Progress 10/01/00 to 09/30/05
Outputs
African rue is an exotic, herbaceous perennial established in several western states that tolerates harsh, water-stressed conditions. The influence of water-deficit stress on herbicide response and subsequent herbicide fate within the plant were compared. African rue seedlings were deprived of water for 0 to 7 d to establish a gradient of water-deficit levels prior to treatment with hexazinone, imazapyr, or metsulfuron. At herbicide application, water-deficit treatments reduced plant water potential values from -1.0 MPa to -4.7 MPa, causing concomitant reductions in photosynthesis. Thirty-five d after treatment, dry weight of metsulfuron- and imazapyr-treated plants was reduced in plants exposed to more than 4 d water-deficit stress prior to herbicide application. In contrast, hexazinone-treated plants had less dry weight than water-stressed, non-sprayed control plants regardless of water-deficit stress. Seventy-two h after herbicide application, African rue leaves
absorbed from 5 to 42% of herbicide applied; however, herbicide absorption did not correlate to efficacy. Less than 12% of absorbed herbicide translocated out of the treated leaf, regardless of herbicide. Radiolabel translocated from the treated leaf to acropetal or root tissue did not differ among herbicide treatments, regardless of water deficit prior to herbicide application. However, compared to other herbicides, translocation to basipetal shoot tissue was greatest in imazapyr-treated seedlings with the largest water deficit at herbicide application. Increased translocation occurred at higher levels of water stress than were necessary to increase herbicide efficacy, suggesting differential translocation was not involved in enhanced efficacy. In summary, African rue seedlings absorbed and mobilized three different herbicides at all levels of water-deficit stress. In addition, the efficacy of metsulfuron and imazapyr increased as water-deficit stress increased, but efficacy of
hexazinone was not influenced by plant water status. This unusual relationship between water-deficit stress and herbicide performance may enable improved African rue management under stressful environments.
Impacts
African rue seedlings under extreme water-deficit conditions were capable of maintaining photosynthesis and stomatal conductance, albeit at reduced rates. Despite stressed conditions, seedlings were able to absorb and mobilize three different herbicides over many levels of water deficit conditions, conditions where seedlings of many plant species would not survive. Compared to other weeds which lose physiological function and thus, herbicide efficacy under water-stressed conditions, African rue's extraordinary ability to tolerate and maintain function under water-stressed conditions may facilitate chemical control throughout its growing season. This characteristic of drought tolerance combined with increased efficacy of some herbicides in stressed plants may help to improve management of this weed. In addition, management will benefit from an increased understanding of how the physiological strategies of African rue plants allow it to establish and survive under
extreme conditions.
Publications
- Branum, K. S., L. B. Abbott, and T. M. Sterling. 2005. The influence of water stress and timing of herbicide application on African rue control. Proc. Western Soc. Weed Sci. 58:58.
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Progress 01/01/04 to 12/31/04
Outputs
Most of the enzymatic and non-enzymatic antioxidant mechanisms evaluated did not contribute to differentially scavenge prometryn-induced ROS in Pima and DP. Therefore, they do not account for differential tolerance to this herbicide between these cotton cultivars. Using the same cotton cultivars, these same antioxidant mechanisms did not account for differential tolerance to plant interference at an early growth stage; except for DPS and -tocopherol. Therefore, these mechanisms are not expected to provide antioxidant protection against other environmental stresses, as suggested in the literature. This is in agreement with our results for a salinity study as well (data not shown), where Pima and DP responded similarly to salt stress. Since most of the antioxidant mechanisms measured in these studies did not explain differential prometryn tolerance between Pima and DP, other possibilities should be considered for future studies. Other enzymes and antioxidant
metabolites, related or not to the ascorbate-glutathione cycle, may provide protection against prometryn. For example, superoxide dismutase (SOD), a superoxide radical (O2) scavenger, might play a role in differentially detoxifying ROS. Other possibilities that could confer tolerance in Pima may include higher levels of saturated fatty acids in thylakoid membranes or higher rates of repair and turnover of the D1 protein.
