Metolachlor, oryzalin, and napropamide when chemigation-applied controlled large crabgrass more effectively than when spray applied in container-grown azalea, liriope, and Japanese holly. Oxadiazon and oxyfluorfen were equally effective as chemigation or spray applications. Azaleas were generally more susceptible to contact injury from sprays of oxadiazon and oxyfluorfen and large crabgrass interference than were holly and liriope.

In field studies conducted in 1984, 1985, and 1986, annual grass control by a microencapsulated (ME) formulation of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] generally was greater than that by the emulsifiable concentrate (EC) in no-till and was comparable to EC-alachlor in conventionally tilled corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.]. In 1986, ME-metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] controlled annual grass similar to EC-metolachlor. In greenhouse studies, shoot height and fresh weight of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] sown in pots and treated with ME-alachlor was significantly greater than that treated with EC-alachlor. Soybean straw on the soil surface did not affect the differences between alachlor formulations in the greenhouse.

Field studies were conducted from 1982 to 1984 to evaluate the effectiveness of SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate) and glyphosate [N-(phosphonomethyl)glycine] for quackgrass [Agropyron repens (L.) Beauv. # AGRRE] control. The herbicides were compared 1) in different rates and carrier volumes, 2) on several spring and fall application dates, and 3) with varying time intervals between application and moldboard plowing. Glyphosate and SC-0224 controlled quackgrass equally well at carrier volumes of 25 to 400 L/ha. Both herbicides generally provided similar control as fall and spring applications and with time intervals of 12 to 96 h between application and plowing. Occasionally the low rate of SC-0024 gave less quackgrass control the next season than the same rate of glyphosate. Adding nonionic surfactant at 0.5% (v/v) did not influence the phytotoxicity of these herbicides at the rates and carrier volumes tested. These herbicides controlled quackgrass comparably and greater than 85% when applied under appropriate environmental conditions.

Chloramben effectively controlled weeds in lettuce and endive grown on muck soils better than thiobencarb and chlorpropham. Chloramben at 1.1 kg ai/ha controlled two weeds economically important on muck soils, livid amaranth and oakleaf goosefoot. Chloramben applied preemergence at 1.1 kg/ha and higher caused early stunting of lettuce which the lettuce outgrew by harvest. Field-seeded endive was stunted severely at these same rates, severely reducing yield. Transplants improved tolerance of all crops. Effective use rates on muck soils were 25% to 50% of those typically used on mineral soils.

Multiflora rose is a major weed in pastures, highway embankments, and recreational areas. A chalcid wasp, Megastigmus aculeatus (Swederus) (Hymenoptera: Torymidae), which feeds on the multiflora rose seeds, is a potential biological control agent for this weed. Distribution of multiflora rose and the seed wasp was studied from 1983 to 1986 in Virginia. Multiflora achenes collected from 58 sites in 51 counties showed that M. aculeatus was present in all but one of the counties surveyed; female:male sex ratio was high (94:1), indicating parthenogenesis. Infestation rates of the achenes averaged 26.5% in 1985 and 23.9% in 1986. Severe winter temperatures appear to affect the wasp population adversely.

The effects of rainfall on the efficacy of 11 foliar-applied herbicides were evaluated for their control of seedling johnsongrass [Sorghum halepense (L.) Pers. # SORHA] in greenhouse experiments during 1984 and 1985 at Stoneville, MS. Time intervals between herbicide application and rainfall (at 1.27 cm in 10 ± 0.5 min) ranged from 5 to 60 and 30 to 240 min depending on herbicide classification. In general, the phosphonic acid herbicides glyphosate [N-(phosphonomethyl)glycine] and SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate) at 0.99 kg ai/ha required rain-free periods ≥240 min to control seedling johnsongrass effectively. The selective postemergence grass herbicides generally required ≥60 min to control seedling johnsongrass effectively when control without rainfall was ≥85%. Among the selective herbicides tested, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} and DPX-Y6202 {ethyl[2-[4-(6-chloro-2-quinoxalinyl)oxy] phenoxy] propionic acid} at 0.06 kg ae/ha required the shortest time between herbicide application and rainfall to be effective. As herbicide rates were reduced, the effects of rainfall increased.

Two years of field research were conducted to determine the additive effects of weed cover and insects on pepper production. When weeds covered less than 10% of test plots, the natural insect populations reduced the marketable fruit yield of bell peppers 32% in 1983 and 22% in 1984. When weeds covered 72 or 94% of the test plots, foliage damage due to insects was from 5.8 to 12.1%, respectively. The high percent weed cover and insects reduced yield 99%. The average fresh weight of pepper foliage approached zero as weed cover approached maximum. Foliar levels of iron and aluminum were reduced greatly in peppers grown in competition with a 100% weed cover. The level of boron, copper, phosphorus, and potassium in pepper foliage increased as percent weed cover increased.

