The interaction of soil applied phosphorus and soil applied herbicides was investigated in field, greenhouse and controlled environment chamber studies. A previously reported diuron-phosphorus interaction could not be repeated under all conditions studied. Amitrole was consistently more toxic to plants grown under high phosphorus levels than under low phosphorus conditions. The phytotoxicity of ten other herbicides was not influenced by the phosphorus content of the soil.

Clearfield™ (CL) rice (Oryza sativa L.) is a weedy rice (Oryza spp.; synonym = red rice) control tool that has been used in Brazil since 2003. This system includes the use of an imidazolinone (IMI)-tolerant cultivar and the application of IMI herbicides. In this review article, Brazilian weed scientists evaluate the challenges and lessons learned over 18 yr of CL use. CL system benefits include selective weedy rice control, better crop establishment during the most advantageous period of the year, and more efficient fertilizer use. In Rio Grande do Sul state, the CL system, in conjunction with other improvements, has contributed to rice grain yield gains from 5,500 kg ha−1 before 2002 to around 8,400 kg ha−1 currently. In contrast, the main problem that has arisen over this period is the rapid evolution of IMI-resistant weedy rice, caused by gene flow from CL rice cultivars. The off-label use (rate and continuous use) of IMI herbicides has contributed to the evolution of resistance in Echinochloa spp. and other weeds. IMI herbicide carryover has also affected susceptible crops grown after CL rice. Crop rotation with soybean [Glycine max (L.) Merr.] is increasing, ensuring system sustainability. The importance of minimum tillage has also become apparent. Such cultivation includes applying nonselective herbicides before sowing or just before crop emergence (at the spiking stage to eliminate as much weedy rice as possible and other weeds at an early growth stage). It also includes the use of certified seeds free of weedy rice, following label instructions for IMI herbicides, applying the herbicide PRE followed by POST, and complementary weedy rice management practices, such as roguing of surviving weedy rice plants.

A growth room study was conducted to evaluate the effect that timing of application has on the distribution of several herbicides in quackgrass. Uniformly labeled 14C-sucrose and the radiolabeled herbicides glyphosate, sethoxydim, the butyl ester of fluazifop, and the methyl ester of haloxyfop were applied to quackgrass (ranging from the three- to eight-leaf stage) propagated from six-bud rhizome segments. Five days after treatment the plants were harvested, lyophilized, and later sectioned, mapped, and oxidized in preparation for 14C quantification. In most cases, slightly more 14C was translocated to the shoots than to the rhizomes. 14C translocation to the rhizomes was similar at all growth stages. The 14C accumulating in the rhizomes exhibited a nonuniform distribution pattern with more 14C in the distal areas of new rhizomes than in the other areas of the rhizome system. Plants treated with haloxyfop had a more uniform distribution of 14C along their rhizomes than did those treated with fluazifop or sethoxydim.

Small broomrape, a holoparasitic weed, was recently introduced to the Pacific Northwest and contaminates a limited number of red clover fields in Oregon. Greenhouse and field studies were conducted to evaluate small broomrape response to common crop and weed species in the Pacific Northwest, and to evaluate a quick-screening method for plant species response to the parasite. In greenhouse studies, plants were grown in a hydroponic polyethylene bag system to allow for continuous visibility of their roots and monitoring of small broomrape seed germination and tubercle development. Results of the greenhouse study were validated in a field contaminated with small broomrape. In the greenhouse polyethylene bag study, small broomrape germinated and tubercles developed on alfalfa, arrowleaf clover, carrot, celery, crimson clover, lettuce, prickly lettuce, red clover, spotted catsear, subterranean clover, white clover, and wild carrot. Small broomrape germinated but did not develop tubercles when grown with barley, birdsfoot trefoil, common vetch, creeping bentgrass, cucumber, field corn, red fescue, flax, Italian ryegrass, nasturtium, oats, orchardgrass, perennial ryegrass, snap bean, sugar pea, sunflower, sweet corn, tall fescue, tomato, and wheat. In the field study, tubercles developed on alfalfa, arrowleaf clover, common vetch, crimson clover, red clover, subterranean clover, and white clover, but small broomrape flower stalks did not emerge in arrowleaf clover or crimson clover. Common vetch was a host for small broomrape in the field study but not in the hydroponic polyethylene bag system, thus, caution is warranted in using the quick screening method to elucidate potential small broomrape host species.

