Field experiments showed that quackgrass could be controlled by glyphosate applied preharvest to barley. In separate experiments, field mint was controlled by glyphosate applied pre- and postharvest to barley and wheat. Suppression of quackgrass regrowth one year following treatment was 90% or greater when glyphosate was applied at 0.9 kg ai/ha alone or at 0.45 kg ai/ha in combination with both tallow amine ethoxylate at 0.5% of total spray volume and ammonium sulfate at 3 kg/ha. Field mint shoot counts were reduced 84% the year following treatment when glyphosate was applied at 0.25 kg ai/ha and 95% when applied at 1.0 kg ai/ha. Suppression of field mint shoot regrowth the following year was 84% when glyphosate was applied postharvest and 93% when applied preharvest. Addition of tallow amine ethoxylate did not improve field mint control. Glyphosate applied preharvest to barley and wheat at less than 30% grain moisture content had no effect on grain yield.

Imidazolinone-resistant and -tolerant corn hybrids give growers a new weed control option. Field experiments were conducted in 1993 and 1994 to evaluate imazethapyr for controlling weeds in no-till corn planted into winter wheat stubble in a winter wheat–ecofallow corn rotation. Imidazolinone-tolerant (IT) and imidazolinone-resistant (IR) corn were protected genetically from injury by imazethapyr that was applied preplant, preemergence, or postemergence to ‘Pioneer Brand 3417,’ ‘Pioneer Brand 3417 IR,’ ‘ICI Seeds 8532,’ and ‘ICI Seeds 8532 IT’ hybrids. No difference in corn injury occurred between IR and IT corn. Imazethapyr applied to resistant or tolerant corn hybrids could be used to control weeds in ecofallow corn. Imazethapyr at 35 or 70 g ai/ha controlled triazine-resistant kochia better than the standard herbicide treatment of metolachlor plus cyanazine.

Field studies were conducted to evaluate preemergence weed control in irrigated potatoes with rimsulfuron plus metribuzin or three-way mixtures of rimsulfuron plus metribuzin plus EPTC, metolachlor, or pendimethalin. Redroot pigweed control was ≥ 96% with rimsulfuron plus metribuzin at 18 g ai/ha + 140 g/ha, and common lambsquarters control was ≥ 97% with rimsulfuron plus metribuzin at 26 g/ha + 210 g/ha. Hairy nightshade control with rimsulfuron plus metribuzin ranged from 58 to 99%, and green foxtail control ranged from 50 to 98%. EPTC, metolachlor, or pendimethalin rates required for acceptable green foxtail and hairy nightshade control in combination with a given rate of rimsulfuron plus metribuzin varied with environmental conditions. Potato tuber yield generally improved with rimsulfuron plus metribuzin application.

Experiments were conducted to compare barnyardgrass control and rice injury and yield with emulsifiable concentrate and dry flowable formulations of propanil as single or repeat applications with crop oil concentrate, methylated seed oil, a blend of organosilicone surfactant and methylated seed oil or conventional nonionic surfactant, and organosilicone surfactant. Two applications of propanil were more effective in controlling barnyardgrass than a single application. The emulsifiable concentrate formulation of propanil controlled barnyardgrass more effectively than the dry flowable formulation in some but not all experiments. Differences in barnyardgrass control with propanil as influenced by adjuvants were minor and inconsistent. The most consistent barnyardgrass control and the highest rice yields were obtained with repeat applications of the emulsifiable concentrate formulation of propanil.

