Experiments were conducted to determine the energy requirements and the most effective rotary tiller configuration for incorporating cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile} on an 18-cm band centered on top of the previous year's corn (Zea mays L.) ridge. When the rotary tiller was operated full width at a 10-cm depth, the least cyanazine concentration was found in the center of the ridge, and the greatest concentration was found between ridges. The treatment having the greatest cyanazine concentrations in the center of the ridge and the least in the inter-row between ridges consisted of a ridge cleaner, a cyanazine application, and the rotary tiller configured to till a. 30-cm strip on the center of the ridge with a rotor enclosure. Energy requirements for operating the rotary tiller increased as the depth of operation increased, and the 10-cm depth of operation required less energy than two passes with a tandem disk.

Greenhouse and growth chamber experiments were conducted to evaluate primisulfuron phytotoxicity to downy brome (Bromus tectorum) and Kentucky bluegrass (Poa pratensis) as a function of herbicide placement, adjuvants, and environmental conditions. Primisulfuron rates needed to produce GR50 (50% growth reduction) values were 0.97 ± 0.57 and 8.07 ± 1.85 g/ha for downy brome and Kentucky bluegrass, respectively. Primisulfuron was applied to downy brome and Kentucky bluegrass at three placement sites: foliar, soil, and foliar plus soil. Foliar or foliar plus soil applications were more effective at reducing downy brome dry weights than the soil application of primisulfuron, whereas Kentucky bluegrass was injured more from the soil or foliar plus soil applications than from the foliar application of primisulfuron. Primisulfuron at 5 g/ha applied alone reduced downy brome dry weights by 5%, whereas when an adjuvant was added, dry weights were reduced by 52 to 83%. Primisulfuron was more phytotoxic to downy brome at alternating temperatures of 8 to 16 C and 16 to 24 C than at 0 to 8 C. Phytotoxicity of primisulfuron was less when downy brome plants were stressed for soil moisture after herbicide treatments than when the plants were not stressed or only stressed before treatment.

Experiments were conducted in a growth chamber to determine the effects of planting depth on the developmental sequence of velvetleaf seedlings and the effect of cyanazine placement relative to velvetleaf planting depth on cyanazine toxicity. Velvetleaf seedling emergence was delayed when seeds were planted 6 cm deep compared to the 2- and 4-cm planting depths. Lateral roots did not appear until after the cotyledons had emerged and expanded. This was followed by secondary root emergence from the primary root which occurred before adventitious roots appeared from the hypocotyl for the 2- and 4-cm planting depths. The first true leaf did not unfold until after the secondary root system was well developed. The quantity of adventitious roots on the hypocotyl increased with increasing planting depth. Velvetleaf adventitious roots appeared to be involved in cyanazine toxicity when cyanazine was placed above the seed. Increasing planting depth increased the proportion of seedling absorptive tissue above compared to below the seed. This resulted in increased cyanazine exposure for the deeper planted velvetleaf seeds when herbicide was placed above the seed.

Studies were conducted to determine the effect of soil moisture, seedling age, and exposure of plant parts on control of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] with diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, formulated as the methyl ester. In a Warden silt loam, moisture content of 10% or more was needed for satisfactory diclofop control of slow-growing barnyardgrass under cool, early-season conditions. Soil moisture was less critical when temperatures were higher and barnyardgrass was growing rapidly. Roots and emerging shoots both absorbed diclofop from the soil, but both plant parts were inhibited more when diclofop was applied to the roots than to the shoots. Barnyardgrass was injured from diclofop applied postemergence to either roots or shoots separately, but phytotoxicity was greatest when the whole plant was exposed. When the soil was treated, control increased with increasing amounts of post-treatment overhead irrigation. Two-leaf and four-leaf barnyardgrass plants were equally susceptible to diclofop applied postemergence, but resistance increased with age in plants with more than four leaves.

