Foliar applications of the dimethylamine salt of 4(2,4-dichlorophenoxy)butyric acid (2,4-DB) were effective for controlling cocklebur in soybeans. Treatments usually caused crop injury, but treated soybeans often produced higher seed yields than untreated soybeans heavily infested with cocklebur plants. Soybean injury was associated with the mechanical shielding of soybeans by the cocklebur infestation and soil moisture stress at time of treatment. Droughty conditions prior to treatment intensified crop injury and reduced soybeans yields.

The control of submersed aquatic weeds is a major problem in the management of Missouri fish ponds. Dense stands of aquatic vegetation in ponds cause serious crowding and stunting of fish populations. Recreational values are impaired by the physical interference of weeds with fishing and boating. Even more serious are the occasional partial or complete kills of fish caused by oxygen depletion as plants decay. These kills may occur either in summer or winter.

The efficacy, absorption, translocation, and metabolism of thiencarbazone-methyl (TCM) in hedge bindweed, field bindweed, ivyleaf morningglory, tall morningglory, and wild buckwheat were evaluated in greenhouse experiments and field trials. Forty-eight hours after foliar microapplication, 14C-TCM absorption was highest in ivyleaf morningglory (60%), followed by field bindweed (50%), wild buckwheat (35%), tall morningglory (17%), and hedge bindweed (9%). In all species, 14C-TCM was translocated systemically. By 24 h after application, 14C-TCM was detected in all parts of the plants. The translocation pattern is species-specific, with more translocation in tall morningglory and wild buckwheat. In all vining weeds 14C-TCM was almost not metabolized whereas corn metabolized almost all 14C-TCM 48 h after application. The efficacy of TCM was analyzed using dose–response curves. Wild buckwheat had the lowest value for the dose at which 50% of the activity occurs (2.1 g ai ha−1 TCM), followed by hedge bindweed and ivyleaf morningglory. Field studies confirmed the high control of wild buckwheat with TCM. Even at the lowest tested concentration of TCM, wild buckwheat was controlled by over 90%. In contrast, efficacy of TCM in field trials against perennial vining weeds was very low, 25% for field bindweed and 65% against hedge bindweed. Control efficacy could be well explained by the translocation pattern of TCM in vining weeds.

Within the past few years the use of chemicals as herbicides has increased so rapidly that today in the United States alone millions of acres are being treated in the fight to control weeds. In addition to determining the effect of these chemicals on the plants involved (both desirable ones as well as weeds), it is most important to find out how the compounds affect the soil microflora. This assemblage of microscopic organisms plays a most vital role in the balance of nature, and, if the herbicide to be employed has as great an effect on the soil population as it does on the higher plants, its use might be impractical due to the resultant imbalance.

Paraquat (1,1′-dimethyl-4,4′-dipyridylium cation) removed weedy annual grasses from seedings of rose clover (Trifolium hirtum All.) and subclover (T. subterraneum L.) with only temporary damage to the clovers when applied at early growth stages. Paraquat applied under weed-free conditions reduced herbage yields of Lana woollypod vetch (Vicia dasycarpa Ten.) and Wimmera ryegrass (Lolium rigidum Gaud.) at three dates of application; neither herbage nor seed yield of rose or subclover was reduced.

(Arbutus menziesii Pursh.) trees in the field (15–20 cm diameter) xyacetic acid (2,4-D*) and 2,4-5-trichlorophenoxyacetic acid (2,4,5-T*) in blue oak (Quercus douglasii H. & A.) seedlings occurred following application of these herbicides to cuts made through the bark into the wood of stems. Downward transport was limited. C14-labeled 3-amino-1,2,4-triazole (amitrole*), maleic hydrazide (MH*), urea*, and P32-labeled phosphate translocated extensively into the roots as well as upward into the shoots. High humidity had little effect on translocation of 2,4-D* and 2,4,5-T* into the roots, but had marked effect on translocation of amitrole*, MH*, and urea*. The addition of herbicidal amounts of unlabeled 2,4-D or 2,4,5-T reduced translocation of labeled compounds into the roots. Unlabeled 4-amino-3,5,6-trichloropicolinic acid (picloram) or 2,4-D applied to cuts prevented translocation into the roots of all but traces of MH* applied to the same cuts. Treatment of blue oak or madrone (Arbutus menziesii Pursh.) trees in the field (15–20 cm diameter) with herbicidal doses of 2,4-D or picloram largely inhibited the downward movement of P32O4 applied to the same cuts at all stages of growth; such interference was less pronounced in madrone than in blue oak.

