No abstract

The plant characteristics which makes ‘Hybelle’ cabbage (Brassica oleracea var. capitata L.) relatively tolerant while ‘Rio Verde’ is susceptible to the toxic action of 2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen) were investigated. No differences between ‘Hybelle’ and ‘Rio Verde’ were found in growth rates, light or dark germination, or stomata density. Little xylem or phloem translocation of nitrofen-14C occurred. Disruption and removal of the cuticle of ‘Hybelle’ increased its susceptibility to nitrofen while ‘Rio Verde’ with more than normal wax deposition was tolerant. Plants with less cuticle were more susceptible, regardless of cultivar. ‘Hybelle’ had more wax per unit surface than ‘Rio Verde’ and wax deposition increased with leaf age. Both cultivars were equally tolerant to nitrofen when 6 weeks old. ‘Rio Verde’ leaves absorbed nitrofen-14C twice as fast as ‘Hybelle’ leaves. The results show that the mechanism of intraspecific selectivity of cabbage to nitrofen is dependent on the amount of cuticular wax on the leaves at the time of nitrofen application.

Pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl)benzamide] was most phytotoxic to oat (Avena sativaL.) when placed in the seed zone and to quackgrass (Agropyron repens(L.) Beauv.), when placed in the rhizome zone. Inhibition of part of the buds by pronamide on detached quackgrass rhizome sections did not influence other buds. Foliar applications of pronamide were not phytotoxic to established oat or quackgrass. Foliar-applied14C-pronamide showed little uptake by quackgrass. Application to the roots of established plants showed rapid root uptake and movement to the foliage.14C-pronamide was rapidly absorbed by oat seedlings for the first 0.5 hr and subsequently at a much slower rate. Over 60% of the pronamide taken up after 1 hr was exchangeable. Pronamide was adsorbed to the cell walls of treated roots, but little was associated with nuclear, mitochondrial, microsomal, or soluble protein fractions. Pronamide was adsorbed to varying degrees depending on soil type. Adsorption was more highly correlated with soil organic matter content than with cation exchange capacity, clay content, or pH.

Excellent agreement between a two-year replicated study relative to chlorosis development by clomazone in thirty-six cabbage cultivars and development of chlorosis in a production field was obtained. The cultivars ‘Bravo’, ‘Cheers', and ‘Genesis' developed the most severe chlorosis symptoms and ‘Bently’, ‘Carlton’, ‘Cecile’, ‘Gourmet’, ‘King Cole’, ‘Ocala’, ‘Red Acre’, ‘Rio Verde’, ‘Roundup’, ‘Sombrero’, ‘Stonehead’, ‘Straton’, ‘Titanic’, and ‘Tristar’ the least chlorosis. During a dry soil period chlorosis symptoms were more pronounced. Yield reduction at an application rate exceeding the suggested use rate for weed control varied positively with level of chlorosis in 1992 for the cultivars Bravo, Cheers, Genesis, ‘Krautman’, and ‘Marvelon’.

The growth and yield of three cucumber (Cucumis sativus L.) genotypes were evaluated in 1987 and 1988 using three planting arrangements and four weed control treatments. A monoecious, indeterminate, normal leaf cultivar, Calypso, a gynoecious, normal leaf size determinate × monoecious determinate F1 hybrid (UW 11234), and a gynoecious, determinate little leaf inbred line (WI 50476) were evaluated for fruit yield at a 30-cm equidistant (109,000 plants/ha), a 20-cm equidistant (242,000 plants/ha), and a 43-cm row (272,000 plants/ha) spacing. Weed control treatments consisted of an unweeded control, naptalam benzoic acid at 6.7 kg ae/ha, chloramben at 4.5 kg ae/ha, and the herbicides in combination. Although number and weight of fruit per hectare increased with increasing plant density, fruit weight per plant decreased with increasing density. Fruit harvested from plants in unweeded control plots were significantly smaller than those in herbicide-treated plots, and fruit yield of unweeded control plots was lower than in nonweedy plots in 1987. In 1987, plants in plots treated with naptalam produced smaller fruit than plants in plots treated with chloramben or chloramben plus naptalam. Although fruit yield per plant in 1987 was similar in chloramben plots with or without naptalam and generally higher than that of plots treated only with naptalam, fruit yields from naptalam-treated plants were highest in 1988. `Calypso' usually produced more and larger fruit than the determinate genotypes. Based on comparisons of fruit per plant under comparable spacings, productivity of WI 5047G was often lower and its fruit were smaller than those of normal leaf genotypes. Plants of WI 5047G may not attain the source capacity needed for adequate fruit growth before the onset of anthesis, thus producing smaller fruit. Chemical names used: (2-[(1-naphtalenylamino)carbonyl)benzoic acid (naptalam); 3-amino-2,5dichlorobenzoic acid (chloramben).