Search

Field research was conducted to evaluate the response of soybean to various herbicides applied at rates to simulate drift damage. Dicamba, glyphosate, glufosinate, and the sulfonylurea herbicides CGA-152005, primisulfuron, nicosulfuron, rimsulfuron plus thifensulfuron, and CGA- 152005 plus primisulfuron were applied to soybean at the two to three trifoliolate leaf stage in 1997 and 1998 at Y/,/33, 1 /li, and 1/3 of the recommended use rates. The order of yield reduction after herbicide treatment was CGA-152005 > dicamba > CGA-152005 plus primisulfuron > rimsulfuron plus thifensulfuron > primisulfuron. Soybean yields were not reduced by glyphosate, glufosinate, and nicosulfuron. Applications of all herbicides at rates higher than 1/33 of the use rate caused injury symptoms within 30 d after treatment. However, soybean plants had partially or fully recovered by the end of the growing season. Therefore, early-season injury symptoms from herbicide drift are not reliable indicators for soybean yield reduction. Nomenclature: Dicamba, 3,6-dichloro-2-methoxybenzoic acid; glufosinate, 2-amino-4-(hydroxy- methylphosphinyl)butanoic acid; glyphosate, N-(phosphonomethyl)glycine; nicosulfuron, 2-(((((4,6- dimethoxy-2-pyrimidinyl)amino)carbonyl)amino)sulfonyl)-N,N-dimethyl-3-pyridinecarboxamide; primisulfuron, 2- (( ( (((4,6-bis(difluoromethoxy)-2-pyrimidinyl) amino) carbonyl) amino) sulfonyl)ben- zoic acid; CGA-152005 (proposed common name, prosulfuron), 1-(4-methoxy-6-methyl-triazin-2- yl)-3-(2-(3,3,3-trifluoropropyl)-phenylsulfonyl)-urea; rimsulfuron, N-(((4,6-dimethoxy-2-pyrimidi- nyl)amino)carbonyl)-3-(ethylsulfonyl)-2-pyridinesulfonamide; thifensulfuron, 3-(((((4-methoxy-6- methyl-1,3,5-triazin-2-yl)amino)carbonyl)amino)sulfonyl)-2-thiophenecarboxylic acid; soybean, Gly

A growth chamber study was conducted to evaluate the effects of temperature and soil moisture on the absorption and translocation of the new sulfonylurea herbicide, MON 37500, in wheat, jointed goatgrass, wild oat, and downy brome. Treatment combinations of temperatures—25/23, 15/13, and 5/3 C—and soil moistures of one-third, two-thirds, and full field capacities were assigned to the germinated plants. Radiolabeled MON 37500 was applied to the second leaf of plants at the three-leaf stage. The plants were then harvested at 6, 24, and 96 h after application. The plants absorbed MON 37500 in the greatest quantity during the first 6 h; however, absorption did continue to increase over time. Absorption was highest in wheat and lowest in wild oat. Temperature influenced absorption, while soil moisture status appeared to have no effect. Translocation of radiolabeled material out of the treated leaf increased over time; however, 90 to 97% of absorbed radioactivity remained in the treated leaf 96 h after treatment. Temperature affected translocation differently in each species, but increasing soil moisture increased translocation.

High temperature limits productivity of crops in many regions of the world, but the physiological basis of tolerance to the stress is not known. Our objective was to determine the relationship between photosynthetic responses to high temperature at the whole-plant level and sensitivity of light reactions, the most labile systems, to brief heat treatment. Wheat (Triticum aestivum L.), a C3 species adapted to cool environments: rice (Oryza sativa L.), a C3 species adapted to warm environments; and millet [Pennesitum glaucum (L.) R. Br.], a C4 species adapted to hot environments, were compared. Photosynthesis was measured in plants grown at 22, 32, or 42 degrees C, and light reactions were measured in protoplasts, chloroplasts, and thylakoids isolated from seedlings grown at 27 degrees C and treated in vitro at 22, 32, and 42 degrees C. Leaf photosynthesis of millet and rice increased from 22 to 32 degrees C and then decreased to 42 degrees C, whereas in wheat it was highest at 22 degrees C and decreased as temperature increased. Photosynthetic rates of protoplasts and chloroplasts from all species decreased after being treated in vitro over the same temperature range. Photosystem II (PSII) activity declined steadily in protoplasts, chloroplasts, and thylakoids of millet and rice from 22 to 42 degrees C but decreased abruptly in organelles of wheat from 32 to 42 degrees C. The results suggest that differences in photosynthetic responses to high temperature are associated with light reactions, and extreme sensitivity of wheat may be attributable to injury to PSII.

Resistance to imazethapyr was identified in a population of common sunflower that had been treated with imazethapyr for seven consecutive years. The imazethapyr-resistant biotype of common sunflower was approximately 170 times more resistant to imazethapyr than the susceptible biotype based on the rate required for 25% control. Resistance was due to altered acetolactate synthase (ALS) that is less sensitive to imazethapyr. The imazethapyr concentration required to inhibit in vitro ALS activity by 25% was 210–fold higher in the resistant biotype than in the susceptible biotype. Differences in absorption, translocation, and metabolism of imazethapyr in common sunflower biotypes were not sufficient to explain the resistance to imazethapyr.

