The adaptation of herbicides to control the encroachment of one warm-season grass into another species is an important management practice. A field study was conducted in Georgia to determine the rates and frequency of herbicide applications needed to suppress three seashore paspalum cultivars and determine what effects these treatments will have on three bermudagrass cultivars. MSMA plus triclopyr plus clopyralid applied at a total of 2.7 kg/ha in each of three applications for a cumulative total of 8.1 kg/ha effectively suppressed (> 70%) ‘Sea Isle 1’ and ‘Sea Isle 2000’ for 13 wk during 1998 and 1999 and ‘K-3’ during 1998. The suppression of K-3 in 1999 was 56%. The suppression was higher in all instances when MSMA was applied with triclopyr plus clopyralid than when it was not included (< 45%). Four-way combinations of MSMA plus 2,4-D plus mecoprop plus dicamba applied at a total of 5.3 kg/ha in each of three applications for a cumulative total of 15.9 kg/ha suppressed K-3 from 37 to 66%, Sea Isle 2000 from 55 to 66%, and Sea Isle 1 from 59 to 65% for 13 wk. The suppression of three paspalum cultivars at 13 wk from tank mixes of MSMA plus 2,4-D plus dicamba applied at a total of 4.5 kg/ha in each of three applications for a total cumulative of 13.5 kgsol:ha was 7 to 12% lower using the four-way combination treatments. Injury to the bermudagrass cultivars from herbicide treatments was not a problem. In some instances, all herbicides caused some degree of bermudagrass injury on selected dates of treatment. Maximum injury from the herbicides ranged from 18 to 40% for ‘common’ bermudagrass, 18 to 39% for ‘Tifway’ and 30% for ‘TifEagle’ bermudagrass. When injury occurred, bermudagrass recovery was within 1- to 2-wk following treatments.

In greenhouse studies, flowering annual bluegrass Poa annua L. var. annua (winter annual) and P. annua L. var. reptans (short-lived perennial) were treated postemergence with rimsulfuron at 54 g ai/ha in such a manner as to permit herbicide interception only by the foliage, interception only by the soil, and interception by both foliage and soil, as would occur in a typical application. The foliar-only, soil-only, and soil + foliar applications provided 57, 73, and 84% control, respectively, as averaged over all other experimental variables. Greater efficacy of the soil-only and soil + foliar applications indicated the importance of root absorption for annual bluegrass control with rimsulfuron. Adjuvant addition was beneficial to postemergence activity only at 18 g/ha, which is below the registered rate. Adjuvant-based control improvement at this rate was inconsistent and generally independent of the adjuvant type. Adding Renex-30 to 18 g/ha of rimsulfuron did increase control on an average from 16 to 51%. Postemergence efficacy was also independent of the annual bluegrass variety and growth media (field soil vs. a sand–peat mixture). Preemergence activity of rimsulfuron against germinating annual bluegrass seeds was slightly greater in the sand–peat mixture than in the soil and with var. annua than with var. reptans, and on uncovered seed compared with 0.5-cm-deep growth media covered seeds.

Glyphosate effectively controls most weeds in glyphosate-resistant soybean. However, it is sometimes only marginally effective on Ipomoea spp. A field experiment was conducted at five locations in North Carolina to determine the effects of mixing 2,4-DB with glyphosate on Ipomoea spp. control and on soybean injury and yield. The isopropylamine salt of glyphosate at 560, 840, and 1,120 g ai/ha controlled mixtures of tall morningglory, entireleaf morningglory, and red morningglory at least 96% at two locations. Mixing the dimethylamine salt of 2,4-DB at 35 g ae/ha with glyphosate did not increase control but reduced soybean yield 6%. At two other locations, 2,4-DB increased control of tall morningglory and a mixture of entireleaf morningglory and ivyleaf morningglory 13 to 22% when mixed with glyphosate at 560 g/ha, but not when mixed with glyphosate at 840 or 1,120 g/ha. Soybean yield was reduced 31% at one location and was unaffected at the other. At the fifth location, 2,4-DB increased control of tall morningglory 25, 11, and 7% when mixed with glyphosate at 560, 840, and 1,120 g/ha, respectively. Soybean yield was increased 15%. In separate field experiments, glyphosate at 560, 840, and 1,120 g/ha controlled large crabgrass at least 99%. Mixing 2,4-DB at 35 g/ha with glyphosate did not affect control. In the greenhouse, mixing 2,4-DB at 35, 70, 140, or 280 g/ha with glyphosate at 70 to 560 g/ha did not affect large crabgrass control by glyphosate.

