A field experiment was conducted in 1986 and 1987 to determine the minimum effective rate (MER)3 of imazaquin and chlorimuron applied postemergence to common cocklebur. MER is defined as the quantity required to provide at least 90% control. Based on probit regression analyses, the mean calculated MERs of imazaquin and chlorimuron for 2-leaf common cocklebur were 27.5 and 4.5 g ai/ha, respectively. Under optimum growing conditions, the calculated MERs of imazaquin and chlorimuron for 6-leaf common cocklebur were 34 and 4.6 g/ha, respectively. When applied to 6-leaf plants under slight moisture stress, the calculated MERs for imazaquin and chlorimuron were 54 and 17.4 g/ha, respectively.

The objective of this study was to determine how selected herbicides affect sod tensile strength and rooting of mature and immature turfs of ‘Tifway’ bermudagrass. Both immature and mature turf had 100% ground cover, but only mature turf had tensile strength adequate for harvesting and handling. Sod tensile strength at 2, 4, and 8 weeks after application generally was unaffected by herbicide treatment, although imazapyr killed bermudagrass top growth. Root number and root length initially were depressed by imazapyr, bensulide, napropamide, sethoxydim, and sulfometuron at most rates and intervals tested. Eight weeks after treatment, root length, root number, and sod tensile strength for all treatments, except those with imazapyr, were similar to that of the untreated control.

The weed control spectrum of clomazone, the influence of clomazone on the performance of other herbicides, and the performance of tank mixtures containing clomazone were evaluated from 1985 through 1987. Clomazone applied preemergence at 280 g ai/ha controlled 90 to 100% of barnyardgrass, giant foxtail, goosegrass, large crabgrass, seedling johnsongrass, prickly sida, and velvetleaf. Clomazone at reduced rates was more effective applied preemergence than preplant-incorporated for 10 of 23 weed species. Clomazone enhanced imazaquin activity on entireleaf morningglory and sicklepod in 1986. A tank mixture of clomazone, imazaquin, and metribuzin at half the labeled rates reduced soybean injury, increased soybean yield, and controlled weeds as well as the mixture at labeled rates.

Field trials were conducted in 1985, 1986, and 1987 to identify effective herbicide treatments to control mayweed chamomile in winter wheat. Dicamba at 280 g ae/ha, 2,4-D at 560 g ae/ha, and bromoxynil at 560 g ai/ha did not control 11-cm-tall or larger mayweed chamomile and inconsistently controlled smaller plants. Mayweed chamomile control generally declined with increasing weed size. DPX-M6316 at 8.8 g ai/ha and DPX-L5300 at 4.4 g ai/ha controlled 89% or more mayweed chamomile. CGA-131036 at 4.9 g ai/ha controlled 95% or more mayweed chamomile. DPX-M6316, DPX-L5300, and CGA-131036 controlled 3- to 18-cm-tall mayweed chamomile similarly.

Barnyardgrass and bearded sprangletop are severe weed pests in rice in the southern United States. These weeds are controlled with standard herbicide programs of propanil alone or propanil combined with pendimethalin or thiobencarb. However, new herbicides, such as fenoxaprop, may be effective alternatives for grass weed control in rice. Fenoxaprop at 0.17 kg ai/ha applied postemergence in programs with propanil, thiobencarb, or pendimethalin controlled barnyardgrass and bearded sprangletop in rice and performed as well as or better than standard treatments of propanil with thiobencarb or pendimethalin. Rice yielded well, and grain was of high quality.

