Thesis (Ph.D.)--Mississippi State University. Department of Plant and Soil Sciences. / Title from title screen. Includes bibliographical references.

The combination of Spotlight* at 1.0 pt/A plus Speedzone* at 4.0 pt/A gave 90% control of khakiweed at 14 days after treatment (DAT) and continued to offer acceptable control of 85% at 49 DAT. Acceptable control of 87 and 90% control was also observed at 14 DAT when Spotlight* was combined with Powerzone* or Speedzone*, respectively. The combinations of Spotlight* with Powerzone* or Trimec* were similar by marginally controlling khakiweed up to 21 DAT. Spotlight when combined with Turflon Ester* or Speedzone Southern* performed very similarly at all rating dates and did not offer acceptable khakiweed control.

Two or three applications of Velocity at 30 g ai/A controlled P. annua 63 to 82% in two field experiments. Multiple applications of Velocity at 17 day intervals provided a higher degree of P. annua control compared to applications made at 28 day intervals. At approximately one month after initial applications, Velocity treatments, single or sequential, demonstrated 50 to 77% control of P. annua. The activity on P. annua was minimal at two weeks after initial applications of 30 to 60 g ai/A and slight chlorosis was evident. Perennial ryegrass exhibited chlorosis at two weeks after applications and appeared to recover at one month.

Seed head production from Poa annua is problematic on winter turfs, whether they are overseeded or not. Flowering culms are unsightly, prevent a uniform surface, and insure a continuous crop of seeds for the future. A field test was conducted to evaluate the effects of PROXY and a PROXY/PRIMO PGR tank mix for seed head control. Treatments were applied on three different dates in order to evaluate the degree of response of treatments and help define treatment window applications for future programs. PROXY when applied alone at 5 ounces/product/M produced a maximum of 60% seed head control at 26 days after a single application on February 15, and 83% seed head control at 27 days after a single application on March 1. A tank mix of PROXY/PRIMO (5.0/0.25 ounces/product/M) generally produced greater seed head control than PROXY alone. The tank mix produced seed head control effects quicker, greater, and longer than PROXY alone. Seed head suppression and percent seed head control was greatest when products were applied initially on either February 15 or March 1, 2001. PROXY/PRIMO produced the darkest color turf when applied on either February 15 or March 1. At least three tank mixes seem to be needed, applied monthly to suppress/control seed heads throughout the winter/spring season.

Post emergence applications of penoxsulam herbicide were generally ineffective in weed control of Khakiweed, (Alternanthera pungens). Moderate control was achieved by the high rate of granular Penoxsulam (0.052 G, 180-lbs. acre). This treatment had 28%, 34%, and 32% Khakiweed control on September 20, September 23 and September 29, respectively. Other rates resulted in minimal or negative control. The liquid SC formulation provided minimal control, at rates tested. Penoxsulam did discolor khakiweed, but did not cause enough injury to result in stand reduction. Further aspects for investigating Penoxsulam for control of this weed is presented.

The efficacy of six ALS herbicides for controlling purple nutsedge in bermudagrass turf was demonstrated in five field experiments during the summer of 2004. The highest degree of nutsedge control at 95% at the end of the summer was observed after three monthly applications of trifloxysulfuron at 0.026 lb a.i./A.. Three monthly applications of halosulfuron at 0.062 lb a.i./A controlled nutsedge 88 to 90% at the end of September to early October. Imazaquin at 0.5 lb a.i./A plus MSMA at 3.0 lb a.i./A gave 91% control of nutsedge with three applications. The most rapid and efficacious nutsedge control was observed with flazasulfuron giving 91% control at 15 days after a single application. The highest degree of nutsedge control with a single application of sulfosulfuron was 91 to 96% control at 28 days after treatment. In general, ALS herbicides applied as a single application or multiple applications provided one month of effective control following a first application. After one month, the degree of control declined unless repeated applications at monthly intervals or as needed were applied for extended control. Penoxsulam at 0.12 lb a.i./A in one test gave only 70% control. MSMA at 3.0 lb a.i./A was applied four times and nutsedge control at the end of the season was 63 to 66%.

