Dose-response experiments showed that three samples of green foxtail collected from fields in southern Manitoba where trifluralin had not controlled the weed in 1987 were resistant to the herbicide. GR50 values indicated that the resistant populations were about 5 times more resistant to trifluralin than susceptible populations, about twice as resistant as wild oat, and about equally resistant as wheat. An additional 33 samples collected in 1988 from southwestern Manitoba where trifluralin has been used for nearly 20 yr in both cereal and oilseed crops were resistant to trifluralin.

Glyphosate and SC-0224 at 75 or 150 g ae/ha, applied to alfalfa foliage after field dodder and largeseed dodder were parasitically well established, controlled dodder selectively. Glyphosate applied at any time over a range of developmental stages stopped the growth of dodder. Control was best when the herbicides were applied when alfalfa was 20 to 30 cm tall, when maximum length of dodder shoots was 30 to 60 cm, and while host and parasite were both vegetative and growing vigorously. Later application allowed dodder to injure alfalfa before being controlled, and earlier application sometimes allowed dodder to recover and suppress alfalfa before the hay was cut.

Established alfalfa treated with glyphosate at 75 or 150 g ae/ha (rates known to control dodder) during the vegetative or bud stage showed symptoms of narrowed leaves and mildly chlorotic new growth, and yield of one cutting of alfalfa usually was reduced by 10 to 20%. Glyphosate, applied in the vegetative stage, affected the treated foliage more than postharvest regrowth. Applied at bud stage, the regrowth that followed harvest of treated foliage was affected more. Symptoms and effect on yield were greater at 300 g ae/ha, but alfalfa always recovered. Applying glyphosate at 75 or 150 g ae/ha in each of two or three sequential cuttings showed no cumulative effect. Glyphosate and SC-0224 had similar effects on alfalfa and suppressed alfalfa much less than would a severe infestation of dodder.

Experimental objectives were to assess metribuzin tolerance of predominately privately developed soybean cultivars and to evaluate a greenhouse screening procedure. In field results in 1982, ‘Vinton 81’, ‘Northrup King 1884’ and ‘L77-1863’ soybean cultivars were extremely sensitive to metribuzin at 0.56 kg/ha, averaging 34% injury. The other 45 cultivars showed no significant injury at the 0.56 kg/ha rate, from 9 to 46% injury at 1.4 kg/ha, and 18 to 72% injury at 2.2 kg/ha. In greenhouse hydroponic studies, these same three soybean cultivars were killed, while the other 45 cultivars were injured from 15 to 82%. A good agreement of greenhouse and field data was determined, with a correlation coefficient of r = 0.82.

Effects and interactions of two soil temperatures, 19 ± 1 and 27 ± 3 C, and seven soil-applied herbicide treatments on the morphological development and concentrations of eight essential nutrients in leaves, stems, and roots of pinto beans were determined. Soil temperature did not affect overall plant morphology but did affect some nutrient concentrations in the roots, stems, and leaves. Combinations of alachlor plus trifluralin at 2.2 plus 0.28 kg ai/ha and EPTC plus trifluralin at 2.2 plus 0.28 kg ai/ha caused greater negative effects than when the herbicides were applied separately. Oryzalin at 0.56 kg ai/ha and EPTC at 3.4 kg ai/ha induced the least number of morphological effects, while alachlor at 3.4 kg ai/ha, chloramben at 2.2 kg ai/ha, and trifluralin applied at 0.56 kg ai/ha produced an intermediate number. Alachlor, trifluralin, and combinations of alachlor plus trifluralin and EPTC plus trifluralin inhibited nodule growth. Each herbicide affected different nutrients. Alachlor plus trifluralin affected the level of each nutrient in at least one plant tissue. Many herbicide-soil temperature interactions occurred.

Two field studies were conducted to compare bentazon tolerance in “Bohemian Chili” (BCH) and “Keystone Resistant Giant” (KRG) with other pepper cultivars and plant introductions (PIs). In the first study, BCH, KRG, “Santaka” (SA), and “Sweet Banana” (SB) were treated with five rates of bentazon from 1.1 to 9.0 kg ai/ha. Based on foliar injury, the cultivars ranked BCH = SA < KRG < SB; based on yield tolerance to bentazon, they ranked KRG ≤ SB < SA ≤ BCH. In the second study, the response of BCH, KRG, SA, SB, and five PIs to 4.5 kg/ha bentazon showed that 3 PIs (127445, 163187, 246123) tolerated bentazon similarly to BCH and SA.

