Absorption and translocation of 14C-ethalfluralin (N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine) were measured in cucumber plants in the field and greenhouse. In field enclosures, cucumbers treated with 1.68 or 3.36 kg ai/ha preemergence soil-surface applications of 14C-ethalfluralin accumulated significantly more 14C in leaves than in petioles, stems, or fruits. In greenhouse studies, 14C-ethalfluralin vapor was absorbed by both cucumber seedling stems and cotyledons. Seedlings absorbed 14C-ethalfluralin from a nutrient solution and translocated 14C into all plant parts. Cucumber absorbed 14C-ethalfluralin topically applied to the stem and translocated 14C acropetally, while only limited basipetal translocation occurred. Although cotyledons absorbed 14C-ethalfluralin, very little 14 C moved out of the treated tissue.

Evaluation and introduction of exotic plant pathogens for biological control of weeds in the United States takes place at the Plant Disease Research Laboratory (PDRL) in Frederick, MD. Pathogens of target weed species collected overseas are sent to PDRL and evaluated in a containment greenhouse for aggressiveness and specificity toward the target weed. Currently, rust fungi (Uredinales) are evaluated at PDRL for control of leafy spurge (Euphorbia esual L. #4 EPHES), musk thistle [Carduus nutans L. ssp. leiophyllus (Petrovic) Stoj. & Stef. # CRUNU (= C. thoermeri Weinm.)], and yellow starthistle (Centaurea solstitialis L. # CENSO). Determination of host range is central to the evaluation of potential pathogens, but some difficulty has been experienced in obtaining propagative material of important plant species, especially if the plant is threatened or endangered. A proposal is made to organize a seed bank to meet this need.

Hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] toxicity, absorption, translocation, metabolism, and effect on photosynthesis were investigated with rooted cuttings of highbush blueberry (Vaccinium corymbosum L.), rabbiteye blueberry (V. ashei Reade), and hollow goldenrod (Solidago fistulosa Miller # SOOFI). Highbush and rabbiteye blueberry plants were three times more tolerant to root applications of hexazinone than hollow goldenrod. Blueberry plants absorbed an average of 7.9% of root-applied 14C-hexazinone and hollow goldenrod absorbed an average of 10.1%. An average of 6.8% of root-absorbed hexazinone (14C-label) was translocated from the roots of blueberry to stem and leaves. Radioactivity in hollow goldenrod was distributed equally between roots and shoots. The majority of radioactivity in both species was recovered as hexazinone. Root-absorbed hexazinone caused a rapid inhibition of photosynthesis in intact hollow goldenrod leaves. Root-absorbed hexazinone was capable of inhibiting photosynthesis in intact blueberry leaves; however, this occurred only when roots were exposed to high concentrations of hexazinone.

Phytotoxicity of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in cell cultures of Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] was approximately 30-fold greater than in leafy spurge (Euphorbia esula L. # EPHES) cultures. Differences in chlorsulfuron phytotoxicity in these two species were attributed to large differences in cellular metabolism of the herbicide. Leafy spurge cells metabolized all of the applied 14C-chlorsulfuron within 72 h of treatment, while Canada thistle metabolized less than 2%. Acid hydrolysis of the metabolic products isolated from leaf disks and cell cultures of leafy spurge yielded a radioactive product that cochromatographed with a 2-chlorobenzenesulfonamide standard. Therefore, metabolic transformation occurred on the heterocyclic portion of the molecule. A major metabolite was further characterized as 2-chloro-N-[[4-(hydroxymethyl)-6-methoxy-1,3,5-triazin-2-yl]aminocarbonyl]-benzenesulfonamide by cochromatography with the authentic standard.