Field observations in 1986 indicated that increased injury to soybean could occur from clomazone plus metribuzin and clomazone plus linuron compared with metribuzin or linuron alone. Field experiments to measure this response were conducted in 1988, 1989, and 1990 at two locations in Michigan. Atrazine at 0, 1120, 2240, and 3360 g ha-1 was applied the year previous to soybean planting to determine if atrazine residues in the soil influenced soybean response. Herbicide treatments in soybean included clomazone, metribuzin, linuron, alachlor, clomazone plus metribuzin or linuron, alachlor plus metribuzin or linuron, and an untreated control. Additive and synergistic responses in soybean to clomazone plus linuron and clomazone plus metribuzin, regardless of atrazine application rate, occurred in some field environments. Experiments in the greenhouse demonstrated that soybean shoot weight was reduced synergistically from clomazone plus metribuzin compared with either herbicide alone, and the response was greater on a soil with 2.5% organic matter compared with a soil with 4.4% organic matter. Clomazone plus metribuzin reduced leaf area and shoot dry weight, regardless of placement, while leaf area and shoot dry weight were reduced more when clomazone plus linuron- and atrazine plus metribuzin-treated soil was placed in the same zone as the soybean seed. The synergistic interaction in soybean to clomazone plus metribuzin occurred under both cool and warm temperature regimes in growth chamber studies.

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.

Controlled-environment experiments were conducted to determine the effects of soil temperatures of 5 to 20 C, seed depths of 0 to 6 cm, and above- or below-seed cyanazine placement on germination and seedling development of giant foxtail and velvetleaf. Giant foxtail did not germinate at 5 C and failed to emerge from 6 cm deep within 21 days at 10 C. Increasing soil temperature above 10 C increased giant foxtail germination and emergence. Velvetleaf germinated at 5 C but did not emerge within 21 days. Velvetleaf emerged within 21 days from soil depths of 2 to 6 cm at soil temperatures of 10, 15, and 20 C. Giant foxtail and velvetleaf seed germinated on a soil surface kept moist by mulch or frequent watering. Giant foxtail seedling survival was 100% after germination on the soil surface. Velvetleaf often failed to become established; only 28% of the velvetleaf that germinated at 20 C survived. Injury to giant foxtail by cyanazine increased with increasing soil temperatures and decreasing seed depths. Cyanazine placement above or below the seed did not have a consistent effect on giant foxtail injury. Cyanazine placed above the seed was more injurious to velvetleaf than placement below at 15 and 20 C. Differential responses of giant foxtail and velvetleaf seed germination and seedling survivability to initial seed depth appears to be a major factor in weed population shifts when tillage is reduced or eliminated.

The absorption and translocation patterns of foliar applied 14C- chlorsulfuron {2-chloro-N- [[(4-methoxy-6-methyl-1,3,5- triazin- 2 - yl)amino] carbonyl] benzenesulfon-amide} and 14C-metsulfuron {2- [[[[(4-methoxy-6-methyl-1,3,5- triazin- 2-yl)amino] carbonyl] amino] sulfonyl] benzoic acid} in wild garlic (Allium vineale L. # ALLVI) were similar. Both 14C-chlorsulfuron and l4C-metsulfuron were readily absorbed by wild garlic, with 62 and 58%, respectively, of the applied doses absorbed 144 h after application. After 144 h, 17% of the applied 14C-chlorsulfuron and 16% of the applied 14C-metsulfuron were translocated out of the treated leaf, with the greatest amounts concentrating in young shoot tissues. Chlorsulfuron and metsulfuron reduced wild garlic shoot dry weight, height, and the number of leaves, more when they were applied to the foliage, or to both the foliage and the soil, than when they were applied to the soil alone.

