The effects of repeated annual applications of nine herbicides on a planting of asparagus (Asparagus officinalis L. ‘Martha Washington’) were studied over a 7-year period. Weed competition during the cutting season seriously reduced yields. Large populations of common lambsquarters (Chenopodium album L.) developed where 3-amino-2,5-dichlorobenzoic acid (chloramben) and N,N-dimethyl-2,2-diphenylacetamide (diphenamid) were used. Large increases in redroot pigweed (Amaranthus retroflexus L.) occurred where dimethyl tetrachloroterephthalate (DCPA) was used. The fiber content of asparagus treated with 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) and 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) increased during slow growing conditions. Spear emergence in the spring was delayed when 2,6-dichlorobenzonitrile (dichlobenil) was applied near bud break. There was no indication that continuous use of any of the herbicides studied resulted in a buildup in the soil or plants causing a deleterious effect upon the yield of asparagus.

Field experiments were conducted to study the competitive ability of green foxtail (Setaria viridis (L.) Beauv.) with wheat (Triticum aestivum L.) and the feasibility of using a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) for the selective control of green foxtail in wheat. Rates of 0.56 to 0.84 kg/ha of trifluralin gave 90 to 100% control of foxtail when growing in competition with wheat. Wheat tolerated rates of trifluralin up to 2.24 kg/ha, the maximum rate used, without injury or reduction in crop yield, when the herbicide was applied and incorporated to a shallow depth 1 day after seeding. A semidwarf and a tall variety of wheat were not affected by trifluralin treatments. Green foxtail had a relatively low competitive ability, and wheat plants suppressed foxtail to a marked degree under normal growing conditions. However, suppressed plants still produced sufficient seed to insure a dense infestation of foxtail plants in the succeeding year. Further, when wheat was grown under less competitive situations, green foxtail resulted in significant reductions in crop yield. It was concluded that green foxtail is an “opportunist-type” weed.

Flooding soil with 5 to 10 cm of water for 7 to 14 days killed all freshly planted johnsongrass (Sorghum halepense (L.) Pers.) rhizomes in greenhouse and field experiments. A delay in flooding until culms emerged greatly reduced control. Flooding the soil in which 4-week-old johnsongrass plants grew had little effect at 15 C, but plants were killed after 8 weeks of flooding at 40 C. Death of buds on immersed johnsongrass rhizomes occurred more rapidly at 40 C than at 10, 20, 25, or 30 C. Flooding for 8 days at 40 C killed all rhizomes, but 16 days of flooding were required to kill all rhizomes at 30 C. Few buds were killed when flooded at 10 or 20 C, but germination was delayed. Immersing rhizomes in water and soil provided better control than immersing them in water without soil.

Hemp dogbane (Apocynum cannabinum L.) was investigated relative to seed germination, depth of seedling emergence, response to clipping, influence of soil type and fertility on vegetative growth, and herbicidal control. Seed germination in this study was influenced by light and scarification. Seedling emergence was influenced by the amount of soil cover. Soil type and fertility affected vegetative growth. In a greenhouse clipping study, hemp dogbane became perennial 41 days after emergence and by 65 days was producing more than one shoot per plant following clipping. Hemp dogbane was more completely controlled following September application of herbicide than from application made in June.

The competitiveness of 10 sorghum [Sorghum bicolor (L.) Moench] hybrids to weeds and their tolerances to commonly used sorghum herbicides were studied across Nebraska. The three best weed competitors in this study were sorghum hybrids ‘RS 671′, ‘RS 690′, and ‘AKS 663′; whereas the three poorest weed competitors were ‘AKS 614′, ‘NB 505′, and ‘RS 633′. Sorghum hybrids showing a significant yield reduction from a 2× rate of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) were ‘SD 441′, ‘SD 451′, and ‘NB 505′. ‘SD 441 also suffered a significant yield reduction from a normal rate of 2-chloro-N-isopropylacetanilide (propachlor) applied preemergence plus a 4× rate of (2,4-dichlorophenoxy)acetic acid (2,4-D) applied postemergence. With the above exceptions, sorghum hybrids generally showed considerable tolerance to 2× rates of herbicides commonly used on sorghum.

