Greenhouse and field studies were conducted to examine weed control with, and potato tolerance to, rimsulfuron or rimsulfuron + metribuzin applied POST. In greenhouse trials, hairy nightshade control with rimsulfuron applied POST at 9 to 35 g/ha was ≥ 90%, but cutleaf nightshade control was < 30%. In field studies, rimsulfuron at 18 to 35 g/ha provided ≥ 85% control of hairy nightshade, redroot pigweed, tumble pigweed, and shepherd's-purse; 75 to 82% control of volunteer oats; and 25 to 87% control of common lambsquarters. Common lambsquarters control was increased to 92 to 100% when rimsulfuron at 18 to 35 g/ha was applied in combination with metribuzin at 280 g/ha. Hairy nightshade and redroot pigweed control usually were not improved by adding metribuzin to the rimsulfuron spray mixture and tumble pigweed and shepherd's-purse control were improved only slightly. Volunteer oat control with rimsulfuron sometimes was antagonized by the addition of metribuzin to the spray mixture. In weed-free trials, yield of potatoes grown for the fresh market or to produce seed tubers was not reduced by rimsulfuron at rates as high as 70 g/ha.

Seven annual weed species were treated under greenhouse conditions with six rates of either nicosulfuron, rimsulfuron, or a 1:1 mixture (DPX-79406). Herbicide rates in g ai/ha producing 90% dry biomass reduction (GR90) were calculated for each weed species. Accordingly, weeds were classified as very susceptible when GR90 ≤ 9, susceptible when 9 < GR90 ≤ 18, moderately susceptible when 18 < GR90 ≤ 27, and tolerant when, GR90 > 27. Giant and green foxtails were very susceptible to the three herbicides. Proso millet was very susceptible to rimsulfuron and DPX-79406, and susceptible to nicosulfuron. Wild oat was susceptible to nicosulfuron and DPX-79406, and moderately susceptible to rimsulfuron. Redroot pigweed was very susceptible to nicosulfuron; whereas, it was susceptible to rimsulfuron and DPX-79406. Common ragweed and smooth crabgrass were tolerant to the three herbicides. In a second experiment, we used regression estimate analysis with an additive reference model to evaluate nicosulfuron and rimsulfuron interaction on corn, soybean, common ragweed, and smooth crabgrass. We found these herbicides synergistic on smooth crabgrass, antagonistic on soybean, less than additive on common ragweed, and additive on corn.

Field trials were conducted in New Jersey during 1991 and 1992 to evaluate the efficacy of nicosulfuron, primisulfuron, dicamba, and clopyralid on horsenettle control in field corn. Horsenettle biomass was reduced 74%, 68%, 64%, 61%, 48%, and 40% by primisulfuron + dicamba, primisulfuron, nicosulfuron + dicamba, dicamba, clopyralid, and nicosulfuron, respectively. No treatment was statistically more effective than dicamba. Corn yields were not influenced by the herbicide treatments. Horsenettle populations were not reduced by any treatment.

The basidiomycete fungus, Chondrostereum purpureum Fr. Pouzar, has been found to be a good potential bioherbicide candidate for control of hardwood vegetation in forests. However, its interaction with some agrochemicals that are normally employed in forest protection was not known. Employing two concentrations (0.01% v/v and 0.1% v/v) of several agrochemicals, a laboratory study was conducted to assess their impacts on the infective mycelia. Except for Bond, and Suntan gel-2, most adjuvants, sunscreen agents, and pesticides (herbicides, fungicides, and insecticides) were fungitoxic at 0.1%. Fungitoxicity was concentration dependent and the results indicate that the possibility of tank-mixing the basidiomycete with agrochemicals appears limited and the possibility of agrochemical residue effects on survival of the basidiomycete is implied.

Field studies were conducted during two soybean-corn rotations to evaluate the effect of tillage systems on quackgrass growth and control with and without glyphosate. In the final year of the study, tillage alone (compared to no-till) resulted in 88%, 78%, 64%, and 31% control of quackgrass with fall moldboard plow, spring moldboard plow, fall soil-saver, and spring soil-saver tillage, respectively. When glyphosate was used to control quackgrass, crop yields increased as tillage was reduced and excellent control of quackgrass in no-till was achieved. Increased shoot growth (in moldboard plowed and fall soil-saver tillage plots), exposure of rhizomes in winter (in fall tilled plots), and increased depth of rhizome burial (in spring tilled plots) increased quackgrass control. In general, the total biomass of quackgrass was reduced in drier years. Nonetheless, drought increased crop yield losses caused by quackgrass interference.

The availability of postemergence grass control herbicides can prevent dependence on potentially unnecessary preemergence herbicides. No postemergence grass control herbicides have federal registration for kenaf in the United States. This research was conducted to collect data to support such registration. Clethodim, fluazifop, quizalofop, and sethoxydim applied at three rates did not injure established kenaf, reduce plant populations, reduce plant heights, or reduce stalk yields.

