared to the untreated check.

Yield reduction due to treatment was somewhat comparable to stand reduction (Table 3). Treatments of azafenidin, metolachlor, halosulfuron and trifluralin plus pyridate caused a yield reduction of collard and kale. The yield of mustard was reduced by treatments of azafenidin and halosulfuron. Treatments of azafenidin at 0.50 lb ai/A, halosulfuron at 0.024 lb ai/A, halosulfuron at 0.016 lb ai/A followed by halosulfuron at 0.016 lb ai/A and sulfentrazone at 0.33 lb ai/A reduced the yield of turnips compared to the untreated check.

Herbicides that appeared to have no potential for collards were azafindin, especially at the 0.50 lb ai/A rate; and halosulfuron at both treatment methods. Herbicides that appeared to have no potential for kale and mustard were azafinidin and halosulfuron (both treatments). Herbicides that injured turnips were azafinidin at 0.5 lb ai/A and halosulfuron (both treatments).

Weed pressure was not very intense in the trial. The crops were planted relatively early and total rainfall was sparse, but was adequate for crop growth. Five prevalent weed species were rated at harvest for percentage control (Table 4). Fall panicum was controlled well by treatments of azafenidin, sulfentrazone at 0.33 lb ai/A, trifluralin plus pyridate and trifluralin plus clopyralid. Large crabgrass was controlled well by all herbicide treatments except clopyralid. All herbicide treatments except clopyralid, and bensulide plus trifluralin controlled spotted spurge effectively. Common purselane was not controlled well by herbicide treatments of metolachlor and clopyralid. Carpetweed was not controlled well by herbicide treatments of metolachlor, clopyralid, and bensulide plus trifluralin. Spotted spurge was not highly competitive with the greens crops, but could be a contaminant in the harvested crop. Carpetweed is a low growing weed that is not much of a problem in greens crops.

Weed control was excellent with treatments of azafendin at rates of 0.25 and 0.50 lb ai/A. Weed control was good with sulfentrazone at 0.1875 lb ai/A and was excellent at 0.33 lb ai/A. Weed control was adequate with combinations of trifluralin and pyridate or clopyralid. Metolachlor did not provide effective weed control at the relatively low rate of 0.5 lb ai/A. Based on these trials, pesticide clearance forms were submitted to the IR-4 for azafendin and sulfentrazone for use on greens crops.

Table 2. Effect of weed control treatments on plant stand of collard, kale, mustard, and turnip at The University of Tennessee Plateau Experiment Station at Crossville, 2000.