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Johnsongrass [Sorghum halepense (L.) Pers.] and mugwort (Artemisia vulgaris L.) are both rhizomatous perennial weeds that are capable of rapidly colonizing a variety of different environments. Separate experiments were conducted throughout Virginia from 1996 to 1999 to determine more effective methods for reducing infestations of these perennial weeds in the future. Field and greenhouse experiments conducted on a resistant johnsongrass population discovered in New Kent County, Virginia revealed that this biotype exhibits low levels of resistance to the aryloxyphenoxypropionate (APP) herbicides quizalofop-P and fluazifop-P and the cyclohexanedione (CHD) herbicide sethoxydim. Additional laboratory experiments revealed that resistance is not due to differential absorption, translocation, or metabolism of the APP and CHD herbicides in the resistant vs. the susceptible biotype. However, acetyl-coenzyme A carboxylase (ACCase) assays revealed that resistance to the APP and CHD herbicides is conferred by an overproduction of the ACCase enzyme in the resistant compared to the susceptible johnsongrass biotype. In field experiments conducted on mugwort infestations discovered in several counties throughout Virginia, 100% mugwort control was achieved with standard application rates of picloram at 4 months after treatment (MAT), and also greater than 70% mugwort control was achieved with the higher application rates of clopyralid, glyphosate, and dicamba at 4 MAT. However, all other herbicides evaluated in these experiments provided less than 65% mugwort control at 4 MAT, even at exceptionally high use rates. Additionally, the results from these trials revealed that sequential herbicide applications and sequential mowings prior to herbicide application are both effective mugwort control strategies. / Ph. D.

Weed seeds contaminating cattle feed can pass unaffected through the animal's digestive tract and may germinate when manure is returned to land as fertilizer. This investigation was undertaken to determine the effects of anaerobic fermentation of raw manure on the viability of Johnsongrass and Fall Panicum seeds which may be present in the waste. Dairy waste containing Johnsongrass and Fall Panicum seeds were subjected to batch and continuously-fed anaerobic fermentation processes in laboratory-scale digesters. The effect of influent solids concentration (4% and 6%) and retention time (15 days and 20 days) on seed viability was observed. The experiments were carried out in the mesophilic temperature range [35°C±1ºC]. Fall Panicum seeds were found to be less resistant to anaerobic digestion than Johnsongrass seeds. Greater seed destruction was achieved in 20-day digesters than in the 15-day digesters. The influent solids concentrations did not have significant effect on seed viability. By applying the Schafer-Chilcote seed population model, it was observed that the fermentation process was more effective in destroying non-dormant seeds than dormant seeds. / Master of Science

5 pp. / This is part of the series on climate variability / Climate change appears to have an effect on invasive species in the forests and woodlands of Arizona. Many invasive plants have been documented. Land managers and educators will find this publication informative.

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Three herbicides, Puma, Achieve and Osprey, have been registered for the control of Littleseed Canarygrass in the last five years. Another, Pinoxaden, is being developed and should be registered in the next few years. These herbicides were compared for weed control and crop safety. All produced very good to excellent levels of control although crop injury, especially when tank mixed with broadleaf herbicides, was significant.

Four herbicides and combinations of these herbicides with MCPA were evaluated for the control of Littleseed canarygrass in durum wheat. The currently registered herbicides, Achieve and Puma (not registered in Arizona) produced control levels of 80 to 95 percent with good crop safety. The new herbicides being developed, Osprey and Olympus produced higher and more consistent levels of control of 95 to 99 percent but caused slight to moderate crop injury. Combinations of Achieve and Puma with MCPA, a broadleaf herbicide, resulted in decreased control. When Osprey was tank mixed with MCPA, crop injury was increased.

There are currently three herbicides registered for the control of littleseed canarygrass in the desert southwest. Hoelon was used with marginal success from 1982 to 1999. In 1999, Achieve was registered in Arizona and Puma was registered in California for the control of this weed in wheat and barley. Both have produced good to excellent levels of control (75 to 95 percent) in our tests and under commercial conditions. Two newer herbicides, Olympus (formerly Bayer MKH6561) and F130060 (Aventis) are being developed and have produced excellent levels of canarygrass control in our tests with less crop safety.

Nine herbicide treatments were evaluated for the control of mature nettleleaf goosefoot in durum wheat that was ten days from harvest. The only effective treatments were combinations of Glyphosate (Roundup Ultra Max and Touchdown) and Paraquat (Gramoxone). Applications of Aim, Gramoxone, and Glyphosate alone were ineffective.