Impacts
Exotic invasive weeds are moving across the United States like wildfire, yet very little is known about the strategies which make them successful or how these might be manipulated to enhance management. Work evaluating the physiological mechanisms of invasive weed survival under stress will increase our ability to adequately manage these weeds.
Publications
- Sterling, T. M., D. C. Thompson, and L. A. Abbott. 2004. Implications of invasive plant variation for weed management. Weed Technology 18:000-000.
- Gibbs, L. A. and T. M. Sterling. 2004. Seasonal variation of picloram metabolism in broom and threadleaf snakeweed populations in a common garden. Weed Sci. 54:206-212.
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Progress 01/01/03 to 12/31/03
Outputs
African rue has become established in several western states, where it poses a threat of further spread because of its capability of reproduction by seed and vegetative lateral roots, as well as its apparent success under water-stressed conditions. In previous studies, applications of hexazinone, imazapyr, and metsulfuron have provided effective control of African rue. In this study, plant-herbicide-water stress interactions were investigated. Greenhouse-grown African rue seedlings, placed under watered (control) and non-watered conditions for 6 d, were screened for their sensitivity to these three herbicides, each applied at increasing rates (0, 0.5x, 1.0x, 2.0x recommended rates). Gas exchange and water potential of each seedling were compared prior to herbicide application (6 d after water treatments were initiated). Photosynthesis was reduced from 18 to 10 umol CO2 m-2 s-1 in well-watered seedlings versus non-watered seedlings. Conductance dropped from 0.8 to 0.1
mmol H2O m-2 s-1 in control versus non-watered treatments. Mean leaf water potential was -1.1 MPa for controls compared to -2.5 MPa in non-watered seedlings. After herbicide application, plants were visually rated up to 21 days. Although less active physiologically, plants under water-stressed conditions were more sensitive to herbicide application, with metsulfuron and imazapyr causing the most damage. One day after treatment (DAT), non-watered plants were the only treatments with visible injury as measured by wilting. By 21 DAT, herbicide activity continued to be greater in the non-watered compared to the watered treatments. This initial screening suggests that water status plays a role in altering African rue's sensitivity to herbicides.
Impacts
Exotic invasive weeds are moving across the United States like wildfire, yet very little is known about the strategies which make them successful or how these might be manipulated to enhance management. Work evaluating the physiological mechanisms of invasive weed survival under stress will increase our ability to adequately manage these weeds.
Publications
- Abbott, L. B. and T. M. Sterling. 2003. Recovery of African rue seedlings from water stress: Implications for recruitment and invasion. Invasive Plants in Natural and Managed Systems: Linking Science and Management and 7th International Conference on the Ecology and Management of Alien Plant Invasion, p. 3.
- Abbott, L. B., T. M. Sterling, and L. M. Hite. 2003. Photosynthesis and growth responses of African rue to progressive drought. SRM Annual Meeting 96:5.
- Abbott, L. B., L. M. Hite, and T. M. Sterling. 2003. Physiological responses of African rue to progressive drought. Proc. Western Soc. Weed Sci. 56:25.
- Bettmann, G. T., H. H. Ratynayaka, Abbott, L. B., and T. M. Sterling. 2003. Antioxidant levels of African rue under water stress. Proc. Western Soc. Weed Sci. 56:27.
- Vallotton, A. D., Abbott, L. B., and T. M. Sterling. 2003. African rue seedling response to herbicides applied under drought stress. Proc. Western Soc. Weed Sci. 56:26.
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Progress 01/01/02 to 12/31/02
Outputs
The noxious weed yellow starthistle (Centaurea solstitialis L.) can be controlled effectively at the seedling stage by foliar application of the auxinic herbicides picloram or clopyralid. Although resistance to these herbicides is rare, a yellow starthistle biotype resistant to picloram and cross-resistant to clopyralid was observed in 1989 near Dayton, WA in a pasture that had been subjected to intensive picloram selective pressure. Our objective was to determine the mode of inheritance for this resistance trait. Transmission of the resistant phenotype was monitored in reciprocal F1 crosses between susceptible (SCI) and resistant (RDW) plants, their test-cross and pseudo-F2 progeny. Progeny from all crosses, as well as RDW and SCI seedlings of original populations, were sprayed with picloram or clopyralid to distinguish between susceptible and resistant individuals. All F1 progeny were susceptible to both herbicides indicating that the resistance trait was of nuclear
origin and recessive in nature. Segregation of the resistant phenotype among pseudo-F2 and test-cross progeny of F1 genotypes demonstrated monofactorial inheritance (P> 0.25) for resistance to both herbicides. The conclusion that resistance is conferred by a single recessive allele is consistent with the observation that no other picloram-resistant yellow starthistle populations have been identified in the area since picloram selection pressure was abated.
