Field and greenhouse studies were conducted to evaluate annual bluegrass (Poa annua L. # POAAN) control and phytotoxicity of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] to selected warm- and cool-season turfgrass species. Annual bluegrass control in non-overseeded dormant hybrid bermudagrass [Cynodon dactylon (L.) Pers. X C. tranvaalensis Burtt-Davy Tifgreen’ # CYNDA] was 75% or greater with at least two ethofumesate applications at monthly intervals starting in December. Tifgreen bermudagrass spring growth was delayed with more than two applications of ethofumesate at 1.1 kg ai/ha, or when the second application was made after January. Under greenhouse conditions the growth of both Tifgreen and Tifdwarf bermudagrass was less when treated with ethofumesate. Stand and shoot growth of 29 cultivars of ryegrass (Lolium spp.), bluegrass (Poa spp.), bentgrass (Agrostis spp.), and red fescue (Festuca rubra L. # FESRU) were reduced by ethofumesate at 1.1 kg/ha as a preemergence or split (0.5 kg/ha preemergence + 0.5 kg/ha postemergence) application. Postemergence applications were less phytotoxic to cool-season turfgrasses than preemergence applications. Perennial ryegrass stands were generally not reduced by postemergence application of ethofumesate at 1.1 kg/ha. However, shoot growth of perennial ryegrass was reduced.

In field and greenhouse studies, tank mixing 0.3 and 0.4 kg ai/ha of the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} with 0.4 kg ai/ha of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} reduced control of large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] and itchgrass (Rottboellia exaltata L.f. # ROOEX) compared to fluazifop applied alone in soybeans [Glycine max (L.) Merr.]. Less antagonism between the two herbicides was observed in a year when conditions were optimum for large crabgrass control with fluazifop. Application of acifluorfen 1 to 3 days before application of fluazifop decreased large crabgrass control. Antagonism between fluazifop and acifluorfen was avoided when fluazifop was applied 3 to 5 days before acifluorfen. No antagonism was observed when fluazifop at 0.3 or 0.4 kg/ha was tank mixed with acifluorfen at 0.4 kg/ha for control of itchgrass. Itchgrass was more susceptible to fluazifop than large crabgrass.

The phytotoxicity of seven herbicides after soil application was determined in the field and greenhouse. Clopropoxydim {(E,E)-2-[1-[[(3-chloro-2-propenyl)oxy] imino] butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, sethoxydim {2-[1-(ethoxyimino)butyl]-5-(2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} applied to soil at 0.21 kg/ha, and the methyl ester of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}applied to soil at 1.12 kg/ha were phytotoxic to oats (Avena sativa L. ‘Moore’) in the field and greenhouse. These rates are equivalent to postemergence use rates of these herbicides. DPX-Y6202 {2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid} and the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} applied to soil at 0.84 kg/ha or greater were phytotoxic to oats. The ethyl ester of fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy] phenoxy] propanoic acid} soil applied exhibited very limited phytotoxicity to oats. Oat stands were reduced when oats were seeded into soil treated with clopropoxydim, sethoxydim, haloxyfop, diclofop, DPX-Y6202, fluazifop, and fenoxaprop, with the amount of stand reduction decreasing from clopropoxydim to fenoxaprop. Oat fresh weight reductions were greatest with all herbicides when the herbicides were in contact with all underground parts (shoots, seeds, and roots). Oat fresh weight reductions were greater when either the shoot or seed of the germinating oat plants were exposed to the herbicides compared to root exposure. Foxtail millet (Setaria italica L. ‘Siberian’) was more susceptible to injury than oats or wheat (Triticum aestivum L. ‘Len’) when seeded into soil treated with any one of the seven postemergence grass control herbicides.

Total alkaloid concentration, percentage water, crude protein, and neutral detergent fiber in velvet lupine (Lupinus leucophyllus Dougl. # LUPLE) were monitored for 3 weeks following application of herbicides registered or soon to be registered for rangeland use. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), dicamba (3,6-dichloro-2-methoxybenzoic acid), and clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) caused some signs of epinasty but did not kill velvet lupine. Total alkaloid concentration and nutrient quality of velvet lupine leaves treated with these herbicides was not significantly different from untreated plants. Esters of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid} killed most velvet lupine plants and caused a subsequent decrease in total alkaloid concentration, crude protein, and water content as the plants desiccated. Herbicides that effectively killed velvet lupine decreased alkaloid levels, thus lowering the potential for increased livestock poisoning.