Glyphosate-resistant corn was no-till planted into alfalfa that was in the early bud stage (UNCUT) or had been cut 3 to 4 d earlier and baled for hay (CUT). Alfalfa control and corn yield were measured in nontreated plots as well as plots treated with glyphosate alone or tank-mixed with 2,4-D or dicamba applied at planting (AP) or POST. Alfalfa control was greater for all AP treatments of UNCUT compared to CUT alfalfa. Glyphosate plus dicamba applied AP controlled alfalfa better than the other AP treatments resulting in increased corn yield compared with other AP treatments. Postemergence applications of glyphosate alone or tank-mixed with 2,4-D or dicamba controlled alfalfa better 6 weeks after treatment than AP applications of the same herbicides; however, corn yield for AP treatments were similar or greater than the yield of POST applications of the same herbicides. Corn yield averaged 13% higher following herbicide applications to UNCUT compared with CUT alfalfa, so the value of alfalfa hay must be weighed against the loss of corn yield when making decisions concerning the management of an alfalfa–corn rotation.

Field research was conducted to determine effects of application rate, spray adjuvants, and spray carriers on visible control of downy brome, jointed goatgrass, and cheat and potential injury to wheat by MON 37500. MON 37500 at 24 and 46 g/ha with and without a methylated seed oil or nonionic surfactant and carriers of water, urea ammonium nitrate (UAN), and a 1:1 water/UAN combination were applied to the weeds at the one- to four-leaf stage. Cheat was the most susceptible weed to MON 37500, with control consistently above 87% with all treatments except MON 37500 at 24 g/ha in water 26 weeks after treatment. Downy brome control was more variable, with ratings ranging from 50 to 99% among treatments. For jointed goatgrass, only moderate stunting was observed from all MON 37500 applications. Both wheat varieties showed early season injury after MON 37500 was applied with UAN and either adjuvant; however, no visible injury or yield reduction to either wheat variety was noticed at harvest.

Glyphosate is often mixed with residual herbicides to control emerged weeds in no-till crop production systems. Field studies were conducted in Ohio from 1992 to 1994 to evaluate the weed control provided by residual herbicides and reduced rates of glyphosate in full-season, no-till soybean. Herbicide treatments were applied at two timings to examine the effect of weed size. At 4 wk after treatment, greater than 85% Pennsylvania smartweed control was obtained with metribuzin plus chlorimuron and linuron plus chlorimuron applied with 280 g ai/ha glyphosate and with imazethapyr and imazaquin applied with 560 g/ha glyphosate. All residual herbicides provided at least 85% common lambsquarters control when applied with 560 g/ha glyphosate. In 1992, the early application of residual herbicides provided this level of common lambsquarters control without glyphosate due to the small weed size at the time of application. Residual herbicides applied with 280 g/ha glyphosate controlled giant foxtail 85% or greater. Higher glyphosate rates were needed to control barnyardgrass. The performance of reduced glyphosate rates was dependent on weed species and weed size.

Field experiments were conducted at Hays and Manhattan, KS, in 2002 and 2003 to determine winter wheat response to simulated drift rates of glyphosate and imazamox. Glyphosate and imazamox at 1/100×, 1/33×, 1/10×, and 1/3× of usage rates of 840 g ae/ha glyphosate and 35 g/ha imzamox were applied individually to wheat in the early jointing or the early flower stages of growth. Wheat injury and yield loss increased as herbicide rate was increased, with minimal effect from either herbicide at the 1/100× rate, and nearly complete kill and yield loss of wheat from both herbicides applied at the 1/3× rate, regardless of growth stage at application. In general, wheat injury and yield reduction were greater from glyphosate than from imazamox. In addition, wheat injury and yield loss were greater from herbicide treatment at the jointing stage than at the flowering stage of development. Correlation analysis suggests that visual injury is an accurate indicator of yield reductions. Germination tests of harvested grain showed that the viability of the wheat seed was not reduced if plants survived the herbicide treatment and produced a harvestable seed.

Turfgrass managers often desire to overseed thin areas during midsummer or late summer, but seeding desirable species too soon after a preemergence herbicide application can interfere with seedling growth. This study was conducted to compare the effects of three herbicides on Kentucky bluegrass seedling growth and to determine whether seeding method affects the interval before seeding can safely occur. Dithiopyr, prodiamine, and pendimethalin were applied to ‘Kentucky 31’ tall fescue plots in late April at 0.56, 0.84, and 3.36 kg ai/ha, respectively. At 2, 4, 8, 12, and 16 wk after treatment, soil cores were extracted from each plot, the existing turf was killed, and the cores were either broadcast seeded or slit seeded with Kentucky bluegrass. Slit seeding resulted in greater and more extended seedling growth suppression than broadcast seeding for all herbicides. Prodiamine suppressed Kentucky bluegrass seedling growth longer than dithiopyr and pendimethalin. Unacceptable seedling growth suppression occurred unless broadcast seeding was delayed for about 6, 8, and 14 wk after dithiopyr, pendimethalin, and prodiamine application, respectively. The required interval between herbicide application and slit seeding was approximately 11, 10, and 16 wk, respectively. Use of dithiopyr or pendimethalin rather than prodiamine and broadcast seeding instead of slit seeding allows earlier overseeding with Kentucky bluegrass.