Impacts
By improving herbicide use efficiency through understanding mechanisms of herbicide action, we will reduce the cost of managing the weed as well as reducing the amount of herbicides necessary for adequate control.
Publications
- Valenzuela-Valenzuela, J. M., N. K. Lownds and T. M. Sterling. 2002. Ethylene plays no role in clopyralid action in yellow starthistle (Centaurea solstitialis L.). Pestic. Biochem. Physiol. 72:142-152.
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Progress 01/01/01 to 12/31/01
Outputs
Broom and threadleaf snakeweed are major weedy pests in the western United States. These weeds can be controlled with herbicides, but their control is not always consistent and can be expensive. Our project is trying to determine the most efficient method of using herbicides on these weeds by understanding what happens to the herbicide after it lands on the leaf surfaces and then how the herbicide enters and moves around in the plant as well as whether or not the plant can alter the herbicide to a non-toxic form. Picloram is the major herbicide used for rangeland weed control. Adequate control can be achieved at recommended rates; however, range weed control is not always consistent. We have characterized picloram uptake from the leaf surface of broom snakeweed as environmentally dependent and determined that its susceptiblity to the herbicide varies greatly due to the environmental conditions previous to application; however, these periods of enhanced uptake and
physiological sensitivity to the herbicide are not related to the growth stage(s) during which broom snakeweed is most susceptible to herbicides in field trials. We are currently evaluating the role of detoxification of the herbicide by analysing the metabolites formed during different times of the year and mechanisms of photodegradation of picloram on leaf surfaces. In addition, our preliminary work characterizing herbicide translocation as it relates to photosynthate redistribution in these woody perennials showed that the herbicide is not redistributed with carbohydrates as one would hypothesize for a weak acid molecule. A more thorough look into carbohydrate chemistry and metabolism as it relates to herbicide translocation in the phloem is being investigated.
Impacts
By improving herbicide use efficiency through understanding mechanisms of herbicide action, we will reduce the cost of managing the weed as well as reducing the amount of herbicides necessary for adequate control.
Publications
- Valenzuela-Valenzuela, J. M., N. K. Lownds and T. M. Sterling. 2001. Clopyralid uptake translocation, metabolism and ethylene induction in picloram-resistant yellow starthistle (Centaurea solstitialis L.). Pestic. Biochem. Physiol. 71:11-19.
- Sterling, T. M., N. K. Lownds and L. W. Murray. 2001. Similar competitive ability between Centaurea solstitialis accessions resistant or susceptible to picloram. Weed Sci. 49:42-47.
- Ratnayaka, H. H., W. T. Molin, and T. M. Sterling. 2001. Oxidative stress tolerance in cotton and spurred anoda under competition and drought. Amer. Soc. Botany Abstracts 2001:75.
- Hernandez-Rios, I. and T. M. Sterling. 2001. Antioxidant response in prometryn-tolerant and -susceptible cotton varieties. Proc. Western Soc. Weed Sci. 54:28.
- Molin, W. T., H. H. Ratnayaka, and T. M. Sterling. 2001. Spurred anoda competition in wide row and ultra narrow row cotton. Proc. Western Soc. Weed Sci. 54:48.
- Ratnayaka, H., W. T. Molin and T. M. Sterling. 2001. Interaction between competition and oxidative stress tolerance in cotton and spurred anoda. Proc. Western Soc. Weed Sci. 54:52.
