A rainfall simulator was used to evaluate the effects of washoff on 10 foliar-applied herbicides on johnsongrass [Sorghum halepense (L.) Pers. # SORHA] in greenhouse experiments during 1983 and 1984 at Stoneville, MS. Time intervals between herbicide application and rainfall ranged from 20 to 240 min. Johnsongrass topgrowth control was equivalent to rain-free treatments using DPX-Y6202 {ethyl [2-[4-(6-chloro-2-quinozalinyl)oxy] phenoxy] propionate} at 0.03 and 0.06 kg/ha at time periods of 90 and 40 min between herbicide application and rainfall, respectively, at 28 days after treatment (DAT). A period of 120 min was required for johnsongrass control equivalent to rain-free treatments using sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.06 kg/ha, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} at 0.03 and 0.06 kg/ha, and cloproxydim {(E,E-2-[1-[[(3-chloro-2-propenyl)oxy] imino] butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 28 DAT. Neither glyphosate [N-(phosphonomethyl)glycine] and SC-0224 (trimethylsulfoniumcarboxy methylaminomethylphosphonate) at 0.45 and 0.99 kg/ha nor other selective herbicides at 0.03 and 0.06 kg/ha gave equivalent johnsongrass topgrowth control to rain-free treatments when rainfall occurred within 240 and 120 min, respectively.

Light reflectance from soybean foliage was compared to visual evaluations for assessing soybean injury caused by postemergence-applied paraquat and glyphosate. Coefficients of variation and of determination from multiple linear regressions for both herbicides indicated that reflectance was better correlated with injury measured by changes in leaf number, leaf weight, and stem weight than visual evaluations. Correlation coefficients among radiometer readings taken by different individuals were ≥0.98 for both herbicides. Correlation coefficients among visual evaluators ranged from 0.69 to 0.96 and from 0.74 to 0.94 for plots treated with paraquat and glyphosate, respectively. Light reflectance measured with a radiometer may be useful in evaluating injury from herbicides that cause chlorosis, necrosis, or defoliation of the target species.

Glufosinate-resistant transgenic creeping and velvet bentgrass plants expressing a bar gene under the control of the maize ubiquitin promoter were inoculated separately with the fungal pathogens, Rhizoctonia solani and Sclerotinia homoeocarpa, before or after treatment with 560 mg L−1 of glufosinate at a rate of 0.56 kg ha−1. Application of the herbicide 3 h before or 1 d after fungal inoculation significantly reduced infection of these transgenic grasses by R. solani and S. homoeocarpa. Assessment of the in vitro antifungal activity of the herbicide showed that 336 and 448 mg L−1 glufosinate completely inhibited the mycelial growth of S. homoeocarpa and R. solani, respectively. The results suggest that the nonselective herbicide glufosinate may also be used to suppress the activity of some fungal pathogens in turf composed of these transgenic glufosinate-resistant creeping and velvet bentgrasses.

Controlled-environment experiments were conducted to determine giant foxtail epicuticular wax (ECW) deposition and fluazifop-P absorption under different environmental conditions and with two adjuvants. Drought stress and low temperature increased leaf ECW content, whereas low light intensity decreased ECW content compared with medium light intensity. Drought stress conditions decreased the fatty acid and primary alcohol content of ECW and increased the hydrocarbon content compared with field capacity. Compositional changes would make the ECW more hydrophobic and reduce leaf wetting by herbicide spray. Increasing air temperature decreased the aldehyde content of ECW, whereas decreasing light intensity increased ECW fatty acid and aldehyde content while decreasing primary alcohols and esters. Compositional changes under low light intensity would make the ECW more hydrophilic and increase leaf wetting by a herbicide spray. Drought stress reduced fluazifop-P absorption regardless of the temperature but could not further reduce fluazifop-P absorption under low light intensity. Fluazifop-P absorption by plants under low light and drought stress conditions was similar to plants under low or medium light intensity and field capacity conditions. Similarly, the rate of fluazifop-P absorption was less under drought stress and low light conditions. Fluazifop-P absorption was greater when crop oil concentrate was added compared with 28% urea ammonium nitrate or no additive. Crop oil concentrate, added to the herbicide solution, overcame reduced fluazifop-P absorption under the low light conditions and in one of the two drought stress regimes but could not overcome reduced fluazifop-P absorption with the high temperature regime.

