The mode of action and selectivity of oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] were investigated in tolerant rice (Oryza sativa L.) and susceptible barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯3 ECHCG]. Oxadiazon produced only brown spots on the foliage of rice plants at higher rates (> 500 ppmv), while LC50 for barnyardgrass was 250 ppmv. Translocation of 14C-oxadiazon from the treated leaf was minimal in both species; after 7 days, about 2 and 3% of applied 14 C translocated in rice and barnyardgrass, respectively. In rice, 14C recovered in water and chloroform washings of the treated leaf was 25% in each and in barnyardgrass, 20 and 18%, respectively. After water and chloroform washings, 14C-oxadiazon present in the treated leaf of barnyardgrass and rice was 36 and 26%, respectively. In rice and barnyardgrass, unaltered 14C-oxadiazon represented 86 and 79% of applied 14C, respectively, 7 days after application. In barnyardgrass 7 days after foliar application, oxadiazon inhibited 14CO2 fixation and the export of fixed carbon. The effects were less marked in rice.

The effects of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one} rate, order, and timing of sequential herbicide applications, and the addition of oil concentrate on sethoxydimbentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H-one 2,2-dioxide] antagonism were studied on broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash. ♯3 BRAPP], fall panicum (Panicum dichotomiflorum Michx. ♯ PANDI), and large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA] in field experiments during 1980 and 1981. Tank-mixing bentazon with sethoxydim reduced control of these species compared to applications of sethoxydim alone. Sequential applications of the herbicides prevented the antagonism. Variations in time between and order of sequential applications had no consistent effect on efficacy. Increases in sethoxydim rate reduced the severity of the antagonism in some cases, while the addition of oil concentrate had no effect.

Research was conducted from 1978 through 1980 at Headland, AL, to evaluate the use of herbicides, mechanical cultivation, and hand-hoeing as components of a total weed control system for peanuts (Arachis hypogaea L.). Herbicides or two cultivations alone failed to provide acceptable weed control, peanut yields, or net returns for the 3-yr period. However, adding two cultivations to the herbicide treatments produced acceptable weed control, peanut yields, and net returns for the 3-yr period. Average peanut yield for herbicide(s) plus two cultivations was 3200 kg/ha with an average net return of $260/ha. Two cultivations plus two hoeings without herbicide(s) produced good results with an average 3-yr yield of 3380 kg/ha and a net return of $280/ha. Herbicide(s) plus two cultivation treatments that had net returns equal to two cultivations plus two hoeing treatments were: dinoseb (2-sec-butyl-4,6-dinitrophenol) at 5.0 kg ai/ha applied at ground-cracking ($300/ha); dinoseb + alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 1.7 + 3.4 kg ai/ha applied at ground-cracking ($310/ha); and alachlor at 4.5 kg/ha applied preemergence ($320/ha). Treatments containing herbicide(s) plus two cultivations plus two hoeings did not substantially improve weed control, peanut yields, or net returns over herbicide(s) plus two cultivations.

Several field studies were conducted during 1981 and 1982 to determine whether early preplant (EPP) applications of residual herbicides would prevent the establishment of vegetation before planting no-till soybeans [Glycine max (L.) Merr. ‘Williams’]. Early preplant applications of either cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} or cyanazine plus oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) were applied in the fall and 3, 2, and 1 month(s) before planting no-till soybeans. In all studies, the treatments prevented vegetation from becoming established before planting, and season-long weed control was achieved with several different treatments. Early preplant cyanazine plus oryzalin provided greater than 90% control for the entire season where grass densities were low. Where grass densities were high (greater than 90% ground cover), EPP cyanazine plus a preemergence application of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] plus metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] or a postemergence application of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} controlled 90% of the weeds, which was equal to or better than the standard preemergence treatments used (80 to 98% weed control).