In greenhouse studies, flowering annual bluegrass Poa annua L. var. annua (winter annual) and P. annua L. var. reptans (short-lived perennial) were treated postemergence with rimsulfuron at 54 g ai/ha in such a manner as to permit herbicide interception only by the foliage, interception only by the soil, and interception by both foliage and soil, as would occur in a typical application. The foliar-only, soil-only, and soil + foliar applications provided 57, 73, and 84% control, respectively, as averaged over all other experimental variables. Greater efficacy of the soil-only and soil + foliar applications indicated the importance of root absorption for annual bluegrass control with rimsulfuron. Adjuvant addition was beneficial to postemergence activity only at 18 g/ha, which is below the registered rate. Adjuvant-based control improvement at this rate was inconsistent and generally independent of the adjuvant type. Adding Renex-30 to 18 g/ha of rimsulfuron did increase control on an average from 16 to 51%. Postemergence efficacy was also independent of the annual bluegrass variety and growth media (field soil vs. a sand–peat mixture). Preemergence activity of rimsulfuron against germinating annual bluegrass seeds was slightly greater in the sand–peat mixture than in the soil and with var. annua than with var. reptans, and on uncovered seed compared with 0.5-cm-deep growth media covered seeds.

Greenhouse studies were conducted to determine yellow nutsedge response to selective placement of a 5-cm layer of norflurazon-treated soil above, below, or above plus below pregerminated nutsedge tubers. Norflurazon at 1.68 kg ai/ha applied postemergence (POST) as a foliar, soil, or foliar plus soil treatment was also evaluated. Soil concentrations of norflurazon at 1.5 mg/kg (w/w) applied below or above plus below nutsedge tubers reduced yellow nutsedge shoot numbers at least 69%, shoot height at least 71%, shoot dry weights at least 77%, and root tuber dry weights at least 89%. Yellow nutsedge growth reduction with norflurazon was greatest when norflurazon was placed in the soil profile below or above plus below the yellow nutsedge tubers. Placement of norflurazon above yellow nutsedge tubers did not reduce shoot number, height, or dry weight until the foliar portion of plants were removed 39 d after treatment. POST application of norflurazon did not reduce initial yellow nutsedge shoot number regardless of application method. Foliar-only POST application of norflurazon was less effective for reducing numbers of emerged yellow nutsedge than application to soil only or soil plus foliage.

Dry edible bean class and cultivar response to dimethenamid and metolachlor was investigated in the greenhouse and field. Kidney and cranberry cultivars, as well as a small red cultivar, were not injured by dimethenamid applied PRE at 2,100 g ai/ha in the greenhouse, whereas pinto bean tolerance varied and navy and black bean cultivars were injured by this rate. Injury to navy bean was greater in the greenhouse when dimethenamid and metolachlor were placed in the zone above and including the seed, compared with placement in the seed, root, or root plus seed zone. In an application timing field study, dimethenamid at 1,300 g/ha applied at the crook or unifoliate growth stage caused injury to navy bean, delayed maturity, and reduced seed yield. Metolachlor at 1,400 g ai/ha delayed maturity when applied at the unifoliate growth stage but did not reduce seed yield. Dimethenamid or metolachlor PRE, at 1,300 or 2,800 g ai/ha, respectively, injured navy and black bean cultivars, but seed yield was not reduced in a cultivar tolerance field study. In a planting date study, dimethenamid PRE at 2,300 g/ha reduced leaf area and delayed maturity compared with the nontreated control when pooled over five planting dates and cultivars in each of 2 yr. Metolachlor PRE at 2,800 g/ha reduced leaf area in 1 yr and delayed maturity in both years when pooled over planting dates and cultivars. If weed control and herbicide costs are comparable, metolachlor at a standard use rate is a safer choice than dimethenamid for use in navy and black bean production.