The potential diversity in tolerance of eight commercial sugarcane cultivars to metribuzin, terbacil, and hexazinone was investigated. Herbicides were applied preemergence in the fall after planting and postemergence to the crop in the spring each year over the 3-yr crop cycle. Reductions in shoot counts and heights were not observed with any of the herbicide treatments in the fall following planting. Cultivar differences in growth and yield responses were obtained, particularly in the plant cane year of the 3-yr crop cycle. Metribuzin was the least phytotoxic and hexazinone the most phytotoxic. Reductions in sugar yields (kg/ha) were attributed to reductions in stalk populations and, to a lesser extent, to reductions in stalk height and sugar (sucrose) content. Cultivars sensitive to hexazinone either were equally sensitive to terbacil or were less sensitive to terbacil. Terminal fluorescence (FT)3 measurements indicated that photosynthesis following postemergence applications of terbacil and hexazinone was no longer inhibited 5 weeks after treatment in the tolerant cultivars, CP 70–321 and CP 74–383, but continued to be reduced in the cultivars showing sensitivity, CP 65–357 and CP 48–103. The order of cultivar tolerance to hexazinone and terbacil from least tolerant to most tolerant is CP 48–103 < CP 65–357 ≤ CP 72–370 < CP 70–321 = CP 70–330 < CP 72–356 = CP 73–351 = CP 74–383.

Field experiments were established to evaluate preemergence and postemergence herbicides for control of triazine-resistant smooth pigweed and common lambsquarters in no-till corn. When applied preemergence, alachlor in the microencapsulated formulation controlled smooth pigweed better than the emulsifiable concentrate formulation and better than either metolachlor or pendimethalin. These herbicides applied preemergence did not control common lambsquarters consistently. Pendimethalin controlled both triazine-resistant species when applied as a sequential treatment of a preemergence and an early postemergence application. Control of triazine-resistant smooth pigweed and common lambsquarters was excellent when dicamba was applied early postemergence in treatments containing alachlor, metolachlor, or pendimethalin applied preemergence and/or early postemergence. Thiameturon and CGA-131036 controlled triazine-resistant smooth pigweed with acceptable crop tolerance. Thiameturon also controlled common lambsquarters, but control was unacceptable with CGA-131036.

The interaction of DPX-A7881 and clopyralid applied as tank mixtures was studied under controlled environment and field conditions on several commonly occurring weeds in canola. Control of wild mustard and wild buckwheat was not affected by mixing these herbicides. DPX-A7881 controlled wild mustard, and clopyralid controlled wild buckwheat independently of the other herbicide. However, redroot pigweed and common lambsquarters were controlled better with DPX-A7881 plus clopyralid than with either herbicide alone. The herbicides interacted in an additive to synergistic manner on redroot pigweed depending on the rate of each herbicide. DPX-A7881 and clopyralid interacted synergistically at all rates on common lambsquarters. Plant height, date of flowering, seed yield, and quality data all indicated that canola completely tolerated DPX-A7881 and clopyralid applied alone or in combination.

Field experiments were conducted in 1986 and 1987 to evaluate the effect of herbicide rate (two-thirds and maximum labeled rate) and timing of application before soybean planting on common cocklebur control. In 1986, chlorimuron plus metribuzin at 50 plus 320 and 80 plus 480 g ai/ha and imazaquin at 90 g ai/ha applied at planting controlled common cocklebur better than when applied 4 weeks before planting (WBP). Imazaquin at 140 g/ha applied at planting controlled common cocklebur better than when applied 6 WBP. All treatments at two-thirds of the labeled rate applied at planting controlled common cocklebur comparable to the full labeled rate applied 2, 4, or 6 WBP. In 1987, all treatments applied 2 WBP controlled common cocklebur better than when applied 4, 6, or 8 WPB.

Velvetleaf, eastern black nightshade, wild mustard, common cocklebur, green foxtail, and yellow foxtail, grown for 4 weeks in nonaerated nutrient solution, developed satisfactorily compared to plants grown in soil. For experiments involving certain weed species grown in nutrient solution, aeration may be unnecessary.

The growth of loblolly pine seedlings was reduced by interference from bermudagrass, tall fescue, and broomsedge. The order for treatment influence on pine seedling growth rate measurements was tall fescue > bermudagrass > broomsedge > weed free for the 2-yr study. The increase in height of seedlings for the weed free, broomsedge, bermudagrass, and tall fescue was 4.1, 2.9, 1.9, and 1.1 cm/month, respectively; and the average increase in seedling stem diameter was 1.3, 0.5, 0.4, and 0.2 mm/month, respectively.

