A field study was conducted for 3 yr to evaluate residual levels of fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) for their effects on injury and yields of rice (Oryza sativa L.). All three herbicides consistently injured rice and reduced yield at application rates above 0.1 kg/ha. These herbicides were similar in their effects on rice, but trifluralin was slightly more phytotoxic than fluchloralin or profluralin. Bioassay showed fluchloralin and trifluralin to be more inhibitory than profluralin of root and shoot elongation. The order of toxicity of the vapors of these herbicides arising from treated soil was found to be trifluralin > profluralin > fluchloralin. Grain sorghum (Sorghum bicolor L. Moench) was slightly more sensitive to these herbicides than was rice when seedlings were grown in treated soil and over 10 times more susceptible than rice to injury from their vapors. Both plant species were less affected by the herbicides in silty clay than in silt loam soil.

The phytotoxicity of terbacil (3-tert-butyl-5-chloro-6-methyluracil) is not closely correlated with the amount applied, the amount in available soil solution, or the concentration in available soil solution since soil type has a pronounced effect on the levels necessary for phytotoxicity. About 19 times more terbacil was needed in a Chalmers silty clay loam (24% organic matter) than in a Bloomfield fine sand (0.3% organic matter) to cause a 30% control of sorghum (Sorghum biclor (L.) Moench ‘R.S. 610’). However, the Bloomfield fine sand required twice as great a concentration of terbacil in the soil solution as the Chalmers silty clay loam (0.314 μg/ml versus 0.157 μg/ml). The total adsorption of terbacil in the latter soil decreased 4.5 fold when the water: soil ratio was increased from 0.6:1 (approximately field capacity) to 32:1, but the ratio of the concentration adsorbed: concentration in the soil solution did not vary appreciably.

Since the first identification of glyphosate resistance in horseweed in California in 2005, the glyphosate-sensitive (GS) biotype has become rare, whereas the glyphosate-resistant (GR) biotype has become dominant in the eastern San Joaquin Valley (SJV). This is an area exposed to regular usage of glyphosate and to high levels of ambient ground-level ozone (O3). A previous study showed that SJV biotypes of GR are more robust than GS in the absence of ozone. This advantage was reduced, though not eliminated, at elevated O3. This suggests that the rapid evolution of resistance to glyphosate was not linked to evolution of resistance to O3. In this study, we contrasted these responses to O3 in the presence of concurrent glyphosate pressure. The GR and GS biotypes differed in growth and injury, reflecting their known differential sensitivities to glyphosate, but responded similarly to O3 with no O3 × biotype interaction. Ozone imposed an unexpected, but ecologically important, impact that enhanced the performance advantage of GR over GS. In the presence of the combination of glyphosate and O3 the biomass of GR was reduced to low but viable levels, whereas the biomass of GS was reduced to nonviable levels that effectively removed it from the population. These data do not support a genetic linkage between resistance to glyphosate and to O3, but suggest that air pollution may have accelerated the fixation of glyphosate-resistance alleles in California horseweed populations.

Thirteen treatments during a 5-year period with a 1 : 1 mixture of the propylene glycol butyl ether esters of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4-5 trichlorophenoxyacetic acid (2,4,5-T) were required to eradicate an established stand of kudzu, Pueraria lobata (Willd.) Ohwi.

At Lincoln 20 lb/A of 2,3,6-trichlorobenzoic acid (2,3,6-TBA) destroyed Clark soybeans five seasons after application. Soil persistence of 2,3,6-TBA in the light textured soils and low rainfall of western Nebraska was less than at Lincoln. A 10 lb/A rate of 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) reduced weed and oat yields at Lincoln the third growing season after its application. Applications of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis-(ethylamino)-s-triazine (simazine), or monuron at 10 lb/A reduced oat yields at North Platte the third growing season after their application. Herbicide carryover is a greater problem in arid than in humid regions of the United States.

2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), ethyl N,N-di-n-propylthiolcarbamate (EPTC), and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) were shown to aid in the establishment of rose clover (Trifolium hirtum All.) and harding-grass (Phalaris tuberosa L. var. stenoptera (Hack.) Hitch.) by reducing competition from resident annual plants, primarily medusahead (Elymus caput-medusae L.). The success of preemergence herbicides was shown to depend on fall precipitation in amounts great enough to permit seed germination and plant growth before winter temperatures become limiting. The degree of weed control necessary to aid in seedling establishment was low, sometimes lower than could be measured by estimates of ground cover.

The following table of chemical and physical properties of some herbicides was compiled as an aid to agricultural research workers.