Retention, absorption, translocation, and metabolism of propanil (3′,4′-dichloropropionanilide) in tolerant wheat (Triticum aestivum L. ‘Era’) and susceptible green foxtail [Setaria viridis (L.) Beauv. ♯3 SETVI] were studied to determine the basis of selectivity. Green foxtail retained 7.7 times more spray on a mg/g fresh weight basis than did wheat. Absorption of 14C-propanil by green foxtail was greater than by wheat during most of the 48-h uptake period, but differences in absorption were not large enough for absorption to be a major selectivity factor. Translocation of foliar-applied 14C-propanil was limited in both species; after 48 h, 96.7% of absorbed 14C remained in the treated wheat leaf and 99.7% remained in the treated green foxtail leaf. Limited metabolism of 14C-propanil occurred in green foxtail, with only 6.4% of extractable 14C-propanil metabolized to dichlorolactanilide and unknown 14C-compounds during a 72-h period. Wheat metabolized 65.8% of the extractable 14C-propanil to dichloroaniline and unknown 14C compounds by 72 h after treatment. The results of this research indicate that spray retention and propanil metabolism are the major factors involved in wheat tolerance and green foxtail susceptibility to propanil.

A 3-yr study was conducted to compare the performance of several herbicides applied alone and in mixtures under three flooding conditions in dry-seeded rice (Oryza sativa L. ‘Labelle’). When the soil remained moist during the 2-week unflooded periods (1979 and 1981), weed emergence was slowed and no advantage with respect to enhanced weed control and increased rice yields could be demonstrated over that of the standard sequential propanil (3′,4′-dichloropropionanilide) application. However, in 1980 when drought stress may have reduced initial postemergence activity and weeds emerged during the 14-day unflooded periods, differences in weed control between herbicides were obtained. Results of this study also indicate that yield losses from weed competition resulted primarily from early season competition, and that the principal advantage of the residual herbicides in dry-seeded rice may be to eliminate the need for retreatment with propanil when flooding is delayed or fields are drained.

The sagebrush (Artemisia)-grass ecosystem is an extensive and important rangeland type in the western United States. Estimates of total area of this ecosystem vary from 38 million ha (21, 22) to 109 million ha (3). Of the sagebrush-grass rangelands, 88% are degraded to the point that they are producing 50% or less of their forage potential (22). Low forage production on these rangelands has been caused by overgrazing and other past land abuses (24) resulting in severe depletion of native perennial grasses, dominance of brush, and, on millions of hectares, downy brome (Bromus tectorum L. # BROTE) dominance of the understory.

The presence of a dinitroaniline-resistant biotype of goosegrass [Eleusine indica (L.) Gaertner. ♯3 ELEIN] was confirmed in the northeastern area of South Carolina. It was also found in seven adjoining counties. It showed resistance to seven dinitroaniline herbicides but not to herbicides from six other chemical groups. One biotype was not affected by trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 3.4 kg ai/ha where a dinitroaniline-susceptible biotype was controlled at 0.3 kg/ha. Under similar conditions, another biotype showed resistance to trifluralin at 0.6 kg/ha but was controlled at 1.1 kg/ha, indicating that at least two unique biotypes may exist.

One to 5.6 μM DCPA (dimethyl tetrachloroterephthalate) inhibited oat (Avena sativa L. ‘Victory’) root growth within 12 to 18 h. Treated roots were severely stunted and swollen. An analysis of cell division in roots treated with DCPA revealed a disruption of normal mitosis after prophase. Metaphase, anaphase, and telophase division figures were absent 8 to 10 h after treatment with 5.6 μM DCPA. In contrast, a 24-h treatment with 5.6 μM DCPA was necessary to eliminate prophase division figures. The number of aberrant division figures increased concomitantly with the reduction in normal division figures. The predominant type of aberrant division figure was a condensed prophase. When the aberrant division cycle was completed and cells entered interphase, the dispersed chromosomes coalesced to form large, polymorphic nuclei and, occasionally, micronuclei. Approximately 60% of the outer four tiers of cells in roots treated with 5.6 μM DCPA developed abnormal cell walls. These data suggest that DCPA causes root growth inhibition by disrupting several processes involving organized microtubules.

