Annual production of native grasses on the Texas Coastal Prairie was decreased by 90, 66, and 67 kg/ha in 1978, 1979, and 1981, respectively, for each 1% increase in mixed-brush canopy cover in the range, from 12 to 57%. Differences in regression coefficients among years were not significant (P$0.05), although rainfall varied from 84% of the 26-yr average (91.5 cm) in 1978 to 150% of the annual average in 1981. Grass production during the growing season (May through October) only was decreased by 58, 113, and 78 kg/ha in 1978, 1979, and 1981, respectively, for each unit percentage increase in brush canopy cover. A greater proportion of the annual rainfall occurred during the growing season of 1979 than during the drier spring and summer of 1978. Native grasses typical of brush-free Coastal Prairie occupy the interstitial areas among the mixed-brush mottes, but bunch cutgrass (Leersia monandra Swartz) is the only grass that persists from the canopy edge to 1.5 m inward from the brush driplines. Little or no herbaceous vegetation grows in the centers of the mottes.

Leaching of dl-strigol at six rates between 0.3 and 4.5 kg/ha through columns of sandy loam soil was estimated using a witchweed [Striga asiatica (L.) Kuntze # STRLU] germination bioassay. After 21 days of leaching daily with 1.27 cm of simulated rainfall, about 86% of the applied chemical remained in the top 2.5 cm of the soil, about 6% in the zone between 2.5 and 7.5 cm, and less than 1% in the soil at depths between 7.5 and 30 cm. However, even with the lowest rate of the chemical application, sufficient dl-strigol was leached to a soil depth between 22.5 and 30 cm to cause most, if not all, of the witchweed seeds to germinate. These results suggest that dl-strigol has a potential for use as an effective tool for a witchweed control or eradication program. No significant degradation of the chemical occurred in moist soil during the 21-day period.

Herbicide effects on vesicular-arbuscular mycorrhizal fungi were studied in greenhouse and field tests. In field plots treated with a bromacil (5-bromo-3-sec-butyl-6-methyluracil) and diuron (3-[3,4-dichlorophenyl]-1,1-dimethylurea) mixture, fungus infection was similar to levels present in cultivated plots. A slight reduction of infection occurred in roots of grove trees in a simazine (2-chloro-4,6-bis [ethylamino]-s-triazine) plus paraquat (1,1′-dimethyl-4,4′-bipyridinium ion)-treated plot compared to a cultivated plot. In the greenhouse studies, diuron, bromacil, and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) had no apparent effect on Glomus etunicatus Becker and Gerd. and plant growth. Paraquat, PPG 844 {1-(carboethoxy) ethyl 5-[2′-chloro-4′-(trifluoromethyl) phenoxy]-2-nitrobenzoate} and simazine adversely affected plant growth and the fungus.

Picloram (4-amino-3,5,6-trichloropicolinic acid) applied at 0.6 to 1.2 kg/ha as 5 or 10% pellets during the summer or fall usually killed 90% or more of the rayless goldenrod [Isocoma wrightii (Gray) Rydb.] on sandy loam soils in western Texas, whereas the higher rates were necessary for 80% or greater control following winter applications. Acceptable control persisted for 4 yr. Applications of tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}at 1.1 kg/ha as 20% pellets during summer controlled 85% of the rayless goldenrod, but summer applications of tebuthiuron at 0.6 kg/ha or winter applications at 0.6 or 1.1 kg/ha did not control the weed effectively. Dicamba (3,6-dichloro-o-anisic acid) applied at 0.6 or 1.1 kg/ha as 5% granules did not control rayless goldenrod. Prescribed burning in late February reduced the density of rayless goldenrod 18 to 41%, but decreased control with soil-applied picloram or tebuthiuron. Reduction in rayless goldenrod densities of 75% or greater following applications of picloram or tebuthiuron pellets more than doubled the estimated carrying capacity of the arid rangeland.