Germination stimulants were tested for effectiveness on velvetleaf seed imbibition and germination and concurrent microbial attack of seed to deplete weed seed in soil. Several chemicals increased in vitro seed germination and decreased the numbers of hard, viable seed. The proportion of nonviable seed, 5% with Fusarium oxysporum (Schlech.), was enhanced to 40% by adding ethephon at 100 μg/ml. Fungal density on seedling roots and imbibed (nonviable seed) was increased by chemical treatment. Seedling emergence was reduced 15% when ethephon or carbofuran was applied to soil with the fungus. Shoot dry weight decreased and root infection increased with all treatments regardless of fungal inoculation. Butylate and carbofuran increased infection of imbibed seed in soil by F. oxysporum while ethephon and AC94377 increased infection by other soil fungi.

Wheat that emerged with alfalfa seeded in the field in late August grew for 20 days after planting without suppressing the alfalfa but reduced yields if allowed to grow with alfalfa for 30 or more days. Uncontrolled wheat reduced the first cutting yield of alfalfa by 80% or more. Sethoxydim at 0.4 kg ai/ha, fluazifop at 0.2 kg ai/ha, and haloxyfop at 0.2 kg ai/ha controlled wheat selectively in alfalfa. Herbicides applied 20 days after seeding protected alfalfa from suppression by wheat. Control of wheat was equal when herbicides were applied 30 days after seeding, but in 1 of 2 yr, the wheat had suppressed the alfalfa enough to reduce yields the following May.

Stipa clandestina Hackel, a native of northern Mexico, has been found in Texas and may become a serious weed problem for range managers in the southwest. Its sharply pointed leaves and tussock-forming habit make it unpalatable to cattle, but in Mexico it tends to increase with heavy grazing or disturbance. Actively growing plants can be killed by applying a foliar spray of either glyphosate or hexazinone.

Clomazone is effective as a chemical fallow herbicide; however, its soil residual properties in the Northern Great Plains are unknown. Clomazone was applied to soil at 0.6, 1.1, and 2.2 kg ai/ha at two locations in Montana in the spring of 1986. Soil samples were taken at each location at monthly intervals for 6 months. Residual levels of the herbicide were estimated by measuring the percent chlorosis by height in oat leaves. Clomazone at 2.2 kg ai/ha applied to a loam soil dissipated to levels below 0.1 mg/kg in 3 months and applied to a silty clay loam soil dissipated to 0.2 mg/kg 6 months after application. Half-lives (t½), determined from first-order rate plots, were 33 and 37 days in the Willow Creek loam and Bozeman silty clay loam, respectively. Thus, clomazone residue from labeled-use rates should not inhibit wheat in a wheat-fallow-wheat cropping system in Montana.

Multiflora rose was defoliated completely 320 days after spring foliar application of metsulfuron. Metsulfuron and 2,4-D plus dicamba spring foliar applied controlled multiflora rose equally. Metsulfuron applied to soil using a spotgun at 20 mg per m diam of multiflora rose in the spring resulted in 95% control 320 days later in one study but only 50% control in another. Control was less when lower rates of metsulfuron were soil-applied with a spotgun. Tebuthiuron spring soil-applied completely controlled multiflora rose. All spring-applied foliar and soil applications seemed to control multiflora rose better than fall treatments.

Alachlor plus linuron tank mixed with paraquat and applied preemergence (PRE) did not control giant foxtail all season in full-season no-till soybeans. Alachlor applied early preplant (EPP) plus PRE was necessary to control (>70%) giant foxtail acceptably all season. Metolachlor applied PRE or EPP plus PRE were equally effective in controlling giant foxtail (71 to 74%). Oryzalin at 1.7 or 2.2 kg ai/ha applied fall or spring EPP controlled giant foxtail better than 70% through July. Oryzalin applied PRE did not control giant foxtail acceptably.