Herbicides and mechanical methods of weed control were tested on 1 and 2-year-old peach trees (Prunus persica (L.) Batsch) on two soil types and locations. Several herbicide methods gave season-long weed control without detriment to growth or yield of peach trees. In general, a cultural system where herbicides were used in rows and 8-ft sodded strips maintained in row middles did not decrease the growth or yield of trees when compared to overall mechanical methods of weed control.

In field studies combinations of herbicides applied preplant, preemergence, or postemergence were compared for control of prickly sida (Sida spinosa L.) in cotton (Gossypium hirsutum L. ‘Stoneville 7A’). All plots received an application of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) incorporated into the soil prior to planting. Additional preemergence applications increased control of prickly sida 94% with 1,1-dimethyl-3-α,α,α-trifluoro-m-tolyl)urea (fluometuron) and 53% with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). Seven postemergence treatments evaluated were at least partially effective in controlling prickly sida. However, trifluralin applied preplant followed by fluometuron applied preemergence gave the most effective prickly sida control in combination with all post-emergence treatments. Prickly sida populations of 130 plants per square meter competed with cotton all season and reduced yield 41 and 37% in 1969 and 1970, respectively. Prickly sida did not appear to affect cotton grade or staple length.

When almost no broadleaf weeds were present, 0.56 kg/ha of the butoxyethanol ester and 0.84 kg/ha of the dimethylamine salt of 4-(2,4-dichlorophenoxy)butyric acid (2, 4-DB) caused no yield reductions of seedling alfalfa (Medicago sativa L.); but 0.56 kg/ha of 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) caused slight reductions. Rates of bromoxynil above 0.56 kg/ha caused significant yield reductions of alfalfa. Broadleaf weeds, when present, shielded alfalfa from the bromoxynil so that reduction in yields of broadleaf weeds and increases in alfalfa were similar to those obtained with 2,4-DB. At equivalent rates 3,5-dichloro-4-hydroxybenzonitrile (hereinafter referred to as chloroxynil) was less effective than bromoxynil for controlling broadleaf weeds and also was less injurious to alfalfa. When no weeds were present at time of application, bromoxynil at a rate of 0.56 kg/ha or greater and chloroxynil at 0.84 and 1.12 kg/ha significantly reduced yields of red clover (Trifolium pratense L.). When weeds were present bromoxynil did not reduce yields of red clover until the 1.12-kg rate was reached. Chloroxynil did not reduce yields at rates as high as 1.12 kg/ha. Excellent control of common lambsquarter (Chenopodium album L.) and common ragweed (Ambrosia artemisiifolia L.) was obtained, and no reduction in alfalfa or red clover occurred with 0.28 kg/ha of bromoxynil or chloroxynil mixed with 0.56 kg/ha of 2,4-DB ester.

Foxtail millet [Setaria italica (L.) Beauv. ‘Empire’] and proso millet (Panicum miliaceum L. ‘White’) seedlings were grown in glass units to expose selectively either roots or shoots to vapors arising from soil containing a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin). The root and shoot growth of both species was inhibited by trifluralin vapors. Suppression of root and shoot growth increased as trifluralin application rates increased. In shoot exposure, vapors arising from soil treated with 5 ppmw of trifluralin were lethal to seedlings of both species. In root exposure, root growth of both species was severely suppressed at 20 ppmw, but shoot growth was unaffected. Phytotoxic effects resulting from a given concentration of trifluralin were more severe as greater carrier volumes were used for application. Trifluralin vapors arising from soil 16 to 22 days after treatment were still sufficient to cause shoot growth inhibition.

Vapor of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-loluidine (trifluralin) emitted from soils was collected in xylene and assayed by gas chromatography. Increasing the trifluralin application rate in soil surface treatments from 0.56 to 4.48 kg/ha resulted in substantial increases in vaporization from soils during the 2 hr immediately after treatment. Increasing the spray volume from 2.34 to 300 kl/ha with water reduced the rate of trifluralin vapor emission by approximately half. When trifluralin was applied as a spray (2.34 kl/ha) and then incorporated into soils of varying moisture contents, 4 to 10 times more trifluralin volatilized in 12 hr than when it was percolated into air-dry soils with sufficient water to yield equivalent soil moisture contents. The techniques employed were not sufficiently sensitive to detect trifluralin vapor loss occurring more than 12 hr after treatment. The amount of trifluralin lost during the first 12 hr was less than 5% of that applied to the soil, even under the most favorable conditions for volatilization.

