Nineteen herbicides in various formulations were tested preemergence and postemergence for control of western bracken (Pteridium aquilinum (L.) Kuhn var. pubescens Underw.). Excellent suppression was obtained for 1 year with fall applications of granular formulations of 2,6-dichlorobenzonitrile (dichlobenil) at 6.7 and 10.1 kg/ha, 4-amino-3,5,6-trichloropicolinic acid (picloram) at 2.2 kg/ha, and 3,6-dichloro-o-anisic acid (dicamba) at 4.5 to 9.0 kg/ha. Bracken recovered rapidly after 1 year of suppression by dichlobenil, but other herbaceous species were killed. Bracken recovered considerably the second growing season after application of picloram or dicamba, although morphological effects were noticeable for 2 to 3 years, particularly from dicamba. No visual injury to grasses was apparent from picloram. Some injury to orchardgrass (Dactylis glomerata L.) was noted from dicamba.

Pelleting rice (Oryza sativa L., ‘IR8′) seeds with activated carbon was developed as a means of overcoming herbicide phytotoxicity to direct-seeded, flooded rice. Field and greenhouse experiments showed that pregerminated rice seeds coated three times with activated carbon with 50% polyvinyl acetate as an adhesive, were adequately protected from the injurious effects of chloramben (3-amino-2,5-dichlorobenzoic acid), butachlor [N-(butoxymethyl)-2-chloro-2′,6′-diethylacetanilide] and oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one]. The performance of carbon-coated rice seeds in flooded soil, however, was dependent on time of flooding, method and rate of sowing, rate and time of herbicide application, and quality of activated carbon.

Metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], when applied pretransplant at 0.28 kg ai/ha, killed peppers (Capsicum annuum L.) that were transplanted bare root or in plugs. Activated carbon applied at 1 g/plant effectively reduced injury of such peppers in soils treated with up to 0.56 kg ai/ha metribuzin. The increase in crop tolerance to metribuzin was dependent on the amount of activated carbon added. The level of crop protection for plug transplants depended on the amount of activated carbon per plant rather than on the percentage in the greenhouse mix by dry weight. One gram was required to protect plug transplants grown in cells that held 10 or 20 g of greenhouse mix.

Two methods of controlling weeds during the establishment of crownvetch (Coronilla varia L. ‘Chemung’) were studied. The first involved broadcast-incorporated spray treatments with either EPTC (S-ethyl dipropylthiocarbamate) or benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) before planting. At planting, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] or bromacil (5-bromo-3-sec-butyl-6-methyluracil) was applied in bands between seeded rows of crownvetch. Excellent weed control and good crownvetch establishment were obtained consistently, but in some years bromacil damaged seedling crownvetch excessively. In the second, weed control and subsequent crownvetch establishment were successful for 4 consecutive years after broadcastpreplanting treatments of EPTC or benefin, followed by a postemergence spraying with dinoseb (2-sec-butyl-4,6-dinitrophenol).

A small laboratory sprayer was designed to spray small quantities of chemicals on test plants. The sprayer apparatus consisted of a spray nozzle assembly, air line, and syringe to inject the test solution into the spray nozzle assembly. In operation, the sprayer provides good coverage of test plants and can be used to treat a large number of subjects rapidly.

Mixtures of 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) plus 2,2-dichloropropionic acid (dalapon) were applied to sugarbeets (Beta vulgaris L.) at three growth stages 1 year and six growth stages another year. The growth of tops and roots was retarded most when sugarbeets were treated in the two-leaf stage of growth. The weight of tops and roots was reduced 43 and 50%, respectively, 6 weeks following an application of a mixture of 3 lb/A each of pyrazon and dalapon. However, when these sugarbeets were sampled 2 weeks later, the tops and roots weighed only 4 and 12% less, respectively, than the untreated controls. Furthermore, the early suppression in the growth of sugarbeets for 3 to 8 weeks following herbicide treatment had no effect on final yield of roots, pounds of sucrose, or sucrose content at harvest.

EPTC (S-ethyl dipropylthiocarbamate) did not reduce emergence of alfalfa (Medicago sativa L. ‘Vernal’) seedlings at 3 to 81 kg/ha in the greenhouse nor at 3 to 243 kg/ha in the field. No rate injured roots, but temporary foliar symptoms were present at all rates. Soaking seeds for 40 days in technical grade EPTC or for 8 days in water saturated with EPTC before seeding in untreated soil did not reduce emergence or injure the seedlings. Seedlings from seeds germinated in paper towels moistened with water saturated with EPTC grew normally when transferred to untreated soil. Alfalfa was injured if seedlings were exposed to EPTC after emergence, but it tolerated exposure to high concentrations during imbibition and germination of the seeds and elongation of the seedlings before they emerged from the soil. EPTC delayed seedling emergence by about 1 day. This effect was separate from that causing typical foliar symptoms.

