Goosegrass is a problematic weed of golf courses, sports fields, and residential lawns that decreases playability and aesthetic quality of turf. With the recent banning of MSMA in sports fields and intensive restrictions in golf and sod production, turfgrass managers are seeking alternatives for postemergence goosegrass control and how to utilize currently labeled goosegrass control products more effectively. Studies were conducted to investigate a suspected-resistant (SR) goosegrass accession in Richmond, VA and characterize the resistance mechanism if present. The SR accession showed a hypersensitive response to oxadiazon treatment and reached maximum electrolyte leakage quicker than the susceptible (S) accession, but had significantly lower electrolyte leakage indicating less tissue damage and suggesting there is a physiological resistance mechanism within the SR accession. In absorption and translocation studies, percent oxadiazon absorption and translocation was not significantly affected by goosegrass biotype. Roots of both the S and resistant (R) biotypes contained over 95% of total detected oxadiazon, while the plant tissue above the treated foliage only contained small quantities. These results suggest that absorption or translocation is not the mechanism conferring oxadiazon resistance in the goosegrass biotype from Richmond, VA. Greenhouse and field trials were conducted to determine the lowest rate at which topramezone, with or without the addition of triclopyr, controls goosegrass while maintaining commercially-acceptable bermudagrass quality. In field trials, topramezone rate did not significantly affect goosegrass cover at 56 and 70 days after initial treatment (DAIT). All treatments reduced goosegrass cover below 3 and 7% with and without the addition of triclopyr, respectively at 70 DAIT. A significant herbicide effect on bermudagrass cultivar showed higher injury from topramezone within three weeks of application, but injury persisted longer from treatments containing triclopyr. Bermudagrass cultivars completely recovered by 4 weeks after treatment (WAT) from all treatments. Greenhouse trials were conducted to determine if goosegrass growth stage affects efficacy of nine postemergent herbicides or programs documented to have goosegrass activity. As goosegrass growth stage increased from four- to five-leaf to greater than eight-tiller stage, goosegrass control and biomass reduction decreased among all of the herbicides except topramezone and MSMA plus metribuzin at 4 and 8 WAT. These data suggest that one application of sulfentrazone is only effective for seedling stage (pre-tiller) goosegrass control; foramsulfuron, topramezone, and metribuzin suppress all growth stages of goosegrass; and diclofop, sulfentrazone plus metribuzin, fenoxaprop, and metamifop control up to three-tiller stage goosegrass. / Ph. D.

Acetolactate synthase (ALS) inhibiting herbicides are commonly used to eliminate weeds from mature turfgrasses. Field trials were conducted from 2004-2006, testing ALS herbicides for preemergence and early postemergence activity on newly seeded turfgrasses, using four species: Riviera bermuda, Zenith and Companion zoysia, L- 93 creeping bentgrass, and Poa annua L. Data collected were phytotoxicity and percent turf cover. Bermuda and zoysia herbicides were metsulfuron-methyl (42 g ha-1), trifloxysulfuron (29 g ha-1), flazasulfuron (53 g ha-1), foramsulfuron (30 g ha-1), bispyribac-sodium (112 g ha-1), and rimsulfuron (35 g ha-1). Treatments occurred the day of seeding and two-three weeks after seeding. Flazasulfuron, trifloxysulfuron and bispyribac-sodium caused significant damage in all treatments. Data suggests that bermuda and zoysia are tolerant of seedling treatments of foramsulfuron, rimsulfuron, and metsulfuron-methyl at these rates. Bentgrass and P. annua herbicides were foramsulfuron (15 and 30 g ha-1), siduron (2803 g ha-1), bispyribac-sodium (49 g ha-1), and paclobutrazol (281 g ha-1). Treatments occurred the day of seeding, two and four weeks after seeding. Foramsulfuron at 15 and 30 g ha-1 caused significant damage regardless of when it was applied. Data suggests that bentgrass and P. annua are tolerant of seedling treatments of siduron, paclobutrazol, and bispyribac-sodium at these rates.

Doctor of Philosophy / Department of Agronomy / Kassim Al-Khatib / Growth chamber, greenhouse and field experiments using conventional grain sorghum were conducted to 1) evaluate the differential response of grain sorghum hybrids to POST application of mesotrione at various rates and application timings, and 2) determine the physiology of tolerance of grain sorghum hybrids to mesotrione. Sorghum response ranged from susceptible to tolerant. Mesotrione dose-response studies on four sorghum hybrids revealed that injury symptoms were greatest in Pioneer 85G01 and least in Asgrow Seneca. Mesotrione applied EPOST (early POST) injured sorghum more than when applied at MPOST (mid POST) or LPOST (late POST) timings. Observed injury symptoms were not well correlated with grain yield and were transient, thus injury did not reduce sorghum grain yield. Foliar absorption or translocation of mesotrione in tolerant hybrids did not differ with that of susceptible hybrids but metabolism was more rapid in tolerant than in susceptible hybrids. Initial grain sorghum injury was severe and will likely be a major concern to producers. Field and growth chambers studies were conducted on herbicide-resistant grain sorghum to 1) determine the effect of quizalofop rates, application timings, and herbicide tank mixes on acetyl-coenzyme A carboxylase (ACCase)-resistant grain sorghum injury and yield, and 2) determine if herbicide metabolism is an additional mechanism that could explain the resistance of ACCase- and acetolactate synthase (ALS)-resistant grain sorghum. Depending on rate, EPOST application caused the greatest injury while the least injury occurred with LPOST application. Crop injury from quizalofop was more prominent at rates higher than the proposed use rate (62 g ha [superscript]-1) in grain sorghum. Sorghum grain yield was not affected by quizalofop regardless of rates or application timings. Weed control was greater when quizalofop was applied with other herbicides than when applied alone. Herbicide treatments except those that included 2,4-D caused slight to no sorghum injury. Results of the quizalofop metabolism study do not support the involvement of differential metabolism in the observed response of grain sorghum to quizalofop. Rimsulfuron metabolism by ALS-resistant sorghum is more rapid than the susceptible genotypes, thus explaining the observed rapid recovery of grain sorghum plants from rimsulfuron injury in the field.