Germination of jointed goatgrass (Aegilops cylindrica Host.) seed in nitrate nitrogen (NO−3-N), gibberellic acid (GA3), or distilled water was studied in the laboratory, and depth of emergence of seedlings from soil was studied in the greenhouse and laboratory. After 14 days in germination chambers in distilled water, no difference in percent germination of 1-yr-old or freshly harvested seed existed between 10, 15, or 20 C. Jointed goatgrass seed germinated at temperatures ranging from 10 to 35 C and responded to temperature more than to NO−3-N. Seedlings did not emerge from below 5 cm in greenhouse and 6 cm in laboratory studies even though germination occurred. Jointed goatgrass has the seed germination and seedling emergence characteristics to develop into a severe annual grass weed in winter wheat (Triticum aestivum L.)-producing regions, particularly where reduced-tillage practices are utilized.

Field experiments designed to determine the efficacy and interaction of hexazinone [(3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] and nitrogen on weeds and lowbush blueberry [Vaccinium angustifolium (Ait.)] growth and yield were established at five locations in 1980 and 13 locations in 1981. Hexazinone was applied after pruning, preemergence with nitrogen, using a split-block design, with locations serving as replications. Grasses, goldenrod (Solidago spp.), and meadowsweet [Spiraea latifolia (Ait.) Borkh. # SPVLF] were reduced significantly as the rate of hexazinone was increased. Blueberry injury, plant stand, number of flower buds, and yield all increased with increases in hexazinone rate. Variations in blueberry yields occurred among locations due to differences in plant stand and productivity, as well as climatic and edaphic factors. Within each nitrogen rate, increases in the rate of hexazinone resulted in a quadratic increase in blueberry yield. Within the hexazinone treatments, increasing nitrogen had no effect on yield. Blueberry yield reached a maximum of 3926 kg/ha at a hexazinone rate of 1.83 kg/ha. Partial budgeting was used to evaluate the effect of combinations of hexazinone and nitrogen on net income. Response function analysis determined yield and profit-maximizing combinations of hexazinone and nitrogen. Partial budgeting indicated that hexazinone alone or combined with nitrogen increased net income, but nitrogen without hexazinone decreased net income. Response function analysis indicated that hexazinone at 1.79 kg/ha without nitrogen maximized profits.

The study was conducted to determine the seasonal and diurnal water stress of soybeans [Glycine max (L.) Merr. ‘Lee 74′] grown under intraspecific competition (competition between plants of the same species) and interspecific competition (competition between plants of different species) with common cocklebur (Xanthium pensylvanicum Wallr.). Midday xylem potentials decreased as the season progressed and were lower in common cocklebur during vegetative growth of soybean and in soybean during reproductive growth. For a given species differences in xylem potential due to mode of competition were small. In the diurnal studies xylem potential for each species decreased to a minimum in the early afternoon but recovered to the original pre-dawn values at night. As the season progressed leaf xylem potential (a) decreased at a greater rate, (b) decreased sooner in the day, and (c) recovered at a slower rate. It was shown that differences in xylem potential between soybean and common cocklebur on a given day were small. Greater diffusive resistance values generally were found with soybean than with common cocklebur and with each species grown under interspecific competition.

Plants started with seed, 'seedlings', and established plants of silverleaf nightshade (Solanum elaeagnifolium Cav.) were grown in the field under shade levels of 0, 47, 63, and 92% of full sunlight to determine vegetative, reproductive, and physiological responses to shade. Dry-matter production of both 'seedling’ and established plants declined markedly with increasing shade levels. Established plants did not bear fruit under 92% shade, and 63% shade prevented fruit production by 'seedlings'. Taproots of plants grown in full sunlight contained 16% more total non-structural carbohydrate (TNC) per gram dry weight than taproots of plants grown under 92% shade. Leaves of established plants grown under moderate shade had significantly more chlorophyll per unit leaf fresh weight than plants grown in full sunlight; however, plants under heavy (92%) shade had 35% less chlorophyll per unit leaf area than unshaded plants. The chlorophyll a/b ratio of the 92%-shaded plants was significantly less than with other treatments. Leaf area increased, with increasing shade; however, leaf weight per unit area decreased because of thinner leaves. Photosynthetic rates of recently expanded leaves were 10.4, 4.6, 3.3, and 0.9 mg CO2 · dm−2 · h−1 for the 0, 47, 63, and 92% shade treatments, respectively.