- Vallotton, A. D., R. P. Sabba, I. Ray and T. M. Sterling. 2001. Inheritance of picloram resistance in yellow starthistle. Proc. Western Soc. Weed Sci. 54:27.
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Progress 01/01/00 to 12/31/00
Outputs
Yellow starthistle is spreading steadily on western rangelands, causing loss of grazing land carrying capacity as well as serious damage to non-grazed land and recreational areas. This noxious weed can be effectively controlled at the seedling stage by foliar application of 0.28 kg a.e./ha picloram. Resistance to picloram in yellow starthistle was observed near Dayton, WA in 1988 and was confirmed in 1990. To determine the inheritance of this resistance, reciprocal F1 crosses between susceptible and resistant plants were performed. Susceptible seeds of yellow starthistle (SCI-1) were collected from wildtype plants growing in Central Grade, ID. Resistant (RDW-1) seeds are second generation progeny of a plant (RDW) resistant to 0.56 kg a.e./ha picloram from Dayton, WA. Progeny of this resistant plant was sprayed with 0.07 to 0.14 kg a.e./ha picloram in the greenhouse and survivors were cross-pollinated to produce RDW-1 seed. Seed from reciprocal F1 crosses was collected
and grown under greenhouse conditions until seedlings were five weeks old. Half of the F1 progeny from reciprocal crosses as well as RDW-1 and SCI-1 seedlings were sprayed with picloram at 0.28 kg a.e./ha and half were sprayed with clopyralid at the same rate. All SCI-1 seedlings and F1 progeny died. Crosses to resistant and susceptible testers were then conducted among F1 progeny, SCI-1 and RDW-1 plants. Selfing rates of individuals used in the crosses were less than 0.1% suggesting that all progeny were hybrids. F2 progeny were screened with both herbicides and segregation ratios determined for the number of progeny surviving and dying. Chi square analyses of F1, F2, and testcross segregation data indicate that the resistant phenotype is recessive and conferred by a single gene with the original SCI-1 population being homozygous dominant for susceptibility. Picloram resistance as a recessive trait is consistent with the observations that while under no additional picloram selection
pressure, resistance has not spread from where it was first identified and that no other picloram-resistant yellow starthistle populations have been identified.
Impacts
By understanding the inheritance of herbicide resistance, weed management can be improved to avoid the development of herbicide resistance.
Publications
- Sterling, T. M., L. W. Murray and Y. Hou. 2000. Morphological variation among broom snakeweed (Gutierrezia sarothrae) populations. Weed Sci. 48:356-365.
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Progress 01/01/99 to 12/31/99
Outputs
Understanding herbicide carryover from one season to the next is very important for successful agriculture production because of the potential for injury and yield reduction of the next season's crop. The potential for carryover is dependent on many things including the relative persistence of the herbicide, soil characteristics and crop sensitivity. The two classes of herbicides, imidazolinone and sulfonylureas, are particularly susceptible to carryover because of their ability to persist in soil. The bioassay technique may be the best method for detecting biologically-active, low levels of these herbicides in soils. Therefore, to understand how pH and moisture influence persistence as well as to optimize a technique for predicting carryover, soil and hydroponic (solution culture of plants) bioassays were compared to evaluate the response of corn to these herbicides. In the soil bioassay, there was greater injury to corn with higher pH soil and higher moisture for
each herbicide. In the hydroponic bioassay, herbicide activity was greater at higher moisture availability levels but was not greatly influenced by pH. Therefore, factors in the soil other than pH such as organic matter were influencing corn sensitivity. Also, as water availability increased in each bioassay, so did herbicide availability. These bioassays should prove useful for further studies investigating the mechanisms of herbicide availability.
Impacts
By understanding herbicide carryover from one season to the next using a plant bioassay, the potential for injury and yield reduction of the next season's crop can be reduced.
Publications
- Sterling, T. M., D.C. Thompson and K.C. McDaniel. 1999. Perennial Snakeweeds. In R. L. Sheley and J. K. Petroff , Eds., Biology and Management of Noxious Rangeland Weeds, Oregon State University Press, Corvallis, pages 323-335.
- Murray, L., T. M. Sterling, and J. Schroeder. 1999. My View. Weed Sci. 47:367-368.