The germination responses of seeds from 11 weed species to various chemical and physical treatments were studied. Germination of nine species was promoted by gibberellic acid and inhibited by abscisic acid, suggesting that germination of some weed seeds may be controlled by appropriate levels of these substances. Most of the weeds that germinated better after a hot-water soak treatment responded to sonication and infrared treatment, indicating that temperature was a factor in the germination response obtained with these methods, although physical disruption of the seed coat also was involved.

Wild cane (Sorghum bicolor (L.) Moench) absorbed equal amounts of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). The plants metabolized 70% of the atrazine and 30% of the simazine absorbed and translocated to the shoot during 24 hr. The major metabolites formed were hydroxyderivatives and very hydrophilic metabolites which were chromatographically identical to peptide conjugates of atrazine, e.g., S-(4-ethylamino-6-isopropylamino-s-triazinyl-2)-glutathione and S-γ-L-glutamyl-(4-ethylamino-6-isopropylamino-s-triazinyl-2)-L-cysteine. Wild cane formed peptide conjugates of atrazine more rapidly than of simazine, but hydroxylation of these s-triazines occurred at approximately the same rate.

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.

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.

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.

Thirty-six collections of foxtail barley (Hordeum jubatum L.) from North Dakota, South Dakota, Minnesota, Wisconsin, and Montana varied in susceptibility to 1-(2-methylcyclohexyl)-3-phenylurea (siduron) as determined from radicle elongation of treated seeds. Data from F2 seedlings of crosses between tolerant and susceptible selections indicated that three complementary dominant factors control the inheritance of siduron tolerance in foxtail barley. Evolution of siduron-tolerant foxtail barley could occur from selection pressure.

A laboratory spray cabinet was constructed of stainless steel with three compartments for separate dosage applications. Overhead spraying is accomplished in all three compartments by a single mobile nozzle activated by an air cylinder and cable drive. The system was designed so that test compounds could be applied safely and accurately at various rates on plants up to 1 m high. The cabinet has an air exchange and filtration system to prevent possible contamination of spray equipment, untreated test materials and the atmosphere.

Growth of green foxtail (Setaria viridis (L.) Beauv.) was effectively controlled in the greenhouse by applying the sodium salt of trichloroacetic acid (TCA) as a postemergence treatment, when a rate of 0.84 kg/ha was used; when application preceded the two-leaf stage; and when 2.54 mm of water were available daily for moving TCA into the soil. There were significant interactions of TCA rate with light intensity, temperature, and source of seeds on the response of green foxtail. Seedhead production was curtailed at rates of 0.56 kg/ha or above when plants were grown under high light intensities (19,250 to 22,000 lux) and at moderate temperatures (20 to 22 C). Rates of 1.68 kg/ha or more were required to stop heading of foxtail grown at high temperature (27 C).

A field and greenhouse study was conducted to determine the relative effectiveness of preemergence herbicides applied at low volume (9.35 to 37.4 L/ha) and conventional volume (187 L/ha). In the field study 11 preemergence herbicides were applied to plots seeded with seven weed species. Five herbicides were used in the greenhouse study each applied at five rates and two volumes. Both field and greenhouse results indicated that water soluble materials and emulsifiable concentrates which need not be incorporated can be applied at low volume with results comparable to conventional volume application. Field results suggested wettable powders can be applied low volume with success; however, greenhouse results indicated that with present equipment and technique wettable powders are not well suited for low volume application. Incorporated materials were included only in the field study and gave irregular results.

Under greenhouse conditions activated carbon, applied as a slurry at the time of seeding, protected Italian ryegrass (Lolium multiflorum Lam.) seedlings from the toxicity of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) applied preemergence. Plants growing from seeds planted 1.3 cm deep received less protection from diuron than plants growing from seeds planted 0.6, 1.9, or 2.5 cm deep. Sandy loam soil required at least three times more activated carbon than a clay loam soil to obtain the same protection. Activated carbon applied at 130 kg/ha in a 2.5-cm band on the soil surface directly over the seeds provided adequate protection on a clay loam soil. On a sandy loam soil the 130-kg/ha rate was not adequate. Wetting agents added to aid in carbon wetting reduced the protective effect of activated carbon when added at 0.9 or 2.7% (v/v) but had only a slight effect on protection when added at 0.3% (v/v). The soil moisture level at the time of carbon application and the amount of subsequent irrigation did not influence the protection obtained with activated carbon.

