Greenhouse studies determined dose responses of winter annual weeds and winter wheat to preemergence (PRE) and postemergence (POST) treatments of MKH 6561 and the residual effects on kochia. MKH 6561 at 11 to 45 g ha−1 did not affect wheat. MKH 6561 at 11, 34, and 45 g ha−1 reduced winter annual weed densities compared to an untreated control. Weed growth was inhibited as the rate of MKH 6561 was increased, but downy brome, cheat, and Japanese brome were three to six times more susceptible than jointed goatgrass. The GR70 values for cheat, downy brome, Japanese brome, and jointed goatgrass were 7, 11, 4, and >45 g ha−1, respectively. Dry weights of kochia seeded after removal of the winter annual grasses decreased as MKH 6561 rate increased, with average control being 77% compared to the nontreated control. Regression analysis indicated that kochia was controlled 80% with MKH 6561 at 28 g ha−1.

Herbicide injury to five coniferous species was determined for the butoxyethanol ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid], the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine], and the triethylamine salt of triclopyr {[(3,5,6-trichloro-2-pyridinyl) oxy] acetic acid} throughout the growing season of 1981. The relationship of herbicide tolerance to growth rate, water stress, and photosynthesis was determined for Jeffrey pine (Pinus jeffreyii Grev. & Balif), sugar pine (P. lambertiana Dougl.), red fir (Abies magnifica A. Murr.), white fir [A. concolor (Gord. & Glend) Lindl.], and Douglas fir [Pseudotsuga menziesii (Mirb.) Franco]. Although most of the species showed a high correlation of injury to leader or needle growth rate and xylem pressure potential, the seasonal trend in the degree of injury and the relationship of herbicide tolerance to various physiological factors were unique for each species. Criteria for determining herbicide application periods depended on species and herbicide.

Eurasian watermilfoil (Myriophyllum spicatum L.) has invaded over 81,000 hectares in the Chesapeake Bay, 2,023 hectares in TVA reservoirs, and upwards of 32,000 hectares in Currituck Sound, North Carolina. Now it is causing concern in Florida because of its invasion of the Crystal-Homosassa River basin. In Yugoslavia and Pakistan, entomologists working on PL-480 grants found some 25 insect species feeding on eurasian watermilfoil. These species are potentially useful for the biological control of the weed in the United States.

Three annual applications of glyphosate [N-(phosphonomethyl)glycine] with three ropewick applicators were compared to hoeing and cultivation for the control of johnsongrass [Sorghum halepense (L.) Pers. ♯3 SORHA] in cotton (Gossypium hirsutum L. ‘Acala SJ-2′) in 1980 and 1981. The three applicators provided about equal control of johnsongrass. Averaged over treatments, years, and dates of application, plots treated with glyphosate contained 83% fewer live johnsongrass shoots (14/m2) than cultivated control plots (84/m2) 2 to 3 weeks after each application. Glyphosate-treated plots yielded an average of 81% more seed cotton (2010 kg/ha) than cultivated control plots (1110 kg/ha). However, yields of treated plots averaged 33% less than plots maintained weed-free by hoeing. Although applications of glyphosate reduced johnsongrass populations 83%, the competitive effect of johnsongrass on cotton prior to the initiation of treatments, plus the competition from escape plants between treatments, prevented cotton from yielding normally.

The effects of the dimethylamine salt of dicamba (3,6-dichloro-2-methoxybenzoic acid) and the dimethylamine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] on fieldbeans (Phaseolus vulgaris L. ‘Great Northern Valley’) were studied in order to assess the potential hazards of using these herbicides in areas adjoining fieldbean production. Dicamba and 2,4-D were applied to fieldbeans at three different rates (1.1, 11.2, and 112.5 g ai/ha) and four different growth stages (preemergence, second trifoliolate leaf, early bloom, and early pod). Application of 2,4-D preemergence or in the second trifoliolate leaf stage of growth did not reduce seed yield, delay maturity, or reduce germination of seed obtained from treated plants. Dicamba or 2,4-D applied at 112.5 g/ha to fieldbeans in the early bloom or early pod stages of growth consistently reduced seed yield, delayed maturity, and reduced germination percentage. Fieldbeans exhibited a greater overall sensitivity to dicamba than to 2,4-D.