Leaves absorbed high amounts of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) as foliar sprays on honey mesquite (Prosopis glandulosa Torr. # PRCJG) as indicated by concentrations of 10 μg/g fresh wt or more in basal stem phloem by 4 days after treatment. Small quantities of clopyralid (< 1 μg/g) were detected in basal stem phloem after spray applications of clopyralid to defoliated plants or roots treated by soil application. When applied to foliated plants, the 0.56 kg/ha of clopyralid killed 60% or more plants, but none were killed when clopyralid sprays were applied to defoliated plants or when 2.2 kg/ha of clopyralid was applied to the soil. Water, diesel oil plus water, or water plus surfactant were equally effective as clopyralid carriers as foliar sprays.

Concern over the development of herbicide-resistant weeds has led to interest in integrated weed management systems that reduce selection pressure by utilizing mechanical and cultural weed control practices in addition to herbicides. Increasing crop seeding rate increases crop competitive ability and thus can enhance herbicide efficacy. However, it is unknown how increasing the seeding rate affects an herbicide’s efficacy. The objective of this study was to examine the interaction between increasing seeding rate and herbicide dose to control weeds. To meet this objective, the herbicide fluthiacet-methyl was applied to field-grown lentil, with Indian mustard, a proxy for wild mustard, used as a model weed. The experiment was a factorial design with four lentil seeding rates and seven herbicide rates. Overall the herbicide dose response was altered by changing lentil seeding rate. Increasing lentil seeding rate decreased the weed biomass production when herbicides were not applied. In two of the four site-years, increasing lentil seeding rate lowered the herbicide ED50, the dose required to result in a 50% reduction in weed biomass. Increasing the crop seeding rate altered the dose response to provide greater weed control at lower herbicide rates compared with normal crop seeding rates. Increased seeding rates also resulted in higher and more stable crop seed yields across a wider range of herbicide dosages. These results suggest that dose–response models can be used to evaluate the efficacy of other weed management practices that can interact with herbicide performance.

Bear oak (Quercus ilicifolia Wang.) is widely recognized as difficult to eradicate. Burning, cutting, and routing, while killing the original stems to the ground, have caused dormant buds on the root collar to become active and produce fast growing sprouts which soon replace the original plant. In fact, single-stemmed plants so treated can produce as many as 40 or more new stems. Moreover, this species has been difficult to control chemically owing to resurging growth from the root collar and lower stem after a kill of original stems. Bear oak is widely distributed as an understory tree in the eastern United States extending from Maine to North Carolina and from the Atlantic Coast to Ohio and Kentucky. Often it develops into dense thickets on burned-over forest land or abandoned fields so that it monopolizes the site, crowding out other more desirable species and making planting of other trees an expensive operation. One hundred and fifty to two hundred thousand acres of such “scrub oak barrens” occur in Pennsylvania.

Wild oat (Avena fatua L.) is one of the most problematic weed species in western Canada due to widespread populations, herbicide resistance, and seed dormancy. In wheat (Triticum aestivum L.), and especially in shorter crops such as lentil (Lens culinaris Medik.), A. fatua seed panicles elongate above the crop canopy, which can facilitate physical cutting of the panicles (clipping) to reduce viable seed return to the seedbank. However, the viability of A. fatua seed at the time of panicle elongation is not known. The objective of this study was to determine the viability of A. fatua seed at successive time intervals after elongation above a wheat or lentil crop canopy. A 2-yr panicle clipping and removal study in wheat and lentil was conducted in Lacombe, AB, and Saskatoon, SK, in 2015 and 2016 to determine the onset of viability in A. fatua seeds at successive clipping intervals. Manual panicle clipping of A. fatua panicles above each crop canopy began when the majority of panicles were visible above respective crop canopies and continued weekly until seed shed began. At the initiation of panicle clipping, A. fatua seed viability was between 0% and 10%. By the last clipping treatment (approximately 6 to 7 wk after elongation), 95% of the A. fatua seeds were viable. Seed moisture and awn angle were not good predictors of A. fatua viability, and therefore were unlikely to provide effective tools to estimate appropriate timing for implementation of A. fatua clipping as a management technique. Based on A. fatua seed viability, earlier clipping of A. fatua is likely to be more effective in terms of population management and easier to implement in shorter crops such as lentil. Investigations into long-term effects of clipping on A. fatua populations are needed to evaluate the efficacy of this management strategy on A. fatua.