Field observations indicate that wheat (Triticum aestivum L.) is considerably more tolerant to soil residues of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} than barley (Hordeum vulgare L.). The basis for relative differences in tolerance was investigated by measuring herbicide dose response, uptake, movement, and metabolism using ‘Clark’ barley and ‘Marberg’ wheat. Barley root fresh and dry weights were significantly reduced when roots were exposed to nutrient solution containing 35 mM chlorsulfuron for 1 day. Wheat roots similarly exposed for 3 days to 1.1 mM chlorsulfuron displayed no growth reduction. The small differences in uptake and movement of chlorsulfuron detected in wheat and barley are inadequate to explain the large response difference between the two species. Both species rapidly metabolize chlorsulfuron in 1 day and there is no significant difference in the level of parent compound remaining in barley compared to wheat. A factor other than uptake, movement, or metabolism must account for barley roots greater sensitivity to root-applied chlorsulfuron.

The effects of adjuvants and relative humidity (RH) on absorption, translocation, and metabolism of the methyl ester of 14C-haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid} in corn (Zea mays L. ‘B73 X Mo17’ hybrid) were evaluated. Addition of 1.0% (v/v) petroleum oil concentrate (POC) to the treatment solution resulted in greater foliar absorption and translocation of 14C than addition of 1.0% (v/v) soybean oil concentrate (SBOC), 0.1% (v/v) oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate) (OXY), or no adjuvant (NONE). The least amount of 14C absorption occurred in the treatment containing OXY. Absorption and translocation of radioactivity were significantly greater at 70% RH than at 30% RH. Thin-layer chromatography revealed that most of the 14C recovered from treated plants was in haloxyfop-methyl 5 h after treatment (HAT). The remaining 14C recovered was haloxyfop and an unidentified polar metabolite. The average percentage of 14C-haloxyfop in the nonabsorbed fraction was 5, 39, 7, and 7% for treatments containing NONE, OXY, POC, and SBOC, respectively. The ratio of haloxyfop-methyl to haloxyfop and the percentage of polar metabolite in the absorbed 14C fraction was not different among adjuvant treatments or between levels of RH.

Detached leaves and whole plants of quackgrass [Agropyron repens (L.) Beauv. # AGRRE] were used to study uptake and translocation of butyl esters of 14C-fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, with or without additional adjuvants. In the absence of adjuvants 3.2% of applied radioactivity entered detached quackgrass leaves by 6 h, and at the end of 24 h, 6.0% had penetrated. The presence of additives increased uptake by leaves significantly. In the presence of the nonionic surfactant Agral (nonyl phenol ethoxylate) at 0.2% (v/v) or the oil-additive Actipron (self-emulsifying adjuvant oil) at 2.0% (v/v), 17.2 and 12.9% of applied radioactivity, respectively, entered the leaves by 24 h. Evidence of dependence of phloem translocation of the radioactivity on source-sink relationships of the plant was obtained in the studies with whole plants. Translocation measured up to 7 days after treatment showed that radioactivity was concentrated in areas such as young developed leaves, young stems, and rhizome apices. Rhizomes appear to be major sinks for the accumulation of radioactivity and at 7 days 0.5% of applied radioactivity was found there. In wholeplant experiments the two adjuvants either individually or in mixture increased the uptake of 14C-fluazifop significantly. However, a corresponding increase in basipetal translocation was found only in one experiment. Much of the increased activity that had entered the leaves in the presence of adjuvants was found to have moved to areas distal to the treated zone or remained within the treated zones. In all experiments, applied 14C was not fully recovered. Evidence of significant volatility losses from treated surfaces was obtained and it is thought that this may be the main reason for the inability to recover all of the applied activity.