Cyanobacteria (blue-green algae) are undesirable in ponds used to raise fish for human food. Management of cyanobacterial communities in aquaculture ponds has been hindered by the small number of herbicides approved for use in food-fish ponds and by the lack of selectivity toward cyanobacteria for those herbicides that are approved for that use. To facilitate development of additional management options, a rapid bioassay utilizing 96-well cell culture plates was developed for screening herbicides and other phytotoxins for selective toxicity toward cyanobacteria. Oscillatoria cf. chalybea and Selenastrum capricornutum were chosen as representatives of cyanobacteria (Cyanophyta) and green algae (Chlorophyta), respectively. In the bioassay, wells of the cell culture plates were inoculated with cyanobacterial or unialgal culture. One of five herbicides (atrazine, diuron, endothall, fluridone, or paraquat) was then added to the wells at various concentrations, and absorbance (650 nm) was measured at 24-h intervals. Growth of treated cultures relative to untreated cultures was used to determine relative toxicity of the herbicide to the two organisms. Paraquat was the most selective of the herbicides tested and was over 10-fold more toxic to O. cf. chalybea than to S. capricornutum. This method was demonstrated to be a rapid, effective, and highly reproducible bioassay to identify selective algicides.

Field and greenhouse experiments evaluated the differential response of 15 green pea varieties to metribuzin applied preemergence. ‘Charo,’ ‘CMG 298,’ ‘Leah,’ ‘Scout,’ and ‘Puget’ were the most tolerant, whereas ‘Bolero’ and ‘Sundance’ were the most susceptible varieties under greenhouse conditions. Variable chlorophyll fluorescence (Fv), efficiency of photosystem II (Fv/Fmax), and leaf area were reduced sharply by metribuzin in susceptible varieties, and metribuzin susceptibility correlated highly with the reduction in shoot dry weight. Green pea varieties grown under field conditions responded to metribuzin similarly to pea varieties grown under greenhouse conditions. Metribuzin reduced shoot dry weight more in peas grown at 30/25 C than in those grown at 25/20 and 20/15 C. Also, metribuzin injured peas more when grown in soil saturated to field capacity compared to soil at 70 and 40% of field capacity.

Experiments were conducted to test the accuracy of a global positioning system (GPS) in measuring the area of simulated weed patches of varying size and to determine the accuracy in navigating back to particular points in a field. Circular areas of 5, 50, and 500 m2 were established and measured using point and polygon features of a GPS. The GPS estimations of the area of those patches had errors ranging from 7 to 45%, 6 to 15%, and 3 to 6%, respectively, when compared to actual measurements. As patch size increased, errors decreased. A curve describing the relationship between GPS error and patch size had an excellent fit (r2 = 0.92). The error remained the same in all measurements across all patch sizes, but composed a smaller percentage of large patches. The GPS had submeter accuracy in navigation to the correct quadrat 73% of the time, located the correct quadrat 27% of the time, and invariably navigated to within 1.58 m of the correct quadrat. The relationship between patch size and measurement error was applied to natural infestations of hemp dogbane.

Twelve grass genotypes were evaluated for competitiveness with leafy spurge and herbage yield in two sites in North Dakota. ‘Rebound’ smooth brome, ‘Rodan’ western wheatgrass, ‘Bozoisky’ Russian wildrye, and ‘Arthur’ Dahurian wildrye reduced leafy spurge stem density an average of 63% after 3 yr in a silty clay soil at Fargo. ‘Reliant’ intermediate wheatgrass reduced leafy spurge stem density every year for 3 yr, including an 85% reduction the second year after planting, and consistently produced high herbage yields. Rebound smooth brome and Reliant intermediate wheatgrass averaged 72% leafy spurge reduction 3 yr after seeding in a loamy sand soil at Jamestown. Reliant intermediate wheatgrass and ‘Manska’ pubescent wheatgrass provided the most consistent herbage production, which averaged about 2,000 kg/ha annually for 3 yr.