Alfalfa (Medicago sativa L. ‘Vernal′) seeded in April in rows 55 cm apart and kept free of weeds produced 820 kg/ha of seed during the year of seeding. Competition from a dense popualtion (40 plants/m of row) of mixed species of annual weeds reduced the seed yield to 45 kg/ha. Competition from a dense population (55 plants/m of row) of broadleaf weeds, a light population (4 plants/m of row) of broadleaf weeds, or a heavy population (75 culms/m of row) of barnyardgrass [Echinochloa crusgalli (L.) Beauv.] reduced yields to 80, 310, and 160 kg/ha, respectively. A weed management system, consisting of EPTC (S-ethyl dipropylthiocarbamate) or profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] applied at or before planting, 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid] applied postemergence, trifluralin (α,α,α- trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) incorporated with the soil when the alfalfa was 20 cm tall, interrow tillage, and a modest input of hand labor brought the crop to harvest free of weeds, and the yields of alfalfa seed were similar to those from plots kept weed-free by hand labor only. When weeds within the rows were controlled by hand labor only, labor inputs as great as 930 h/ha were required to bring the crop to harvest free of weeds, whereas labor inputs of 7 to 17 h/ha removed all surviving weeds when effective weed management systems had been applied.

Weed population estimates were collected from four Glycine max fields during the summers of 1997 and 1998. Seedling weed populations were sampled using a regular coordinate system on a grid either 50 by 50, 30 by 30, or 10 by 10 m. MSU-HERB and Mississippi Herbicide Application Decision Support System (HADSS) (yield loss prediction and herbicide recommendation models for G. max) were used to determine the estimated net gain resulting from simulated herbicide applications at each sample location in each field. When necessary, the appropriate data points from the 10- by 10-m grid were removed to form population data sets on grids 20 by 20, 40 by 40, and 80 by 80 m. The objectives of this research were to compare estimated economic returns of site-specific herbicide management and broadcast herbicide management in nontransgenic and glyphosate-tolerant G. max and to evaluate the effects of various weed sampling intensities on estimated economic returns from site-specific herbicide applications. Site-specific herbicide management was the compilation of simulated herbicide treatments giving the highest estimated net gains at each location within each field. Broadcast herbicide management was the simulated broadcast application giving the highest estimated net gain for each field. Sampling costs and the unattainable site-specific application costs were not included in the estimated net gain calculations. In nontransgenic G. max production, the estimated net gain for treating the four fields with site-specific technology was $104.76 ha−1 higher than when using the optimum broadcast herbicide. In glyphosate-tolerant G. max production, the average estimated net gain for site-specific treatment of the fields was $96.24 ha−1 higher than for treatment with the best broadcast herbicide application. In nontransgenic G. max, the estimated net gain resulting from site-specific applications on a 10-m grid was $77.17 ha−1 higher than from site-specific applications on a 20-m grid; however, in glyphosate-tolerant G. max, this difference was only $19.84 ha−1. Increased estimated net gain resulted primarily from the use of herbicides that maximized return for each field area and from the decrease of unnecessary herbicide applications because of below-threshold weed infestations.

Restoring range sites dominated by western juniper is central to maintaining healthy functioning shrub–steppe ecosystems. On sites without adequate species composition to respond favorably to juniper controlled by fire, revegetation is necessary. We tested the following two hypotheses related to restoration after juniper control: (1) higher seeding rates would translate into higher density of seeded species, and (2) a rich seeding mixture would provide higher density and biomass than monocultures. Western juniper control was done by cutting 25% of the trees in 2002, allowing cut trees to dry for one year, followed by a broadcast fire applied in October 2003 which killed the remaining live juniper trees. Seeding treatments were applied in 2003 and included seeding six native species in monocultures, seeding a mixture of all six species at four rates (16.8, 22.4, 28.0, or 33.6 kg ha−1 of pure live seeds), and a nonseeded control. Treatments were applied on a Sagebrush/bunchgrass and Snowberry/fescue site. We found that bluebunch wheatgrass, Idaho fescue, big bluegrass, and western yarrow density ranged from 450 to 700 plants m−2, which was over six-fold that of the control in 2004 at both sites. Only arrowleaf balsamroot did not establish successfully. The density of big bluegrass nearly doubled from 2004 to 2005. The highest plant density resulted from the highest seeding rate. The highest biomass production was combination seeding at 22.4 kg ha−1 on the Sagebrush/bunchgrass site and 33.6 kg ha−1 on the Snowberry/fescue site. Seeding a combination of species resulted in a moderate to high density of plants and optimized plant diversity and richness over seeding monocultures.