Experiments are conducted to evaluate the tolerance of three deciduous species: black locust, honeylocust, apple, and three coniferous species: Douglas fir, ponderosa pine, and Japanese black pine, in the seedling stage to napropamide. Deciduous species were more susceptible to napropamide than coniferous species. Domestic apple had the slowest seed germination and root development and was more susceptible. The deciduous species had more secondary roots in the shallow soil layer which contained most of the herbicide than the coniferous species. The roots of all woody species tested in vitro were inhibited significantly by contact with the herbicide, but only shoot growth of domestic apple and black locust was inhibited. Injury to woody nursery crop seedlings may be avoided by delaying herbicide application.

Linuron, metribuzin, oryzalin, and dinoseb were evaluated for weed control in conventional (CT) and rye-stubble reduced-tillage (RT) systems for potatoes. Early season control of weeds was equivalent for all herbicides in both tillage systems. In 1985, redroot pigweed populations were significantly greater in RT than in CT control plots. Populations of common lambsquarters were equivalent, regardless of the tillage system. In 1986, the rye mulch reduced early emergence of both species in untreated RT plots when compared to the untreated CT controls. During both seasons, potato stands decreased 16% with RT. In 1985, total yields did not differ between tillage systems; however, in 1986, total potato yields in RT plots decreased an average of 22% compared to yields in CT plots.

Imazethapyr at 0.05 to 0.14 kg ai/ha applied preplant incorporated, preemergence, and postemergence was evaluated alone and with complementary herbicides in the field for weed control in soybean. Imazethapyr controlled 90% or more smooth pigweed regardless of application method or herbicide rate. Imazethapyr at 0.05 kg/ha controlled jimsonweed 30% better postemergence compared to soil applications. Imazethapyr at 0.10 kg/ha controlled 90% or more velvetleaf regardless of application method. The addition of alachlor to soil-applied imazethapyr enhanced giant foxtail, jimsonweed, and velvetleaf control. Adding acifluorfen or bentazon to postemergence imazethapyr antagonized weed control. Adding sethoxydim to postemergence imazethapyr was not beneficial.

Tolerance of tomato cultivars to diphenyl ether herbicides applied postemergence was determined in greenhouse and field experiments. In greenhouse experiments, tomato cultivar tolerance differed, but acifluorfen injured all genotypes. ‘Carmen’, ‘PetoPride 2’ and ‘Heinz 1350’ tolerated acifluorfen while ‘Advantage’, and ‘Red Plum’ were susceptible. Growth habit and tolerance to 1.1 kg ae/ha acifluorfen was significantly correlated (r2 = 0.24). Field-planted tomato cultivars' tolerance to diphenyl ether herbicides applied postemergence differed. Heinz 1350 and ‘Veeroma’ tolerated diphenyl ethers, while Advantage and Red Plum were susceptible. Potency of diphenyl ethers also varied with oxyfluorfen the most injurious and acifluorfen and fomesafen the least injurious.

Five broadleaf crops, alfalfa, peanut, soybean, tobacco, and tomato, were tested for their susceptibility to three broomrape species, branched, Egyptian and crenate, in the greenhouse. All five crop species were parasitized by one or more broomrape species. Peanut plants were most susceptible and soybean plants were least susceptible to parasitism by broomrape. Egyptian and branched broomrapes had a wider host range affecting plants in both the Solanaceae and Fabaceae. Crenate broomrape mainly infected plants belonging to Fabaceae, except for the few attachments to tomato and tobacco. Apparently, this is the first report on parasitism of peanut plants by branched broomrape and that of peanut and alfalfa plants by crenate broomrape. Parasitism of soybean plants by any of the broomrape species also was observed for the first time in these experiments. These results indicate that broomrapes, although not a major problem on any of the crops in the United States, could parasitize several major broadleaf crops should the parasite become established.

Rhizome johnsongrass control with sethoxydim and clethodim was evaluated with the addition of three adjuvants: Agrioil3, BAS8153, and Li7003. Johnsongrass control was similar with the three adjuvants when either sethoxydim or clethodim was applied alone, but when bentazon was added, johnsongrass control declined with both sethoxydim and clethodim. Control generally declined less with BAS815 than with Agrioil or Li700, but the addition of BAS815 did not completely reverse the effects of adding bentazon to sethoxydim or clethodim. Johnsongrass control was not affected by adjusting pH when sethoxydim or clethodim was applied with bentazon and Agrioil. Johnsongrass control over a pH range of 3.5 to 6.5 via the addition of glacial acetic acid and calcium hydroxide or ammonium hydroxide indicated a lack of pH dependence for these herbicides. The addition of ammonium hydroxide resulted in slight, but inconsistent increases in johnsongrass control.