Sorghum cultivars were compared for their root development and production of the witchweed germination stimulant sorgoleone. In pot experiments, the resistant cultivar IS-7777 yielded a greater root biomass and root length, but a smaller root length/biomass ratio than the highly susceptible cultivars CK-60B and Bimbiri. Seedlings of these latter two cultivars exuded a high concentration of sorgoleone, while the low-susceptible cultivar IS-14825 exhibited a low production of this compound. In contrast, the low-susceptible cultivar Seguetana Niarabougou exhibited a high production of sorgoleone, while the resistant cultivars IS-7777 and Framida exuded a moderate amount of this compound. These results indicate that witchweed seed avoidance by means of reduced root growth is unlikely to be an important factor involved in the resistance of IS-7777. Low production of sorgoleone could partly explain low susceptibility of IS-14825, but other compounds may play a more significant role in the stimulation of witchweed germination.

Soil water from plots containing cotton, devil's-claw, cotton with devil's-claw, and bare soil was measured throughout the growing season using a neutron probe and related to weed interference with the crop. Volumetric water content throughout the soil profile to a depth of 180 cm did not differ among treatments before the 5th or 6th week after cotton emergence. Greater water depletion occurred early in the season in plots containing devil's-claw which corresponded to a period of rapid weed growth. In plots containing only cotton, the largest reduction in water content occurred later in the season during peak bloom and early boll formation. Soil water content at depths greater than 105 cm remained unchanged in all plots throughout the season. Interference from devil's-claw reduced cotton lint yield 96% in 1986 and 46% in 1987. Higher rainfall and reduced weed populations in 1987 reduced the impact of weed interference on cotton lint yield.

Studies were undertaken to evaluate the phytotoxicity to yellow nutsedge (Cyperus esculentus L.), length of soil persistence, and tolerance of corn (Zea mays L.) to several acetanilide herbicides. The herbicides involved were alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide]. diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl)glycine], H-26910 [N-(chloroacetyl)-N-(2-ethyl-6-methylphenyl)glycine-1-methylethyl ester], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], Ortho 19790 [1-(chloroacetyl)-2,2-dimethyl-3-oxa-1-azaspiro-[4, 5]-decane], and Vel 5052 [2-chloro-N-(2,6-dimethylphenyl)-N-(1,3-dioxolan-2-ylmethyl)acetamide]. Most of these herbicides were equally active on yellow nutsedge in solution culture; only metolachlor and Vel 5052 were significantly more active than H-26910. Metolachlor and alachlor were the most toxic to yellow nutsedge in greenhouse and field experiments. Metolachlor persisted the longest of the herbicides in the field after spring applications. The tolerances of corn differed little among the herbicides at expected use rates.

The influence of hot-dry and cool-moist environments on primisulfuron efficacy on giant foxtail and quackgrass was compared at the University of Wisconsin Biotron. Primisulfuron was applied POST at 20 and 40 g ai ha-1 with nonionic surfactant (NIS) or crop oil concentrate (COC) and with or without 28% nitrogen fertilizer (28% N). Giant foxtail control 3 wk after treatment was not affected by primisulfuron rates or adjuvants. Adding 28% N tended to improve quackgrass control with primisulfuron plus NIS or COC. Primisulfuron was more injurious to both giant foxtail and quackgrass in the cool-moist than the hot-dry environment. Absorption of 14C-primisulfuron into giant foxtail tissue 3 days after treatment (DAT) was greater in the cool-moist than the hot-dry environment Translocation of 14C out of treated leaf of quackgrass 3 DAT was greater in the cool-moist than the hot-dry environment. More 14C was absorbed and translocated in giant foxtail than quackgrass. Absorbed 14C was translocated equally to underground and above treated leaf sections of quackgrass, whereas more 14C was translocated above the treated leaf of giant foxtail.

Studies were conducted to evaluate uptake, translocation, and metabolism of root-absorbed 14C-sulfentrazone in peanut, prickly sida, and pitted morningglory. Peanut absorbed more than five and three times greater 14C-sulfentrazone than pitted morningglory and prickly sida, respectively. All plant species translocated appreciable amounts (≥ 39%) of radioactivity to the leaves. The three plant species had some capacity to metabolize 14C-sulfentrazone. At 3 h after treatment, 7, 29, and 71% of the radioactivity in the shoots of peanut, prickly sida, and pitted morningglory, respectively, was sulfentrazone. Sulfentrazone levels in the shoots at 3 and 6 h after treatment correspond to reported tolerance levels, with peanut being the most tolerant of the three species, whereas prickly sida and pitted morningglory are moderately tolerant and completely susceptible to sulfentrazone, respectively. Levels of metabolites varied among species, plant part, and harvest timing. On the basis of these data, tolerance in peanut is largely due to its ability to rapidly metabolize sulfentrazone.