Sorghum [Sorghum bicolor (L.) Moench. ‘G-623 GBR’] bioassays indicated that shoot growth was more susceptible to metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] and more responsive to the antidote CGA-92194 {α-[(1,3-dioxolan-2-yl-methoxy)-imino] benzeneacetonitrile} than root growth. Seed treatment with CGA-92194 increased seedling shoot tolerance to metolachlor approximately tenfold. CGA-92194 seed treatment enhanced shoot absorption of 14C-metolachlor approximately twofold. Metolachlor was initially metabolized to the glutathione conjugate in untreated shoots and those treated with CGA-92194. However, CGA-92194 seed treatment caused accelerated metolachlor metabolism in the shoot, decreasing metolachlor content and increasing formation of the glutathione conjugate. Cyometrinil {(Z)-α[(cyanomethoxy)imino] benzeneacetonitrile}, flurazole [phenylmethyl 2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylate], naphthalic anhydride (1H,3H-naphtho[1,8-cd]-pyran-1,3-dione), and dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide) also protected sorghum from metolachlor injury and enhanced metolachlor absorption and metabolism. The degree of protection conferred by a particular antidote was correlated with its ability to enhance metabolism of metolachlor in shoot tissue. These results are consistent with the hypothesis that the above antidotes protect sorghum from metolachlor injury by inducing rapid detoxification of metolachlor through conjugation with glutathione.

Pricklypear (Opuntia spp.) is a major constraint to rangeland livestock production in several resource areas of Texas. The phenological and physiological stages of pricklypear have heretofore been ignored in relation to timing of herbicide applications. The phenology, percent total nonstructural carbohydrates (TNC), and water content in Lindheimer pricklypear (Opuntia lindheimeri Engelm. # OPULI) were monitored biweekly for 2 yr in the southern Rolling Plains of Texas. TNC in cladophylls, crowns, and roots declined sharply from bud break (late March to late April) through the period of rapid development of new cladophylls and fruits, with minimum levels occurring during mid-July to early August. This depletion period coincides with the period when control has traditionally been attempted with broadcast applications of translocated herbicides with erratic results. Replenishment of TNC in cladophylls and basal crowns occurred during August through March or mid-April; major increases in root TNC occurred from early autumn through midwinter. Application of herbicide in late summer, autumn, or winter when TNC is being replenished in organs bearing meristematic tissue may be more effective for pricklypear control if the herbicide is translocated with photosynthates.

The herbicide cinmethylin {exo-1-methyl-4-(1-methylethyl)-2-[(2-methylphenyl)methoxy]-7-oxabicyclo [2.2.1] heptane} inhibited oat (Avena sativa L. ‘Porter’) root growth during the first 6 h of treatment at a concentration of 6.7 × 10-8 M. A concentration of 1 × 10-8 M cinmethylin inhibited root growth within 12 to 18 h. Inhibition of shoot growth was less sensitive, but was inhibited by 36 to 48 h after treatment with 1 × 10-7 M and by 12 to 24 h after treatment with 1 × 10-5 M cinmethylin. Cinmethylin concentrations of 1 × 10-5 M and lower did not inhibit cell elongation in isolated oat coleoptiles during a 24-h exposure. Mitotic frequency in oat root tips was reduced after 12 h of treatment with 1 × 10-7 M cinmethylin. The frequency of all stages of mitosis (prophase, metaphase, and anaphase + telophase) was reduced. Concentrations of 1 × 10-6 M cinmethylin resulted in nearly complete arrest (87% inhibition) of mitosis. These data suggest cinmethylin inhibits growth by inhibiting entry of cells into mitosis. The cause of mitotic arrest is unknown; however, the mechanism appears to be different from other herbicides known to inhibit mitosis.

The use of biological control agents for the control of noxious pests is not new conceptual research. There are examples that predate by centuries the modern use of both herbicides and insecticides. For example, the successful control of insects by biological control was shown in 1762 by the introduction of the Mynah bird (Gracula religiosa Linnaeus) from India to Mauritius (4). In 1888, the Vedalia beetle (Rodolia cardinalis Muslant) was introduced to control the cottony-cushion scale (Icerya purchasi Maskell) of citrus (3). An example of biological control of weeds was reported in 1863 when it was observed that an infestation of prickly pear cactus (Opuntia humifusa Raf. # OPUHU) was decimated by the imported cochineal insect (Dactylopius tomentosus Lam.) (5).