Field and greenhouse experiments evaluated the differential response of 15 green pea varieties to metribuzin applied preemergence. ‘Charo,’ ‘CMG 298,’ ‘Leah,’ ‘Scout,’ and ‘Puget’ were the most tolerant, whereas ‘Bolero’ and ‘Sundance’ were the most susceptible varieties under greenhouse conditions. Variable chlorophyll fluorescence (Fv), efficiency of photosystem II (Fv/Fmax), and leaf area were reduced sharply by metribuzin in susceptible varieties, and metribuzin susceptibility correlated highly with the reduction in shoot dry weight. Green pea varieties grown under field conditions responded to metribuzin similarly to pea varieties grown under greenhouse conditions. Metribuzin reduced shoot dry weight more in peas grown at 30/25 C than in those grown at 25/20 and 20/15 C. Also, metribuzin injured peas more when grown in soil saturated to field capacity compared to soil at 70 and 40% of field capacity.

Lemberger' wine grape response to fall application of selected herbicides applied at simulated drift rates was studied in 1992 and 1993. Chlorsulfuron, thifensulfuron, 2,4-D, glyphosate, bromoxynil, and 2,4-D plus glyphosate were applied at 1/100, 1/33, 1/10, and 1/3 of a selected maximum rate for use in wheat or fallow. All herbicides, except bromoxynil and thifensufluron, caused symptoms on grapevines at the highest rate during the spring following fall application. The most severe symptoms were caused by 2,4-D and 2,4-D plus glyphosate, whereas the least symptoms were caused by chlorsulfuron and glyphosate. The severity of symptoms increased and shoot growth, leaf area, internode length, and dry cane weight decreased as the rates of 2,4-D and 2,4-D plus glyphosate increased. Chlorsulfuron and glyphosate reduced the growth of grapevines only when applied at the highest rate during the fall. The data show that exposure of wine grapes to 2,4-D or 2,4-D plus glyphosate during the fall can adversely affect the growth of grapevines the following spring. Nomenclature: Bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile; chlorsulfuron, 2-chloro-N-(((4- methoxy-6-methyl- 1 ,3,5-triazin-2-yl)amino)carbonyl)benzenesulfonamide; glyphosate, N-(phosphon- omethyl)glycine; thifensulfuron, 3-(((((4-methoxy-6-methyl- 1,3,5-triazin-2-yl)amino)carbonyl)amino) sulfonyl)-2-thiophenecarboxylic acid; 2,4-D, (2,4-dichlorophenoxy)acetic acid; wheat, Triticum aestivum L.; wine grape, Vitis vinifera L. Additional index words: Herbicide drift, herbicide symptoms, bromoxynil, chlorsulfuron, glyphos- ate, thifensulfuron, 2,4-D.

Weed suppression in green pea was evaluated when green pea was planted after a fall planting of rapeseed, white mustard, rye, or wheat had been incorporated into the soil in spring. Tests were conducted at Mount Vernon, WA, in 1994 and 1995. Weed suppression in peas varied between different green manure crops. One month after planting, the highest weed population was in green pea following wheat, whereas the lowest was in green pea following rapeseed. Rye and white mustard suppressed early weeds relative to wheat by 25 and 30%, respectively. However, at harvest, weed density was similar in green pea planted after all green manure crops. Weed suppression improved when cultivation or metribuzin at 0.14 kg ha−1was used in combination with white mustard, rapeseed, or rye. Pea population was not affected by green manure crops, except for rapeseed, which reduced pea population. In greenhouse experiments, white mustard added to the soil at 20 g per 400 g air dry soil reduced emergence of shepherd's-purse, kochia, and green foxtail by 97, 54, and 49%, respectively. Rapeseed suppressed emergence of shepherd's-purse, kochia, and green foxtail by 76, 25, and 25%, respectively.

Author(s): Miller, Tim; Hanson, Brad; Peachey, Ed; Boydston, Rick; Al-Khatib, Kassim | Abstract: Glyphosate (Roundup) is very effective against weeds, but you can't use it just any old way or you'll end up encouraging the development of resistant weeds. Learn to find the best timing, mix, and application method, and complementary control methods.

Author(s): Al-Khatib, Kassim; Hanson, Brad; Miller, Tim; Peachey, Ed; Boydston, Rick | Abstract: Glyphosate-resistant crops made farming a lot easier when they first came out, but then the weeds started to catch on, too. Nowadays, herbicide-tolerant crops will only work as part of a more comprehensive, Integrated Pest Management plan.

Author(s): Peachey, Ed; Boydston, Rick; Hanson, Brad; Miller, Tim; Al-Khatib, Kassim | Abstract: Rely too much on any one herbicide and you end up with weeds that will resist its effects—and that's just what is happening now with glyphosate (Roundup). See how you can increase effectiveness by diversifying your weed-management strategies.