Effective control of Artemisia vulgaris L. (mugwort) was obtained with 2,3,6-trichlorophenylacetic acid (fenac) and 4-amino-3,5,6-trichloropicolinic acid (picloram). Dimethylamine salt of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) gave control when applied in April when mugwort shoots were small. Dicamba was less effective later in the season even after clipping to obtain small new shoots. The amount of fenac necessary for effective control was reduced by mixing with dicamba, the butoxyethanol ester of 2,4-dichlorophenoxyacetic acid (2,4-D) or oleyl-1,3-propylenediamine salt of 2,4-D. Late in the season, fenac was more effective when applied after mowing than when applied to large mugwort. Soil incorporated ethyl N,N-dipropylthiolcarbamate and propyl dipropylthiolcarbamate reduced mugwort stands and rhizome weight; however, regrowth occurred in the same season.

Experiments were conducted on black locust (Robinia pseudoacacia L.) to determine the effect of auxin distribution and degradation on the formation of root suckers. Stump sprouting and root suckering occurred when black locust seedlings were decapitated, and the presence of stump sprouts prevented root suckering. The influence of stump sprouts could be replaced by applying indoleacetic acid (IAA) in lanolin paste to the cut surfaces of root stubs. These results provide additional support for an apical dominance theory of suckering. When IAA-2-C14 in lanolin was applied to the cut surfaces of root stubs, autoradiographs showed that C14 activity was concentrated where the majority of root suckers normally would develop. Apparently, IAA accumulated in this region and inhibited root suckering. When the IAA-lanolin paste was removed from the root stubs after inhibiting suckering for a month, vigorous root suckering took place. This indicated the possibility that black locust roots contain an IAA oxidase system. The existence of such a system was demonstrated by dialyzed enzyme preparations extracted from black locust roots which oxidized IAA in a Warburg apparatus.

The rates of decarboxylation of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-chloro-4-fluorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in excised leaves of blackjack oak (Quercus marilandica Muenchh,) were determined by collecting the C14O2 evolved from carboxyl-labeled herbicides. 2,4,5-T was decarboxylated only in trace amounts. 2,4-D was decarboxylated to a maximum of about 1 per cent and 2-chloro-4-fluorophenoxyacetic acid of about 7 per cent, of the amounts taken up by the leaf. Decarboxylation rates for 2,4-D in June were highest in persimmon (Diospryos virginiana L.) and blackjack oak, and were very low in winged elm (Ulmus alata Michx.), sweet gum (Liquidambar styraciflua L.), and green ash (Fraxinus pennsylvanica Marsh.). The rates of decarboxylation of 2,4-D apparently were not correlated with susceptibility to 2,4-D.

Crabgrass (Digitaria spp.) control by different herbicides in field experiments varied from 84 to 100%. These extremes were not significantly different. Greenhouse studies showed that increased moisture content in soils may increase the growth rate of crabgrass seedlings so that they may escape herbicidal injury. Effects of herbicides on root stunting were similar in both dry and wet soils, indicating immobility of the herbicides under these experimental conditions. Competition between mature bluegrass plants and crabgrass seedlings was an important determinant of effective crabgrass control with preemergence herbicides.

Reserve carbohydrates of Dalmatian toadflax (Linaria dalmatica (L.) Mill.) in eastern Washington were at their highest levels in autumn at the end of the growing season, and the lowest point occurred at the beginning of flowering about June 15. A one-time removal of first-year floral stems (June 11, 1964) did not significantly lower reserve carbohydrates when measured in September, but similar clipping of floral stems the second year (June 16, 1965) did cause a significant reduction. Reserves were reduced by 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) at 1.12 or 1.68 kg/ha but were not reduced by 4-amino-3,5,6-trichloropicolinic acid (picloram) at the same rates. Combinations of equal weights of the two herbicides to total 1.12 or 1.68 kg/ha caused a significant reduction in reserve carbohydrates. The combinations of silvex and picloram appeared to have an additive toxic effect, but the reduction of reserve carbohydrates was no greater than that caused by silvex alone at 1.12 or 1.68 kg/ha. Lethal action of the herbicides did not appear to be caused by reserve carbohydrate depletion. Glucose and fructose were the major reducing sugars detected in chromatographic analysis.