There is an increasing interest in the use of cover crops in agriculture, in Sweden mainly for the use as catch crops to reduce nitrogen leakage. Some of these crops are known for their allelopathic abilities, which may play a role in the control of weeds and contribute to reduced herbicide use. This study aimed to explore the possible suppressive effect of the cover crop species white mustard, fodder radish, rye, and annual ryegrass on the early growth of the weed species silky windgrass, shepherd's-purse, and scentless false mayweed. In a greenhouse experiment using fresh cover crop residues, white mustard was the only crop that showed an effect. It reduced both seedling establishment, by 51 to 73%, and biomass, by 59 to 86%, of shepherd's-purse and scentless false mayweed. In contrast, in a growth chamber experiment using frozen material, mean germination time of silky windgrass was extended by 20 to 66% by all cover crops. Also, three out of four cover crops reduced root growth in scentless false mayweed by 40 to 46%, and two out of four cover crops reduced root growth in shepherd's-purse by 13 to 61%. However, considering seedling survival, white mustard was the most prominent cover crop, reducing survival by 21 to 57% in shepherd's-purse and scentless false mayweed. In this paper we provide evidence that different weed species show different response to different cover crops under climatic conditions prevailing in Scandinavia. Such results emphasize the importance of understanding weed–cover crop interactions as necessary for developing cropping systems that can utilize cover crops to suppress local weed flora.

Barnyardgrass (Echinochloa crusgalli (L.) Beauv.) emerged in fields as early as May 3. The shortest period between seeding and emergence and between emergence and tillering was during the warmest period of the growing season. The number of days from emergence to heading and maturity decreased progressively for later seedings. The height of plants was greatest when the plants emerged early in the growing season. The highest number of tiller and heads per tiller were produced by plants emerging in July. Plants which emerged in May and June produced the highest yields. Barnyardgrass seedlings grown under 11-hr photoperiod and 16-hr photoperiod produced mature seeds in 52 and 84 days, respectively. Barnyardgrass grew best under wet soil moisture conditions.

Five bio-ionic liquids (BILs) with choline cations and fatty acid anions derived from pelargonic acid, glycerol tristearate, glycerol trioleate, canola oil, and coconut oil were synthesized and applied as spray adjuvants with three sulfonylurea herbicides: metsulfuron-methyl, iodosulfuron-methyl-sodium, and tribenuron-methyl. Physicochemical properties, including thermal stability, solubility, and surface activity, were determined, and the influence of these BILs on herbicidal efficacy was studied in greenhouse tests using four target weed species: common lambsquarters (Chenopodium album L.), cornflower (Centaurea cyanus L.), corn poppy (Papaver rhoeas L.), and oilseed rape (Brassica napus L.). BILs, particularly those with the oleic anion and anions derived from canola oil and coconut oil, greatly improved herbicidal activity. Addition of BILs to the spray solution significantly reduced the surface tension and contact angle of spray droplets and increased the area of herbicide deposit on the leaf surface.

