AbstractsBiology & Animal Science

Experiments were conducted under field and greenhouse conditions to investigate the effects of chlorpropham (isopropyl mchlorocarbanilate) on vegetative and reproductive development in Chewings fescue (Festuca rubra L. subsp. commutata Gaud.) and to determine the time of induction and initiation under natural conditions. Chewings fescue was found to be very susceptible to chlorpropham treatment and the use of this herbicide for weed control in Chewings fescue caused seed yield reduction. Time of chlorpropham application in relation to environmental factors of temperature and photoperiod was more important than the actual toxicity of the herbicide. Chlorpropham used at the recommended rate of 2 lbs/A was lethal to all tillers that were exposed to the herbicide irrespective of time of application. Seed production from treated plants depended on development of new tillers from axillary buds and on prevalence of environmental conditions conducive to induction and initiation. Extent of chlorpropham injury was dependent on type and maturity of tissue, state of activity of the organ, soil temperature, and length of time after treatment. Apical meristems of the shoot were little affected during the initial stages of injury to the shoots and remained intact even after necrosis of surrounding tissues. When plants were grown at low and high temperature levels and treated with varying herbicide concentrations, tiller production proved to be a more sensitive measure of herbicide-temperature effects than dry matter production. High temperatures favored tiller production and enhanced herbicide toxicity. Time of induction and initiation under natural conditions were determined. Induction was found to occur late in the fall (December) and initiation takes place in February. Plants taken to the field as late as February were induced but seedhead production was reduced because environmental conditions were inhibitory to initiation.