The effects of the dimethylamine salt of dicamba (3,6-dichloro-2-methoxybenzoic acid) and the dimethylamine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] on fieldbeans (Phaseolus vulgaris L. ‘Great Northern Valley’) were studied in order to assess the potential hazards of using these herbicides in areas adjoining fieldbean production. Dicamba and 2,4-D were applied to fieldbeans at three different rates (1.1, 11.2, and 112.5 g ai/ha) and four different growth stages (preemergence, second trifoliolate leaf, early bloom, and early pod). Application of 2,4-D preemergence or in the second trifoliolate leaf stage of growth did not reduce seed yield, delay maturity, or reduce germination of seed obtained from treated plants. Dicamba or 2,4-D applied at 112.5 g/ha to fieldbeans in the early bloom or early pod stages of growth consistently reduced seed yield, delayed maturity, and reduced germination percentage. Fieldbeans exhibited a greater overall sensitivity to dicamba than to 2,4-D.

Multiple applications of several preemergence herbicides were evaluated for weed control and for phytotoxicity to gladiolus (Gladiolus X hortulanus L.) grown from cormels in 1984 and 1985. Oryzalin [4-(dipropylamino)-3,5-dinitrobenzenesulfonamide] consistently provided acceptable control of southern crabgrass [Digitaria ciliaris (Retz.) Koel. # DIGSP], goosegrass [Eleusine indica (L.) Gaertn. # ELEIN], and smooth pigweed (Amaranthus hybridus L. # AMACH) and had minimal effect on gladiolus plant growth even after four applications. Pronamide [3,5-dichloro (N-1,1-dimethyl-2-propynyl)benzamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] provided erratic weed control and reduced yields of gladiolus corms.

Butylate [S-ethyl bis(2-methylpropyl)carbamothioate] persistence was compared in three soils that were treated annually with four thiocarbamate herbicides in 1981 and 1982. Butylate degraded faster in soils treated two consecutive years with butylate + dichlormid (2,2-dichloro-N,N-di-2-prophenylacetamide) than in soils treated for 2 yr with EPTC (S-ethyl dipropyl carbamothioate) + dichlormid, cycloate (S-ethyl cyclohexylethylcarbamothioate), vernolate (S-propyl dipropylcarbamothioate) + dichlormid, or from previously untreated soils. Butylate + dichlormid applications in 1981 and 1982 enhanced butylate degradation in 1983 at all locations and reduced weed control at two locations. Previously untreated soil or soil previously treated with two annual applications of butylate + dichlormid was treated with 6 ppmw butylate, incubated for 14 days, analyzed for residual butylate, and bioassayed for herbicide activity. Bioassay indicated higher herbicidal activity than was predicted by the residual butylate concentration. A herbicidally active metabolite may be produced during the soil degradation of butylate.

Field plot experiments were conducted to examine the interactions between tall fescue grass (Festuca arundinacea Schreb.), musk thistle (Carduus nutans L. = thoermeri Weinmann # CRUNU), and two thistle weevils Trichosirocalus horridus (Panzer) and Rhinocyllus conicus Froelich. Restriction of musk thistle growth was greatest when the weevils were allowed to feed on the musk thistles competing with tall fescue. Significant reductions were found in total musk thistle seeds per plant, root weight, flower buds per plant, stem dry weight, seeds per head, root crown diameter, stem height, rosette diameter, and head diameter. Seed weight and viability were not reduced. Of the three stress factors (tall fescue and the two Carduus thistle weevils), tall fescue had the greatest impact. When musk thistle seeds were planted in 1-yr-old tall fescue, germination was low. Seeds that germinated did not grow more than four Leaves and none of the thistles developed to the reproductive stage. A 1-year-old tall fescue stand effectively prevented musk thistle reproduction. Thus, tall fescue helped suppress musk thistle growth more quickly than the use of Carduus thistle weevils alone without competitive vegetation. Dry weight of tall fescue grass was lower in musk thistle-infested plots than in the thistle-free plots.

Grass and broadleaf weed densities and seed numbers, weed control practices, and grain yields were included in a bioeconomic model that evaluates alternative weed management strategies for continuous corn (Zea mays L.). Weed seed numbers in soil and herbicide carry-over provided intertemporal links. Four weed management strategies – two fixed, one mixed, and one flexible – were evaluated with annualized net returns as the performance indicator. The flexible strategy (weed control based on observed conditions) had the largest annualized net return for high and low initial weed seed numbers. The fixed weed management strategy (weed control predetermined) of an annual application of only a preemergence herbicide ranked second in terms of annualized net returns for high weed seed numbers. The mixed weed management strategy of alternative year applications of preemergence herbicide and “as needed” applications of postemergence herbicide ranked second for low initial weed seed numbers. The fixed weed management strategy of alternate year application of preemergence herbicide only generated the lowest annualized net return, regardless of initial weed seed numbers.