Dodder (Cuscuta gronovii Willd.) is a weed of serious concern to cranberry (Vaccinium macrocarpon Ait.) growers. It develops vigorously and has a long-lived seed bank. Cranberries are a perennial crop and therefore strategies available to growers of annual crops are not practical. Herbicides, the primary management tool for dodder, although effective, have a narrow window of application and extended seedling emergence after applications can result in escapes. This project examined the effect of water temperature on dodder seed germination and the use of short-term floods (less than 72 hr) for dodder management. Experiments investigated the effect of water temperature on dodder seed germination. Studies, ran twice, submerged dodder seed in water for 0 to 48 hr at 10, 15, and 20 C in one experiment (simulating spring water temperatures) and 0 to 48 hr at 15, 20, and 25 C in a separate experiment (simulating summer water temperatures). In Run 1, the effect of temperature on percent seed germination varied by flood duration; and by temperature alone in Run 2. Percent seed germination however, always fell within normal ranges (35-59%), indicating that flooding may not impact seed germination. Two 1-yr field studies were conducted to evaluate the use of short-term floods (24 to 48 hr) for managing dodder in cranberries. Two scenarios were simulated: cranberry beds with no emergent weed populations (cranberries alone) and cranberries with emergent weed populations (cranberries with additional host). There were three flood durations (0, 24, and 48 hr) and four flood initiations (1 to 4 wk after first seedling emergence). In 2006, mean percent germination from seeds incubated in Petri dishes was lower for seeds submerged 3 and 4 wk after first emergence (AFE) for the 48-hr flood durations. In 2007, mean percent germination for seeds submerged for 24 and 48-hr decreased for floods initiated at 4 wk AFE. Flooding 4 wk AFE resulted in lowest mean attachment ratings in both years and lowest mean dodder biomass on cranberry in the 2007 cranberry and tomato study, suggesting later flood initiation may provide better dodder management.

One potential alternative to chemical weed control is the use of microwave radiation, a particular form of indirect thermal weeding. Absorption of microwave radiation causes water molecules within the tissue to oscillate, thereby converting electromagnetic energy into heat. This technique is rapid, versatile and effective, as the electromagnetic waves heat the plant tissue and destroy cellular integrity. The objective of this research was to evaluate the potential use of dielectric heating for weed management. Ten weed species representing monocots and dicots were selected for this study: southern crabgrass, dallisgrass, yellow nutsedge, fragrant flatsedge, false green kyllinga, common ragweed, field bindweed, henbit, white clover, and pitted morningglory. There was a lag or warm up period between energizing the magnetron and actual microwave radiation production. To eliminate the gap between electric power supplied to magnetron and actual microwave radiation produced, a conveyer was used. Overall injury to grasses, sedges and broadleaf weeds was higher at each dose when weeds were treated by microwave radiation while moving on a conveyer in comparison to being stationary. Grasses showed slightly more tolerance to microwave treatments in comparison to broadleaf weeds. Older weeds (8 to 10 weeks old) showed more tolerance to microwave treatments in comparison to younger weed plants (4 to 6 weeks old). Microwave radiation was able to control a range of weed species, although larger weeds were more likely to regrow after treatment. Ambient temperature had a significant effect on injuries caused by microwave radiation to target weeds, with control increasing as the air temperature increased. Weed control using microwave radiation required more energy when weeds were treated at 13 C compared to 35 C. More energy was needed at lower air temperatures to raise the plant canopy temperature from ambient levels to beyond the biological limit. Microwave radiation at lower doses caused greater injury to common chickweed and yellow woodsorrel than bermudagrass, suggesting the potential for selective weed control in certain situations. A custom built microwave applicator provided similar control of emerged weeds as the contact herbicides diquat and acetic acid. / Ph. D.