Weed Control in Pepper and Sweet Corn - UKREC - 2003
Joseph Masabni, Department of Horticulture, Princeton

Two experiments were conducted in 2003 to test labeled and two experimental herbicides on pepper and sweet corn. The experimental herbicides are not labeled yet on pepper and must not be used as this is against federal law. The purpose of trying new and experimental herbicides is to collect data to support their registration, in the case they performed well.

The two experiments were conducted at the University of Kentucky Research and Education Center (UKREC) in Princeton, KY.

The experimental design used for both experiments was a randomized complete block design with 3 replications. Prior to planting, lime and fertilizer were amended per soil test recommendations. A final soil workup was performed prior to planting to level any plow ridges and to break up any soil clods.

Pepper: Plot size was 6 ft wide by 35 ft long. Raised beds, 6" high, were shaped and drip-irrigation was installed using a plastic layer. No plastic was laid for this experiment since bareground was essential to test the effectiveness of the herbicides used. Once all the herbicide treatments were applied, 2 rows of peppers, one for Olympus and one for Wizard varieties, were hand-transplanted on May 22, 2003, at 2 ft spacing within rows. This is equivalent to 17 plants for each variety per bed/treatment. Herbicide treatments were applied using a 4 8002-nozzle boom backpack sprayer set at 30 psi and 20 GPA with a 5.3 ft spray swath width. For the preplant incorporated treatments, a garden rake was used to manually incorporate the herbicides on the sprayed beds. The postemergence treatments were applied on July 9, 2003, or 69 days after transplanting when plants were about 12" tall. Of all the herbicides used, only Sencor and Matrix are not currently registered for use on pepper.

Sweet corn: Plot size was 6.5 ft wide by 80 ft long. Ten sh2 sweet corn varieties were seeded on April 22, 2003, using a John Deere plate seeder at 9" spacing. Three varieties had yellow kernels (6800 Y, AC945 Y, and Saturn Y). Four varieties had bicolor kernels (6802R BC, Camas BC, Saturn BC, and 8102R BC). Three varieties had white kernels (Boreal W, Saturn W, and 8101R W). The herbicide treatments were applied perpendicular to the seeded corn, in order to test the effect of herbicide treatments on each variety. The preemergence herbicide treatments were applied on May 15, 2003, and the postemergence treatments were applied on June 18, 2003. All sprays were applied using a 2 8002-nozzle boom backpack sprayer set at 30 psi and 20 GPA with a spray swath width of 3.3 ft. The herbicide treatments were 3.3 ft wide and ran across all 3 replications. With sweet corn seeded at 9" spacing, there’s about 4.3 seeds in the 3.3 ft herbicide band. Of the herbicides used in this experiment, Axiom, Callisto, Option, and Lumax are experimental herbicides and their labels specifically ban their use in sweet corn.

For both experiments, weed control effectiveness were determined by a visual injury ratings using a scale of 1 – 10, with 1 equivalent to no injury or similar to the control plot, and 10 equivalent to complete kill or none present.

The following are abbreviations used in the tables below: DAT = days after treatment; PPI = preplant incorporated; PRT = pre-transplant; POT = post-transplant; PO1 = postemergence; EBNS = eastern black nightshade; LACG = large crabgrass; ILMG = Ivy leaf morningglory; JG = Johnsongrass; HVMW = honeyvine milkweed; CAWE = carpetweed, COPU = common purslane; COCO = common cocklebur.

* Only treatments already applied at this date are included in this table.

Table 2. Weed control effectiveness in pepper rated at 47 days after treatment.

* Only treatments already applied at this date are included in this table.

Table 3. Total yields of Olympus and Wizard peppers.

The 10 sweet corn varieties were not rated for visual injury due to the complexity of this experiment 10 varieties/treatment and 12 treatments). Table 4 lists the weed control ratings taken at 33 DAT. Only preemergence treatments are listed in this table, since postemergence treatments weren’t applied at this rating date.

Of the registered sweet corn herbicides, Outlook and Dual Magnum were best for common purslane and large crabgrass control, whereas Aatrex and Outlook were slightly better on common cocklebur. The non-labeled herbicide Axiom completely killed all 3 weeds present at this rating date. Lumax followed closely with 100% kill of common purslane and common cocklebur and about 80% control of large crabgrass. Of the 3 non-labeled herbicides, Callisto was weakest on common purslane and large crabgrass, but still had excellent control (95%) of common cocklebur.

Tables 5 shows sweet corn yields in kg/plot and Table 6 lists the number of ears/plot for all 10 sweet corn varieties. Both tables clearly indicate that the 10 sweet corn variety responded differently to an herbicide. Differences or similarities in kernel color are not a good predictor of the response of the sweet corn variety to an herbicide treatment. Yields ranged from 0.5 – 3 kg/plot for Outlook preemergence, and from 0.2 – 1.4 when applied postemergence. Yields of plots treated with Aatrex were similar to those treated with Outlook. In addition, there were no observed differences in yields and number of ears per plot with Outlook applied either preemergence or postemergence.

Axiom (treatment 3) and Lumax (treatment 10), both not labeled for sweet corn, performed equally if not better than Outlook and Aatrex for all 10 varieties both in yields (Table 5) and number of ears / plot (Table 6). Similarly, when Option was applied postemergence following a preemergence application of Dual Magnum (treatment 8), yield and number of ears / plot were equal if not better than Outlook or Aatrex applied alone.

Table 4. Weed control effectiveness in sweet corn rated at 33 days after treatment.

Table 5. Yield in kg/plot of ten sh2 sweet corn varieties treated with herbicides.

Table 6. Yield in number of ears/plot of ten sh2 sweet corn varieties treated with various herbicides.