Greenhouse and laboratory investigations using four soils were conducted to determine the influence of seven herbicides on symbiotic nitrogen (N2) fixation by soybeans [Glycine max (L.) Merr. ‘Davis’]. Soils were treated with recommended rates of herbicides immediately after planting. After 8 to 10 weeks the nodulated root systems were assayed for nitrogenase activity using the acetylene (C2H2) to ethylene (C2H4) reduction technique, and total numbers and dry weights of nodules were determined. Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] (0.3 kg/ha) decreased nodule dry weight and C2H4 production per plant per hour in a Convent sandy loam. Alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl) acetanilide] (2.2 kg/ha) and prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] (0.6 kg/ha) also decreased C2H4 production per plant per hour in a Convent sandy loam, while metribuzin (0.6 kg/ha) increased C2H4 production per plant per hour and per milligram of nodule dry weight in a Mhoon silt loam. Prometryn (1.7 kg/ha) increased production of C2H4 per plant per hour in a Moreland silt loam. None of the herbicides affected C2H4 production, nodule number, or nodule dry weight in a Commerce silt loam.

Laboratory batch equilibrium studies were conducted to evaluate the sorption-desorption behavior of imazethapyr and its major plant metabolite, 5-hydroxyimazethapyr, in three Minnesota soils. Sorption of both compounds on all soils was low, and pH did not significantly influence sorption in the range of 4,8 to 7.1. Less 5-hydroxyimazethapyr was sorbed than imazethapyr on the same soil. Once sorbed, both compounds were only partially desorbable from all soils. Significant hysteresis and formation of nonextractable residues indicate that the small amount of chemical sorbed is bound to selective surfaces with strong bonds. Webster clay loam had greater irreversibility than Waukegen silt loam and Estherville sandy loam soil. The hysteresis observed in desorption may be responsible for the difference between mobility estimations made from laboratory sorption studies and the limited mobility observed in field experiments.

The response of 22 potato (Solanum tuberosum L.) cultivars to soil-incorporated and foliar applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one] at rates of 0.5 and 1.0 kg ai/ha, was evaluated in field experiments from 1979 to 1982. Metribuzin significantly reduced the yield of marketable tubers in several potato cultivars. Foliar applications generally resulted in more injury than soil applications. Yields were reduced primarily through stand reduction and a decreased number of tubers per plant. Neither tuber size nor specific gravity of tubers was significantly reduced in the cultivars studied. The most susceptible cultivar was ‘Alaska Red’, followed by ‘Rhine Red’, F72117, ‘Caribe’, and ‘Shepody’. Other cultivars evaluated were highly tolerant to metribuzin, irrespective of rate or method of application. There was an increase in hollow heart in cultivars ‘Atlantic’ and ‘Lemhi Russet’ following treatment with metribuzin.

Specific knowledge about the dormancy, germination, and emergence patterns of weed species aids the development of integrated management strategies. The after-ripening period for jointed goatgrass seed was quantified, and the effects of germination conditions and spikelet structures on jointed goatgrass seed germination were measured. As the duration of after-ripening increased, jointed goatgrass seed germinated earlier, at faster rates, and to greater final percentages compared to non–after-ripened seed. Both primary and secondary positioned seed within jointed goatgrass spikelets were nondormant after 16 wk after-ripening at 22 ± 2 C. Germination of dormant seed depended on incubation temperature and dark/light conditions. Sixty-seven percent of spikelets produced a radicle when exposed to low temperatures in the dark, and light at warm temperatures increased germination by 7%. The relationship between light and incubation temperature was similar also for germination of the primary positioned seed in nondormant spikelets; however, the magnitude of the effect increased. Light increased germination of seed incubated at warm temperatures by 18%. Coleoptile emergence was dependent on planting depth for three jointed goatgrass populations, winter wheat, and spring wheat. Under optimum conditions in the greenhouse, no planting depth selectively allowed wheat germination and emergence while preventing jointed goatgrass germination and emergence. Glume removal increased jointed goatgrass secondary positioned seed final germination percentage to 96%, increased the germination rate, and decreased the number of days required to reach 50% germination to 6 d. Glume removal also promoted germination of the primary seed within jointed goatgrass spikelets. Glume removal resulted in 80% of the spikelets having two coleoptiles, but did not alleviate dormancy completely in jointed goatgrass seed. Tillage and herbicide applications for jointed goatgrass control will be most effective in the fall when primary dormancy is lost, but before secondary dormancy is imposed.