Field and greenhouse studies conducted in North Carolina in 1981 and 1982 evaluated the effect of the dimethylamine salt of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid] on soybeans. In the field, 2,4-DB at and above 0.07 kg ae/ha reduced soybean shoot mass, leaf nitrogen levels, and nodule activity. Soybean seed yields were reduced by 2,4-DB at and above 0.07 kg/ha. In greenhouse studies, total nodule activity was reduced by 0.07 and 0.14 kg/ha of 2,4-DB. Soybeans treated with 2,4-DB at initiation of flowering (R1 stage) or when pods were 1.9 cm long (R4 stage) yielded progeny with visible injury symptoms. Seedling emergence was also reduced in progeny of soybeans.

The response of 22 potato (Solanum tuberosum L.) cultivars to soil-incorporated and foliar applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one] at rates of 0.5 and 1.0 kg ai/ha, was evaluated in field experiments from 1979 to 1982. Metribuzin significantly reduced the yield of marketable tubers in several potato cultivars. Foliar applications generally resulted in more injury than soil applications. Yields were reduced primarily through stand reduction and a decreased number of tubers per plant. Neither tuber size nor specific gravity of tubers was significantly reduced in the cultivars studied. The most susceptible cultivar was ‘Alaska Red’, followed by ‘Rhine Red’, F72117, ‘Caribe’, and ‘Shepody’. Other cultivars evaluated were highly tolerant to metribuzin, irrespective of rate or method of application. There was an increase in hollow heart in cultivars ‘Atlantic’ and ‘Lemhi Russet’ following treatment with metribuzin.

The basis for differences in response of eastern black nightshade (Solanum ptycanthum Dun.), a tolerant species, and velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH), a susceptible species, to foliar-applied chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide} was investigated by evaluating differences in spray retention and herbicide absorption, translocation, and metabolism. Based upon a foliar-applied rate causing a 50% reduction in dry weight, velvetleaf was greater than 20000 times more susceptible to chlorsulfuron than was eastern black nightshade. The differences detected in spray retention, absorption, and translocation were inadequate to account for the large response differences between the two species. The primary difference found was in the rate of chlorsulfuron degradation. In eastern black nightshade, 69.9% of the absorbed chlorsulfuron was metabolized within 24 h of application and 81.1% within 72 h of application. Only 7.1% of absorbed chlorsulfuron was metabolized in velvetleaf in a 72-h period.

The absorption and translocation of sethoxydim {2[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} as influenced by bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] were studied in goosegrass [Eleusine indica (L.) Gaertn. ♯3 ELEIN]. The presence of bentazon in the treatment emulsion decreased foliar absorption of 14C applied as 14C-sethoxydim by about half. Significantly less 14C was found in the treated leaf, shoot tissue above the treated leaf, shoot tissue below the treated leaf, and roots of plants treated with a mixture of 14C-sethoxydim and bentazon than with 14C-sethoxydim alone. After 6 h, 3.5% of applied 14C was recovered from plant parts other than the treated leaf in the absence of bentazon, compared to 1.1% of that applied in combination with bentazon. The difference in foliar absorption between the two treatments may account for the antagonistic interaction between these herbicides observed in the field.

Seedlings of winged elm (Ulmus data Michx.), bur oak (Quercus macrocarpa Michx.), black walnut (Juglans nigra L.), eastern redcedar (Juniperus virginiana L.), and loblolly pine (Pinus taeda L.) were treated in nutrient solution with ring-labeled 14C-tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} or 14C-hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione]. Four hours later, 14C was detected in all sections of winged elm treated with 14C-tebuthiuron and 14C-hexazinone. Root absorption of the tebuthiuron label by the other species occurred in the order: loblolly pine > bur oak > black walnut = eastern redcedar. The sequence of 14C-hexazinone absorption was: loblolly pine > black walnut ≥ bur oak = eastern redcedar. Foliar accumulation of the tebuthiuron label occurred in the order: bur oak > loblolly pine > eastern redcedar = black walnut, whereas the sequence with hexazinone was loblolly pine > bur oak > black walnut = eastern redcedar. The presence of the three metabolites of hexazinone in loblolly pine suggests that it may be resistant to hexazinone as a result of its ability to degrade hexazinone rather than its ability to limit uptake.