The effects of metribuzin herbicide and phorate insecticide were studied on summer harvest chipping-potatoes at Muscatine, IA, from 1989 to 1991. Phorate at 1.5 kg/ha increased total and ‘A’-size tuber yield and tuber specific gravity. Metribuzin applied at 0.56 kg/ha postemergence decreased total and ‘A’-size tuber yield. Metribuzin applied at 0.56 kg/ha preemergence and 0.28 kg/ha postemergence did not reduce Atlantic cultivar yield. Metribuzin did not affect ‘B’-size tuber yield or specific gravity. Phorate in combination with metribuzin did not increase plant injury or reduce tuber yield.

Understanding the biology of tropical soda apple (TSA) is necessary to develop effective control strategies. Tropical soda apple seedling emergence, growth, and regeneration from roots were evaluated. Plant growth (height, leaf number, flowering) was monitored over 110 d in a greenhouse experiment. Emerged seedlings required 83 d to reach a height of 40 cm and 108 d to flower. Total nonstructural carbohydrate concentrations in TSA root and stem fractions, monitored monthly for 1 yr, were highest in December (35%-root, 18%-stem). Seedling emergence as affected by planting depth (0, 1, 2, 4, 8 cm) and regeneration from root segments (7.5, 15 cm long) placed on the soil surface and 5 and 10 cm deep were studied in separate greenhouse experiments. Seedling emergence was lowest (P < 0.05) for seed placed on the soil surface (6.9%) and at a depth of 8 cm (19.4%) with the highest level of TSA emergence predicted at 63% for seed planted 3.6 cm deep. Regeneration from roots was higher (P < 0.05) for the 15-cm root segments than for the 7.5-cm segments while depth of root segment placement did not affect regeneration. Weed control strategies should involve cultural and chemical practices that affect both roots and seeds.

Kansas and North Dakota kochia populations identified as chlorsulfuron resistant (R) contained 20 and 30% susceptible (S) plants, respectively. Biotypes that were chlorsulfuron R or S were selected from each field R or S collection and selfed through three generations in the greenhouse. Chlorsulfuron at 7.6 and 17.8 g ai/ha suppressed shoot biomass of the Kansas and North Dakota R biotypes by 50%, respectively, which was a 30- and 105-fold greater dose than that required to reduce the respective S biotypes growth 50%. The R and S kochia biotypes are diploid with 2N = 18 chromosomes. Chlorsulfuron resistance is inherited in kochia as a dominant trait controlled by a single nuclear gene. Thus, the resistance trait can be spread by seed and pollen.

The effectiveness of single and repeated annual preharvest glyphosate applications (1 to 2 wk before crop harvest) to reduce Canada thistle populations was evaluated in field experiments near Bezanson, AB, Scott, SK, and St. Albert, AB. Single applications of glyphosate at 0.45 to 1.8 kg/ha at Bezanson and St. Albert reduced Canada thistle shoot density by more than 75% but in the three experiments at Scott 1.8 kg/ha was required to consistently obtain a similar reduction. Four consecutive, annual applications of glyphosate at 0.45 kg/ha or more did not eliminate Canada thistle but reduced shoot densities by more than 98% at Bezanson. At Scott, similar reductions occurred in two of three sites following two consecutive, annual preharvest applications of glyphosate at the same rates. In the third Scott site the 1.8 kg/ha rate of glyphosate provided a similar reduction but lower rates did not. At Bezanson, barley yields following the first, second, and third applications of glyphosate at 0.45 kg/ha or more were 14% greater than check plots where MCPA was applied in the spring. Yields of wheat seeded 1 yr after a single application of glyphosate at St. Albert were 26% greater than from unsprayed checks. Barley yields seeded 1 yr after each glyphosate application at Scott were not affected because Canada thistle populations were sparse.

In field studies effective dogfennel control was obtained with glyphosate, dicamba + 2,4-D, triclopyr + 2,4-D, and fluroxypyr at rates of 1.68, 0.44 + 1.25, 0.56 + 1.12, and 0.28 kg ai/ha, respectively, applied after dogfennel was 75 cm tall. Mowing alone reduced dogfennel regrowth by 81% and when combined with dicamba + 2,4-D or triclopyr + 2,4-D regrowth was reduced over 94%. Triclopyr, dichlorprop, and sulfometuron also controlled dogfennel greater than 90% but metsulfuron did not.

In growth chamber research, infection by Puccinia punctiformis, a rust fungus, reduced flowering and vegetative reproduction in Canada thistle. Disease symptoms were greatest when Canada thistle roots were stored at 5, 10, or 15 C following inoculation. Exposure of roots to different temperatures before inoculation did not affect disease. All Canada thistle clones tested, regardless of gender became diseased although there were differences in susceptibility to P. punctiformis.