Injection of undiluted dimethylamine salt of (2,4-dichlorophenoxy)acetic acid (2,4-D) containing 479 g/L killed several species of bottom-land hardwoods when applied in 1 or 2-ml dosages in injections spaced from edge-to-edge to 23 cm apart. Most hardwoods were easier to kill in June than in September or December. For greatest economy, treatments should be varied by species and seasons. A 4:1 mixture of triisopropanolamine salts of 2,4-D and 4-amino-3,5,6-trichloropicolinic acid (picloram) containing 305 g/L was effective on some species resistant to 2,4-D, including eastern persimmon (Diospyros virginiana L.), swamp privet (Forestiera acuminata (Michx.)Poir.), and bitter pecan (Carya x lecontei Little).

Injury from 2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine (terbutryn) was greater on winter wheat (Triticum aestivun Vill. ‘Host’) grown at high soil temperature than on that grown at low soil temperature. The injury was more severe when the herbicide was incorporated into the soil close to the root system. In postemergence applications 2-week-old plants were more susceptible to terbutryn injury than 4-week-old plants. High soil water content (75% to 100% of field capacity) favored the uptake of terbutryn through the root system. Terbutryn caused greatest damage under high transpiration rates and in sandy soils.

Annual applications for 4 years of 2,6-dichlorobenzonitrile (dichlobenil), N,N-dimethyl-2,2-diphenylacetamide (diphenamid), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 3-amino-2,5-dichlorobenzoic acid (chloramben), and 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) to a red raspberry (Rubus sp. ‘Newburgh’) planting had no direct deleterious effect upon the raspberry plants. Dichlobenil, simazine, and paraquat gave excellent weed control. Weed competition in control plots seriously reduced yields. Shoot development was delayed when dichlobenil was applied near the time of normal bud break.

Field experiments were conducted to study the feasibility of using α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) for selective control of green foxtail (Setaria viridis (L.) Beauv.) in barley (Hordeum vulgare L.) and flax (Linum usitatissimum L.), and to determine the effect of crop competition on the phytotoxicity of trifluralin to green foxtail. Barley tolerated rates of trifluralin up to 2.24 kg/ha, the maximum rate used, without injury or reduction in grain yield when the herbicide was applied and incorporated to a shallow depth 1 day after seeding. Flax seeded in trifluralin-treated soil 5 or 10 days after application of the herbicide suffered a stand reduction from rates of 1.12 kg/ha or more; however, no significant reduction occurred in the seed yield. Trifluralin provided excellent control of green foxtail in both crops. Barley was a strong competitor against green foxtail while flax had poor competitive ability. Crop competition had a complementary effect on the degree of green foxtail control obtained with trifluralin.

Mortality rates of Geyer larkspur (Delphinium geyeri Greene), a poisonous plant, were determined after spraying with (2,4-dichlorophenoxy)acetic acid at various stages of plant development in 1967 to 1969. Sprays of 2,4-D at 2.2 kg/ha were more effective at early than at late stages of development, but seldom exceeded 40% mortality. Uneven-aged stands and early drying (dormancy) of small non-flowering plants often prevented the exposure of all plants to a single application of spray; treated plants contorted but continued growth for 5 to 8 weeks after spraying; residual seed provided a source of new plants; and previously dormant rootstock buds gave rise to new shoot and root growth the year after spraying. These characteristics and escape mechanisms direct attention to possibilities of improving effectiveness by spraying two or three times in a single season.

Cottonseed (Gossypium hirsutum L. ‘Atlas 67′) oil quality was measured by gas-liquid chromatography. Postemergent applications of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) (0.22, 0.34, or 0.45 kg/ha); 1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea (fluometuron) (0.56, 1.12, or 1.68 kg/ha); or 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) (0.22, 0.45, or 0.90 kg/ha) in phytobland oil (4.7, 9.3, or 14.0 L/ha) did not modify the percentage myristic, palmitic, palmitoleic, stearic, oleic, linoleic, linolenic, or arachidic acids when compared to cotton treated with phytobland oil alone or the three herbicides without oil.