Wheat (Triticum aestivum L. ‘Holley’) was grown for 14 days in 0.5 strength Hoagland and Arnon's complete mineral nutrient solution containing 0. 15.6, 31.25, 62.5, 125.0, or 250.0 ppbw EPTC (S-ethyl dipropylthiocarbamate). Gibberellic acid (GA) content, as measured by gas-liquid chromatography, was decreased 96.4% by 125.0 ppbw EPTC. When 0.05 μCi mevalonic acid-2-14C-(MVA-2-14C) (DBED salt) (0.15 mCi/mg MVA) was added to the nutrient solution, incorporation of MVA-2-14C into total kaurenoids was decreased 90% by 250 ppbw EPTC. Metabolism of kaurene was reduced by 250 ppbw EPTC with resultant 3-fold accumulations of kaurene.

Controlled environment experiments were completed to determine the effect of temperature on giant foxtail and fall panicum germination, emergence, and growth. Giant foxtail seed germination decreased when exposed to a constant 30 C compared to 20 C. Germination also decreased in the alternating 20/30 C temperature regime when the hours of exposure to 30 C as compared to 20 C increased. Fall panicum required alternating temperatures of 14 C (9 h)/28 C (15 h) to germinate. Giant foxtail seed germination exceeded 60% 4 d after exposure to an alternating temperature of 7 C (9.4 h)/20 C (14.6 h). Conversely, fall panicum seed did not germinate at the 7 C (9.4 h)/20 C (14.6 h) temperature regime and required a minimum of 7 d exposure to alternating temperatures of 13 C (8.7 h)/26 C (15.3 h) for 88% of the seed to germinate. The greatest emergence of giant foxtail and fall panicum was from 1 cm and 1 to 2.5 cm, respectively. Less than 5% of the giant foxtail and fall panicum seed emerged from 7.5 cm. The growth of giant foxtail seedlings was five times greater than that of fall panicum at each temperature regime tested. Incorporation of this information into bioeconomic models could result in accurate predictions of weed germination for effective weed management strategies.

Alternative herbicide formulations may have the potential to reduce atrazine leaching. This study was conducted to determine if starch-encapsulation produced using an extrusion process or several acrylic polymer additives reduced atrazine leaching in soil columns packed with Plainfield sand (98% sand and 0.7% organic matter). Three watering regimes were evaluated to determine the effects of water volume and rate of application on atrazine movement When 7.6 cm of water (0.44-pore volumes) was applied over 2 h, polymer treatments reduced atrazine movement from the soil surface by 9 to 21% compared to atrazine without the additives. With increased water volume and time, the effectiveness of several polymer treatments diminished. Acrysol ASE-108 and G110 polymers (mixed with atrazine at a 1:1 ratio) most effectively reduced atrazine leaching over all watering regimes. Starch encapsulation was more effective than any polymer additive in retarding atrazine movement Increasing the water volume from 7.6 to 15.2 cm (0.88-pore volumes) did not increase leaching of starch-encapsulated atrazine. Ninety-nine percent of the starch-encapsulated atrazine was retained in the top 5 cm of the column compared to only 18 and 13% of the dry flowable formulation (DF) when 0.44- and 0.88-pore volumes of water were applied over 2 and 4 h, respectively. When 0.88-pore volumes of water were applied over 12 d, 81% of the starch-encapsulated atrazine was retained in the upper 5 cm of the column compared to only 5% of the DF formulation of atrazine. This study indicates that starch encapsulation reduces atrazine movement to a greater extent than polymer additives and suggests that starch encapsulation may be an effective method of reducing atrazine leaching.