Author(s): Hanson, Brad; Fischer, Albert; Shrestha, Anil; Jasieniuk, Marie; Peachey, Ed; Boydston, Rick; Miller, Tim; Al-Khatib, Kassim | Abstract: A good herbicide will control the current population of weeds, but also create a powerful “selection pressure”: any weeds that survive its effects will go on to thrive, immune to any further applications. Learn how to keep selection pressure in check.

'Lemberger' wine grape response was evaluated when chlorsulfuron, tribenuron, thifensulfuron, chlorsulfuron plus metsulfuron, thifensulfuron plus tribenuron, and 2,4-D were applied up to three times at weekly intervals in 1992 and 1993 at rates simulating drift. All herbicides injured grapevines visibly. Symptoms increased and total leaf area and grape pruning weight decreased as the herbicide rate and number of applications increased. Grapevines generally recovered within 45 to 60 d from symptoms caused by single exposures to low levels of sulfonylurea herbicides. Multiple exposures of grapevines to 2,4-D, tribenuron, and chlorsulfuron plus metsulfuron at 1/100 of the maximum use rate for wheat caused the greatest injury, which persisted throughout the entire growing season and reduced pruning weight. Based on potential use rate, the order of herbicide phytotoxicity was 2,4-D > tribenuron > chlorsulfuron plus metsulfuron > thifensulfuron plus tribenuron > chlorsulfuron > thifensulfuron. Rates that slightly injured grapevines did not reduce growth as measured by pruning weight. However, multiple exposure to high rates of 2,4-D, tribenuron, and chlorsulfuron plus metsulfuron adversely affected growth. Nomenclature: Chlorsulfuron, 2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]- carbonyl]benzenesulfonamide; metsulfuron, 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid; thifensulfuron, 3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2- yl)amino]carbonyl]amino]sulfonyl]-2-thiophenecarboxylic acid; tribenuron, 2-[[[[(4-methoxy-6- methyl-1,3,5-triazin-2-yl)methylamino]carbonyl]amino]sulfonyl]benzoic acid; 2,4-D, (2,4-dichlorophenoxy)acetic acid; wheat (Triticum aestivum L); wine grape (Vitis vinifera L.).

Broadleaf weed control and tulip, daffodil, and iris response to alachlor, dithiopyr, diuron, isoxaben, napropamide, oryzalin, oxadiazon, oxyfluorfen, pendimethalin, pronamide, and thiazopyr applied preemergence were evaluated. All herbicides controlled broadleaf weeds for five months after application, but control with oxyfluorfen, pendimethalin, alachlor, pronamide, and napropamide decreased six months after application. The greatest weed control was with oxadiazon, isoxaben, thiazopyr, dithiopyr, and diuron, whereas the least weed control was with napropamide and alachlor. In general, tulip was more sensitive to herbicides than daffodil and iris. All herbicides injured tulips at early growth stages but bulb yield of tulip was reduced only by oxadiazon, oxyfluorfen at 0.28 kg ai/ha, pronamide, and dithiopyr. Tulip flower quality was reduced only by oxadiazon, oxyfluorfen at 0.28 lb/ha, and pronamide. Daffodil and iris were tolerant to thiazopyr, isoxaben, pronamide, alachlor, oryzalin, napropamide, and diuron. Nomenclature: Alachlor, 2-chloro-N-(2,6-diethylphenyl)-N-(methoxy-methyl)acetoamide ; dithiopyr, S,S-dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoro-methyl)-3,5-pyridinedicarbothioate ; diuron, N'-(3,4-dichlorophenyl)-N,N-dimethylurea; isoxaben, N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide; napropamide, N,N-diethyl-2-(1 -naphthalenyloxy)propanamide; oryzalin, 4-(dipropylamino)-3,5-dinitrobenzenesulfonamide; oxadiazon, 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one; oxyfluorfen, 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene; pendimethalin, N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine; pronamide, 3,5-dichloro(N-1,1 -dimethyl-2-propynyl)benzamide ; thiazopyr; methyl 2-(difluoromethyl)-5-(4,5-dihydro-2-thiazolyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3-pyridinecarboxylate; daffodil, Narcissus spp., 'Ice Follies'; iris, Iris spp., 'Ideal'; tulip, Tulipa spp., 'Golden Apeldoorn.'

Broadleaf weed control with trifluralin, oxyfluorfen, pendimethalin, clopyralid, pyridate, and metolachlor in cabbage (Brassica oleracea L.) grown for seed was evaluated. No single herbicide controlled broadleaf weeds adequately, with the exception of pendimethalin at 1.92 and 3.84 kg a.i./ha. However, combinations of trifluralin + oxyfluorfen, pendimethalin + clopyralid, and oxyfluorfen + pyridate effectively controlled weeds and did not reduce seed yields. Herbicides caused slight to moderate injury symptoms to cabbage plants, with the greatest injury caused by pendimethalin and the least by trifluralin and metolachlor. However, plants recovered from these symptoms and appeared normal at the bud stage. None of the herbicides applied alone or in combinations adversely affected cabbage population, height, or flowering date. Chemical names used: 3,6-dichloro-2-pyridinecarboxylic acid (clopyralid); 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide (metolachlor); 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene (oxyfluorfen); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin); O-(6-chloro-3-phenyl-4-pyridazin-yl)S-octylcarbonothioate (pyridate); 2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine (trifluralin).