- Sterling, T. M. and D. C. Thompson, editors. 1999. Locoweed Research: Updates and Highlights. New Mexico State Univ., Res. Rep. 730. 88 pages.
- Campanella, M. C., T. M. Sterling, and D. C. Thompson. 1999. Walshia miscecolorella caterpillars may alter swainsonine levels in white locoweed. In Locoweed Research: Updates and Highlights. Sterling, T. M. and D. C. Thompson, eds., New Mexico State Univ., Res. Rep. 730, pp. 36-37.
- Sterling, T. M. and H. S. Jochem. 1999. Understanding why white locoweed is more sensitive to herbicides than woolly locoweed. In Locoweed Research: Updates and Highlights. Sterling, T. M. and D. C. Thompson, eds., New Mexico State Univ., Res. Rep. 730, pp. 46-47.
- Sterling, T. M. and H. S. Jochem. 1999. Do differences in locoweed leaf surfaces affect herbicide uptake? In Locoweed Research: Updates and Highlights. Sterling, T. M. and D. C. Thompson, eds., New Mexico State Univ., Res. Rep. 730, pp. 55-56.
- Thompson, D. C., J. L. Knight, T. M. Sterling, and K. T. Gardner. 1999. Locoweed weevils prefer certain varieties of locoweed. In Locoweed Research: Updates and Highlights. Sterling, T. M. and D. C. Thompson, eds., New Mexico State Univ., Res. Rep. 730, 48-49.
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Progress 01/01/98 to 12/31/98
Outputs
The herbicides dicamba and picloram are auxinic because their action mimics the plant hormone, auxin. Each is an important herbicide for the suppression of many weedy broadleaf species across the western United States. Unfortunately, yellow starthistle and kochia plants that are resistant to picloram and dicamba, respectively, have been detected. Our work has shown that picloram-resistant (R) plants are just as competitive as susceptible (S) plants; therefore, these R weeds will be with us for a long time because the S plants will be unable to outcompete them. Also, we have found that resistance to either herbicide is not due to differences in uptake, translocation or metabolism. Studies were initiated to identify any differences in herbicide binding and also to find any genes which may be differentially expressed in the S compared to the R weeds when sprayed with the herbicide. We optimized an ultrafiltration technique and specific ligand binding to affinity-purified
kochia fractions was obtained. Preliminary results show competitive 3H-IAA binding in kochia microsomal protein samples and in affinity-purified samples. Using differential display, we have selected mRNAs specifically up- or down-regulated in S and R yellow starthistle plants at early time points after picloram treatment as well as those constitutively expressed in either accession but not the other. Sequence data indicates that one the 18 clones of interest (HAR4) which is induced in R, but not S within 15 min has high homology with several chaperonin proteins.
Impacts
(N/A)
Publications
- Sabba, R.P., T.M. Sterling and N.K. Lownds. 1998. Effect of picloram on resistant and susceptible yellow starthistle: The role of ethylene. Weed Sci. 46:297-300.
- Sterling, T.M., W.E. Dyer, M.E.Chaverra, J.K. Pepelnjak, and R.P. Sabba. 1998. Auxin-binding proteins from susceptible and dicamba-resistant kochia accessions. Proc. West Soc. Weed Sci. 51:29-30.
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Progress 01/01/97 to 12/31/97
Outputs
The herbicide picloram is termed auxinic because its action mimics the natural plant hormone, auxin. It is an important herbicide for the suppression of many weedy broadleaf species across the western United States. Yellow starthistle a poisonous thistle, is spreading steadily on western rangelands, causing loss of grazing land carrying capacity as well as serious damage to non-grazed ecosystems and major land-use loss for recreational and wild-life areas. Unfortunately, starthistle plants that are resistant to picloram, a major herbicide used for starthistle control, have been detected in a pasture which had been treated frequently with picloram over the preceding ten years. Our work has shown that picloram-resistant plants are just as competitive as susceptible plants; therefore, these resistant weeds will be with us for a long time because the susceptible plants will be unable to outcompete them. Understanding the mechanism of resistance will allow us to formulate
effective solutions to the problem. We have found that resistance is not due to differences in uptake, translocation or metabolism of the herbicide. However, susceptible plants produce much more of the stress hormone, ethylene than resistant plants when exposed to picloram. Interestingly, we found that the ethylene induced by this herbicide is not responsible for the herbicidal effects of picloram; therefore, other potential sites of resistance are being investigated.