Field research was conducted in 1983 and 1984 at Scottsbluff, NE, to determine the effect of cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methyl-propanenitrile} applied in corn (Zea mays L. ‘Pioneer 3732’) on fieldbeans (Phaseolus vulgaris L. ‘Valley’) planted 30 days later to replace corn. Cyanazine preplant incorporated at 1.1 kg ai/ha or higher reduced the vigor, stand, and yield of fieldbeans as a replant crop.

Conservation tillage systems for cotton production were monitored for their influence on horseweed populations. Without fall tillage, horseweed became established and was present the following spring. Disking in the fall or spring controlled horseweed for the subsequent cotton crop.

Velvet lupine planst were defoliated (50% of upper foliage) in 1983 and 1984 to determine total alkaloid concentration (TAC), percent crude protein (CP), and fiber in regrowth foliage. TAC in regrowth leaves was 15% lower than in the original leaves removed at the beginning of the study. Percent CP of regrowth leaves was 22% lower than in original defoliated leaves. Alkaloids and CP did not increase in response to defoliation stress from simulated herbivory as plant defense theories predicted.

A technique based on the relationship between leaf area index (LAI) and the transmittance of direct sunlight was developed for the in situ study of competition for light between plant species. Field studies were conducted in 1984 and 1985 using monocultures and mixtures of rapeseed (Brassica napus L.), wild mustard (Sinapis arvensis L. # SINAR), and common lambsquarters (Chenopodium album L. # CHEAL). LAI estimated nondestructively by this method agreed closely with LAI determined by conventional destructive techniques. Light measurements at several heights in the canopy were used to determine the vertical distribution of canopy leaf area. Combining this information with species heights allowed the separation of the canopy LAI into individual species LAI, from which light competition could be estimated by calculating the sunlit LAI of each species. The technique permits many detailed measurements in the same canopy throughout the growing season. The light sensor required is not costly and is simple to operate and to maintain.

The butoxyethyl ester of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} was more effective than either the triethylamine salt formulation or an equivalent combined rate of the butoxyethyl esters of triclopyr plus 2,4-D [(2,4-dichlorophenoxy)acetic acid] (1:2, w/w) for the control of Virginia creeper [Parthenocissus quinquefolia (L.) Planch. # PRTQU]. Carrier volume did not affect 14C-triclopyr absorption and distribution, but control generally was greater after high carrier-volume application (281 L/ha) because the dense Virginia creeper canopy was thoroughly penetrated. In orchards, Virginia creeper was controlled by triclopyr ester at 0.6 kg ae/ha through the second season after treatment if foliage was covered thoroughly.

Field experiments were conducted to determine the effects of tank-mix and sequential postemergence (POE) applications of the insecticides carbaryl and dimethoate with sethoxydim on large crabgrass control and cotton tolerance. Large crabgrass control was similar with sethoxydim and sethoxydim-dimethoate tank mixtures. Although tank mixing carbaryl with sethoxydim reduced control, it was not reduced when carbaryl was applied 2 days before or 2 days after applying sethoxydim. Neither the insecticides nor sethoxydim applied alone or as tank mixtures injured cotton or affected lint yield, percent lint, fiber length, fiber length uniformity, fiber strength, or micronaire.

Field studies were conducted to measure the response of sorghum [Sorghum bicolor (L.) Moench. ‘Conlee's Top Hand’] to foliar applications of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} or fluazifop-P {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} plus either bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] at 0.84 kg ai/ha imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} at 0.21 kg ae/ha, or chlorimuron {2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl) amino] carbonyl] amino] sulfonyl] benzoic acid} at 12 g ae/ha. Tank-mixing imazaquin or chlorimuron with haloxyfop or fluazifop-P reduced phytotoxicity to sorghum 12 days after treatment (DAT) by 14 to 64% compared to applications of haloxyfop or fluazifop-P alone. Much of this antagonism was reduced 24 DAT as imazaquin and chlorimuron apparently delayed the activity of haloxyfop and fluazifop-P when losses in activity ranged from 13 to 21%. Increases in haloxyfop and fluazifop-P rates tended to reduce the severity of the antagonism. Tank-mixing bentazon with haloxyfop or fluazifop-P did not reduce phytotoxicity to sorghum compared to applications of haloxyfop and fluazifop-P alone.

In a 3-y field study, the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] at 1.7 kg ai/ha and sulphosate [trimethyl sulfonium salt of N-(phosphonomethyl)glycine] at three rates, a split application of 0.6 + 0.6 or single applications of 1.1 or 1.7 kg ai/ha satisfactorily controlled swamp dodder (Cuscuta gronovii Willd. ex R. & S. # CVCGR) in cranberry (Vaccinium macrocarpon Ait.). While none of these treatments decreased cranberry yield, sulphosate at 1.1 or 1.7 kg/ha did increase yield. Glyphosate at 0.4 kg/ha applied late in the life cycle of carrot (Daucus carota L.) when swamp dodder was in full flower satisfactorily controlled swamp dodder while increasing yield of carrot roots. Glyphosate applied early in the life cycle of carrot and dodder controlled swamp dodder but lowered yield of carrot roots.

