Second year field studies continued to evaluate and determine efficacy and safety of postemergence herbicides for broccoli weed control. Goal® 2XL. a newly introduced formulation of oxyfluorfen. severely injured broccoli after application. London rocket (Sisvmhrium irio) control was not acceptable at less than 80%. Pvridate (Lentagran®) and clopyralid (Stinger®) were relatively safe on broccoli but did not affect London rocket.

Three commonly used herbicides for use in broccoli were effective when applied alone or in combinations as a preplant incorporated (PPI) or a preemergence (PE) application. DCPA (Dacthal®) at 10.0 lb product/A PE gave acceptable control of most weeds. Trifluralin (Treflan® SEC) at 1.0 pt/A and bensulide (Prefar® 4EC) PPI were also effective but mustard weeds were not adequately controlled. Combinations of the herbicides at lower rates did not provide any advantage in improving weed control efficacy.

Response of Direct-seeded Broccoli to Preemergence Oxyfluorfen and BAS 514 Preemergence treatments of oxyfluorfen at 0.14, 0.28, and 0.56 kg ai/ha caused a 40 to 99% reduction in stand of direct-seeded broccoli, while BAS 514 applied at the same rates caused no reduction in stand. All rates of oxyfluorfen completely controlled Venice mallow while only the 0.56 kg/ha rate of BAS 514 provided acceptable (>70%) control. Broccoli plants that survived preemergence applications of oxyfluorfen exhibited injury ranging from 32 to 97% 6 to 9 weeks after treatment. BAS 514 applied at 0.14, 0.28, 0.56 kg ai/ha provided excellent control of common ragweed with little or no visible crop injury. Common ragweed control with oxyfluorfen varied with soil moisture and organic matter. Applications of 0.28 and 0.56 kg/ha oxyfluorfen significantly reduced yield when compared to the cultivated check. Yields from plots treated with 0.14 kg/ha BAS 514 equalled or exceeded the cultivated check. Treatments of oxyfluorfen and BAS 514 to seeded broccoli caused approximately a one week delay in harvest. Nomenclature: oxyfluorfen, [2-chloro-1-(3-ethoxy-4- nitrophenoxy)-4-(trifluoromethyl)benzene]; BAS 514, quinclorac, (3,7-dicloro-8-quinoline-carboxylic acid); broccoli, [Brassica oleracea(L.) var botrytis]; common ragweed, (Ambrosia artemisifoliaL. #³ AMBEL); Venice mallow (Hibiscus trionum L. #3 HIBTR); Additional index words: Brassica oleracea (L.) botrytis, quinclorac. Weed Control and Crop Yield with Postemergence Applications of Oxyfluorfen, Pyridate, and BAS 514 to Direct-seeded Broccoli Postemergence applications of oxyfluorfen in field studies caused white chlorotic speckling on broccoli foliage. Plants treated with 0.07 kg/ha oxyfluorfen produced yields similar to the cultivated check. High rates of pyridate (4.03 kg/ha) caused yellow lesions on broccoli foliage. Total broccoli yields from plots treated with pyridate at 0.28 and 0.50 kg/ha were not significantly different from the cultivated check. BAS 514 caused moderate growth stunting to broccoli in field studies. At two out of four locations, injury increased with time. At these sites, total broccoli yield from plots treated with 0.28 and 0.56 kg/ ha BAS 514 was lower than the cultivated check. Total number of broccoli heads per hectare for plots treated with BAS 514 equaled or exceeded that of the cultivated check. Broccoli treated with BAS 514 plus the experimental adjuvant BAS 090 showed increased injury and decreased yield with increasing rates when compared to applications of BAS 514 alone. Broccoli developed foliar veinal chlorosis and whitish elongated heads following applications of BAS 514 plus BAS 090. High rates of BAS 514 (0.56 kg/ha) with or without BAS 090 reduced average head weight. Little to no stand reduction or delay in harvest was observed with any herbicide treatment. A two fold safety margin for herbicide rate was observed for oxyfluorfen at 0.07 kg/ha, pyridate at 0.50 kg/ha and BAS 514 at 0.14 kg/ha. In greenhouse studies, oxyfluorfen at 0.28 kg/ha provided >90% control of common ragweed and common lambsquarters, and 77% control of common pigweed. Pyridate at 2.02 kg/ha provided excellent control of horseweed, and greater than 70% control of prickly sida, common ragweed and common lambsquarters. All rates of pyridate controlled common pigweed. Applications of BAS 514 at 0.14 to 0.56 kg/ha provided 88 to 100% control of horseweed and 76 to 82% control of common ragweed. Greater than 90% control of large crabgrass was observed with BAS 514 plus BAS 090 at 0.28 kg/ha. Nomenclature: oxyfluorfen, 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene; pyridate 6-chloro-3-phenylpyridazine-4-yl-S-octyl carbonothionate; BAS 514, quinclorac, 3,7-dichloro-8-quinoline-carboxylic acid; broccoli Brassica oleracea L. var. botrytis; common ragweed Ambrosia artemisiifolia L. #3 AMBEL; redroot pigweed Amaranthus retroflesus L. #AMARE; common lambsquarters Chenopodium album L. #CHEAL; Prickly sida Sida spinosa L. #SIDSP; Horseweed Conyza canadensis L. #ERICA; Large crabgrass Digitaria sanguinalis L. #DIGSA; Additional index words. quinclorac, BAS 090, Brassica oleracea L. botrytis. / Master of Science

Experiments were conducted with 'BigSur' broccoli (<i>Brassica oleracea</i> var. <i>italica</i> Plenck) at two sites in fall of 1993 and at two sites in the spring of 1994 on a Hayter loam in southwestern Virginia. Objectives were to determine the tillage main-plot (CT = conventional tillage, and NT = no-tillage) and weed-control subplot (C = no overseeding or preemergent herbicide; HB = oxyfluorfen; RC = red clover (<i>Trifolium pratense</i> L.); WC = Dutch white clover (<i>Trifolium repens</i> L.); and HV = hairy vetch (<i>Vicia villosa</i> Roth) effects on broccoli yield and weed suppression. At all sites, marketable broccoli yield was equal or higher in NT than CT and was unaffected by overseeded legume living mulches. Overseeded legumes suppressed weeds as well as the HB in three of the four sites. These data show that the NT systems used in these experiments can suppress weeds and produce high broccoli yields and that overseeded legume living mulches can be effectively established after transplanting to suppress weeds without reducing broccoli yield. / Master of Science

Experiments were conducted at two sites in Blacksburg, Virginia to study the effects of tillage (conventional plow-disk and no-tillage) and overseeding (underseeding) of legume cover crops (red clover, Trifolium pratense L.; white clover, Trifolium repens L.; and hairy vetch, Vicia villosa Roth.) at transplanting on weed suppression and yield of ’Big Sur’ broccoli (Brassica oleracea var. italica Plenck). In both sites, weed suppression from overseeded red clover, white clover, and hairy vetch equalled or surpassed that of the preemergent herbicide (oxyfluorfen) control. The legumes did not affect broccoli yield components in site 1 nor head number in site 2. However, hairy vetch reduced broccoli yield and head size in site 2. These reductions were attributed to competition with the broccoli. Overseeding tended to delay broccoli yield and head number in the two sites, but this trend was not significant. Tillage system did not affect weed suppression or broccoli yield components, and there were no tillage x overseeding effects. Based on this data, overseeded legumes can provide residual weed control in no-till broccoli, thus allowing a more sustainable production method. / Master of Science