Control of natural infestations of dogfennel [Eupatorium capillifolium (Lam.) Small # EUPCP] and woolly croton (Croton capitatus Michx. # CYNCP) in a bermudagrass [Cynodon dactylon (L.) Pers. # CYNDA] – dallisgrass (Paspalum dilitatum Poir. # PASDI) sward ranged from 20 to 100% with surface-applied tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N-dimethylurea}. In general, efficacy increased with rate of application from 0.6 to 1.1 kg ai/ha, and with time to 107 days after treatment. Only 0.6 kg ai/ha controlled less than 90% of the weeds during the growing season. Dry matter yields of desirable forage ranged from 60 to 290 kg/ha more with tebuthiuron treatment than in the untreated check. There were no consistent differences in forage quality among treatments, which indicates that tebuthiuron had no detrimental effects upon the bermudagrass or dallisgrass.

Both gibberellic acid and the substituted phthalimide AC-94377 [1-(3-chlorophthalimido)cyclohexanecarboximide] actively promoted germination of dormant seeds in five species out of nine. The species that responded to both compounds included wild oat (Avena fatua L.), wild mustard [Brassica kaber (DC.) L.C. Wheeler], curly dock (Rumex crispus L.), field pennycress (Thlapsi arvense L.) and tansy phacelia (Phacelia tanacetifolia L. Benth.). on a weight-per-weight basis, the ability of AC-94377 to stimulate germination was equal to, or greater than, GA3. The other two substituted phthalimides tested, AC-92803 [2-(3-chlorophthalimido)-2-methyl-2-isobutyl-acetamide] and AC-99524 [1-tetrahydrophthalimido-cyclohexane-carboximide], had either slight or no stimulatory activity.

The growth retardant activity of MBR 18337 {N-[4-(ethylthio)-2-(trifluoromethyl)phenyl]-methanesulfonamide} was determined by injection into bean plants (Phaseolus vulgaris L. ‘Black Valentine’), California privet seedlings (Ligustrum ovalifolium Hassk.), and saplings of white ash (Fraxinus americana L.) and red maple (Acer rubrum L.). Height and leaf expansion of bean were inhibited by 8 μg of MBR 18337 per plant in growth chamber studies. Sprout growth of California privet grown in the greenhouse was inhibited for 92 days by 80 μg of MBR 18337 per tree, and the growth in the field of ash and maple saplings was retarded by 3.2 mg of MBR 18337 per tree for an entire growing season with little injury. Radioassays for 14C-MBR 18337 indicated rapid translocation of 14C-activity in privet from the lower stem to the region of the apical shoot. More than 80% of the MBR 18337 in the xylem and phloem was oxidized within 14 days.

Retention, absorption, translocation, and metabolism of 2,4-D [(2,4-dichlorophenoxy)acetic acid] by common waterplantain (Alisma triviale Pursh. # ALSPA) at three growth stages were investigated to determine the basis for differential susceptibility of common waterplantain at different growth stages. Plants in the five-leaf and scape elongation stages retained more 2,4-D than plants in the early flowering stage. Absorption of 14C-2,4-D by the flower stalk was less than absorption by the treated leaves regardless of growth stage. The majority of the absorbed 14C translocated out of the treated plant part was recovered in the aerial portion of the plant younger than the treated leaves or in the corm, with greater movement of 14C into the corm at the older growth stages. Metabolism of 14C-2,4-D did not differ among the growth stages. The results suggest that the greater sensitivity of common waterplantain at the scape elongation stage to 2,4-D is due to greater translocation to the corm when compared to the five-leaf stage, and greater retention when compared to the early flowering stage.

Investigations were conducted to determine whether light, temperature, or their interaction stimulated primary basal-bulb formation on underground stems of yellow nutsedge (Cyperus esculentus L.) seedlings grown from tubers. Basal-bulb formation results when internodes shorten and leaves lengthen. When seedlings were grown without medium around the underground shoots, a temperature alternation of 10C stimulated basal-bulb formation; light did not affect the process. When seedlings were grown with medium around the underground shoots, either light or alternating temperature stimulated basal-bulb formation. Nine colors of light gave the same stimulus as white (fluorescent) light. Phytochrome did not appear to be the photoreceptor for the stimulus, as both red and far-red light responses were identical to that of white light.

For 3 yr, fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} at 0.1, 0.2, and 0.3 kg/ha, was applied with or without 0.6 kg/ha of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) before the preplanting irrigation for cotton (Gossypium hirsutum L.). Without trifluralin, fluridone at 0.1 kg/ha controlled less than 60% of annual grasses or redroot pigweed (Amaranthus retroflexus L.), but the 0.3-kg/ha rate controlled 90%. With trifluralin, fluridone at all rates controlled 98% of these weeds. Fluridone alone controlled 85% or more of black nightshade (Solanum nigrum L.). Fluridone did not alter cotton stand or yield. Fluridone residues 8 months after treatment reduced growth of several crops and weeds by 75% or more.