Bentazon efficacy was evaluated in early, normal, and late plantings of green pea with the addition of four adjuvants: crop oil concentrate (COC), LI-700, Sylgard 309, and X-77. Weed control was improved by all adjuvants in normal and late plantings of green pea, but only by Sylgard 309, X-77, and LI-700 in the early planting. In normal and late plantings, weed control with bentazon applied at 0.56 kg/ha with any adjuvant was equal to weed control with bentazon applied alone at 1.12 kg/ha. Bentazon injury on green pea plants varied from slight to severe, with the lowest injury resulting from bentazon applied with COC and LI-700 and highest injury from bentazon applied with Sylgard 309. Bentazon injury was greater in normal and late plantings than in the early planting.

Field experiments were conducted at the Irrigated Agricultural Research and Extension Center, Prosser, Washington, in 1992 and 1993 to study the effects of simulated chlorsulfuron (2 chloro-N [[(4 methoxy-6 methyl 1,3,5-tnazin 2 yl)amino]-carbonyl]benzenesulfonamide) drift at different reproductive growth stages of three cherry (Prunus avium L ) cultivars, Rainier, Chinook, and Bing Branches of each cultivar were treated at side-green, full bloom, postbloom, and pit hardening growth stages with 0, 251 1 × 10 7, 83 8 × 10 7, 27 9 × 10−7, 9 3 × 10−7, and 3 1 × 10−7 M chlorsulfuron In single-exposure expetiments, Chinook was adversely affected by the lower levels of chlorsulfuron Bing was not affected by levels of chlorsulfuron below 27 9 × 10 7 M The yield and quality of fruit decreased significantly with the increase in chlorsulfuron concentrations applied at full bloom and postbloom stages Reduction in yield was correlated with the severity of injury symptoms on leaves In the multiple exposure experiments, fruit yield, fruit size, and color were significantly reduced by increasing chlorsulfuron concentration and number of exposures Average firmness of fruit increased with increases in chlorsulfuron concentration The data suggested that multiple exposures of a susceptible cherry cultivar to low levels of chlorsulfuron at full bloom and postbloom stage can reduce fruit yield and delay maturity of cherries while increasing fruit firmness

Broadleaf weed control ranged from 80% with clomazone at 0.14 kg/ha to 100% with clomazone at 1.12 kg/ha. Broadleaf weed control was higher with clomazone than naptalam or ethalfluralin. The combination of clomazone at 0.14 kg/ha and naptalam at 5 kg/ha or ethalfluralin at 1.25 kg/ha gave more than 90% broadleaf weed control. Clomazone caused chlorosis and bleaching on cucumber leaves but plants rapidly recovered. Cucumber yields were higher in plots treated with clomazone alone at 0.14 to 0.56 kg/ha than with ethalfluralin or naptalam alone. Clomazone dose response studies were conducted in weed-free plots with five cucumber varieties. The 0.28 kg/ha rate caused low levels of visible injury and did not decrease yields. Cultivar differences were more pronounced at higher clomazone rates. The five cucumber cultivars were, in order of increasing clomazone tolerance, ‘Sunre 3537,’ ‘Pioneer,’ ‘Quest,’ ‘Prince,’ and ‘Calypso.’ We concluded that clomazone is an effective and selective herbicide for broadleaf weed control in pickling cucumber.

Greenhouse experiments were conducted to evaluate phytotoxicity, absorption, and translocation of thifensulfuron when applied to pea at different rates, droplet sizes, and as dry particles. Thifensulfuron rates that reduced shoot dry weight by 25% were 0.46, 0.59, 0.98, and 1.21 g ai ha-1for droplet diameters of 110, 155, 300, and 450 μm, respectively. The14C-thifensulfuron absorption as percent of applied increased twofold, whereas translocation decreased 36% as herbicide concentration increased from 18 to 146 mg L-1in 980-μm droplets. Small droplets (50 μm) that dried to particles before contact with leaves did not damage pea plants. However, under dew conditions, dry particles damaged peas to a similar degree as liquid droplets. We concluded that small and concentrated droplets of thifensulfuron can damage peas more than large and diluted droplets as a result of increased herbicide absorption.

DC X2-5309 organosilicone adjuvant added at 1% (v/v) spray solution increased the efficacy of bentazon, pyridate, and terbacil on kochia in greenhouse trials. DC X2-5309 decreased the rain-free period needed after application of bentazon and bromoxynil to 6 and 1 h, respectively, and increased the uptake of 14C-bentazon and 14C-bromoxynil by kochia at 1, 3, 6, and 24 h after application compared with crop oil concentrate (COC). In field trials, bentazon and bromoxynil rates required to control equal amounts of kochia were reduced by half when adding DC X2-5309 compared with adding crop oil concentrate. DC X2-5309 added at 0.5% (v/v) spray solution with bentazon did not injure spearmint and controlled kochia equal to or better than bentazon with COC added at 1 % (v/v) spray solution. Nomenclature: Bentazon, 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide; bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile; pyridate, octyl 0-(6-chloro-3-phenylpyridazin-4-yl)carbonothioate; terbacil, 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione); kochia, Kochia scoparia (L.) Schrad. #3 KCHSC; spearmint, Mentha spicata L. Additional index words: Crop oil concentrate, herbicide uptake, rainfastness, pyridate, surfactant, terbacil, KCHSC.