Impacts
(N/A)
Publications
- Maynard, R. L. and T. M. Sterling. 1997. Picloram Photodegradation in plant epicuticular wax. Weed Sci. Soc. Am. Abstracts 36:128.
- Sabba, R. P., T. M. Sterling, and N. K. Lownds. 1997. Complex genetics of yellow starthistle (Centaurea solstitialis L.) resistance to the auxinic herbicides picloram and clopyralid. Weed Sci. Soc. Am.
- Maynard, R. L. and T. M. Sterling. 1997. The influence of epicuticular wax on picloram photodegradation. Proc. Western Soc.
- Valenzuela-Valenzuela, J., N. K. Lownds, and T. M. Sterling. 1997. Clopyralid uptake, translocation and ethylene production in resistant and susceptible yellow starthistle plants. Proc. Western Soc. Weed
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Progress 10/01/92 to 09/30/97
Outputs
Bioassay experiments to determine the influence of soil, pH and water potential on the response of corn to increasing concentrations of imazethapyr, imazaquin, and chlorimuron in soil and hydroponics systems were completed. Inhibition of corn growth variables was related to herbicide concentration, soil and moisture in the soil system, and pH and water potential in the hydroponic system. In the hydroponics system, an interaction between pH and water potential influenced corn growth response to all the herbicides. All three herbicides were more toxic in the hydroponic system than the soil bioassay and herbicide activity was greater at high pH and high water potential. Pyrithiobac applied POST and POST-late at 107 g ai/ha did not injure alfalfa, lettuce or sorghum planted the following season. Onion stand was reduced at one location; however, yield was not affected.
Impacts
(N/A)
Publications
- A. Rios-Torres. 1997. Effect of imazethapyr, imazaquin, and chlorimuron in soils and nutrient solutions at different pHs and water potentials. M.S. thesis. New Mexico State University.
- J. Schroeder and G.P. Hoxworth. 1997. Cucumber response to selected sulfonylurea herbicides. Proceedings Western Society of Weed Science
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Progress 01/01/96 to 12/30/96
Outputs
Bioassay experiments were established in the greenhouse to determine the influence of soil texture (NM (Belen clay loam (pH 7.7, 34% sand, 36% silt, 30% clay, 1.4% organic matter)), GA (Appling sandy loam (pH 5.8, 72% sand, 16% silt 12% clay, 3.1% organic matter))) and soil moisture content (-0.01, -0.02 and -0.2 MPa; based on water retention curves) on the response of corn (cv. Pioneer 3369A) to increasing concentrations of imazethapyr, imazaquin, and chlorimuron. Belen soil had lower I50 values for corn root parameters compared with the Appling soil at all moisture levels. I50 values were lower at the optimum soil moisture content for all three herbicides regardless of soil type. Therefore, biological activity of the herbicides increased as soil moisture content and soil pH increased and soil organic matter content decreased. I50 values for corn root length were lower than root dry weight indicating that root length was more sensitive to these herbicides than root
dry weight. However, root dry weight response was more sensitive to soil moisture levels than root length. Research to support these results is being continued using a hydroponics system. Rotational studies were initiated in 1996 at two locations in southern NM (Belen soil near Las Cruces and Reagan loam (fine, carbonatic, thermic Typic Calciorthid, 36% sand, 38% silt, 26% clay; near Artesia) to evaluate rotational crop yield to POST and POST-late treatments of pyrithiobac applied at 71.5 and 107 g ai/ha.
Impacts
(N/A)
Publications
- Rios-Torres, A., J. Schroeder, and T.M. Sterling. 1996. Behavior of three ALS inhibitors in two soils at different moisture levels. Proc. West. Soc. Weed Sci.49:35.