Interference of common lambsquarters (Chenopodium album L.) in sugarbeets (Beta vulgaris L. ‘Mono Hy D2′) was determined in a 2-yr field experiment. Yield of sugarbeet roots and recoverable sucrose/ha decreased as the density of common lambsquarters increased. At densities of 6, 12, 18, and 24 common lambsquarters plants/30 m of row, root yields were reduced 13, 29, 38, and 48%, respectively, and recoverable sucrose yields were reduced 11, 27, 37, and 46%, respectively. The minimum number of common lambsquarters plants required per 30 m of row to reduce sugarbeet root yields was estimated to be six in 1980 and four in 1981.

Increasing the corn (Zea mays L. “CO-OP S265”) population from 33 300 to 133 300 plants per hectare in the field significantly reduced yellow nutsedge (Cyperus esculentus L. # CYPES) above-ground biomass, tuber number, tuber weight and yellow nutsedge height at the end of growing season, and significantly increased corn yield. Photosynthetically active radiation below corn canopies decreased with increasing corn population and corresponded to reductions in yellow nutsedge above-ground biomass, tuber weight and tuber number. These results demonstrate that available light is a major factor in yellow nutsedge competition with corn. The size of yellow nutsedge was also reduced at high corn densities. These results support the use of crop manipulation in an integrated yellow nutsedge management system in corn.

Diclofop [2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid] was evaluated to determine Italian ryegrass (Lolium multiflorum Lam.) control and effect on yield of winter wheat (Triticum aestivum L.). Diclofop applied at 0.5, 0.75, 1.0, and 1.5 kg/ha postemergence provided excellent control of ryegrass and resulted in significant yield increases of winter wheat. Diclofop was most effective when applied at the two- to three-leaf stage of Italian ryegrass growth. Postemergence applications of diclofop plus bentazon [3-isopropyi-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] gave excellent control of ryegrass and significant increases in wheat yields.

Curly dock (Rumex crispus L.) seeds failed to germinate in the dark, but germinated readily in light at 15, 20, and 25C. A secondary dormancy was induced in these seeds by 6 days of dark or light incubation at 30C (thermodormancy), by 6 days of dark incubation at 15C, or by a prolonged soaking in −15.7 bar polyethylene glycol-6000 (PEG) solution at 15C in light. The secondary dormancy induced at 15C was partially removed by 2-chloroethylphosphonic acid (ethephon) in presence of light; however, when the dormancy was induced at 30C, an addition of gibberellin A4+7 (GA4+7) to ethephon was necessary for effective removal of the dormancy. The ability of growth regulators to remove the secondary dormancy induced by prolonged dark incubation at 15C decreased progressively in light as the duration of dark incubation increased. The water-potential studies indicate that the thermodormancy can be attributed, at least in part, to the inability of the embryonic cells to lower their water potential to a level sufficient to cause radicle protrusion.

In four field experiments, acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} applied preemergence at 1.1 kg/ha was not phytotoxic to peas (Pisum sativum L.) and increased the yield of shelled peas by an average of 25% compared to the weedy control. Yields were highest in all four experiments at the 1.1 kg/ha rate and tended to decline at higher rates of application. Growth chamber studies demonstrated that pea tolerance to acifluorfen was not affected by temperatures of 16/10 to 27/21C (light/dark) nor by stimulated rainfall of 0.5 to 5.0 cm. Peas and soybeans [Glycine max (L.) Merr.] were more tolerant of acifluorfen than were snap beans (Phaseolus vulgaris L.) and lima beans (Phaseolus lunatus L.) when acifluorfen was applied preemergence in the greenhouse or in hydroponic nutrient solution.