Higher SU herbicide rates provided more effective ryegrass removal that resulted in improved establishment of the seeded bermudagrass. In most instances in this study, the percent bermudagrass coverage increased as herbicide rates increased. Glyphosate was very effective in completely removing ryegrass non-selectively. Flazasulfuron at 0.018 lb ai/A eliminated 88% of the ryegrass. Observations also showed that foramsulfuron, rimsulfuron,and chlorsulfuron were effective in removing ryegrass. In plots where ryegrass had been eliminated, faster bermudagrass coverage in a greater area of the plot was achieved. The least amount of bermudagrass coverage occurred in the untreated plots. It appeared that most of the herbicides evaluated in this study were relatively safe on seeded Princess 77 bermudagrass since emergence and establishment occurred in all plots. The speed and degree of coverage in the plots increased due to efficacy of the herbicides in eliminating ryegrass prior to seeding.

Velocity, (bis pyrobac-sodium) was applied at different ai/a rates in multiple application series to evaluate treatments for post emergence seed head and vegetative control of Poa annua var. annua. Velocity herbicide, when applied to perennial ryegrass overseed turf with heavy PA infestations, caused periodic discoloration of the ryegrass and yellowing/bronzing of the PA. The leaf yellowing of PA caused by Velocity is in contrast to color enhancement of PA from Proxy/Primo tank mixes. Seed head suppression of PA from Velocity was slightly greater in early April, than in early March. As cumulative treatment amounts of active ingredient of Velocity increased, the seed head suppression increased for treatments beyond the 30 + 30 gm ai/a rate. Above this rate, seed head suppression was increased, but not consistently with the applied active ingredient rate. Seed head suppression of PA on March 5 from Velocity ranged from 35% to 75% among Velocity treatments applied at 30, 45 and 60 grams ai/a. Embark alone had fair seed head suppression from early to mid-March, but decreased dramatically afterwards. There was no benefit of the 30 + 60 gm ai/a treatment, over the 60 + 60 gm ai/a treatment for seed head suppression of PA. Biological response in terms of absolute rate of ai/a applied and response to cumulative amounts of total Velocity were not consistent for PA seed head suppression or vegetative control. No product affectively reduced vegetative control of PA in a highly infested stand of PA which was 40-50% PA. If Velocity is to be competitive against other PA seed head reducing products, rate structures and timings may have to be amended for more multiple applications.

Several items need consideration when products are evaluated for use as transition agents. These are (1) efficacy of ryegrass removal [rate of ryegrass decline and appearance of turf during transition], (2) tolerance and performance of incoming bermudagrass and (3) application safety for next season’s repeat overseed operations. This test was designed to evaluate application safety for the next overseeding which occurs in the early fall. Therefore, AEF was applied in the summer to bermudagrass turf prior to overseed operations. Most responses of the perennial ryegrass (overseed) turf to previous treatments of AEF 130360 occurred immediately after overseeding, from mid-October to early November. AEF 130360 applied 2 weeks before overseeding caused a significant decrease in seedling vigor, percent plot ryegrass cover, and percent bermudagrass plot straw present. Both AEF treatments applied closest to overseeding (2 weeks prior) had the least amount of initial ryegrass, the greatest amount of green bermudagrass, and later in the season, the most amount of straw (dormant) bermudagrass. Differences in turfgrass quality were not significant due to treatments at any time throughout the test, and most treatments ranked higher than the control in overall quality. Under the conditions of this test, application of AEF 130360 at either 0.64 or 1.28 ounces/product/M made one month before actual oversseding did not cause detrimental effects to ryegrass emergence, ryegrass cover, turfgrass color or overall quality.

Proxy (ethephon) was applied to 100% pure stands of Poa annua as either a single or repeat application 24 days apart at both a five and ten-ounce product rate per 1000 square feet. Percent plot seed heads were decreased significantly on three of five evaluation dates before either the loss of treatment effect and/or environmental conditions triggered profuse flowering (by 20 April, 2000). The five-ounce rate produced moderate seed head suppression at 16 and 25 days after the first treatments by which afterwards, control was minimal. By April, the five-ounce repeat applications were no better in suppression of seed heads than either of the single applications, regardless of application timing (March 3 or 29). The ten-ounce rates generally produced 40% - 80% greater seed heads suppression than the five-ounce rate treatments. Maximum seed head control was achieved by the repeat applications (March 3 and 29) of the ten-ounce rate, which consistently produced between 8% and 19%, seed head cover up until the first ten days of April 2000. Proxy, when applied at the five-ounce/M rate had the greatest effect in seed head suppression early in the test (10 March). Perhaps earlier season applications at the five-ounce rate may be necessary to manifest greater suppression initially, and perhaps in a cumulative fashion for season long control.