Difficulties in chemically controlling large crabgrass in corn in South Africa have recently been attributed to the occurrence of naked crabgrass. In contrast to large crabgrass, naked crabgrass is not easily controlled with acetanilide herbicides. Critical periods of weed control (CPWC) for naked crabgrass in corn was determined in field studies during the 2009/2010 and 2010/2011 growing seasons at two separate localities for an early and late planting date of corn. Weed-free and weed–crop interference treatments of increasing duration were maintained at various crop growth stages in the presence of naked crabgrass. Biomass of naked crabgrass was determined as dry weight per square meter quadrant, which yielded 428 g m−2 at Potchefstroom and 594 g m−2 at Wesselsbron. An exponential regression model was used to determine the CPWC expressed as growing degree days after crop emergence, on the basis of an estimated 10% relative yield loss in corn. The onset and ending, as well as the duration of the CPWC, differed between seasons and localities. At 10% relative yield loss, the onset of the CPWC ranged between the two-leaf (V2) and six-leaf (V6) stages, and the ending between the 12-leaf (V12) stage and 2 wk after tasseling (T + 2). The duration of the CPWC ranged between 22 and 80 d for the respective planting dates, years, and localities. Yield losses ranged from 28 to 82% in the season-long weedy plots. The shifting of planting dates alone did not reduce yield losses since the effect of late infestations of naked crabgrass is significant. Naked crabgrass control from crop emergence is essential, followed by POST herbicide application during the critical period of weed control to lower the risk of corn yield losses.

Flax (Linum usitatissimum L., var. Bolley) was susceptible very early, when less than 2 inches tall, 1965 only, and during flowering, to 3,6-dichloro-o-anisic acid (dicamba) as determined from 9 consecutive weekly applications in the field in 1965 and 1966. Dicamba decreased flaxseed yield, percent oil and iodine number of the oil, seed size, seed germination, and plant height, and increased the days to maturity by application at either one or both of the susceptible stages of flax.

The herbicide safener OTC (L-2-oxothiazolidine-4-carboxylic acid) increased the amount of reduced thiol compounds in sorghum [Sorghum bicolor (L.) Moench. ‘DK 427′] seedlings. When seedlings were grown in liquid culture medium containing 35S-OTC, the compound was metabolized to radiolabeled cysteine and glutathione. The addition of tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane] increased conversion of 35S-OTC to cysteine and resulted in the formation of one additional 35S-labeled compound. When 35S-glutathione was injected into germinating seeds it was converted to 35S-cysteine and both thiols were subsequently found in roots and shoots. Seeds injected with 35S-OTC both translocated the compound to developing roots and shoots and metabolized 35S-OTC to cysteine and glutathione. Excised roots and shoots also metabolized 35S-OTC to the thiols. In an in vitro assay the enzyme 5-oxoprolinase converted OTC to cysteine.

Weed control in cole crops and onion by postemergence spraying with liquid ammonium nitrate was studied to determine its feasibility under Fraser Valley, British Columbia conditions. Ammonium nitrate solutions (7.5, 10, 15 and 20% N) were applied at 800 L ha−1 on warm, sunny days. Shepherd's-purse, low cudweed, redroot pigweed and ladysthumb were susceptible to this treatment; common lambsquarters, common purslane and annual bluegrass were tolerant. In order to determine the effect of weed density on weed control, several shepherd's-purse densities were established in broccoli and sprayed with ammonium nitrate solution (20% N; 800 L ha−1). Two days after treatment, weed control was 87.2% for an initial density of 500 shepherd's-purse plants m−2 (1987) and 76.1% for an initial density of 988 plants m−2 (1988). The seedlings that survived the treatment were sufficiently set back that they did not cause any adverse effect on crop yield. In a separate study, cabbage and onion were found to be tolerant to the ammonium nitrate treatment. Initially, cauliflower, broccoli and Brussels sprouts growth was slightly inhibited by the ammonium nitrate treatment but the plants recovered and crop yield was not affected.

Field studies were conducted at nine locations in southern Spain during 2 yr to develop models of nodding broomrape competition with sunflower and to establish economic thresholds. At each location, 30 to 35 small plots, each consisting of three sunflower plants, were chosen at random. The infection severity (BIS, no. of emerged broomrapes per sunflower plant) varied from 0 to 35. Plots were harvested at maturity to assess several sunflower and broomrape population variables. The percent sunflower yield reduction averaged over locations due to broomrape was estimated by the equation: % SYR = 1.7 x BIS (r2 = 0.92). Crop yield loss per BIS unit increased with the expected yield and was estimated to be about 25, 50, and 75 kg ha−1 for yields of 1000, 2000, and 3000 kg ha−1, respectively. A consistent relationship could be established between broomrape-infected sunflower yield, crop and broomrape biomass, and BIS parameters: SSYI = 0.2259 x PoBio/(1 + 0.0687 x BIS) (r2 = 0.7820). The BIS economic threshold was about 1.5 and 3.5 for control treatment cost of $ 40 ha−1 and potential yields of 2000 and 1000 kg ha−1, respectively.