Herbicides play an important role in the production of nursery crops by reducing weed problems and improving production efficiency. Herbicides applied to nursery crops may move in runoff water into retention basins, which are used to irrigate container plants. Studies investigated the growth and development of containerized landscape plants subjected to irrigation water containing herbicide residues. Containerized dwarf gardenia, Snow azalea, Buccaneer azalea, Hellers Japanese holly, fountain grass, and daylily were grown in fine pine bark medium in the greenhouse and were irrigated with water containing 1 mg/L and 10 mg/L of oryzalin, oxyfluorfen, and isoxaben. Fountain grass and daylily were the most sensitive to herbicide application with reduced root and shoot growth. Oryzalin was the most phytotoxic to fountain grass followed by oxyfluorfen and isoxaben. Oryzalin and oxyfluorfen at 10 mg/L reduced the growth index of fountain grass. Oryzalin was the most phytotoxic herbicide to daylily, followed by isoxaben and oxyfluorfen. Only the high rate (10 mg/L) of oryzalin reduced the growth index of daylily. Among woody species, the root weights of Hellers holly were reduced by 10 mg/L of isoxaben. The growth of other woody species was not affected by the herbicides.

We examined whether image analysis could separate leafy spurge from other plant species and objects by comparing image analysis to the ocular method of estimating cover. Image analysis was acceptably precise at low and medium cover levels. Image analysis was as repeatable as the ocular method at all sites and cover levels and acceptably reliable at low and medium cover levels but estimated cover lower by 12 to 22% than the ocular method at high cover levels. The average error levels of image analysis and the ocular method did not differ. Estimating leafy spurge cover with a 10% error required only 20 quadrats when image analysis was used, while twice as many quadrats were needed when cover was measured ocularly. Image analysis was recommended as a measurement tool because quantification was efficient, the equipment is inexpensive, and the color prints provide a permanent photo record of the study.

Eleven field experiments were conducted during 1994 and 1995 to compare rhizomatous johnsongrass control and soybean yield with single POST applications of quizalofop-P, fluazifop-P, clethodim, and sethoxydim at costs of $9.88, 19.76, 29.64, and 39.52/ha for each graminicide. Cost of the manufacturer's suggested use rate for these graminicides was approximately $29.64/ha, which corresponded to 0.09, 0.22, 0.14, and 0.27 kg ai/ha for these respective graminicides. When applied at a cost of $9.88/ha, quizalofop-P controlled rhizomatous johnsongrass more effectively than the other graminicides in five of 11 experiments. Quizalofop-P and fluazifop-P controlled johnsongrass similarly when applied at higher costs per hectare in 10 of 11 experiments. Sethoxydim was less effective than quizalofop-P or fluazifop-P in most instances, especially when graminicides were applied at costs of $9.88 or $19.76/ha. Clethodim was generally more effective than sethoxydim. Fluazifop-P and clethodim controlled rhizomatous johnsongrass similarly in six of 11 experiments regardless of cost. Differences in rhizomatous johnsongrass control among graminicides did not always translate into differences in soybean yield, although graminicides increased yield over the nontreated control in most experiments regardless of the graminicide cost. In several experiments, soybean treated with clethodim or sethoxydim applied at a cost of $9.88/ha yielded lower than when applied at higher costs.

Field experiments were conducted from 1993 to 1995 to evaluate the response of ALS-resistant and ALS-susceptible corn to imazethapyr, imazaquin, chlorimuron, and CGA-152005 at label and twice label rates applied preplant incorporated (PPI) and postemergence (POST). The susceptible hybrid (P3245) and the resistant hybrid (P3245IR) grain yield were not different where weeds were removed by hand-weeding alone. Alachlor plus atrazine alone plus hand-weeding reduced grain yield by 5% compared to hand-weeding only. Imazethapyr applied PPI and POST reduced height of the susceptible hybrid 11 and 6%, respectively, averaged across imazethapyr rates. Imazaquin reduced the final height of the susceptible hybrid by 30 to 75% and reduced corn density by 62 to 78%. Chlorimuron applied PPI reduced final corn height of the susceptible hybrid by 26 to 36% and density by 27%. Chlorimuron applied PPI and imazaquin applied PPI and POST reduced grain yield of the susceptible hybrid. Imazethapyr did not reduce grain yield of the susceptible hybrid, regardless of application timing or rate. Imazethapyr, imazaquin, and chlorimuron did not reduce height, density, or grain yield of the resistant hybrid, regardless of application timing or rate. CGA-152005 applied PPI reduced grain yield of the susceptible and resistant hybrid. CGA-152005 applied POST did not reduce grain yield, regardless of hybrid or rate.