In comparative evaluation of adjuvant effects in eight species, nonionic silicone-glycol surfactants enhanced the activity of six herbicides to a greater extent than a standard organic surfactant, whereas cationic amino silicone surfactants enhanced to a lesser extent. The efficacy of the nonionic silicones was associated with (a) a greater enhancing action in species, particularly grasses, that were relatively resistant to herbicides applied without adjuvants and (b) a greater ability to enhance herbicides with very low water solubility. The cationic silicones in combination with some of the herbicides provided less enhancement in moderately sensitive crops than did the standard organic surfactant but provided equivalent enhancement on some weeds. The threshhold concentration for enhancement by silicone-glycols was 0.01% in a susceptible species and 0.1% in a resistant species. In yellow nutsedge (Cyperus esculentus L.), a silicone-glycol surfactant at a concentration of 0.5% provided greater enhancement of several herbicides than any of three organic surfactants or an emulsifiable oil.

Real-time polymerase chain reaction (real-time PCR), also known as quantitative PCR, is used to determine relative gene expression or to quantify exact levels of mRNA in cells or tissues. Before the advent of real-time PCR, the major difficulty associated with traditional quantitative or semiquantitative PCR was to ensure that PCR reactions were quantified within the exponential phase of amplification. Real-time PCR alleviates that problem by detecting and quantifying fluorescent signals after each amplification cycle. Additionally, it does not require running gels and thus is able to produce data in 2 to 3 h. Four different types of chemistries, DNA-binding agents (SYBR Green), hydrolysis probes (TaqMan), hairpin probes (molecular beacons, scorpions), and fluorescent-labeled hybridization probes (Light Cycler), have been commonly used for real-time PCR. Among those chemistries, SYBR Green is the most economical choice. We have used real-time PCR and SYBR Green to examine the expression of a number of leafy spurge genes after growth induction and during normal seasonal growth. Because no reliable endogenous reference genes have been identified in leafy spurge, we performed PCR without an endogenous reference gene and analyzed messenger RNA (mRNA) expression based on the threshold cycle (CT) value of amplification. Excluding an endogenous reference gene from that data analysis was rather straightforward and reliable if RNA was properly prepared and quantified. Given that genomic tools, such as expressed sequence tags (ESTs), and their expression profiles are lacking for most weedy species, avoiding the use of endogenous reference genes in real-time PCR simplifies the optimization process and reduces the cost tremendously. However, we found that using a passive reference dye (ROX) to normalize non-PCR–related fluctuations in fluorescent signal is desirable.

Field studies were conducted over a 3-yr period to evaluate weed control systems for soybeans [Glycine max (L.) Merr.] grown in 18- and 76-cm rows. Combinations of herbicides satisfactorily controlled a broad spectrum of annual grass and broadleaf weeds in soybeans grown in 76-cm rows with cultivation and in 18-cm rows without cultivation. Where a single herbicide treatment was used to control only annual grasses, the 76-cm rows (which were cultivated once) yielded from essentially the same as 18-cm rows up to almost 50% more than the 18-cm rows, which received no cultivation, depending on the year and broadleaf weed infestation. However, where herbicide combinations were used to effectively control all weeds, soybeans in 18-cm rows averaged up to 9% higher yields than those in the 76-cm rows.

The antifungal activity of the herbicides bialaphos and glufosinate, the active moiety of bialaphos, was assessed. Bialaphos showed a higher level of in vitro antifungal activity against Rhizoctonia solani, Sclerotinia homoeocarpa, and Pythium aphanidermatum than glufosinate. Glufosinate suppressed the mycelial growth of R. solani and S. homoeocarpa, but it had no inhibitory effect on P. aphanidermatum up to the highest concentration in our testing regimes. Various concentrations of bialaphos solutions were applied to transgenic, bialaphos- and glufosinate-resistant creeping bentgrass inoculated with fungal pathogens. Bialaphos applications were able to significantly reduce symptomatic infection by R. solani and S. homoeocarpa on transgenic plants. Bialaphos significantly inhibited P. aphanidermatum, but not to the same degree that R. solani and S. homoeocarpa were inhibited. These results indicate that bialaphos may provide a means for the simultaneous control of weeds and fungal pathogens in turf areas with transgenic, bialaphos-resistant creeping bentgrass.