Growth-chamber studies were conducted to determine the effect of p-chlorophenyl-N-methylcarbamate (PPG-124) and 1-naphthyl N-methyl carbamate (carbaryl) on the response of safflower (Carthamus tinctorius L. ‘Gila’) and common buckwheat (Fagopyrum esculentum Moench.) to isopropyl m-chlorocarbanilate (chlorpropham). Addition of PPG-124 or carbaryl did not increase the sensitivity of safflower, a resistant species, to chlorpropham and affected buckwheat, a susceptible species, only at the lowest dosage level.

Cell cultures of soybean (Glycine max (L.) Merrill ‘Acme’) were exposed to media containing 4-amino-3,5,6-trichloropicolinic acid (picloram) for 15 days. Picloram also was supplied once in droplets (water) to cotyledons of 10 to 13-day-old seedlings of cotton (Gossypium hirsutum L. ‘Champion’). The amounts of picloram necessary to reach and exceed the 50% tolerance limit (TL50) of the cell cultures (inhibition) and of the primary leaf buds (toxicity) were established, and internal picloram concentrations then were determined. Internal concentrations at the TL50 were 0.17 nM/g fresh weight and 14.7 nM/g fresh weight for cell cultures and leaf buds, respectively. These values are approximately 10−7 and 10−5 molar. In leaf buds, concentrations increased rapidly for 36 hr after treatment and declined slowly thereafter. Primary leaf buds accumulated up to several times the lethal internal concentration of picloram when the dosage to the cotyledons was increased by one order of magnitude.

In laboratory experiments, plant extracts of small everlasting (Antennaria microphylla Rydb.), field pussytoes (A. neglecta Greene), and leafy spurge (Euphorbia esula L.) were toxic to germinating seeds. Extracts of small everlasting inhibited vegetative development of leafy spurge, and soil taken from the immediate vicinity of roots inhibited germination and radicle elongation of germinating seeds of some species. Small everlasting competes vigorously with leafy spurge, and this competition cannot be attributed to morphology and growth habit. It suppressed vegetative growth of leafy spurge from rhizome sections in which the two species were competing in pots. In field experiments, this shallow-rooted, lowgrowing plant exhibited a marked inhibition on the growth of the vigorous, deep-rooted perennial, leafy spurge, as did the soil in which small everlasting had been growing. Antibiotic competition appears to be significant with the Antennaria spp., and the paucity of forbs in patches of leafy spurge, even when bare ground is visible between shoots, suggests that this species also exerts antibiotic effects on other plants. Allelopathy is probably a significant influence in interspacial relationships of species in most plant communities. A fuller knowledge of these relationships and their causes could lead to the utilization of this phenomenon in weed control.

A system for controlling yellow nutsedge (Cyperus esculentus L.) in soybeans [Glycine max (L.) Merr.] which involved preplanting tillage, late planting, herbicides, and cultivation was evaluated in 1969 and 1970. In Illinois on a Drummer silty clay loam, S-ethyl dipropylthiocarbamate (EPTC) and S-ethyl diisobutylthiocarbamate (butylate), incorporated in the soil before planting, gave good and fair control of yellow nutsedge, respectively, but both injured soybeans initially. S-propyl dipropylthiocarbamate (vernolate), also incorporated before planting, controlled yellow nutsedge as well as EPTC did, and resulted in less injury to soybeans. Soybean yields were not reduced by any of the thiocarbamate treatments. Incorporation of 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) or 2-chloro-N-isopropylacetanilide (propachlor), just before planting, controlled at least 90% of the yellow nutsedge in both years, whereas preemergence applications were only moderately successful and dependent on rainfall. In field microplots, alachlor and vernolate provided only fair control of yellow nutsedge when applied to the soil surface, but they both controlled 95% of the yellow nutsedge when incorporated 7.6 cm. In greenhouse studies on selective control of yellow nutsedge in soybeans, alachlor exhibited a wider margin of safety to soybeans than did vernolate.