The airless paint sprayer was investigated as an alternative to compressed-gas spray systems. The airless sprayer was adapted to a conventional agricultural spray nozzle system. In addition, modifications to the airless sprayer's on/off switch were made to achieve a more consistent delivery. The equipment was found satisfactory for applying either emulsifiable concentrates or wettable powder herbicides at typical concentrations in water. The addition of a conventional conveyer-belt system completed the steps necessary to make the commercially available airless sprayer a viable alternative to compressed-gas propulsion systems.

Postemergence applications or a combination of preemergence and postemergence treatments in double cropped soybeans [Glycine max (L.) Merr. ‘Ransom’] resulted in higher soybean yields than preemergence applications. Preemergence-treated plots were 98% weed free early in the growing season; however, weeds emerged later and reduced yields. Weeds had to be controlled in soybeans for 90% of the growing season to avoid yield loss. Soybean yields were higher under no-till than conventionally tilled management in two of three years and tended to be higher during the third year. Distribution and timing of rainfall were more important in determining soybean yield than the total amount received during the growing season.

The tolerance of broad bean (Vicia faba L. Moruna and Alameda) to glyphosate [N-(phosphonomethyl)glycine] was studied under field conditions. Chlorosis, rolling of apical leaves, and reduced growth were the typical symptoms caused by glyphosate on broad bean plants. Visual phytotoxicity from glyphosate at 60 and 120 g ae/ha was very slight. Moderate or severe crop injury was caused by glyphosate at 360 and 600 g ae/ha, when applied before blooming. Seed yields were 2, 4, 9, 23, and 47% lower than the control after glyphosate applications at 60, 120, 240, 360, and 600 g ae/ha, respectively, when averaged over stages of growth and locations. Broad bean was more susceptible to glyphosate at the vegetative stage, when the plants had five to seven nodes, and less susceptible at the late-flowering and pod-bearing stage. Double applications of glyphosate at 120 g ae/ha reduced seed yield more than 10% compared with similar treatments at 60 g ae/ha, regardless of growth stage. Glyphosate decreased seed yields mainly by reducing the number of pods per plant, but germination, fiber content, and gross energy of the seeds were not altered.

As an agrestal weed, downy brome (Bromus tectorum L. # BROTE) is most troublesome in winter wheat (Triticum aestivum L. # TRIAE) and alfalfa (Medicago sativa L. # MEDSA) because of the ability of downy brome to reproduce prior to crop harvesting (70, 76). Geographically, downy brome is most common in the western half of the United States where annual rainfall totals 15 to 55 cm and autumn rainfall ranges from 5 to 12 cm (10, 11, 86, 98). In contrast, cheat (Bromus secalinus L. # BROSE) is more common in the eastern portion of the hard red winter wheat producing regions and in the more humid soft red winter wheat region. Behrendt and Hanf (12) state that cheat has been more common on acid sandy or loamy soils while downy brome commonly occurs on dry, mostly alkaline, sandy to loamy soils. Since soils are frequently alkaline in the relatively dry climate of the western regions (61), it is not clear exactly what role pH plays in affecting geographical distribution of the various Bromus spp. Recent serious problems with downy brome in the New England nursery industry (69) and orchards (57) indicate that downy brome could thrive under a relatively wide range of edaphic and climatic conditions. However, as a weed problem in wheat, the common prevalent conditions of low annual precipitation and alkaline soils should not go unnoticed in the development of chemical weed control practices.