One of the major problems in present-day soybean production is weed control. The increased interest in profitable soybean production in recent years has stimulated a demand for a satisfactory and economical means of chemical control to supplement cultural practices. The gradual shift from solid planting to row planting has practically eliminated the problem of weeds between rows, but it has not solved the critical problem of weed growth in the row.

Treatments made at 2-week intervals on guava (Psidium guajava L.) with a 1:1 ratio of butoxyethanol esters of 2,4-dichlorophenoxyacetic acid:2,4,5-trichlorophenoxyacetic acid (2,4-D:2,4,5-T) have shown it to be more susceptible when treatments are made during the wet season than during the dry season. Greater susceptibility is related to a plant condition characterized by many new leaves but little or no terminal twig elongation. A similar pattern of defoliation response is caused by 2-methoxy-3,6-dichlorobenzoic acid (dicamba) and 2,3,6-trichloropicolinic acid (picloram) as by 2,4-D:2,4,5-T, but the period of maximum susceptibility based on defoliation percentages 1 year after treatment occurred later in the season.

Virginia chain fern (Woodwardia virginica (L.) Smith) was controlled by 2,6-dichlorobenzonitrile (dichlobenil) in cranberry bogs on a St. Johns soil at Chatsworth, New Jersey, in experiments conducted during 1960, 1961, 1962, 1963, and 1964. The treatments were applied at emergence of the weed. Stalk counts of the fern were recorded the year following treatment. Excellent control was obtained at either 4 or 8 lb/A of dichlobenil. No re-growth occurred in subsequent years.

Diquat (6,7-dihydropyrido[1,2-a:2’,1′-c] pyrazidiinium salt) was applied to several emergent, submersed, floating-leaved, and free-floating aquatic plants common in Central Illinois ponds. At relatively low rates, it was effective in controlling several submersed aquatic plants but not American pondweed, Potamogeton nodosus, and cabomba, Cabomba caroliniana. This herbicide also was effective on several common emergent species.

In the last few years the possibility of growing small fruits and several vegetable crops without any soil disturbance has been demonstrated. On many soil types crop yield has been unaffected and has sometimes shown a slight increase compared with traditional cultivation. Advantages of non-cultivation include the possibility of increasing crop uniformity and yield by using closer row spacings and completely new methods of crop production, the avoidance of injury to surface-feeding roots, decreased risk of frost and easier mechanical harvesting of some crops. In small-fruit plantations the weed problem has greatly diminished after about 3 years, because of non-disturbance of seeds lying below the germinating zone and the absence of a “seed-bed”. While the surface crust that sometimes forms where the soil is not disturbed may affect plant growth in certain circumstances, no evidence was obtained in recent experiments in Britain that a crust was detrimental to the growth of established plants. However, water infiltration on bare non-cultivated soil was sometimes retarded and increased run-off occurred on sloping sites. Due to the wide diversity of soil types, climatic conditions and crop response it is impossible to generalize about the effect of eliminating cultivation. Nevertheless, as some of the advantages are considerable while the disadvantages can often be overcome it seems likely that non-cultivation practice will extend to many horticultural crops in the future.

Weed problems in Alaska are relatively new because man's agricultural activities in this region have been limited until very recently to isolated clearings. These early clearings made by prospectors and homesteaders to produce feed for their stock also unintentionally served as increase plots for some troublesome weeds.

In 1955, three British workers (2) described a variable dosage sprayer which was designed for large field plots. The original description did not attract much attention in the United States when it was first published, but the principles described therein are receiving more attention at the present time, both in this country and abroad (1).

Cotton is the major cash crop in Missouri's seven southeastern delta counties, and is second in cash value for the entire state, even though it comprises only about 6 per cent of the total acreage. Heavy infestations of weeds late in the season materially complicate the defoliation process, reduce the efficiency of both mechanical and hand pickers, lower the grade of the lint by contributing stains and trash, and account for greatly diminished net returns. Despite advances in this field, weed control still constitutes the principal remaining barrier to complete mechanization of cotton production.