Response of creeping bentgrass, annual bluegrass, and Kentucky bluegrass to foliar, soil, or foliar plus soil applications of bispyribac-sodium was evaluated in greenhouse studies. Soil-alone and foliar plus soil applications of bispyribac-sodium at 148 or 296 g ai/ha resulted in greater injury and shoot dry weight reduction of all species 28 d after treatment (DAT) compared to foliar-alone treatments. Creeping bentgrass was less injured than annual or Kentucky bluegrass regardless of application placement. Further studies evaluated foliar and root absorption and translocation of 14C-bispyribac-sodium in creeping bentgrass, annual bluegrass, Kentucky bluegrass, and roughtstalk bluegrass. Foliar absorption into creeping bentgrass was less than that of other species at most harvest timings from 4 to 72 h after treatment. Annual and roughstalk bluegrass translocated greater amounts of foliar-absorbed 14C to the crown and shoots compared to creeping bentgrass. Annual and roughstalk bluegrass accumulated approximately 47% more 14C per dry weight of plant tissue than creeping bentgrass and 74% more than Kentucky bluegrass after 72 h in nutrient solution containing 14C-bispyribac-sodium. Annual and roughstalk bluegrass translocated approximately 80% of root-absorbed 14C to shoots, whereas creeping bentgrass and Kentucky bluegrass translocated slightly less (66% of absorbed for both species). These studies suggest that bispyribac-sodium is readily absorbed by roots and translocated to shoots which may contribute to its total activity within a plant. In addition, creeping bentgrass displayed lower amounts of foliar and root absorption and subsequent translocation than annual and roughstalk bluegrass which may contribute to greater bispyribac-sodium tolerance displayed by creeping bentgrass.

Field studies were conducted at Clinton, NC (2009, 2010), and Kinston, NC (2010), to determine ‘Covington' sweetpotato tolerance to flumioxazin applied after transplanting. Flumioxazin was directed to 25% of the sweetpotato vine beginning at the distal end (shoot tip), 25% of the vine beginning at the proximal end (crown), or to the entire vine (over-the-top) and was applied at 2 or 5 wk after transplanting (WAP). Applications made at 2 WAP resulted in 10 to 16% foliar necrosis at 3 WAP. Necrosis was transient and ≤ 2% by 6 WAP. Stunting injury at 6 WAP for flumioxazin applied at 2 WAP was greatest (12%) with the over-the-top application, followed by crown (5%), and shoot tip (1%) applications. Applications made at 5 WAP resulted in 35, 23, and 15% foliar necrosis at 6 WAP for over-the-top, crown, and shoot tip applications, respectively. By 12 WAP, stunting injury for all treatments was ≤ 3%. No. 1, jumbo, canner, and total marketable sweetpotato yield of the nontreated check was 36,670; 7,610; 7,170; and 51,450 kg ha−1, respectively. No. 1 and total marketable sweetpotato yields were reduced when flumioxazin was applied at 2 or 5 WAP. No. 1 sweetpotato yield was reduced when flumioxazin was applied to the crown or over-the-top (27,240 and 28,330 kg ha−1, respectively). Sweetpotato receiving flumioxazin applied to the shoot tip had similar no. 1 (31,770 kg ha−1) yields as the nontreated check, crown, and over-the-top applications. Total marketable sweetpotato yield was reduced by flumioxazin application to shoot tip, crown, and over-the-top (45,350; 40,100; 40,370 kg ha−1, respectively). Neither flumioxazin application timing nor placement influenced either jumbo- or canner-grade sweetpotato yields. Currently, after-transplant applications of flumioxazin do not appear to be a suitable fit for POST weed control in North Carolina sweetpotato production systems.

Growth chamber experiments were conducted to assess the effects of foliage-only, soil-only, and foliage-plus-soil placements of amicarbazone on annual bluegrass and creeping bentgrass growth. Evaluated herbicide treatments included amicarbazone at 49 or 147 g ai ha−1, as well as bispyribac-sodium at 74 g ai ha−1 for comparative purposes. Data from this research agree with previous reports of amicarbazone plant uptake. Amicarbazone is absorbed via above- and belowground pathways; however, plant growth is inhibited more by root uptake. Compared to foliage-only amicarbazone placement, soil-only placement more than doubled reductions in aboveground biomass and root mass 56 d after treatment (DAT), whereas no differences were detected between placements including soil contact. Across all evaluated parameters in this research, amicarbazone (49 g ha−1) impacted creeping bentgrass growth similarly to bispyribac-sodium, whereas annual bluegrass growth was inhibited more by amicarbazone, suggesting it provides a more efficacious chemical option for end-user applications.