EVALUATION OF LAYBY HERBICIDE APPLICATIONS TO SEED CARROTS, Abstract. Introduction. Methods and Materials

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1 EVALUATION OF LAYBY HERBICIDE APPLICATIONS TO SEED CARROTS, 1995 Marvin Butler, Bruce Martens, Les Gilmore and Kurt Feigner Abstract Four herbicides, metribuzin (, Du Pont), bromoxynil (, Rhone-Poulenc), oxyfluorfen (Goal, Rohm and Haas), and EPTC (Eptam, ZENECA), were applied alone and in combination to plots in commercial seed carrots fields at three locations in central Oregon using a drop nozzle directed at the furrow and base of the plants at layby. at 1.3 lb provided the greatest overall control of the five major weed species evaluated. provided the best control of redroot pigweed and common groundsel; and Goal performed well on hairy nightshade; and kochia control was best achieved with and, which along with Goal performed well on mustards. There were no visible symptoms of phytotoxicity or stunting from herbicide application. Introduction Carrot seed production is a major component of the central Oregon vegetable seed industry. Of the nearly 5,000 acres of vegetable seed grown in the area, about 1,500 acres are seed carrots with a value of over $5 million. Few herbicides are registered for use on carrots grown for seed, and efficacy data are required as the first step in the registration of new materials. Methods and Materials Evaluation of the herbicides,,, Goal, and Eptam alone, and in combination, was conducted in commercial seed carrot fields on three commercial farms in central Oregon. Application was made to 3 row x 20 ft replicated plots with a CO2 pressurized, hand-held, boom sprayer at 40 psi and 20 gal/a of water, using a single TeeJet nozzle directed at the furrow and base of the plants at layby. Spray Booster-S at 1 qt/100 gal was applied in combination with all herbicides. Sixteen herbicide treatments were applied at the Cloud location June 15, with very few weeds emerged. Application at the S & L location was made on June 23, with weeds mostly 1-2 inches high and some up to 12 inches. At the K & S location, application was made June 29, except for the Eptam applications on July 5, Many of the weeds were 6 to.18 inches tall at the time of application. Plots at the Cloud and K & S locations were sprinkler irrigated following herbicide application. S & L Farms furrow irrigated alternate rows following herbicide treatments. Evaluation of plots for herbicide phytotoxicity and percent weed control by dominant species was conducted July 21 at S & L Farms, July 24 at K & S Farms, and July 25 at Cloud Farms. Groundsel made up nearly 100 percent of the weeds present in untreated plots on Cloud Farms at the time of evaluation. In untreated plots at S & L Farms, 72 percent of the weeds were common groundsel, 19 percent mustards, 6 percent hairy nightshade, and 3 percent redroot pigweed. At K 72

2 & S Farms, 70 percent of the weeds in untreated plots were redroot pigweed and 30 percent were hairy nightshade. Twenty-umbel samples per plot were randomly selected from plots at the S & L and K & S locations for germination testing prior to swathing of the female rows. Results and Discussion There were no visible symptoms of phytotoxicity or stunting due to any of the herbicide applications. Because of variability between plots, there was often no significant difference between treatments. A summary of results at the three locations is provided in Table 1, with specific data from each location shown in Tables 2, 3 and 4. at 1.3 lb provided the greatest overall control of the major weed species, while Eptam generally did not perform satisfactorily. provided the best control of redroot pigweed, followed by the high rates of and Goal. For hairy nightshade and Goal performed well, followed by the high rate of. The best common groundsel control was achieved by, followed by and Goal. This is somewhat unexpected, since Goal followed by is generally considered to provide better control of groundsel by local industry representatives. However, Goal is sensitive to soil and weather conditions at the time of application. Both and provided control of kochia, and along with Goal, performed well on the mustards. The only combination treatment providing greater control than either material alone was plus on redroot pigweed. Results of germination testing at the two locations indicate no detrimental effect from herbicide applications (Table 1). 73

3 Table 1. Evaluation of layby herbicide applications on commercial seed carrots at 3 locations near Culver and Madras, Oregon during Redroot Hairy Common Percent Material Rate Pigweed Nightshade Groundsel Kochia Mustards Germination (product/a) (percent control) a 65 abc 97 a lb 98 a 81 abc 99 a lb 99 a Eptam 4 pt 58 a 48 c 64 a Eptam 7 pt 70 a 50 be 47 ab pt 77 a 87 abc 83 a a 93 a pt 98 a 99 a 84 a Goal 94 a 75 a Goal 2 pt 98 a 99 a 79 a Goal 4 pt 89 a 64 abc 86 a Eptam 4 pt 96 a 97 a 97 a Goal 75 a 91 a Eptam 4 pt 97 a 94 ab 99 a a Untreated 0 b 0 d 0 b Mean separation with the T-method at P 0.05

4 Table 2. Evaluation of layby herbicide applications on commercial seed carrots (S & L Fauns) on the Agency Plains near Madras, Oregon during Material Rate Redroot Pigweed Common Groundsel Hairy Nightshade Mustards (product/a) (percent control) lb 1.3 lb 93 ab i 93 a 67 ab 97 a 95 a 93 a -Eptam 4 pt 67 ab 48 abc 63 ab 67 a Eptam 7 pt 27 bc 33 ab 60 a 0.5 pt 43 bc 83 a 73 ab 68 a 80 ab 98 a 90 a 2 pt 95 ab 97 a 93 a Goal 95 ab 50 abc Goal 2 pt 97 ab 57 ab 97 a Goal 4 pt 93 ab 75 ab 60 ab 97 a + Eptam 4 pt 97 ab 97 a 93 a + Goal 87 ab 87 a + Eptam 4 pt 98 a 97 a + 83 a 98 a Untreated 0 c 0 c 0 b 0 b 1 Mean separation with the T-method at P

5 Table 3. Evaluation of layby herbicide applications on commercial seed carrots (K & S Farms) on the Agency Plains near Madras, Oregon during Material Rate Redroot Pigweed Kochia Hairy Nightshade (product/a) (percent control) ab l 63 ab 0.7 lb 93 a 67 ab 1.3 lb 97 a Eptam 4 pt 10 bc 87 a 33 ab Eptam 7 pt 10 bc 67 ab 0.5 pt 87 a 90 a 83 a 2 pt Goal 87 a 90 a Goal 2 pt 97 a Goal 4 pt 73 a 67 a 67 ab + Eptam 4 pt 92 a + Goal 70 a + Eptam 4 pt 93 a 90 ab + Untreated 0 c 0 b 0 b I Mean separation with the T-method at P _

6 Table 4. Evaluation of layby herbicide applications on commercial seed carrots (Cloud Farms) near Culver, Oregon during Redroot Common Material Rate Pigweed Groundsel (product/a) (percent control) 0.7 lb 1.3 lb Eptam 4 pt Eptam 7 pt 0.5 pt 2 pt Goal Goal 2 pt Goal 4 pt + Eptam 4 pt + Goal + Eptam 4 pt + Untreated a 100a 100a a a 95 a a 0 b 0 b 1 Mean separation with the T-method at P