Horse purslane (Trianthema portulacastrum L. # TRTPO) seeds germinated from 20 to 45 C. Maximum germination of 90% was observed at 35 C. Germination was highest between the 4th and 8th days of incubation. Horse purslane seeds did not exhibit dormancy. Freshly harvested seeds when incubated at 35 C germinated to the extent of 54 to 56%. Seed germination steadily increased up to 7 and 8 months when stored under laboratory and field conditions, respectively. Seeds stored in soil had significantly higher germination than those stored in the laboratory. Maximum seedling emergence resulted when seeds were planted at 1 cm and gradually declined with the increased seeding depth. Seeds lying on the surface gave very poor seedling emergence.

Simultaneous treatment with certain carbamate insecticides inhibited degradation of 3-(p-chlorophenyl)-1,1-dimethyrurea (monuron) in cotton (Gossypium hirsutum L.) leaf discs. Monuron degradation was strongly inhibited by 1-naphthyl methylcarbamate (carbaryl) and 4-benzothiophene-N-methylcarbamate, but 2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate was ineffective. Effective carbamates did not prevent the metabolism of monuron to 1-(p-chlorophenyl)-3-methylurea (hereinafter referred to as monomethylmonuron), but they inhibited subsequent degradation of monomethylmonuron.

The transgenic corn line 98140 has a high level of resistance to glyphosate and all five chemical classes of herbicides that inhibit acetolactate synthase (ALS). The dual herbicide resistance is due to a molecular stack of two constitutively expressed genes: gat4621, which produces a glyphosate acetyltransferase that rapidly inactivates glyphosate, and hra, which produces a highly resistant ALS. On a rate basis, the positive 98140 isoline with a single copy of the gat4621 gene is over 1,000-fold more resistant to glyphosate than a negative isoline without the transgene. Similarly, the positive 98140 isoline with the hra gene is over 1,000-fold more resistant to ALS-inhibiting herbicides such as chlorimuron and sulfometuron at the whole-plant and enzyme level. The gat4621 and hra genes do not change the natural tolerance of corn to selective herbicides, so new corn hybrids based on 98140 will give growers more options to manage weeds and delay the evolution of herbicide-resistant weeds.

The control of winter annuals in dormant bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’] has not been consistent with available herbicides. Experiments were conducted to evaluate rates and number of glyphosate [N-(phosphonomethyl)glycine] applications for control of winter annuals growing in dormant bermudagrass. Glyphosate applied as a single treatment at 0.6 kg/ha consistently controlled more parsley-piert (Alchemilla microcorpa Boissier Reuter), corn speedwell (Veronica arvensis L.), and henbit (Lamium amplexicaule L.) than paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or 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). There was no difference between glyphosate and paraquat control of annual bluegrass (Poa annua L.) and common chickweed [Stellaria media (L.) Cyrillo]. Glyphosate treatments did not injure the bermudagrass the following spring.

The differential response of three selections of johnsongrass (Sorghum halepense (L.) Pers.) to different temperatures and dark periods was studied in two experiments conducted in growth chambers. The three selections of johnsongrass were obtained from locations representing different climates. At 20 C all three selections grew equally with respect to most parameters of growth studied; however, at 35 C the selection from the southern climate produced more total fresh weight than the other two selections. Rhizome production and the number of stems also were greater in the southern selection at 35 C. An 8-hr dark period prevented flowering in all three selections and significantly reduced rhizome production in two selections compared to the 12-hr dark period. Flowering occurred most rapidly in the selection from a northern climate and most slowly in the selection from a southern climate. The results are discussed in relation to the possible plant adaptive changes and the possibility of weed control through dark period interruption.

Four field locations were used to compare environmental factors on efficacy of four postemergence grass herbicides in Kentucky bluegrass and bermudagrass turf. Imazaquin, BAS 514, and tridiphane were compared to fenoxaprop-ethyl, a registered herbicide, for postemergence control of large crabgrass. Best large crabgrass control was provided by BAS 514 and fenoxaprop-ethyl. Use of BAS 514 gave equal turf quality, phytotoxicity to the turf, large crabgrass control, and stand compared to fenoxaprop-ethyl. Imazaquin and tridiphane reduced turf quality and were phytotoxic to both turf types, and did not control large crabgrass adequately.