Large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA] control was higher when either DCPA (dimethyl tetrachloroterephthalate) or napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] was applied to bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’] growing in soil with a pH of 5 than in soil with a pH of 6.4 in 2 of 3 yr. Soil pH did not influence the response of large crabgrass to oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] or benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine). Herbicides alone did not produce high-quality turf unless fertilizer was applied annually at 300 kg N/ha or more. Bermudagrass quality was higher after three yearly applications of 300 kg N/ha or more of fertilizer when soil pH was 5 than when soil pH was 5.6 or 6.4.

Labeled 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2, 4, 5-T), 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 4-amino-3, 5, 6-trichloropicolinic acid (picloram), 1,2-dihydropyridazine-3,6-dione (MH), assimilates, and phosphoric acid were absorbed and transported basipetally from the lamina into the petioles of detached bean leaves (Phaseolus vulgaris L.). Upward transport in the lamina was slight, except when the petioles were in water. In contrast, labeled 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) was not transported basipetally, but some acropetal transport did occur. Vein-loading and transport of labeled assimilates, 2,4-D, dicamba, MH, and phosphate were greatly reduced by a prior treatment with 7-oxabicyclo(2.2.1)heptane-2,3-dicarboxylic acid (endothall). Detached leaves hold promise for use in absorption and transport studies.

Purple-leaf button weed and Indian heliotrope are widespread and common weed species of rain-fed rice in many tropical countries. The influence of various environmental factors on seed germination of these species was studied. Seeds of both species germinated at a range of alternating temperatures (25/15, 30/20, and 35/25 C day/night). Germination of purple-leaf button weed was similar among light conditions after an after-ripening period of 3 mo, whereas germination of Indian heliotrope was always greater in light. Seed germination of both species was not affected by a high level of salt and a range of pH between 5 and 9, but was sensitive to high degrees of water stress. Seed burial strongly inhibited germination and emergence of these species. Seedling emergence of purple-leaf button weed (82 to 86%) and Indian heliotrope (70%) was optimal when seeds were sown in the top 0.2-cm soil layer. A burial depth of 2 cm completely inhibited emergence of Indian heliotrope, whereas, for purple-leaf button weed, this depth was 5 cm. Most of these seeds germinated, however, when brought to the soil surface. The information gained from this study would help in predicting the potential of these species for spreading into new areas, and could contribute to their control.

Saflufenacil is a PRE herbicide for the control of broadleaf weeds. Field and growth room studies were conducted to explore the tolerance of corn to POST treatments of saflufenacil and BAS 781. Additionally, the potential use of sodium as a safener for saflufenacil was evaluated. Crop injury caused by saflufenacil or BAS 781 was 8 and 38%, respectively, when applied at twice the recommended dose at the spike to two-leaf stage of crop growth. This injury increased to 28 and 65%, respectively, when applied at the three- to four-leaf stage. This level of crop injury resulted in yield loss, particularly when applied at the three- to four-leaf stage. The addition of Na-bentazon to saflufenacil reduced this injury and increased crop dry weight under both field and laboratory conditions. In the field, Na-bentazon also increased corn collar height and yield compared with saflufenacil applied alone. Na-bentazon reduced injury through a reduction in foliar uptake of saflufenacil. Sodium derived from baking soda also provided a safening effect, but only at the lowest dose of saflufenacil tested.

Laboratory experiments were conducted to evaluate absorption, translocation, and metabolism of AE F130060 03 in wheat, barley, and Italian ryegrass. An additional objective was to evaluate how combinations of AE F130060 03 with dicamba affect absorption, translocation, and metabolism in wheat, barley, and Italian ryegrass. Experiments were conducted in a completely randomized design, and data were subjected to a factorial analysis. The factors included for analysis were plant type, time, and presence or absence of dicamba. Italian ryegrass absorbed 2.5, 2.0, and 1.5 times the amount of applied radioactivity 24, 48, and 96 h after treatment (HAT), respectively, compared with wheat or barley. Translocation of radiolabeled AE F130060 03 from the treated leaf blade was low and did not differ among wheat, barley, or Italian ryegrass. The rates of AE F130060 03 metabolism by the two cereal crops and Italian ryegrass were different. Ninety-six HAT, the total absorbed radioactivity metabolized by wheat, barley, and Italian ryegrass was 67, 51, and 34%, respectively. Conversely, 96 HAT, the levels of nonmetabolized AE F130060 03 were highest in Italian ryegrass, intermediate in barley, and lowest in wheat. The lower absorption of herbicide and a more rapid rate of metabolism by wheat and barley in comparison with Italian ryegrass most likely account for differential selectivity among the three plant species. Dicamba did not influence translocation or metabolism in wheat, barley, or Italian ryegrass.