Annual bluegrass and roughstalk bluegrass are turfgrasses, but they can also be two of the most serious weed problems in highly maintained turfgrass. Ethofumesate has been used to control annual bluegrass; however, the results have been erratic, and ethofumesate is not widely utilized for annual bluegrass control in turfgrass. The objective of this research was to characterize the response of annual, roughstalk, and Kentucky bluegrasses and creeping bentgrass to a range of ethofumesate rates. Single applications of ethofumesate from 3.4 to 20.2 kg ai/ha were made to all four species during May of 1999 to 2001. All four species were injured from rates of ≥6.7 kg/ha. Roughstalk bluegrass was most injured by a single ethofumesate application. Percent roughstalk bluegrass control increased linearly with rate, and greater than 85% control was observed for rates of ≥16.8 kg/ha. In contrast, annual bluegrass showed almost no control, with rates ≤10.2 kg/ha, and the highest rate tested, 20.2 kg/ha, controlled only 47 to 62% of the annual bluegrass. Kentucky bluegrass was the least sensitive bluegrass species, with a maximum control of 3 to 15% from 20.2 kg/ha of ethofumesate. Creeping bentgrass was the least sensitive of the species tested, with low levels of control regardless of rate. During 3 yr of testing, maximum control of bentgrass from any rate was 4%. Single, high-rate applications of ethofumesate hold promise to control roughstalk bluegrass in creeping bentgrass turf. Sixteen Kentucky bluegrass cultivars used for low-cut athletic fields were evaluated for their tolerance to sequential ethofumesate applications during 1999 and 2002. The cultivars showed significant differences in ethofumesate tolerance, with ‘Moonlight’ and ‘America’ never showing any injury to sequential ethofumesate applications, while ‘Northstar’ and ‘Total Eclipse’ were severely injured.

Kyllinga squamulata has become problematic in bermudagrass turf in recent years, probably related to shifts in herbicide use strategies. Preemergence and postemergence greenhouse and field herbicide studies evaluated K. squamulata control in bermudagrass turf. Excellent (≥90%) postemergence control at 6 wk after initial treatment (WAIT) followed single and sequential applications of imazaquin at 0.42 kg ai/ha, MSMA plus imazaquin at 1.12 + 0.42 kg ai/ha, and sulfentrazone at 0.56 kg ai/ha. In one of two experiments, unacceptable (>30%) bermudagrass injury occurred with imazaquin at 0.42 and 0.56 kg ai/ha and MSMA plus imazaquin at 1.12 + 0.42 kg ai/ha 1 wk after application; however, plots recovered fully by 2 wk. In the field at 18 WAIT, preemergence control of greater than 70% was obtained with a single application of oxadiazon at 1.12 or 2.24 kg ai/ha and sequential applications of 1.12 kg ai/ha each 8 wk apart. Sequential applications 8 wk apart of sulfentrazone at 0.28 followed by 0.28 kg/ha also provided greater than 70% preemergence control. In two greenhouse studies, oxadiazon at 2.24 kg/ha and sulfentrazone at 0.56 kg/ha provided greater than 90% preemergence control.

Two studies were conducted near Bronson, MI, to determine gladiolus tolerance and weed control with flumioxazin and other herbicide treatments. The first study was conducted in 2002, 2003, and 2004 to evaluate weed control and gladiolus injury with flumioxazin and 14 other preemergence treatments. Crop injury over the 3-yr period was less than 6% and was considered commercially acceptable with flumioxazin, linuron, oryzalin, pendimethalin, prometryn, S-metolachlor, and sulfentrazone. Gladiolus stand count, height, and flower count were similar to those of the nontreated control with these treatments. Clomazone, halosulfuron, imazamox, imazapic, mesotrione, oxyfluorfen, rimsulfuron, and trifloxysulfuron resulted in unacceptable crop injury. Of the acceptable treatments, only flumioxazin controlled common ragweed, yellow nutsedge, and foxtail species at least 68%. The second study was conducted in 2003 and 2004. Flumioxazin was evaluated at four rates, in mixtures with S-metolachlor and oryzalin, and in comparison with isoxaben plus oryzalin. Gladiolus injury did not exceed 6%. Common ragweed, annual grass, and yellow nutsedge control were at least 63% with all flumioxazin treatments.