This study was designed to develop a protocol for using a biologically-based system to detect and tract airborne herbicides. Common bean, lentil, and pea were selected for their quasi-diagnostic sensitivity to chlorsulfuron, thifensulfuron, metsulfuron, tribenuron, paraquat, glyphosate, bromoxynil, 2,4-D, and dicamba. Plants were grown in the greenhouse at Prosser, WA, and placed at 25 exposure sites at weekly intervals between Apr. 2 and Oct. 15, 1991. After 1 wk of field exposure plants were brought back and observed for herbicide symptoms over a 28-d period. Symptoms that developed were compared with symptoms caused by disease, insects, adverse weather conditions, and herbicides applied at different rates under controlled conditions on these species. In addition, if herbicide symptoms were observed, herbicide spray records and weather data in the area were used in a computer model to determine the source of potential herbicide drift. This study demonstrates that indicator plant species selected for high sensitivity to herbicides can be used to monitor the occurrence of herbicide movement.

Bromoxynil efficacy, uptake, translocation, and spray retention were investigated when bromoxynil was applied in conventional water volumes of 234 L ha−1and in simulated sprinkler irrigation at 127 000 L ha−1to common lambsquarters. Bromoxynil controlled common lambsquarters similarly regardless of water volume, whereas injury to spearmint, a tolerant crop, was greatest using low water volume. Spray retention was 18 and 38 times greater on common lambsquarters and spearmint, respectively, when bromoxynil was applied in 234 L ha−1than 127 000 L ha−1. Two weeks after applying bromoxynil in 127 000 L ha−1water volume, common lambsquarters dry weight was 60% of the nontreated check where only soil was treated but was 5% of the nontreated check where only leaves were treated. Roots of lambsquarters absorbed 22% of14C-bromoxynil applied to hydroponic solution by 7 d, but only 2% was translocated to the shoots. Percent absorption and translocation of foliar-applied14C-bromoxynil were 15 and 6% greater, respectively, from 0.0096 g L−1than from a 1.2 g L−1bromoxynil solution by 24 h after application. Uptake of bromoxynil was 13% greater through lower than upper leaf surfaces. These results suggest efficacy of bromoxynil applied in large spray volumes is, in part, due to root uptake, efficient foliar uptake and translocation, and uptake from lower leaf surfaces.

This investigation determined whether thylakoid proteins would be degraded more rapidly or not in senescing wheat (Triticum aestivum L. em. Thell.) leaves concurrently exposed to high temperatures. Excised leaves were pulse-labelled with [35S]-methionine for a 12 h period, and then incubated at 22,32 or 42°C for 0, 1, 2, or 3 d, before extracting a thylakoid enriched membrane sample. After electrophoretic separation, two prominent [35S]-labelled protein bands were chosen for further analyses. Band A contained the D-1 thylakoid protein and band B contained thylakoid proteins of the light harvesting complex (LHCII) associated with photosystem II (PSII). Total protein, [35S]-labelled protein, band A protein, and band B protein within the thylakoid enriched membrane samples were measured. Unlabelled thylakoid enriched membrane samples, extracted from leaves given similar treatments, were used to measure uncoupled whole-chain and photosystem II (PSII) electron transport and chlorophyll fluorescence. Accentuated decline in whole-chain and PSII electron transport, increasing Fo values, and decreasing Fmax values were a result of high temperature injury in leaves treated at 42°C. None of the thylakoid enriched membrane protein fractions were degraded more rapidly in high-temperature treated leaves. Degradation of the total [35S]-labelled membrane proteins and band B was inhibited by the 42°C treatment. The results indicate that high temperature stress may disrupt some aspects of normal senescence.

Chlorsulfuron, thifensulfuron, bromoxynil, 2,4-D, glyphosate, and a combination of 2,4-D plus glyphosate were applied on newly planted and established ‘Lemberger’ wine grape at 1/3, 1/10, 1/33, and 1/100 of the maximum labelled rate in wheat or fallow to simulate exposure to drifted herbicides. All herbicides produced symptoms on grape but the most severe symptoms were with 2,4-D and the least severe with bromoxynil. Newly planted grape was more sensitive to herbicides than established grape. Although established grape recovered from injury caused by all treatments except 2,4-D and the highest rate of chlorsulfuron and glyphosate, newly planted grape recovered only from lower rates of bromoxynil. All herbicides resulted in diagnostic symptoms, but other symptoms were very similar to those caused by other stresses.