- Barnes, R.J. and J. Schroeder. 1996. Detection of residual concentrations of imazapyr in soil by bioassay techniques. Proc. West. Soc. Weed Sci. 49:36.
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Progress 01/01/94 to 12/30/94
Outputs
Picloram metabolism among rangeland weeds common to the western United States was compared. Terminal shoots or leaves of broom snakeweed (Gutierrezia sarothrae), threadleaf snakeweed (Gutierrezia microcephala), yellow starhistle (Centaurea soltitialis), Russian knapweed (Centaurea repens), and the locoweeds, silky crazyweed (Oxytropis sericea) and woolly loco (Astragalus mollisimus) were incubated with 14C-picloram for 72h. Radiolabel was extracted and metabolites were separated and detected using an HPLC system with a 254-nm UV detector and B-Ram in-line radioactivity monitor. The metabolites detected were species specific. Gutierrezia species converted only 2 to 3% of the parent picloram to metabolites less polar than the parent herbicide. Centaurea species also metabolized picloram but to a greater extent and to different metabolites than Gutierrezia. The locoweeds, Astragalus and Oxytropis, also metabolized picloram but to a lesser extent than Centaurea. The
identity of these metabolites is unknown but may be similar to those found in other plant species in the literature. Further work is needed to better characterize these metabolites in rangeland weeds at different stages of growth and determine their role in susceptibility to picloram.
Impacts
(N/A)
Publications
- STERLING, T. M., N. K. LOWNDS, and L. W. MURRAY. 1994. Effect of broom snakeweed stage of plant growth on picloram uptake and picloram-induced ethylene production. Proc. Western Soc. Weed Sci. 47:17-18. 1994. Persistence of Pest.
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Progress 01/01/92 to 12/30/92
Outputs
A primary mechanism of herbicide selectivity is the ability of a plant species to degrade the parent herbicide to a nonphytotoxic compound. Picloram is a major herbicide used to control rangeland weeds. Therefore, studies were initiated to determine metabolism of picloram in broom snakeweed. Picloram metabolism was determined by using non-woody terminal shoots excised from greenhouse-grown plants. Cut ends of stems were submerged in a 7-ml vial containing 1 ml distilled water and 30 MBq/ml of picloram-2,6-14C. Tissue was allowed to take up the solution at 25 C for 72 hours. Control vials contained radiolabelled picloram but no plant tissue. After 72 hours, plant tissue was homogenized and radiolabel was extracted using MeOH:water (80:20; v/v). The homogenate was centrifuged to remove soluble radiolabel from plant debris. The final pellet was oxidized and radiolabel remaining in supernatant was quantitated by liquid scintillation spectrometry. The clear supernatant was
concentrated and this aqueous concentrate was adjusted to pH 7.5 and eluted through a C18-Seppak cartridge. Metabolites of picloram were separated using a water (4% acetic acid):acetonitrile linear gradient from 0 to 60% acetonitrile over 15 min through a C18 HPLC column and detected with an in-line radioactivity monitor. Total recovery of radiolabel was greater than 95% of 14C-picloram applied. HPLC results indicate that approximately 20 to 30% of the absorbed picloram is metabolized in broom snakeweed within 72 h.
Impacts
(N/A)
Publications
- NO PUBLICATIONS REPORTED THIS PERIOD.
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Progress 01/01/91 to 12/30/91
Outputs
Picloram is the major herbicide used for control of the rangeland weed, broom snakeweed (Gutierrezia sarothrae). Adequate control can be achieved at recommended rates; however, broom snakeweed control is not always consistent. The environmental conditions and growth stage(s) during which broom snakeweed is most susceptible to herbicides have not been defined. Foliar absorption of picloram by broom snakeweed was studied. Terminal shoots were excised and leaves were treated with radiolabelled picloram. After incubation, leaf surfaces were rinsed and radiolabel determined in rinsate using liquid scintillation counting.
Impacts
(N/A)
Publications
- STERLING, T.M. AND LOWNDS, N.K. 1991. Factors affecting picloram absorption by broom snakeweed. Western Soc. Weed Sci. Proc. 44:47-48.
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