Field experiments were conducted in 1994 and 1995 to determine if the sodium salt of pyrithiobac or bromoxynil applied in a low-volume, air-assist spray system controlled entireleaf morningglory, pitted morningglory, and smallflower morningglory as well as treatments applied with a conventional hydraulic fan spraying system, and to determine if herbicide rates could be reduced when using the low-volume spraying system. Pyrithiobac at 0.035 and 0.071 kg ai/ha and bromoxynil at 0.56 and 1.12 kg ai/ha were applied alone and in combination with DSMA at 1.7 kg ai/ha or MSMA at 1.7 kg ai/ha. Spraying systems were calibrated to deliver 26 L/ha and 140 L/ha for the low-volume and conventional systems, respectively. No significant differences in control were noted between low-volume and conventional spray systems when herbicides were applied at the suggested use rates of 0.071 and 1.12 kg ai/ha for pyrithiobac and bromoxynil, respectively. Morningglory control was reduced when pyrithiobac and bromoxynil were applied at one-half the suggested use rate regardless of the spraying systems. Bromoxynil alone generally controlled pitted and entireleaf morningglory better than pyrithiobac alone regardless of rate and application method. However, pyrithiobac generally provided better control of smallflower morningglory than bromoxynil. Adding MSMA or DSMA to bromoxynil and pyrithiobac increased control of both weed species.

Green kyllinga is a relatively new weed species in well-irrigated turfs in the southwest US. To understand the germination requirements of green kyllinga, the effects of planting depth, temperature, pH, and osmotic potential were determined. Green kyllinga emergence was sensitive to planting depth. At 21 days after planting (DAP), emergence of green kyllinga was 60% when planted at the soil surface but only 20% at 0.5 cm and less than 5% at 1 cm. Germination occurred at temperatures between 17 and 30 C but was notably better between 20 and 24 C. Germination was uniform from pH 5.5 to 9.5. Germination decreased between the water potentials −0.1 to −0.6 MPa, although germination was high at water potentials found in irrigated turf. The environmental conditions found in nonstressed turf areas in Arizona will likely support the establishment of green kyllinga. The efficacy of herbicides for the control of green kyllinga was also determined. Control of kyllinga (95% or greater) was obtained with preemergence applications of oxadiazon, dithiopyr, and metolachlor, and with postemergence applications of DSMA, halosulfuron-methyl, and imazaquin.

The presence of a common cocklebur (Xanthium strumarium L. # XANST) population resistant to organic arsenical herbicides was confirmed in three adjoining counties of South Carolina's ten-county cotton-growing region, but little evidence of resistance was found in the remaining seven counties. This population was resistant to both disodium salt of methylarsonic acid (DSMA) and monosodium salt of methylarsonic acid (MSMA) but not to herbicides from nine other chemical groups. A much greater level of resistance was apparent in the field than under greenhouse conditions and larger plants were more resistant than small plants.

Four field experiments conducted over 3 yr indicated that cultivation alone failed to prevent johnsongrass [Sorghum halepense (L.) Pers.] from reaching densities that severely reduced yields of cotton (Gossypium hirsutum L. ‘Acala SJ-2’). Density of johnsongrass in plots cultivated four times and hoed weekly for 8 weeks after emergence was reduced to 1 shoot/m2 at harvest compared to 74 shoots/m2 for plots that were only cultivated. In addition to a 60% average yield loss of seed cotton, yield losses ranging from 40 to 76%, ginning losses were also greater from cultivated than from hand-weeded plots. Compared to cultivated plots, supplementing cultivation with two postemergence applications of 3.0 kg/ha of DSMA (disodium methanearsonate) increased the average yield of cotton by 20% and reduced perennial johnsongrass densities by 64% at harvest. Although yields were improved by applying DSMA, they averaged 40% less than those of hand-weeded plots. The temporary weed control obtained with DSMA was profitable in terms of the additional lint and seed obtained, but insufficient cotton was produced to pay expenses for producing the crop by any of the methods of weed control. High labor costs for hoeing prevented this treatment from being profitable.

Experiments were conducted to evaluate PRE and POST cotton herbicides for control of MSMA-resistant (R) and -susceptible (S) common cocklebur biotypes, and to determine potential cross-resistance of the R biotype to other arsenical and membrane disruptor herbicides. Cyanazine and clomazone applied PRE were the most effective herbicides for control of R populations. Lactofen or cyanazine in combination with MSMA controlled R and S biotypes better than fluometuron or pyrithiobac combined with MSMA. MSMA-resistant common cocklebur was not cross-resistant to other arsenical herbicides. Significant differences in cellular electrolyte leakage and chlorophyll content of the treated leaf between biotypes were not evident for paraquat, acifluorfen, and MSMA.

Various combinations of methods were evaluated for the control of ivyleaf morningglory growing in cotton. The combinations included chemicals incorporated to two depths or tanked-mixed as postemergence treatments and cultural methods that included in-row cultivation and hand weeding. The most effective combinations of methods included a herbicide such as cyanazine or prometryn in some treatments resulting in reduced ivyleaf morningglory population and improved cotton yields. Cultural methods without chemical assistance gave little or no control of ivyleaf morningglory based on weed populations and cotton yield. Statistically the best combinations had lint yields equal to the weed-free treatment, but the yields were reduced from 114 to 372 kg/ha. Also, most combination treatments had enough plant debris in the lint to reduce fiber grade.

When postemergence applications of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} were compared with DSMA (disodium salt of methylarsonic acid), MSMA (monosodium salt of methylarsonic acid), and glyphosate [N-(phosphonomethyl)glycine] for control of johnsongrass [Sorghum halepense (L.) Pers. # SORHA] in cotton (Gossypium hirsutum L. ‘Acala SJ-2′), repeated annual applications of sethoxydim were more successful than other herbicides in protecting yields of cotton and reducing populations of rhizome johnsongrass over time. After the first year of treatment with sethoxydim in 1982, when an 18% yield loss of cotton occurred, populations of rhizome johnsongrass were reduced to the extent that they were no longer a threat to yields in plots treated with sethoxydim in 1983 and 1984. Although DSMA and glyphosate improved yields when compared to cultivated control plots, substantial yield losses occurred every year, and populations of johnsongrass remained unchanged after 3 yr of treatment. Averaged over 3 yr, plots treated with sethoxydim produced 94% as much cotton as weed-free plots, compared to 60 and 45% for plots treated with glyphosate and DSMA/MSMA, respectively.