The soil-borne fungus, Fusarium solani (Mart.) App. & Wr. f. sp. cucurbitae, has shown potential as a mycoherbicide to control Texas gourd. Formulations and times of application that effectively controlled Texas gourd were determined in field studies. Aqueous conidial suspensions (1 × 108 microconidia/ml) were applied preplant incorporated, postemergence, or both at 280 L/ha alone or combined with trifluralin at 1 kg ai/ha. Alginate granules containing fungal spores and hyphae and amended with 2% (w/v) soyflour were applied pre- or postemergence at 220 kg/ha alone or sequentially with conidial applications. Mortality of 70% or greater was achieved with eight of nine fungal treatments. The fungus applied as conidia combined with trifluralin, as well as trifluralin alone, significantly reduced Texas gourd emergence.

Laboratory experiments with 14C-herbicides were conducted with grain sorghum as an indicator species to determine the effects of imposed moisture stress on absorption, precent recovery, and acropetal and basipetal translocation of the butyl ester of fluazifop, the methyl ester of haloxyfop, the ethyl ester of quizalofop, and sethoxydim. Haloxyfop was the only herbicide where recovery decreased between the 3-and 48-h interval. All plants absorbed more of the herbicide at the 48-h interval than at the 3- or 6-h interval under both stressed and non-stressed conditions. Increased drought stress caused more acropetal movement with fluazifop and sethoxydim and less acropetal movement with quizalofop at the 3-h interval. Basipetal transloation, although different among herbicides, responded similarly to imposed moisture stress, which decreased basipetal translocation approximately 19%.

Backcross-derived isolines of soybean [Glycine max (L.) Merr.] cultivars with and without the Rps1-k gene for resistance to Phytophthora rot (Pythopthora megasperma f. sp. glycinea) were grown in hydroponic culture with and without metribuzin [4-amino-6-(1,1-dimethylethyl)-3-3(methylthio)-1,2,4-triazin-5(4H)-one] added at 0.15 mg L−1. A marked tolerance to metribuzin was associated with Rps1-k possibly from an allele at the Hm/hm locus which is known to be linked closely with the Rps1 locus. This improved tolerance could reduce the occurrence of injury from metribuzin applications.

The response of irrigated spring barley (Hordeum vulgare L. ‘Steptoe’) to broadleaf herbicides applied at three growth stages was studied at Torrington, WY, in 1984 and 1985. Dicamba (3,6-dichloro-2-methoxybenzoic acid), dicamba plus 2,4-D [(2,4-dichlorophenoxy)acetic acid], and dicamba plus MCPA [(4-chloro-2-methylphenoxy)acetic acid] visibly injured barley when applied at all growth stages. These same treatments reduced barley height when applied at the 2- to 4-leaf and fully tillered stages. Yield differences among treatments were not significant. However, kernels/spike and kernel weight were reduced by dicamba or dicamba plus MCPA when applied at the fully tillered or boot stages, and test weight was reduced when dicamba was applied at all growth stages. Seed protein content did not differ in 1984. However, several herbicide treatments increased seed protein in 1985, especially when applied at the boot stage. Proline or lysine content did not differ among treatments.

Field studies on time of emergence, influence of planting date on growth and reproduction, and winter survival of rhizomes were conducted on sorghum-almum grown in corn and crop-free environments. In 1985, peak emergence of sorghum-almum occurred during early May in crop-free plots and mid-May in corn. In 1986, two peaks of emergence, one in early June and one in late June, were noted in both crop-free and corn plots. Emergence after mid-July was 4% or less of the total emerged in 1985, and no sorghum-almum emerged after mid-July in 1986. In planting date studies, sorghum-almum was seeded alone or in corn at 2-week intervals. Corn competition reduced sorghum-almum shoot, rhizome, and root growth at all planting dates. Maximum sorghum-almum seed production was 43 110 seed/plant when grown without competition but only 1050 seed/plant when grown with corn competition. When grown with corn competition, no seed developed on sorghum-almum seeded 6 or more weeks (mid-June or later) after corn planting. Shoot dry weight of sorghum-almum grown with corn competition was 3 g/plant or less for plants seeded 4 or more weeks (early June or later) after corn planting. Therefore, controlling sorghum-almum in corn through mid-June should prevent seed production and corn yield losses due to sorghum-almum competition. Rhizomes produced by sorghum-almum grown alone or with corn competition did not survive the winter; therefore, in Minnesota, sorghum-almum survival from one growing season to the next depends on seed production.