Olive production in the southeastern United States has recently begun to increase from demand for locally produced virgin olive oil. With no established commercial production as a reference, information about the effects of indaziflam residual herbicide on newly established trees was evaluated over time for up to 3 yr on loamy sand soils. Multiple spring and autumn applications of indaziflam at different rates were applied to the same newly planted or 1-yr-old olive trees in different experiments in consecutive years. Visual injury, height, and caliper diameter measures were taken monthly during the growing season up to six times. Regression analysis of treatments over time indicated no differences in olive tree growth for plots treated with indaziflam at 38, 75, or 150 g ai ha–1 up to five times in 3 yr, compared with nontreated controls. This information will be beneficial as olive growers seek viable weed control options when establishing new groves in the region.

Field studies were conducted in 1996 and 1997 to determine the effects of RP-201772 and RP-201772 tank mixtures applied to emerged Zea mays. RP-201772 at 105 g ha−1 and tank-mixed metolachlor/benoxacor or atrazine were applied preemergence and to spike, 2-leaf, and 4-leaf Z. mays. Herbicide treatments over the four application timings provided greater than 90% Chenopodium album, Ambrosia artemisiifolia, Amaranthus retroflexus, and Abutilon theophrasti control. However, Setaria faberi control varied among years and application timings. Severe Z. mays injury, 70% and 40%, was observed when RP-201772 tank-mixed with metolachlor/benoxacor was applied to 2-leaf and 4-leaf Z. mays, respectively. Greenhouse studies confirmed Z. mays sensitivity from delayed applications of RP-201772 tank-mixed with metolachlor/benoxacor. Similarly, increased Z. mays injury was observed from postemergence applications of RP-201772 tank-mixed with acetochlor/MON-13900. Herbicide absorption, translocation, metabolism, and retention studies were conducted to determine the physiological basis for the observed Z. mays injury from delayed applications of the RP-201772 tank mixture with metolachlor/benoxacor. Metolachlor/benoxacor increased radiolabeled RP-201772 absorption when applied to spike, 2-leaf, and 4-leaf Z. mays. RP-201772 translocation and metabolism did not explain enhanced Z. mays injury. However, RP-201772 retention increased fivefold when metolachlor/benoxacor was present in the spray solution and applied to 2-leaf and 4-leaf Z. mays. Increased RP-201772 absorption and retention appeared to be the basis for Z. mays injury when tank-mixed with metolachlor/benoxacor and applied to emerged Z. mays.

Knowledge of the influence of environmental factors on weed populations is important in developing sustainable turfgrass management practices. Studies were conducted to evaluate the relationship of green and false-green kyllinga population densities with elevation and edaphic factors in turfgrass systems. Studies were conducted on five different golf courses in North Carolina, three affected by green kyllinga, and two affected by false-green kyllinga. According to Spearman correlation coefficients, both green and false-green kyllinga were correlated with increasing soil volumetric water content, whereas correlation of other edaphic variables varied among sites and species. Stepwise logistic regression confirmed the correlation of volumetric water with green kyllinga presence, but model components varied among sites for false-green kyllinga. Increasing green kyllinga populations correlated with increasing soil sodium; however, sodium did not reach a level believed to be detrimental to turfgrass growth. No other variables correlated with green or false-green kyllinga across all sites. We hypothesized that the lack of significant correlations was due to the overall influence of relative elevation on edaphic variables. According to principal components analysis (PCA), relative elevation had a profound impact on the measured edaphic variables at all sites. However, results of PCA at one site differed sharply from other sites. Results from that site demonstrate the potentially strong effects of management practices to alter edaphic trends normally observed with topography.

Most workers with herbicides agree that the effects brought about by many of these substances must be the results of altered enzymatic action within the plant. The actual mechanism is still a matter of conjecture in spite of some excellent research and well founded theorizing. A brief examination of enzymes and enzyme action in the light of results obtained with 2,4-D particularly, may suggest how this herbicide fits into the enzyme picture.

Carboxyl labeled 2,4–dichlorophenoxyacetic acid (2,4–D) was applied to ironweed, a perennial composite, at various stages of growth in the field and greenhouse. During phases of rapid plant development, C14 tended to concentrate in new leaves, axillary buds, petioles and stems. As plants approached full vegetative development greater quantities were detected in rhizomes and roots and less in stems and leaves. The herbicide was translocated readily into new leaves, stems and roots of ironweed seedlings. Considerable quantities of 2,4–D–C14 absorbed by ironweed were rapidly metabolized to compounds not extracted by alcohol. Non-herbicide activity was also found in alcohol extracted fractions. C14 accumulations in field-treated ironweed were detected in roots and rhizomes 3 to 6 weeks after treatment.