A total of 452 rice farmers from three main granary areas of Muda Agricultural Development Authority (MADA), Kemubu Agricultural Development Authority (KADA), and Integrated Agricultural Development Area Barat Laut Selangor (IADA BLS) were surveyed in 2019. The goal was to determine farmers’ knowledge of and management practices for weedy rice (Oryza spp.) as well as the adoption level of Clearfield® rice technology (CRT) in Malaysia. Most farmers (74%) were adept at recognizing weedy rice. The majority of farmers (77%) perceived transplanting and water seeding rice systems as the best options to manage weedy rice, while only 10% of the farmers adopted CRT. The low level of adoption of this technology was due to several constraints, including the high cost of the CRT package and occurrence of imidazolinone (IMI)-resistant weedy rice in their farms. Farmers from MADA and IADA BLS reported the occurrence of IMI weedy rice in their farms for more than nine planting seasons, whereas those from KADA reported having resistant weedy rice for five to six planting seasons. The main factor contributing to the evolution of IMI-resistant weedy rice was ignorance about the technology and deliberate disregard of stewardship guidelines. The survey revealed that there is a need to increase awareness about CRT through training and educational programs for proper adoption of this technology.

In the central Great Plains, late summer seedings of alfalfa have often been used in order to avoid the annual weed problem associated with spring seedings. Because moisture conditions are unreliable in the fall, development of techniques to reduce the hazard of annual weed competition in spring seedings offers considerable promise. The authors, in previous reports, indicated that materials that give adequate control of annual weedy grasses and broadleaved weeds are available. These tests were made on plantings of Ranger alfalfa.

Absorption and translocation of 14C-fluroxypyr were determined for leafy spurge at various growth stages, under differing relative humidity and temperature conditions, and when applied with picloram or 2,4-D. Absorption of 14C-fluroxypyr was greater in vegetative plants (39%) than in flowering or postflowering plants (25%), while total translocated to roots averaged 2% of applied herbicide regardless of growth stage. Greater 14C-fluroxypyr absorption and translocation occurred in plants exposed to high relative humidity (>90%) compared to low humidity (<30%) for 6 h or longer following treatment. Absorption and translocation to roots was independent of temperature (18 or 24 C). Absorption and translocation declined by 50% when applied with picloram or 2,4-D. However, absorption and translocation of 14C-picloram or 14C-2,4-D were not affected by fluroxypyr. Fluroxypyr would likely be used in a leafy spurge control program only during environmental conditions adverse to control with picloram such as unseasonably warm or cold temperatures or in areas with a high water table.

Sicyos deppei G. Don (Cucurbitaceae) is an annual weed that disperses dormant seeds. The influence of scarification and light on their germination was studied in the laboratory. Scarified seeds collected in 1987, 6, 7, 8, and 9 mo postharvest, gave high germination both in white light (89 to 100%) and darkness (64 to 96%), in comparison with nonscarified seeds which germinated 7 to 20% in both conditions. Scarified seeds collected in 1989, 3 mo postharvest, germinated higher (52 to 69%) than nonscarified seeds (0 to 5%). Exposure to light did not break dormancy of nonscarified seeds. The reversal of dormancy by scarification describes them as hard seeds. Scarified seeds, 3 mo postharvest, were light indifferent, germinating even in the usually inhibitory condition of far-red light. However, a low proportion of scarified seeds, 6 and 7 mo postharvest, presented a positive photoblastic response and germinated 23 and 36%, respectively.

Parasitic weeds such as Phelipanche and Orobanche are obligate holoparasites that attack roots of almost all economically important crops in semiarid regions of the world. A wide variety of parasitic weed control strategies (chemical, biological, cultural, and resistant crops) has been tried. Unfortunately, most are partially effective and have significant limitations. The current mini review will discuss the needs for alternative methods and will summarize current and new biotechnology-based approaches for broomrape control. At present, we have generated transgenic tobacco plants expressing a cecropin peptide (sarcotoxin IA), under the control of the inducible HMG2 promoter. Transgenic lines enhanced host resistance to the parasitic weed; transgenes showed higher numbers of aborted parasitization events, reduced Phelipanche biomass, and increased host biomass. Sarcotoxin IA had no obvious effect on growth and development of transgenic host plants. Mannitol content in the parasite is regulated by Mannose 6-Phosphate Reductase (M6PR) gene, an essential process to broomrape species for water and nutrient uptake from the host. In our study, we used the inverted repeat technique to silence the parasite target gene, M6PR. In this study it was shown that the endogenous M6PR mRNA from P. aegyptiaca tubercles or shoots grown on transgenic tomato plants harboring the M6PR silencing construct was reduced by 60 to 80%. The number of dead tubercles was also increased significantly on transgenic plants as compared with the control plants. The strategies presented here are potentially superior to other methods in that they are effective, have a low cost of implementation for producers, and are safe for the environment.

When seed coats of scarlet morningglory (Ipomoea coccinea L.) were pricked with a needle or scarified by H2SO4, seed germination was improved. The highest percent germination was obtained with seeds pricked with a needle or exposed to H2SO4 for 180 min prior to incubation in moist paper towels. Seed planted in a potting mixture of sandy clay loam, ground sphagnum moss, and sand had the highest germination after 75 min exposure to acid. Scarlet morningglory seed germination was highest (74%) between 15 and 30 C after 144 h incubation.