In a 2-yr field study, selective application of a 2.5% (v/v) solution of the ammonium salt of fosamine [ethyl hydrogen(aminocarbonyl)phosphonate] plus 0.5% (v/v) nonionic surfactant to multiflora rose (Rosa multiflora Thunb. # ROSMU) demonstrated leaves to be the major site of uptake for suppressing growth. In greenhouse studies, 14C-fosamine was absorbed in decreasing order by axillary bud, leaf, and stem treatments, respectively. 14C was rapidly translocated throughout multiflora rose plants when applied to leaf, stem, or bud tissue. The highest 14C concentration always occurred at the site of uptake. In a 32-day study, the treated leaf, the treated bud, and treated stem had the highest 14C concentration when 14C-fosamine was leaf, bud, or stem applied, respectively.

The effects of haloxyfop {2-[4-[[3-chloro-5(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} and haloxyfop-methyl on elongation and respiration of primary roots of corn [Zea mays L. ‘B37 X Oh43’] and soybean [Glycine max (L.) Merr. ‘Hodgson 78’] were examined. Intact roots of etiolated seedlings were exposed to both forms of the herbicide. At a concentration of 10-6 M, neither form of the herbicide had an effect on elongation or respiration of soybean roots. In contrast, elongation of corn roots was completely inhibited within 24 h of exposure to 10-6 M haloxyfop. This treatment reduced the respiration rate of corn root apices by 30% but had little effect on ATP content. After 72 h of exposure to haloxyfop [10-6 M], both ATP content and respiration rate of corn root apices had declined 35%. Haloxyfop-methyl produced equivalent effects on elongation and respiration of corn roots. Studies with isolated corn root mitochondria indicated that haloxyfop inhibits electron transport at relatively high concentrations (I50 = approximately 2 mM for various substrates). Because significant reductions in ATP content and respiration rate of corn root apices were not detected during the period when elongation was inhibited (initial 24 h of exposure), it is concluded that impairment of respiration is a secondary response to the herbicide.

Buried seeds of witchgrass (Panicum capillare L., # PANCA) exposed to natural seasonal temperature changes in Lexington, KY, for 0 to 35 months exhibited annual dormancy/nondormancy cycles. Seeds were dormant at maturity in early October. During burial in late autumn and winter, fresh seeds and those that had been buried for 1 and 2 years became nondormant. Nondormant seeds germinated from 76 to 100% in light at daily thermoperiods of 15/6, 20/10, 25/15, 30/15, and 35/20 C, while in darkness they germinated from 1 to 24%. In late spring, seeds lost the ability to germinate in darkness, and by late summer 63 to 100% of them had lost the ability to germinate in light. As seeds became nondormant, they germinated (in light) at high (35/20, 30/15 C) and then at lower (25/15, 20/10, and 15/6 C) temperatures. As seeds reentered dormancy, they lost the ability to germinate (in light) at 15/6 C and at higher thermoperiods 2 to 3 months later.

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.

The effect of environmental conditions on horse purslane (Trianthema portulacastrum L. # TRTPO) emergence, growth, and reproduction was studied by sowing seeds on June 10, June 30, July 20, August 10, and August 30, 1984. The first three seeding dates resulted in significantly higher seedling emergence than the August 30 date. Leaf number, leaf area, dry matter, and number of branches per plant at the peak growth stages of this weed were significantly higher for the July 20 sowing than for the other sowing dates, followed closely by the June 30 sowing. Similarly, number of nodes per plant, seeds per plant, and seed weight per plant were also significantly higher for the July 20 sowing, followed closely by the June 30 sowing. Phenological behavior of the plants indicate that: a) maximum seedling emergence takes place during June and July, b) rapid and vigorous growth occurs during July and August (rainy season) when conditions for growth are optimum, and c) production of flowers and seeds starts 20 to 30 days after sowing.