Experiments were conducted to determine the efficacy of imidazolinone and sulfonylurea herbicides applied alone or in combination to control leafy spurge. Imazapyr (840 g ai/ha), imazethapyr (140 g/ha), sulfometuron (100 g/ha), and chlorsulfuron (20 g/ha) were applied in the fall on rangeland sites near Ainsworth and Columbus, NE. Imidazolinone and sulfonylurea herbicide combinations did not improve leafy spurge control nor affect forage grass yields when compared with herbicides applied alone. Imazapyr and sulfometuron were the most efficacious, providing greater than 80% leafy spurge control 9 mo after treatment (MAT). Imazethapyr provided 80% control of leafy spurge 9 MAT when applied to a coarse textured, low organic matter soil. In contrast, leafy spurge control was only 15% when imazethapyr was applied to a fine textured soil. Chlorsulfuron did not control leafy spurge, regardless of site characteristics. Imazapyr reduced perennial grass yields by more than 60%.

Laboratory, greenhouse, and field experiments were conducted at the Lacombe Research Station to determine if CCC, ethephon, or CCC/ethephon had direct activity on quackgrass rhizome buds, and to determine if foliar applications of CCC/ethephon could predispose quackgrass to more effective control with sethoxydim. CCC, ethephon, and CCC/ethephon had growth regulating effects on the axillary buds and the apex of detached quackgrass rhizomes. CCC increased rhizome bud sprouting on rhizomes with the apex excised, but not on rhizomes with an intact apex. Ethephon or CCC/ethephon inhibited bud sprouting on rhizomes with an intact or excised apex. CCC/ethephon, but not CCC or ethephon alone, increased rhizome elongation on rhizomes with intact apices. In the greenhouse, pretreatments of CCC/ethephon increased sethoxydim activity on quackgrass rhizome buds and caused lower shoot emergence from one-bud rhizome segments. Results of field experiments were less consistent than those in the greenhouse. However, sometimes CCC or CCC/ethephon pretreatments resulted in increased quackgrass control in the field with sethoxydim.

Research was conducted in central Georgia to determine the influence of norflurazon on bermudagrass stand and production when applied to newly sprigged bermudagrass and in the spring to dormant bermudagrass. Norflurazon at rates up to 1.12 kg ai/ha on newly sprigged bermudagrass caused moderate chlorosis to the emerging leaves but did not adversely influence stand density or ground cover at 60 and 90 days after treatment (DAT). Norflurazon applied to dormant bermudagrass the spring of 1993 resulted in greater than 50% foliage chlorosis at rates ≥ 1.68 kg/ha. Foliage chlorosis was 94% on bermudagrass treated with 3.36 kg/ha 30 DAT and at spring growth initiation. However, chlorosis level was reduced when bermudagrass began rapid growth. Forage production was not influenced by the early season chlorosis when compared to nontreated areas or areas treated with diuron at 1.12 kg/ha and the weed free check.

Field studies were conducted in 1988/89 and 1989/90 at two locations to determine the effect of rye, wheat, and triticale cover crop mulches on weed emergence patterns, weed biomass, and soybean development. Redroot pigweed and common lambsquarters emergence patterns were not altered by mulches. Early in the season, mulches reduced weed biomass; however, the results were inconsistent between locations and years. Under weed-free conditions, the cover crop mulches had no detrimental effects on soybean development and yields were not different from bare soil controls.

The leaves of tall morningglory, giant duckweed, and common purslane were treated with nine surfactants at a concentration of 0.1% and examined after 24 hr using cryo-scanning electron microscopy for phytotoxicity as evidenced by tissue damage and epicuticular wax morphology changes. In some instances, tissue damage could be discerned; however, the effects of a particular surfactant were not uniform across the three species. Morphological alteration of epicuticular waxes was not observed. Gas chromatographic analyses of the epicuticular waxes of the species used in the study reveal component differences and may, in part, explain the lack of uniform response across species for a particular surfactant.

In greenhouse experiments, unrefined corn oil was tested as an adjuvant with the mycoherbicidal fungus, Colletotrichum truncatum. A1:1 (V/V) fungus/corn oil tank mixture extended by at least 70 h the period of time in which the fungus remains infective between inoculation and the onset of dew. This formulation also reduced the dew period requirements for optimal weed pathogenesis and mortality from 12 h to 2 h, and reduced the required spray volume by 100-fold, from 500 L/ha to 5 L/ha. These results suggest that formulating C. truncatum in unrefined corn oil greatly improves the bioherbicidal potential of this pathogen.

Field studies were conducted in 1990 and 1991 at Davis and Five Points, CA to evaluate weed control with napropamide and hand-weeding and the effect on yield and profitability in transplanted bell pepper. Weed cover 8 wk after transplanting averaged less than 10% in plots hand-weeded biweekly for 6 wk after transplanting. Weed cover at harvest was less than 30% in plots hand-weeded at 8 wk after transplanting. Napropamide treatment reduced weed cover at 8 wk after transplanting an average of 34% compared to untreated plots, but differences declined to 14% at harvest. Time required to hand-weed plots was greater if the interval between weeding was 4 instead of 2 wk. The time needed to hand-weed plots was reduced from 38% to 71% by napropamide treatment. When weeds were excluded by hand-weeding for the entire season, bell pepper yielded 25 810 kg/ha and was 4% to 18% higher than other treatments. Net returns were greater for plots that were hand-weeded the entire season or when napropamide was combined with hand-weeding at 4 and 8 wk after transplanting, compared to other treatments.