Weed control is essential in managing high quality turfgrasses. Some preemergent (PRE) herbicides may pose a negative effect on rooting architecture (total length, surface area, diameter, and mass) of desirable species. Several PRE herbicides work by negatively affecting normal cell division and development. Evaluations were performed to determine the effects of four PRE herbicides (dithiopyr, oxadiazon, pendimethalin, and quinclorac) on hybrid bermudagrass (Cynodon dactylon L. X C. transvaalensis Burtt-Davy) (BG) root architecture. Herbicide treatments were applied to field grown dormant BG in Mid-March of 2008 and 2009. A decrease in root length, and in surface area, was observed at 8 WAT by pendimethalin (55% of control). Twelve WAT the greatest decrease occurred in dithiopyr (40%) and pendimethalin (20%). Sixteen WAT, the greatest decrease was observed by dithiopyr (50%). The results indicate that the PRE’s tested can have a negative influence on BG root parameters and possibly water use efficiency.

No description available.

Switchgrass (Panicum virgatum) is a native warm-season grass where weed control during establishment is a limiting factor for stand. Objectives of this research are to develop a herbicide resistant cultivar and to test a variety of seed safeners to improve first year growth. Phenotypic recurrent selection (PRS) was used to select ‘Alamo’ switchgrass seedlings that showed resistance to imazapic herbicide at 245 g a.i./ha. Initial screenings of 364, 650 seedlings resulted in 63 survivors, a selection intensity of 0.0172%. Subsequent testing of the next generation of seedlings indicated that multiple generations of selection were needed in order to transfer greater resistance to the offspring. Seed safener testing consisted of three trials. Field data taken included emergence counts, weed control ratings, and end of season harvest. Results showed fluxofenin (a.i. in Concep III) as being only safener providing protection against metolachlor (83.7% a.i.).

Dicamba drift is a common issue and has been known to cause injury and yield reduction in a wide range of susceptible crops. A study was established to evaluate the effects of a simulated drift on the plant growth and yield of two pumpkin varieties (Cucurbita pepo ‘Magic Wand’ and C. moschata ‘Autumn Buckskin’) during 2019 and 2020 at the Southern Illinois University Horticulture Research Center in Carbondale. Six rates of dicamba were applied to simulate a mid-post-emergence application made in soybean which drifted onto pumpkins at two growth stages, 8-leaf and 12-leaf. These two pumpkin growth stages would be the approximate size of pumpkins when a mid-post-emergence application would typically be made in soybean. The 12-leaf growth stage also corresponds with Simulated drift rates were targeted at 1/1026, 1/513, 1/256, 1/128, 1/64, 1/32 of a 0.56 kg ae ha-1 rate, corresponding to 0.00056, 0.00112, 0.00224, 0.00448, 0.00896, and 0.01792 kg ae ha-1. Actual dicamba deposition was measured used filter papers (surface area = 176.1 cm2) in each treatment and these measured exposure amounts were used in correlational analyses with pumpkin injury, growth, and yield responses. Pumpkin plants did not develop chlorosis or necrosis at any point of the growing season with any of the dicamba application treatments. However, some injury and stunting were observed on pumpkin plants, regardless of drift rate, although pumpkin plant growth and responses were minimal at the drift rates evaluated. Our results indicated that typical dicamba drift rates cause minimal dicamba injury on pumpkin plants at 8- and 12-leaf growth stages with negligible effects on resulting yields. Pumpkin plant injury and stunting would most likely be observed at dicamba drift rates > 1 μg per 176.1 cm2 of leaf area, which converts to 0.62 g per ha. Pumpkins receiving dicamba drift at different growth stages appear to be less sensitive than some other crops, but a drift event at higher rates than those evaluated in this study may impact plant growth and yield. It is important to note that other pumpkin varieties or other Cucurbita species not evaluated in this study may be more susceptible. Producers using dicamba in soybean rotations that are near pumpkin fields should spray under proper wind, temperature, and humidity conditions to best mitigate the occurrence of any drift events. Nomenclature: 3,6-dichloro-2-methloxybenzoic acid, Cucurbita pepo, C. moschata, dicamba, pumpkin.

No description available.