Salicylic acid, p-hydroxybenzoic acid, caffeine, hydroquinone, and umbelliferone were evaluated in the greenhouse for their effects on shoot dry-weight accumulation of several crop and weed species. With the exception of caffeine, all the chemicals reduced shoot growth in oats (Avena sativa L. ‘Goodfield’). Chemicals applied preplant incorporated, preemergence, or postemergence were effective, depending upon the rate of chemical. When applied preplant incorporated at rates as high as 56.0 kg/ha, most of the chemicals reduced growth of corn (Zea mays L. ‘B73 × Mo17′), soybean [Glycine max (L.) Merr. ‘Corsoy’], velvetleaf (Abutilon theophrasti Medic.), redroot pigweed (Amaranthus retroflexus L.), and wild proso millet (Panicum miliaceum L.). Exceptions were caffeine on corn and soybean and hydroquinone on soybean. At 11.2 kg/ha the chemicals inhibited the weed species more than the crop species. Postemergence applications of caffeine and hydroquinone inhibited growth of the weed species more than the crop species. Hydroquinone at 1.1 kg/ha inhibited redroot pigweed, but rates as high as 11.2 kg/ha did not inhibit soybean. These experiments show that growth of agronomically important crops and weeds can be inhibited differentially by allelopathic chemicals.

Detection and degradation of linuron [3-(3,4-dichlorophenyl) -1 - methoxy -1 - methylurea] in organic soils were studied using biological assays and chromatographic techniques. The level of linuron that caused 50% growth reduction of onion (Allium cepa L.) varied among three soils of greatly differing organic matter contents. Linuron and its metabolites were successfully separated with florisil column chromatography using a five-fraction solvent system; however, only linuron and 3 - (3,4 - dichlorophenyl) -1 -methylurea could be extracted from organic soil samples at satisfactory recovery rates. Soil samples from eight grower fields and from field plots were analyzed to determine the residue level of these two compounds. Quantitative assessment of the compounds was made with high pressure liquid chromatography. Results of the biological assay and chromatographic analysis showed that linuron and its phytotoxic metabolite, 3 - (3,4 - dichlorophenyl) -1 - methylurea, were not accumulating in the organic soils of Ontario and that the levels detected were not phytotoxic to onions when grown in pot bioassays.

Combination treatments of 2,4-D [(2,4-dichlorophenoxy)acetic acid] + mecoprop {2-[(4-chloro-o-tolyl) oxy] propionic acid} + dicamba (3,6-dichloro-o-anisic acid) injured actively growing bermudagrass [Cynodon dactylon (L.) Pers. # CYNDA] immediately after treatment. Treatments made at the normal (1.1 + 0.6 + 0.1 kg ai/ha) rate in August, September, or October, did not affect winter survival. A triple rate (3.3 + 1.8 + 0.3 kg/ha) delayed growth of ‘Tifgreen’ and ‘Tifdwarf’ more the following April than ‘Tifway’ and ‘Ormond’. Due to a reduction in turf stand from herbicide treatments, the cover of common chickweed [Stellaria media (L.) Cyrillo # STEME] was higher in plots to which herbicides were applied in August or September than in untreated plots. The cover of weeds was lower in Tifway and Ormond plots than in Tifgreen and Tifdwarf plots.

Soil uptake, translocation, and metabolism of simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) by tolerant poplar clone Populus × euramericana I-45/51, a section Aigeiros hybrid, and intolerant clone P. maximowiczii × P. trichocarpa Kingston, a section Tacamahaca hybrid were compared. Concentrations of simazine in the two clones were not different 48 h and 1 week after application. However, the presence of 2-chloro-4-amino-6-ethylamino-s-triazine (G-28279), a less toxic simazine metabolite, was detected in tolerant clone I-45/51 after 12 h and it increased steadily through 1 week after simazine application. In contrast, no trace of G-28279 was found in susceptible clone, Kingston.

Large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] control with BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one} was similar whether applied alone or in combination with acifluorfen {5-[2-chloro-4-(trifluoromethyl) phenoxy]-2-nitrobenzoic acid}. Combinations of BAS 9052 OH and bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4-(3H)-one 2,2-dioxide] gave decreased grass control compared to BAS 9052 OH alone. This antagonism between BAS 9052 OH and bentazon was eliminated by applying bentazon as a separate application 1.5 h or longer before the application of BAS 9052 OH. A 0.2 h interval between applications of the herbicides decreased large crabgrass control compared to control obtained with BAS 9052 OH applied alone, but the decrease was signifciantly less than occurred with a concurrent application of the two herbicides.