A triazine-resistant Powell amaranth biotype collected in Idaho was approximately six times more resistant to terbacil and sixteen times more resistant to bromacil than a normal susceptible biotype when planted into terbacil- or bromacil-treated soil. The concentration of terbacil required to reduce photosystem II activity by 50% (I50) in isolated thylakoids was 0.24 and 13.33 μM for the susceptible and resistant biotypes, respectively. Likewise, the I50values for bromacil were 0.33 and 18.4 μM for the susceptible and resistant biotypes, respectively. More14C-terbacil was bound to isolated thylakoids of the susceptible than the resistant biotype with binding constants (Kb) of 0.26 and 12.9 μM, respectively, indicating that resistance was at the chloroplast level.

This study evaluated the response of sweet cherry to different herbicides applied at rates simulating drift. Chlorsulfuron, thifensulfuron, bromoxynil, 2,4-D, glyphosate, and a combination of 2,4-D and glyphosate were applied on one side of one- and two-year-old established cherry trees at 1/3, 1/10, 1/33, and 1/100 of the maximum rate for small grain production. The order of herbicide phytotoxicity was chlorsulfuron > 2,4-D > glyphosate > 2,4-D + glyphosate > thifensulfuron > bromoxynil. Trees recovered from injury caused by all treatments except higher rates of chlorsulfuron, 2,4-D, and glyphosate. The herbicides caused characteristic symptoms, but some resembled disease, mineral deficiency, and environmental stress symptoms. Therefore, any allegations about herbicide drift based on chronic symptoms should be supported by analysis of plant tissue.

‘Vernal’ alfalfa response was evaluated when chlorsulfuron, thifensulfuron, 2,4-D, glyphosate, bromoxynil, and selected combinations of those herbicides were applied at rates simulating spray drift during the fourth trifoliolate leaf stage following the first cutting in 1990 and 1991. The order of phytotoxicity was 2,4-D > chlorsulfuron > thifensulfuron > glyphosate > bromoxynil. By the end of each growing season, alfalfa had recovered from injury caused by all herbicides except the highest rates of 2,4-D and 2,4-D plus glyphosate. The alfalfa stand was reduced only by 2,4-D and 2,4-D plus glyphosate. All herbicides caused characteristic symptoms, but some specific symptoms were similar among different herbicides or resembled symptoms caused by disease, mineral imbalance, and adverse weather conditions.

A triazine-resistant (TR) biotype of Powell amaranth was discovered in 1989 in a potato field treated with metribuzin. A survey of all agricultural counties in Idaho showed that the TR Powell amaranth infestation was localized in the southeastern corner of Gooding county in southern Idaho. To determine the mechanism of triazine resistance, 150 values for inhibition of pho- tosystem II were determined for atrazine, metribuzin, and diuron using thylakoids isolated from TR and triazine- susceptible (TS) biotypes. TR/TS ratios based on 150 values were 134 for atrazine, 62 for metribuzin, and 1.9 for diuron. Results of binding studies with atrazine and metribuzin were consistent with the I50 studies, indicating that resistance was due to reduced binding of triazines to the thylakoid membrane DI protein. Sequencing the chloroplast psbA gene from TR and TS biotypes revealed a serine 264 to glycine change in the TR biotype. The mutation presumably resulted in reduced hydrogen bonding between triazine herbicides and the Dl protein. Nomenclature: Atrazine, 6-chloro-N-ethyl-N'-(1- methylethyl)-1,3,5-triazine-2,4-diamine; diuron, N'-(3,4- dichlorophenyl)-N, N-dimethylurea; metribuzin, 4-amino- 6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)- one; Powell amaranth, Amaranthus powellii S. Wats. #3 AMAPO; potato, Solanum tuberosum L. Additional index words. Herbicide resistance, DNA se- quence, chloroplast assay, herbicide binding, AMAPO.

The basis for increased phytotoxicity of foliar-applied atrazine at high temperature in common bean and redroot pigweed was investigated. Plants were grown under low (15/10 C), medium (25/20 C), or high (35/30 C) temperature regimes. Atrazine absorption by plants grown under different temperatures increased with increasing temperatures in both species. Greater than 90% of absorbed atrazine remained in treated leaves and translocation was not altered by temperature in both species. Metabolism of atrazine by both hydroxylation and glutathione-conjugation was greater in plants grown at 35/30 than 15/10 C in both species. Foliar-applied atrazine reduced extractable photosystem II (PS II) activity as temperature increased in both species. Studies were also conducted on thylakoid membranes from plants not treated with atrazine. The I50for atrazine inhibition of PS II decreased and affinity of atrazine binding to thylakoid membranes increased as temperature increased in both species. We concluded that the increased phytotoxicity of atrazine at high temperatures is caused by enhanced foliar absorption and greater affinity of atrazine for the binding site.

It has been suggested that soil treated with a herbicide and subsequently carried by wind and deposited on plant foliage can cause crop injury. This study compared foliar uptake and translocation of herbicides applied to plants as an aqueous solution or in herbicide-treated soil. Leaves of 3-wk-old seedling alfalfa, grape, and pea were treated with14C-labeled thifensulfuron, chlorsulfuron, glyphosate, 2,4-D, and bromoxynil. Significant amounts of all herbicides were absorbed by pea, alfalfa, and grape from the aqueous solutions, whereas very limited absorption occurred from herbicide-treated soil. Prolonged and multiple exposure to herbicide-treated soil did not increase herbicide uptake. High relative humidity enhanced herbicide absorption from aqueous solutions but not from herbicide-treated soil. All herbicides except bromoxynil were readily translocated in alfalfa, grape, and pea. Limited quantities of herbicides were absorbed from herbicide-treated soil by plant foliage, and this small amount is unlikely to cause crop damage.