Concern has been raised that herbicides recently registered for use in warm-season turf to control perennial ryegrass could be dislodged from treated areas and deposited on neighboring cool-season grasses. In a field study, rimsulfuron was applied at 17.5 or 35 g ai/ha to perennial ryegrass in the afternoon; the following morning while dew was still present, a greens mower was driven through the perennial ryegrass and across adjacent creeping bentgrass. Irrigation had no effect on perennial ryegrass control but reduced visible track length and injury of neighboring creeping bentgrass. When treated perennial ryegrass was not irrigated prior to simulated mowing, tire tracks were evident on adjacent creeping bentgrass for up to 30 days. Gibberellic acid at 0.12 kg ai/ha and foliar iron at 1.3 kg ai/ha, applied to creeping bentgrass when tracks first appeared, did not enhance recovery of injured creeping bentgrass. Persistence and stability of [2-pyridine 14C] rimsulfuron on turf foliage was also assessed. Rimsulfuron was absorbed by annual bluegrass and perennial ryegrass equivalently and persisted equally on turf foliage. Water extractable rimsulfuron decreased from 60% at 10 minutes after treatment to 40% at 96 hours after treatment. A substantial amount of stable rimsulfuron persists on turf foliage for up to four days. Results from both studies suggest that when applying rimsulfuron near susceptible bentgrass the lowest effective rate should be used, and irrigation should follow two hours after treatment to prevent nontarget injury. / Master of Science

Sustainable weed control in managed agricultural systems requires the judicious use of multiple weed control tactics and prevents over-reliance on any one tactic. In this context, sustainable weed management plays a critical role in the mitigation of one of agriculture's most pressing problems- herbicide resistance. Research conducted in Virginia sought to explore the effects of integrating multiple weed management tactics in corn and cool-season turfgrass. Additionally, research was conducted to confirm nicosulfuron and glyphosate herbicide resistance in Virginia johnsongrass and elucidate the molecular mechanisms conferring those resistances. Rye and hairy vetch cover crop residues, combined with reduced rates of preemergence herbicide and postemergence glyphosate applications, were shown to provide sufficient weed control and corn yield. Cover crop type or residue level did not augment weed control in corn production systems, but the use of glyphosate was essential for late-season weed control. Rye and vetch biculture as a cover crop increased corn yield compared to rye cover crop alone. In cool-season turfgrass, the addition of reduced preemergence herbicide rates to corn gluten meal, an organic herbicide product, reduced crabgrass 25%. Moreover, control was dependent on herbicide choice. Herbicides applied at half of recommended labeled rates or less did not control crabgrass at a commercially-acceptable level, regardless of corn gluten meal addition. In field experiments, Virginia johnsongrass expressed resistance to nicosulfuron and glyphosate. Glyphosate at 0.88 kg ae ha-1 controlled johnsongrass 65%. Nicosulfuron at 0.14 kg ai ha-1 controlled the same population 10%. Greenhouse experiments confirmed differential sensitivity of putative herbicide-resistant johnsongrass seedlings to nicosulfuron and glyphosate when compared to a susceptible population. Herbicide resistance was not conferred via target-site mutation. Five ALS-gene site mutations were confirmed absent in Virginia johnsongrass, while three others were located in coding regions that could not be elucidated in johnsongrass. Further investigations showed glyphosate resistance was not conferred via reduction in herbicide absorption or translocation. The susceptible johnsongrass caused an increase in a polar metabolite at Rf = 0.17 with concomitant reduction in glyphosate over time. Although the mechanism is not clear, these data suggests that glyphosate resistance in johnsongrass may be associated with differential metabolism. / Ph. D.

2 pp. / Persistent woody plants can sometimes conflict with gardening and landscape goals. In many cases, plant removal becomes necessary. This may be accomplished through manual stump removal or the use of herbicides. With some knowledge of the life history of the target plant, cut stumps can be safely and effectively treated with herbicides to prevent regrowth. Species lists, safety tips, examples, photos, and non-herbicide alternatives are provided to ensure optimum stump killing success.

A field study was conducted in Yuma, Arizona during the late fall 2001 growing season to determine the optimum postemergence (POST) timing of glyphosate application on glyphosate- tolerant Lactuca sativa (head lettuce) for weed control. Head lettuce cv. Raider demonstrated excellent tolerance and no injury was observed on the crop after any glyphosate application at the 2, 4, 6, or 8 leaf stage of growth. A single application of glyphosate at 1.0 lb AI/A at the 4 or 6 leaf stage of lettuce growth was optimal for providing near complete control of Portulaca oleracea (common purslane), Chenopodium album (common lambsquarters), C. murale (nettleleaf goosefoot), Physalis wrightii (Wright’s groundcherry), volunteer cantaloupe (Cucumis melo), and Echinochloa colonum (junglerice). An early application at the 2 leaf stage resulted in few new weeds emerging after the application. A later application at the 8 leaf stage resulted in reduced yields of lettuce fresh weight due to weed competition. POST applications of glyphosate on lettuce offered superior weed control compared to soil-applied preemergence (PREE) herbicide treatments.

Revised; Originally Published: 2006 / 2 pp.