Five thiocarbamate herbicides, butylate (S-ethyl diisobutylthiocarbamate), EPTC (S-ethyl dipropylthiocarbamate), molinate (S-ethyl-hexahydro-1H-azepine-1-carbothioate), pebulate (S-propyl butylethyl-thiocarbamate), and vernolate (S-propyl dipropylthiocarbamate) were used in the greenhouse at doses of 0.5 to 5 kg/ha incorporated 6 cm deep in a silt loam. Purple nutsedge (Cyperus rotundus L.) tubers were planted 5 cm deep. Three and 9 weeks after treatments were applied, nutsedge plants were harvested. EPTC also was used at doses of 0.25 to 10 kg/ha and plants were harvested every 2 days up to 20 days and every 3 weeks up to 24 weeks. The most effective reduction in the number of sprouts above ground was given by butylate, EPTC, and vernolate followed by pebulate and molinate. Persistence was directly related to level of initial activity. No effect was observed on the number of tubers which sprouted. However, all the thiocarbamates stimulated the number of sprouts produced per nondormant tuber. These sprouts were abnormal and did not reach the soil surface. Treated tubers produced approximately twice as many sprouts as controls. The number of rhizomes produced from the basal bulb was reduced with all the thiocarbamates used, even 24 weeks after treatment for the higher doses.

A field and greenhouse study was conducted to determine the relative effectiveness of preemergence herbicides applied at low volume (9.35 to 37.4 L/ha) and conventional volume (187 L/ha). In the field study 11 preemergence herbicides were applied to plots seeded with seven weed species. Five herbicides were used in the greenhouse study each applied at five rates and two volumes. Both field and greenhouse results indicated that water soluble materials and emulsifiable concentrates which need not be incorporated can be applied at low volume with results comparable to conventional volume application. Field results suggested wettable powders can be applied low volume with success; however, greenhouse results indicated that with present equipment and technique wettable powders are not well suited for low volume application. Incorporated materials were included only in the field study and gave irregular results.

The movement and persistence of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and its degradation product, 3,4-DCA (3,4-dichloraniline) were studied in an orchard soil which had received diuron annually at the rate of 4.5 kg/ha for 7 yr. Accumulation of residues was not observed at significant levels although carry-over of the herbicide occurred between years. The bulk of the herbicide residue was confined to the upper 15 cm of soil. The degradation rate of diuron generally followed first-order kinetics and the residual levels of diuron in the soil were highly phytotoxic to oat (Avena sativa L.) plants during the 3 yr after the last application. The levels of 3,4-DCA were low in all soil samples (< 21 ppb) and its relative distribution in the soil profile was similar to that of diuron.

In field studies, a preemergence application of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] followed by an early postemergence application of dicamba (3,6-dichloro-o-anisic acid) gave good season-long control of smooth pigweed (Amaranthus hybridus L. ♯ AMACH) in conventional and no-till corn (Zea mays L. ‘Pioneer 3184’ and ‘Pioneer 3382’). In soybeans [Glycine max (L.) Merr. ‘Williams' and ‘Essex’], best control of smooth pigweed was achieved with an early postemergence application of sethoxydim {2-[1-(ethyoxy-imino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one} plus acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}. Tillage played a role in the degree of smooth pigweed control. Best control of smooth pigweed in corn was obtained when the ground was moldboard plowed and disced, and least control was obtained when corn was no-till planted in the previous year's corn stalks or in a rye (Secale cereale L.) cover crop.

Studies were conducted to examine the micromorphology of leaf surfaces of coca and nova plants and to determine which spray diluents provided optimum coverage of leaf surfaces. Adaxial leaf surfaces of both species were covered with a smooth layer of polygonal-shaped epidermal cells which were covered with wax crystals. Abaxial leaf surfaces were composed only of papillae cells and the guard and subsidiary cells surrounding stomata. Abaxial leaf surfaces of both species were also covered with wax crystals. Average wax weights were 28 to 53 μg cm−2. Water droplets containing an organosilicone surfactant at 0.1% by vol spread better on leaf surfaces that did other adjuvants. Droplets of several different petroleum-based oils spread much better on leaf surfaces than either water droplets with adjuvants or droplets of soybean or cottonseed oil.

Variability in weed control following pyrithiobac applications has been observed under field conditions. The influence of temperature on this variability was investigated. Results from field studies performed over two growing seasons identified plant and air temperatures at the time of herbicide treatment that correlated with whole-plant efficacy differences. Based on the field data, weed control with pyrithiobac was acceptable at application temperatures of 20 to 34 C. To investigate a potential source of thermal limitations on pyrithiobac efficacy, the thermal dependence of in vitro inhibition of acetolactate synthase (ALS), the site of action for pyrithiobac, was examined. A crude leaf extract of ALS was obtained from Amaranthus palmeri. Relative inhibitor potency (I50) values were obtained at saturating substrate conditions for temperatures from 10 to 50 C. Regression analysis of field activity against I50 values showed the two data sets to be highly correlated (R 2 = 0.88). The thermal dependence of enzyme/herbicide interactions may provide another means of understanding environmental factors limiting herbicidal efficacy and predicting herbicide inhibition at the whole-plant level.