Research in Kansas from 1983 to 1986 evaluated early preplant (30 to 45 days) and late preplant (10 to 14 days) herbicide treatments for weed control before ridge-till planting in a soybean and sorghum rotation. Control of fall panicum and common lambsquarters at planting time averaged at least 95% for all early preplant and 92% for late preplant treatments. Where no preplant treatment was used, heavy weed growth in spring delayed soil dry-down, which resulted in poor ridge-till planting conditions and reduced plant stands, and ultimately reduced sorghum grain yields by 24% and soybean yields by 12%. Horsenettle population declined significantly, and honeyvine milkweed population increased. Smooth groundcherry populations fluctuated from year to year with no overall change.

The influence of spotted knapweed on surface runoff and sediment yield was determined under simulated rainfall conditions near Garrison, MT. Comparisons were made in 12 paired plots: one of each pair dominated by bunchgrass and the other dominated by spotted knapweed. Runoff and sediment yield were 56% and 192% higher, respectively, for the spotted knapweed, rather than the bunchgrass vegetation types. Spotted knapweed invasion onto bunchgrass range of western Montana is thus detrimental to the protection of soil and water resources.

Field experiments were conducted from 1983 through 1985 to evaluate the influence of tridiphane at 0.3, 0.6, 1.1, and 2.2 kg ai/ha when tank mixed with propanil at 2.2 or 3.4 kg ai/ha on control of 3- to 4-leaf or 4- to 6-leaf barnyardgrass in rice. Tridiphane at 0.6 kg/ha or greater tank mixed with propanil at 2.2 or 3.4 kg/ha enhanced control of 3- to 4-leaf barnyardgrass compared to propanil applied alone at 3.4 kg/ha. Rates of tridiphane at 1.1 kg/ha or greater plus propanil at 3.4 kg/ha were necessary to control 4- to 6-leaf barnyardgrass. ‘Starbonnet’ rice injury was minimal for all treatments.

The influence of pH on the behavior of metribuzin and ethyl-metribuzin in soil and nutrient solution was studied. Toxicity of both herbicides to oats decreased as soil pH decreased from 8.4 to 4.2 in a sandy loam. Herbicide adsorption increased as soil pH decreased. In nutrient solution, pH did not change the phytotoxicity of either herbicide, indicating that pH primarily influences herbicide availability in soil and not plant uptake.

The economic feasibility of four Wyoming big sagebrush control methods: burning, spraying with 2,4-D, plowing and seeding, and rotocutting was analyzed. Perennial grass response to big sagebrush treatment was measured to estimate a treatment response function for each control method which provided the biological informational base to develop cost and benefits. Annualized present values of net additional returns for single 2,4-D and burning treatments were $1.10/ha and $1.16/ha, respectively. When big sagebrush was retreated at optimal intervals, 2,4-D and burning generated annualized net additional returns of $2.88/ha and $2.57/ha, respectively. Rotocutting was marginally feasible, and plowing was not feasible.

Chlorsulfuron at 0.018 kg ai/ha, metsulfuron at 0.0045 kg ai/ha, and 2,4-D at 1.1 kg ae/ha plus dicamba at 0.28 kg ae/ha were applied over snow-covered winter wheat to study the feasibility of combining herbicides with a graphite snow-removal treatment. Chlorsulfuron or metsulfuron applied on snow effectively controlled annual broadleaf weeds when tank mixed with urea ammonium nitrate (UAN) at 28 kg N/ha and graphite powder at 20 kg/ha. Over-snow treatments of 2,4-D plus dicamba plus UAN did not control weeds. There was no antagonism or synergism among herbicides, UAN, or graphite.

The potential interactive effects between metolachlor [0, 0.1, 0.5, and 1.0 ppm (w/w)] and the air pollutant ozone (O3) [0.2 and 0.4 ppm (v/v)], on growth of corn, bean, and soybean were examined under controlled conditions. At both concentrations, O3 alone reduced corn and bean dry weights but only affected bean at 0.4 ppm (v/v). Shoot dry weight of corn was reduced by O3 plus metolachlor more than expected, thus indicating synergism. The expected dry weights of bean and soybean treated with metolachlor plus O3 were similar to or higher than expected, thus indicating additive or antagonistic interactions.