Samples of the spray pattern delivered by a tractormounted field sprayer were intercepted with 10 petri dishes divided between two heights in each of eight plots sprayed with 1.12 kg/ha of 4-amino-3,5,6-trichloropicolinic acid (picloram). The sprayer produced predictable residues on the intercept plates; no differences occurred between residues collected at ground level and 46 cm above the ground; and no differences occurred between replicate plots. Fractionation and analysis of specific plant parts, whose position relative to direction of spray and surrounding brush had been noted, revealed that the spray system delivered uniform coverage almost regardless of brush orientation.

Dimethyl tetrachloroterephthalate (DCPA) caused localized swelling of the hypocotyl of tomato (Lycopersicon esculentum Mill. ‘VF-99′). DCPA caused phloem and xylem parenchyma cells to become multinucleate and to develop into masses undifferentiated tissue within the stele of the tomato hypocotyl. Xylem procambium differentiated earlier than that of controls and matured into shortened and often disconnected elements. Xylem formed prior to treatment was often disrupted due to pressure from the dividing xylem parenchyma. Xylem parenchyma tended to break down resulting in the formation of air cavities within the stele. Cells in the stele of treated hypocotyls tended to stain more intensely with safranin than did the cells in the steles of untreated tomato hypocotyls indicating a difference in cell wall composition. Treated tissue had a higher concentration of total oxalates than did untreated tissue.

Barley (Hordeum vulgare L. ‘Coho’), rye (Secale cereale L. ‘MSU Exp.’) and oat (Avena sativa L. ‘Gary’) seedlings were grown in nutrient solutions containing 0 and 10−9 to 10−7 M concentrations of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). In kinetic studies with rye and barley seedlings, simazine increased water and nitrate uptake after 3 days' exposure to 10−9 M simazine compared to controls; there was no effect from 10−7 M simazine. The effect was manifested in an increase in both plant weight and total protein. After 12 days, companion plants treated with 10−7 M simazine were the same size as controls but contained a higher protein concentration especially in the shoots. Regression analyses showed that the simazine-induced increases in total nitrogen content of the three grain species were closely related to the nitrate and water uptake, whether manifested by greater plant growth or more protein per gram of plant.

The relative drift of droplet and vapor of butyl ester and dimethylamine formulations of (2,4-dichlorophenoxy)acetic acid (2,4-D) was determined under conventional crop spraying procedures in the field. Labelled herbicides were mixed with spray solution or emulsion, and the ground deposit and the air-borne droplet and vapor clouds drifting from the target area were collected. The mass of the dimethylamine formulation drifting as droplets was 3 to 4% of the material sprayed. No significant amounts of this material were collected as vapor or particulate drift. For the butyl ester, in addition to the droplet drift, 25 to 30% of the material was collected as vapor drift in the half hour after spraying. Thus the drift potential from the butyl ester was about 8 to 10 times greater than that from the dimethylamine formulation under the conditions of these tests.

The phytotoxicities of four substituted dinitroanilines, N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine (benefin), 2,6-dinitro-N,N-dipropylcumidine (isopropalin), 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin), and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), to eggplant (Solarium melongena L. ‘Black Beauty’), pepper (Capsicum annuum L. ‘Vindale’), and tomato (Lycopersicon esculentum Mill. ‘VF 145-B-7879′) were studied. Nitralin and trifluralin were most active in inhibiting root elongation and top growth of these plants, the effect of benefin was intermediate, and isopropalin was the least active herbicide. The order of crop tolerance was as follows: tomato > pepper > eggplant. The effect of these herbicides on two pathogenic fungi, Rhizoctonia solani Kuehn and Fusarium oxysporum f. sp. lycopersici (Sacc.) Snyd. and Hans. was tested in culture and was found to be quantitatively and qualitatively different from that on plants. With both fungi benefin and trifluralin were more toxic than isopropalin, while nitralin showed a very low toxicity. R. solani was the less sensitive fungus.