This study was conducted to compare foliar absorption and translocation of dicamba applied to plants as an aqueous solution or as dicamba-treated soil deposits. When applied as an aqueous solution, 65 to 95% of14C-dicamba was absorbed by pea, alfalfa, and grape; whereas, limited absorption (0.4 to 4.7%) occurred from dicamba-treated soil. Based on dose-response evaluation, the low levels absorbed from treated soil are unlikely to cause crop damage.14C-dicamba translocation was more than 80% of absorbed14C in pea, alfalfa, and grape. Acropetal translocation exceeded basipetal translocation.

Witchweed (Striga spp.) infestations are the greatest obstacle to sorghum [Sorghum bicolor (L.) Moench] grain production in many areas in Africa. The objective of this study was to evaluate the efficacy of herbicide seed treatments for controlling Striga infestation of sorghum. Seeds of an acetolactate synthase (ALS) herbicide–tolerant sorghum hybrid were treated with two ALS-inhibiting herbicides. Treatments included three rates of imazapyr (IMI), three rates of metsulfuron-methyl (MET), and an untreated control group. In greenhouse trials, observations at 32, 46, and 60 d after planting showed that seeds treated with the highest herbicide rates had the fewest Striga attachments and the greatest delay in attachment. All plants in the untreated group died at or before sorghum flowering; however, herbicide seed treatments, particularly metsulfuron, reduced Striga emergence and significantly increased sorghum grain yield and dry matter production. Field studies comparing seed treatments produced similar results with delayed Striga emergence and fewer emerged Striga plants in herbicide-treated plots. These studies indicate that herbicide seed treatments may provide a highly effective tool for managing Striga in sorghum

Chloroplast thylakoids isolated from bean (Phaseolus vulgaris L.) leaves have been used as a model system to identify heat-induced changes in membrane protein structure. Susceptibility of SDS gel electrophoresis bands to trypsin digestion was used as an assay for altered structure of proteins comprising the bands. Both reversible and irreversible alternations in membrane protein structure have been observed as a result of exposure to 35 or 45°C for varying time periods.

This paper defines several solution properties that alter the effects of heat on isolated chloroplast thylakoid membranes. Isolated bean (Phaseolus vulgaris L.) «Oregon 1604» thylakoids in various milieus were exposed to 25 or 45 °C, and the repercussion(s) of heat were determined. Raffinose (0.4-0.5 M) wass lightly more thermostabilizing than 2 M sucrose as evidenced by an amelioration of the: (i) heat-induced decline in electron transport, (ii) heat-induced alteration in the susceptibility of thylakoid polypeptides to trypsin digestion, and (iii) heat-induced decline in the maximum fluorescence transient measured at 685 nm...

Soil residual herbicides registered for use on grapes can be applied from fall to spring, before weed emergence. However, ample early-spring moisture and warm weather may enhance weed emergence before herbicide application in the spring and prevent timely application. Therefore, fall application of herbicides can be beneficial if herbicides would provide adequate weed control in the following spring. Warm and wet winters may enhance herbicide degradation and shorten herbicide residual activity that result in poor weed control the following spring. Fall and spring application of oryzalin or norflurazon applied alone or in combination with diuron, simazine, or oxyfluorfen were evaluated for weed control in commercial vineyards at Oskaloosa and Eudora in northeast Kansas in 2003 and 2004. Weeds were not controlled adequately with oryzalin or norflurazon applied alone. At the end of the growing season, however, weed control was greater with spring than fall application. In addition, weed control with norflurazon was slightly greater than oryzalin. Norflurazon or oryzalin applied in combination with simazine, diuron, or oxyfluorfen controlled more weeds than norflurazon or oryzalin applied alone. The greatest control was with norflurazon or oryzalin applied with oxyfluorfen. In general, all herbicide combinations applied in the spring and fall provided similar weed control 4 months after spring application. However, at the end of the growing season, weed control was 10% to 20% greater when herbicides applied in the spring than fall. This study showed that acceptable weed control can be achieved when norflurazon or oryzalin is applied with oxyfluorfen and diuron in the fall.