Field tests in 1980 and 1981 indicated that smooth pigweed (Amaranthus hybridus L.) competition affected cotton (Gossypium hirsutum L. ‘GSA 71′) water relations by reducing plant water status early in the season and by shading late in the season. Early in the growing season, cotton leaf water potential and turgor pressure reductions as great as 0.53 and 0.21 MPa, respectively, were measured at a smooth pigweed density of 2.5 plants m-2. Late in the 1981 growing season, smooth pigweed reduced the photon flux density reaching the cotton canopy by 90% at midday. The shaded conditions resulted in increased cotton water potential under low soil water conditions, but the inability to reduce solute potential lowered the turgor pressure of cotton, irrespective of soil water level. Comparisons of smooth pigweed and cotton water relations indicated that smooth pigweed had the capacity to maintain higher water potential and turgor pressure than cotton. The more favorable water status of smooth pigweed resulted in part from increased water extraction at lower depths in the soil profile and higher diffusive resistance, thereby reducing transpirational water loss.

The persistence of 4-amino-3,5,6-trichloropicolinic acid (picloram) in soil was measured after varying periods of time up to 3 years with bioassay technique using sunflowers (Helianthus annuus L., var. Advent) as the indicator plant. Rates of application ranged from 0.5 to 48 oz/A on two soil types at Scott, Saskatchewan and two at Lacombe, Alberta. After 1 year, recovery ranged from 20 to 30% of the original application in the 0 to 9-inch depth in each soil not disturbed by tillage directly after application. Recovery of the herbicide applied at rates of 8 oz/A or higher in the fall declined to about 10% after 24 months and to 6% or less after 35 months for even the highest rates. Picloram activity generally was concentrated in the surface 6 inches, indicating limited downward movement due to water in each of the soils. However, there was a tendency toward greater downward movement in the soils having lower organic matter content.

Field studies in 1990 and 1991 at six locations in Georgia and one location in North Carolina evaluated AC 263,222 for weed control, peanut tolerance, and yield. AC 263,222 applied early postemergence at 71 g ai ha−1 controlled bristly starbur, coffee senna, common lambsquarters, Ipomoea species, prickly sida, sicklepod, smallflower morningglory, and yellow nutsedge at least 91%. AC 263,222 controlled common cocklebur 77% and Florida beggarweed from 47 to 100%. Crop injury was 4% for AC 263,222 applied once and 12% or less from two applications. Mixtures of bentazon with AC 263,222 did not improve control compared to AC 263,222 alone. Imazethapyr did not improve control of AC 263,222 systems. In several locations, bentazon reduced control of Florida beggarweed with AC 263,222 when applied in a mixture compared to AC 263,222 alone. Weed control from the standard of paraquat plus bentazon applied early postemergence followed by paraquat, bentazon plus 2,4-DB applied POST did not provide the level or spectrum of weed control as AC 263,222 systems.

Dryland and irrigated field experiments were established to measure differences in soil water relations throughout the growing season between plots in which cotton was grown with and without silverleaf nightshade interference. Soil moisture readings were taken weekly at 15-cm increments to a maximum depth of 120 and 150 cm during 1984 and 1985, respectively. When cotton was grown with silverleaf nightshade, soil water loss was greater at the lower portion of the soil profile earlier in the growing season than when cotton was grown alone. In the irrigated environment in 1985 when precipitation was higher than normal and the soil moisture content remained above normal, soil water loss did not differ. Cotton lint yield, plant height, and boll size reflected the amount of soil moisture available for growth and development of the crop. A statistical technique for quantifying soil water relations between the crop growing alone and growing with interference from the weed is demonstrated.

A population of rigid ryegrass (Lolium rigidum Gaudin) from a field on the Eyre Peninsula, South Australia, was suspected of resistance to thiocarbamate herbicides. Dose–response studies were conducted on this population (EP162) and two susceptible populations (SLR4 and VLR1). The resistant population exhibited cross-resistance to triallate, prosulfocarb, EPTC, and thiobencarb with higher LD50 to triallate (14.9-fold), prosulfocarb (9.4-fold), EPTC (9.7-fold), and thiobencarb (13.6-fold) compared with the susceptible populations SLR4 and VLR1. The resistant population also displayed resistance to trifluralin, pyroxasulfone, and propyzamide. The LD50 of the resistant population was higher for trifluralin (13.8-fold), pyroxasulfone (8.1-fold), and propyzamide (2.7-fold) compared with the susceptible populations. This study documents the first case of field-evolved resistance to thiocarbamate herbicides in L. rigidum.