In laboratory experiments, the safener CGA-92194 {α-[(1,3-dioxolan-2-yl-methoxy)imino] benzeneacetonitrile} increased the in vitro chemical reactivity of the herbicide metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] for glutathione (GSH) when tested at 1, 50, and 100 μM. Pretreatment of sorghum [Sorghum bicolor (L.) Moench. cv. ‘G623’] seeds with the safener CGA-92194 (1.25 g ai/kg of seeds) enhanced significantly the amount of 14C-metolachlor absorbed by the roots and translocated to the shoots and leaves of grain sorghum seedlings grown hydroponically in a nutrient solution. Thin-layer chromatographic analysis of methanol-soluble extracts from roots or shoots and leaves of sorghum seedlings treated with 14C-metolachlor revealed the detection of 8 to 10 metabolites of this herbicide. One of the major metabolites detected was tentatively identified as the conjugate of metolachlor with GSH. A safener-induced stimulation of metolachlor metabolism via conjugation to GSH was observed in sorghum seedlings grown from seeds pretreated with CGA-92194. Addition of tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane], a potent inhibitor of plant GSH-S-transferase enzymes, to the nutrient solution of hydroponically grown sorghum seedlings reduced the formation of GS-metolachlor in both control and safener-treated seedlings and minimized the stimulatory effect of the safener CGA-92194 on the conjugation of metolachlor to GSH. It is suggested that the safener CGA-92194 may protect grain sorghum against injury from the herbicide metolachlor by stimulating the spontaneous and enzymatic conjugation of this herbicide with GSH.

Yellow nutsedge (Cyperus esculentus L. # CYPES) was treated with unlabeled and 14C-labeled glyphosate [N-(phosphonomethyl)glycine] to study the toxicity and translocation of glyphosate into parent tubers of this weed. When plants of 2 and 4 weeks of age were treated with 0.6 kg ai/ha of glyphosate, fewer parent tubers from treated plants resprouted (14 and 32%) than tubers from control plants (73 and 59%, respectively) of equal age. Also, fewer tubers resprouted from 2-week than from 4-week-old treated plants. The radioactivity of parent tubers from plants treated at 2 weeks of age, which exceeded that of tubers from plants of 4 and 6 weeks of age, indicated that translocation of 14C into parent tubers decreased as the treated plants increased in age. The differential amounts of 14C translocated appear to explain why applications of glyphosate were more effective in suppressing resprouting of parent tubers from 2-week than 4-week-old plants.

Field experiments were conducted to select winter wheat (Triticum aestivum L.) cultivar(s) that were competitive to downy brome (Bromus tectorum L. # BROTE). Downy brome significantly reduced winter wheat grain yields of all cultivars by 9 to 21% at Lincoln, while at North Platte yield reduction ranged from 20 to 41% depending upon cultivar. ‘Turkey’ was the most competitive cultivar to downy brome but it had the lowest grain yield. Compared to ‘Centurk 78’, ‘Centura’ at Lincoln and ‘SD 75284’ at North Platte proved to be significantly higher yielding and more competitive to downy brome. Winter wheat tiller number, canopy diameter, and plant height were negatively correlated with downy brome yield, but changes in these growth parameters did not always translate into grain yield advantage in downy brome-infested plots. Based on stepwise regression analysis, wheat height was better correlated with reduction in downy brome yield than were canopy diameter or number of tillers.

Weed control strategies for rice (Oryza sativa L.) and soybean [Glycine max (L.) Merr.] emphasize integration of cultural and chemical practices (16, 30, 31). Numerous herbicides are registered and used as preplant, preemergence, or post-emergence applications for control of weeds in rice and soybean (3, 16, 25). Although these herbicide treatments control most of the problem weeds in rice and soybean, most fail to control northern jointvetch [Aeschynomene virginica (L.) B.S.P. # AESVI] in either crop. The two most effective herbicides, 2,4,5-T [2-(2,4,5-trichlorophenoxy) acetic acid] and silvex [2-(2,4,5-trichlorophenoxy) propanoic acid], for control of northern jointvetch in rice have been under the U.S. Environmental Protection Agency's (EPA) Rebuttal Presumption Against Registration (RPAR) process which may ultimately cancel the use of both herbicides in rice (50). New, effective control strategies are needed for control of northern jointvetch in rice and soybean.