Agricultural production in China occurs via three distinct organizational units: the countryside farmer, state farms, and military farms. The countryside farmer in northeast China carries out most production operations with hand tools, some animal and tractor power, and little additional mechanization. Most weeds in row crops are controlled by hand, although a high percentage of the rice crop is treated with herbicides as is about 20% of the wheat. Countryside farmers independently manage small plots of land. State and military farms, the majority of which are located in China's northeastern-most province of Heilongjiang, are highly mechanized and accomplish most weed control with herbicides. Military farms range from ~500–2,500 ha, and state farms generally occupy 50,000–100,000 ha, with some much larger. Primary crops on the military farms are soybeans, oilseed rape, and wheat. State farms generally have more diversity in crops. The need for herbicide adjuvants to increase postemergence (POST) herbicide efficacy and for reduced tillage practices to combat soil erosion are recognized concerns, as is the threat of herbicide resistance.

Oviposition site preferences for Galerucella calmariensis and G. pusilla, biological weed control agents against purple loosestrife, were examined in 1994 and 1995. The leaves, stems, axils, and flower buds (G. pusilla did not oviposit on flower buds) were found to be the preferred oviposition sites. Oviposited egg masses may be used as a parameter within a biological control monitoring plan, providing information on Galerucella establishment and/or presence, estimating future population size, and providing biological control agent dispersal information. Monitoring for egg masses should concentrate on host plant leaves, where over 56% of all egg masses were oviposited.

Although economic thresholds are often used to make insect control decisions, the use of thresholds for weed management has been limited. Surveys of growers, agricultural chemical dealers, and farm managers/rural appraisers helped identify limitations to grower acceptance of economic thresholds for weed management. Most growers were concerned about harvest problems due to weeds, with 64% identifying this factor as a major limitation. Landlord perception and weed seed production were identified by 38% of the growers as major limitations, while 36% of the growers listed general appearance of the field as reasons. In contrast, 75% of the agricultural chemical dealers and 63% of the farm managers surveyed listed field appearance as a major reason limiting grower acceptance of economic thresholds for weed management. Since grower concerns involve risk management and future profitability, economic weed thresholds that address long-term costs and benefits of weed control decisions may be more fully accepted.

Characterization of herbicide dissipation under field conditions is an important component in determining the environmental impact of herbicides, and much information is available on this subject. However, this research area could be improved by standardizing and implementing several quality control procedures. The purpose of this review is to evaluate the recent literature on herbicide dissipation published in journals of the Weed Science Society of America. This review is not comprehensive with respect to all experimental parameters associated with field dissipation studies, but it is aimed at addressing specific areas of concern in the experimental approach to this research.

The sedge genus Kyllinga consists of 40 to 45 species distributed in tropical, subtropical, and warm temperate regions around the world (KUkenthal 1936; Tucker 1987). This genus of low rhizomatous perennials or cespitose annuals is classified in the large cosmopolitan family Cyperaceae. Many Kyllinga species are considered weedy (Holm et al. 1979; Tucker 1987), while Kyllinga nervosa Steudel is considered an important forage plant in Africa (McNaughton 1985).

Fumitory (Fumaria officinalis L.) is a member of Fumariaceae, a family of annual and perennial herbs, whose best-known genera, in addition to Fumaria, are Corydalis and Dicentra (bleeding heart and Dutchman's breeches). Fumariaceae is mainly a temperate family that embraces 16 genera and 400 species. Economically, its use is limited to garden ornamentals (Heywood 1993). Brummitt (1992) and Hyam and Pankhurst (1995) place fumitory in Papaveraceae, but most authorities, including Mabberley (1989), put it in Fumariaceae.