The effect of three diphenylether herbicides on the control of green foxtail, kochia, velvetleaf, and ivyleaf morningglory with imazamox in soybean was evaluated in a field study conducted near Manhattan, Kansas in 1997 and 1998. Herbicide treatments were: imazamox at 26 and 44 g ai/ha; acifluorfen and fomesafen each at 140 and 280 g ai/ha; lactofen at 70 and 140 g ai/ha; and tank mixtures of imazamox at both rates with both rates of acifluorfen, fomesafen, and lactofen. Tank mixtures of 26 g/ha imazamox with either rate of acifluorfen, or fomesafen were antagonistic on kochia control, as was 44 g/ha imazamox with 280 g/ha acifluorfen 4 weeks after treatment. Tank mixtures of 26 g/ha imazamox and 280 g/ha acifluorfen or fomesafen were antagonistic on velvetleaf control. The only tank mixture that resulted in reduced ivyleaf morningglory control was 26 g/ha imazamox plus 70 g/ha lactofen. The tank mixture of 26 g/ha imazamox plus 280 g/ ha fomesafen was antagonistic for green foxtail. When a diphenylether herbicide was applied with imazamox, 44 g/ha imazamox resulted in fewer antagonistic interactions than mixtures with 26 g/ha.

(...) objectives were to ascertain relationships and genotypic variability among single-leaf photosynthesis, thylakoid activity, and productivity during high-temperature stress at vegetative and reproductive stages. Ten genotypes from major world wheat-producing regions were grown under moderate (22/17 °C day/night) and high (32/27 °C day/night) temperatures for 2 wk as seedlings or from anthesis to maturity. Net photosynthesis, chlorophyll variable fluorescence (Fv), and productivity were measured at both stages (....)

High temperature stress adversely affects wheat growth in many important production regions, but the mode of injury is unclear. Wheat (Triticum aestivum L. cv. Newton) was grown under controlled conditions to determine the relative magnitude and sequences of responses of source and sink processes to high temperature stress during grain development. Regimes of 25°C day/15°C night, 30°C day/20°C night, and 35°C day/25°C night from 5 days after anthesis to maturity differentially affected source and sink processes. High temperatures accelerated the normal decline in viable leaf blade area and photosynthetic activities per unit leaf area. Electron transport, as measured by Hill reaction activity, declined earlier and faster than other photosynthetic processes at the optimum temperature of 25/15 °C and at elevated temperatures. Changes in RUBP carboxylase activities were similar in direction but smaller in magnitude than changes in photosynthesic rate. Increased protease activity during senscence was markedly accentuated by high temperature stress. Specific protease activity increased 4-fold at 25/15 °C and 28-fold at 35/25 °C from 0 to 21 days after initiation of temperature treatments. Grain-filling rate decreased from the lowest to the highest temperature, but the change was smaller than the decrease in grain-filling duration at the same temperatures. We concluded that a major effect of high temperature is acceleration of senescence, including cessation of vegetative and reproductive growth, deterioration of photosynthetic activities, and degradation of proteinaceous constituents.

Thermal inhibition and photoinhibition of plants, which may occur simultaneously in nature, were investigated to determine whether the two causal stresses interact and to characterize any interactions that occurred. Photosynthetic rates of wheat (Triticum aestivum L. cv Len) seedlings declined gradually after temperature treatment increased from 22 to 42°C or after photosynthetically active radiation (PAR) treatment increased from 450 to 2000 micromoles per square meter per second and fell rapidly after the stresses were simultaneously imposed. Stomatal conductance and internal CO2 were affected little, indicating the interaction occurred in chloroplasts. Thylakoid whole chain electron transport, quantum yield, and saturating PAR intensity were decreased by high temperature and an additional amount by high PAR treatments. Photosystem reactions involving water oxidation were inhibited more than other reactions, and chlorophyll fluorescence transients indicated most inhibition was on the photooxidizing side of photosystem II. Injury was influenced little by the order in which the stresses were imposed and was always most severe when they were combined. Release of proteins from thylakoid membranes was not detected. Lability to the stresses was lowest in thylakoids from vegetative stage plants and increased as plants matured. We concluded that thermal injury is accentuated by high PAR, the two stresses may act at a common site near the water oxidizing complex, and their interaction may be involved in photosynthetic decline during adverse conditions.

Background: Non-transgenic chemical mutagen application, particularly ethyl methanesulfonate (EMS), is an important tool to create mutations and gain a new genetic makeup for plants. It is useful to obtain a sufficient number of mutant plants instead of working with a severe mutation in a few plants. EMS dose and exposure period have been previously studied in several crops; however, EMS used to create point mutations in presoaked rice seeds has not been sufficiently studied and there is no standard protocol for such treatment. The aim of this study is to establish a standard protocol for EMS mutagenesis application in rice. Methods: Two studies were conducted to evaluate the effect of four durations of rice seed presoaking (0, 6, 12, and 24 hours), four EMS concentration doses (0.0%, 0.5%, 1.0%, and 2.0%), and four EMS exposure periods (6, 12, 24, and 48 hours). Germination rate, plumula and radicle length, seedling survival, LD50 (Lethal Dose) determination, shoot length, root length and fresh seedling weight were evaluated. Results: Results showed that a 12-hour presoaking duration, 0.5% EMS dose, and six hours of EMS exposure were the best practices for the optimum number of mutant plants. Conclusions: In light of both this study and the literature, a standard application protocol was established. This application protocol, detailed in this article, contains the following guidelines: (1) Presoaking: 12 hours, (2) EMS application: 0.5% dose EMS and six hours, (3) Final washing: six hours, (4) Drying: 72 hours at 38°C. A user-friendly protocol has been presented for utilization by researchers.