Postemergence herbicide treatments that controlled tighthead sprangletop [Leptochloa panicoides (Presl) Hitchc.] and redstem (Ammannia auriculata Willd.), did not injure water-seeded rice (Oryza sativa L.), and substantially improved grain yields included: (a) a single application of propanil (3′,4′-dichloropropionanilide) at 4.5 kg/ha applied to weeds 8- to 10-cm tall; (b) two sequential treatments of propanil each at 3.4 kg/ha, with the first treatment applied to weeds 2- to 5-cm tall, and a second treatment applied 4 to 8 days later; (c) a tank mixture of propanil at 3.4 kg/ha and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] at 0.6 kg/ha, applied to weeds 8- to 10-cm tall; and (d) a tank mixture of propanil and molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate), each at 2.2 kg/ha, applied to weeds 8- to 10-cm tall. Treatments that controlled tighthead sprangletop or redstem unsatisfactorily or inconsistently and did not improve grain yields as much as more effective treatments included: preplant or postemergence treatments of molinate, or preplant treatments of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether), fluorodifen (p-nitrophenyl α,α,α-trifluoro-2-nitro-p-tolyl ether), CNP (2,4,6-trichlorophenyl-p-nitrophenyl ether), or He-314 (p-nitrophenyl-m-tolyl ether).

Extensive variability in total lipid composition was observed in seeds of different plant species as well as cultivars within the same species. Susceptibility of plants to soil-incorporated trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and oryzalin (3,5-dinitro-N4,N4-dipropyisulfanilamide) under greenhouse conditions decreased as the percentage of total lipid in dry seeds increased. Species with high seed lipid levels such as jimsonweed (Datura stramonium L.), soybean [Glycine max (L.) Merr.], and velvetleaf (Abutilon theophrasti Medic.) were less susceptible to these herbicides than were oat [Avena sativa (L.), giant foxtail (Setaria faberi Herrm.), and sorghum [Sorghum bicolor (L.) Moench.] with low seed lipid levels. Velvetleaf was the most tolerant to the herbicides. Corn (Zea mays L.) cultivars with a wide range of seed lipid content (4.45 to 17.0% of dry weight) were germinated in herbicide-free soil, but their roots were allowed to grow through trifluralin- or oryzalin-treated soil. Roots of seedlings from seeds with high lipid content had higher lipid contents than those from low-lipid seeds. There was a significant correlation between root lipid content and sensitivity to trifluralin or oryzalin. Roots high in lipids were less susceptible than those with low amounts of lipids. Similar results were obtained for oat cultivars. The fatty acid composition of plant roots differed among plant species and also among cultivars of the same species. The individual fatty acids did not significantly correlate with susceptibility of roots to trifluralin or oryzalin. Root lipid and fatty acid compositions were not significantly altered by trifluralin or oryzalin treatment.

Vegetable injury and yield loss has occurred when applying halosulfuron to low-density polyethylene mulch (LDPE) prior to transplanting. Research determined vegetable crop response to halosulfuron applied over LDPE mulch from 1 to 28 d prior to transplanting using (1) temperature effects in aqueous solution in laboratory experiments, (2) analytical evaluation of degradation from LDPE under field conditions, and (3) a field bioassay. Halosulfuron stability was evaluated on a thermal gradient table for temperatures at 10 to 42 C for 15 d. Half-life was inversely related to temperatures ranging from 38.5 d at 20 C to 3.2 d at 42 C, with little to no degradation at temperatures of 11 and 15 C. Analytical data indicated that the field half-life of halosulfuron at 26 or 52 g ha−1 applied to LDPE mulch under dry conditions was 2.6 and 2.8 d, respectively. Given the changes in the microclimate effects at the mulch surface by absorption of solar radiation, daily thermal energy quantified halosulfuron degradation (at the same rates) to be 51 and 55 MJ m−2, respectively. At 21 d after treatment (DAT), 90% of halosulfuron had dissipated from the mulch, with none detectable 35 DAT under dry conditions. When watermelon or yellow crookneck squash was transplanted into mulch previously treated with halosulfuron at 79 g ha−1, plant growth and development were equal to nontreated controls as long as there was a 14 d prior to transplant (DPT) interval accompanied by 13.5 cm of rain, or a 17 DPT interval accompanied by 6.2 cm of rain. However, at 79 g ha−1 applied at 9 or 1 DPT in 2013, and 1 DPT in 2014, halosulfuron injured yellow squash and reduced yield and fruit number. Halosulfuron at 79 g ha−1 applied 1 DPT significantly reduced watermelon yield in 2013, which was confirmed by vine length and plant biomass reductions in 2014. Halosulfuron POST controls Cyperus spp. in mulch vegetable production, but time and rainfall are required for dissipation to occur in order to prevent injury and yield loss.