Combinations of 4-amino-3,5,6-trichloropicolinic acid (picloram) and 5-bromo-3-sec-butyl-6-methyluracil (bromacil) pellets applied to the soil gave antagonistic responses on oats (Avena sativa L. ‘Clintland 64′) with either 5.6 plus 11.2 kg/ha or 11.2 plus 11.2 kg/ha of picloram plus bromacil. In nutrient culture a significant antagonistic response occurred over a 15-day period with a picloram to bromacil ratio of 30 to 1. Of the ratios evaluated, picloram appeared to interfere with the phytotoxic effect of bromacil. The uptake of 14C-bromacil alone by oats from nutrient solution was nearly double that of 14C-bromacil when combined with picloram. Thin layer chromatographic analyses revealed that 47% of the 14C activity from bromacil in the oat was intact bromacil and that 70% of the labeled activity from picloram was unaltered picloram. The loss of nutrient solution by evapotranspiration was less from containers with picloram and bromacil than from those with bromacil alone. Picloramtreated roots were shorter than untreated or bromacil-treated roots.

The effects of weed species on the anatomy of roots of cabbage (Brassica oleracea L.) and tomato (Lycopersicum esculentum Mill.) were studied. One crop seed was placed on agar in a test tube to germinate in association with four additional seeds of a weed species. All the weed species caused abnormal changes in the anatomy of cabbage and tomato roots. Jimsonweed (Datura stramonium L.) inhibited cell elongation and caused disruption of epidermis and disorganization of the root tissue in cabbage. Green foxtail (Setaria viridis (L.) Beauv.) also caused disruption of cabbage roots. Mustard (Brassica kaber DC.) and velvetleaf (Abutilon theophrasti Medic.) induced enlarged parenchyma cells of cabbage roots. The combination of tomato and jimsonweed resulted in disorganized root tissue or large roots with large parenchyma cells.

Root sections of seven Canada thistle (Cirsium arvense (L.) Scop.) ecotypes were grown under 8, 12, 14, and 16-hr photoperiods at 16, 21, and 27 C. Flowering occurred in all ecotypes under a 16-hr photoperiod. At the 14-hr photoperiod five ecotypes flowered; flowering in three of them was temperature-dependent. Shoot and root development and plant height varied with ecotype. Both the root-to-shoot ratios and the number of shoot buds formed on the roots were inversely related to temperature and length of photoperiod. Herbicides tested for their effects on Canada thistle were 4-amino-3,5,6-trichloropicolinic acid (picloram), 3,6-dichloro-o-anisic acid (dicamba), and (2,4-dichlorophenoxy)acetic acid (2,4-D). Control of top growth increased with increasing temperature. Similarly, root control was maximum at 27 C, at which temperature there were few fleshy roots. Picloram, unlike 2,4-D and dicamba, caused little leaf damage but completely destroyed the root system.

Four herbicides were applied at 6-month intervals, and incorporated by disking, to desert cropland soils at two locations. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) was applied at 0.9 kg/ha; and 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) were applied at 1.8 kg/ha. Following treatment the soils remained fallow without irrigation for 24, 18, 12, 6, or 0 months before planting eight crops. Sugarbeet (Beta vulgaris L.) growth was affected 24 months after applications of trifluralin. Growth of two or three crops at each location was affected 18 months after application of prometryne. Residues of atrazine and diuron usually caused greater injury to most crops than did prometryne or trifluralin. Six months after the first planting four additional crops were planted. In plots planted 30 months after treatment diuron reduced sorghum (Sorghum bicolor (L.) Moench) stands by 70% and reduced fresh weights of three crops at Mesa. Trifluralin reduced fresh weight of sorghum by 80% at Yuma. Crops responded differently to herbicide residues at the two locations. Injury to crops was most severe at Mesa despite higher rainfall during the fallow period at this location.