The response of beans to fluorodifen as affected by light and other factors

Graduation date: 1974Studies with fluorodifen were conducted to gain more information\ud about its field performance and the influence of light quantity,\ud quality and timing of exposure on its phytotoxic properties. Uptake\ud and trans location in three plant species were also investigated.\ud These studies were aimed at evaluating the usefulness of this chemical\ud as a selective herbicide for controlling weeds in beans\ud (Phaseolus vulgaris L.) in Oregon.\ud Field data compiled for a period of three consecutive years\ud indicated that the highest yields of green beans were obtained when\ud fluorodifen was applied at a rate of 6 lb/A preemergence. At\ud higher rates, crop injury was noticeable in the form of shortening\ud of midrib and necrotic lesions on hypocotyls and other plant tissues such as cotyledons that came into contact with the herbicide.\ud Occasionally these symptoms were observed at rates as low as\ud 1 lb/A under an unspecified set of conditions occurring in the field.\ud A combination of fluorodifen applied preemergence and cultivation\ud two weeks after emergence of the crop provided the best weed controls\ud Shading the crop at different stages of development did not provide an\ud explanation for the cause of stem lesion development, but when shade\ud was provided from application until the first true leaf, phytotoxicity\ud was noticeable. Three soil types and two watering regimes did not\ud provide significant, consistent phytotoxicity or stem burning.\ud By the use of neutral density filters, different intensities of\ud light with the same spectral emission were obtained in growth chambers.\ud Bean and soybean plants were more sensitive to fluorodifen at\ud low levels of light. The percentage dry weight reduction decreased as\ud the light intensity increased from 1,000 to 2,000 ft/c. In determining\ud the critical period in which light enhances fluorodifen injury to beans\ud and soybeans, it was found that plants exposed to light on the second\ud to third day after planting were most severely injured. When filters\ud were used to evaluate the influence of light quality on fluorodifen\ud toxicity to beans and soybeans, these plants were more sensitive to\ud fluorodifen when exposed to yellow and red light than when exposed to\ud blue or white light. Phytotoxic symptoms were observed especially\ud under yellow light. Exposure to light at the time of crop emergence\ud resulted in the greatest phytotoxicity.\ud Autoradiography and radioassay results indicated that ¹⁴C-fluorodifen\ud was absorbed mostly within six hours after application.\ud The distribution pattern remained fairly constant in beans and soybeans\ud with the largest percentage of activity remaining in the treated\ud portion at all times. Greater mobility of the label was observed in\ud cucumber plants with some acropetal and basipetal movement\ud recorded from the treated leaves 12 hours after applications. Covering\ud the treated leaf did not alter the uptake of fluorodifen in any of the\ud three plant species. Following applications to stem and roots, a\ud similar pattern was observed, rapid uptake but little or no mobility.\ud The unicellular algae Chlorella was used to assess the effect of\ud fluorodifen on photosynthesis and respiration of green plant tissues.\ud It was found that the growth of Chlorella was severely affected by low\ud concentrations of fluorodifen in the light. The same herbicide concentrations\ud had no effect in the dark. Under the conditions of this study,\ud fluorodifen caused just a slight increase in the respiration of\ud Chlorella, while photosynthesis was severely inhibited at concentrations\ud of 1 ppm of fluorodifen.\ud In a separate study, the persistence of fluorodifen in soil subjected\ud to different environmental conditions was evaluated by gas\ud chromatography. Fluorodifen was degraded more readily under high\ud temperatures, provided that the soil was dry