Prior exposure to plants cues can enhance assortative mating in insects. We hypothesized that, as previously reported for females, males of Cotesia congregata would display inherent responses to plant cues that could be modified by postemergence experience and further, that males originating from two different host-plant complexes (HPCs) would display different behavioral responses to these HPCs. In no-choice contact assays with a non-host plant, searching responses of males and females increased sharply at Day 2 and remained stable through Day 4. In no-choice assays with potential host plants, males searched longer on catalpa than tobacco; responses were not modified by postemergence experience. In choice assays with both HPCs, naïve males did not display orientation preferences; however, males experienced with their natal plant preferred their natal HPC. Results indicate that postemergence experience on the natal host plant induces an orientation preference for the natal HPC and thus, can facilitate assortative mating.

Italian ryegrass (Lolium multiflorum Lam.) is a competitive weed in small grain production areas throughout the northwestern and southeastern US. In small grains, Italian ryegrass has generally been controlled with postemergence treatments of diclofop, or diclofop-methyl, a member of the subfamily of the aromatic carboxylic acid family, the aryloxyphenoxypropionates. The first incidence of diclofop resistance in Italian ryegrass was reported in Virginia in 1995. Experiments to characterize diclofop resistance in several Virginia biotypes of Italian ryegrass included the following objectives: (1) evaluation of the presence of diclofop resistance in several Italian ryegrass biotypes collected across Virginia, (2) evaluation of alternative herbicide efficacy for diclofop resistant Italian ryegrass control, and (3) characterization of the aryloxyphenoxypropionate (APP) resistance mechanism in resistant Italian ryegrass biotypes. The response of 32 biotypes to diclofop collected from various locations statewide with varying histories of diclofop applications confirmed diclofop resistance in Virginian Italian ryegrass populations. At 4-times the label-recommended application rate, only 50% of biotypes previously exposed to diclofop in a cropping situation were adequately controlled versus 94% of the biotypes not previously treated with diclofop. Tralkoxydim provided the most effective control of four of the biotypes. No postemergence treatment effectively controlled one biotype previously exposed to diclofop applications. Effective preemergence herbicide treatments for Italian ryegrass control in the greenhouse included acetochlor (two formulations) and flufenacet plus metribuzin. In the field, flufenacet plus metribuzin resulted in excellent Italian ryegrass control, little crop injury, and acceptable barley yields. Acetyl-coenzyme A carboxylase (ACCase) assays and herbicide absorption, translocation, and metabolism studies were conducted to investigate resistant mechanism(s) to two APP herbicides, diclofop and quizalofop. ACCase assays indicated no differences in enzyme activity between the two biotypes of Italian ryegrass evaluated. Furthermore, no significant differences in the specific activity of ACCase were detected between the two biotypes in the absence of diclofop. [14C]Quizalofop-P absorption, translocation, and metabolism did not differ between resistant and susceptible Italian ryegrass biotypes. Lack of a significant biotype effect suggests that differential metabolism does not explain the differential response to diclofop treatments observed in the herbicide dose-plant response experiment. / Ph. D.

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.

Canada fleabane is the second glyphosate-resistant (GR) weed species to be confirmed in Ontario. In 2010, GR populations were identified at eight sites in Essex County. In 2011 and 2012, 147 additional sites across eight counties were confirmed to be resistant. Twelve and seven sites were identified with multiple resistance (glyphosate and cloransulam) in 2011 and 2012, respectively, across five counties. In soybeans, preplant tankmixes of glyphosate (900 g a.e.ha-1) plus saflufenacil (25 g a.i. ha-1), saflufenacil/dimethenamid-p (245 g a.i. ha-1), metribuzin (1120 g a.i. ha-1), or flumetsulam (70 g a.i. ha-1) provided greater than 87% up to 8 weeks after application (WAA). Glyphosate rates 21 to 48X the label rate (900 g a.e. ha-1) were required for 95% control. Postemergence tankmixes did not provide acceptable control. In dicamba-tolerant soybean, dicamba applied preplant at 600 g a.e. ha-1 provided the most consistent control of GR Canada fleabane. / Monsanto Canada Inc., Grain Farmers of Ontario, Agricultural Adaptation Council