Identification and Management of Herbicide Resistant Weeds in Virginia's Agronomic Crops

IDENTIFICATION AND MANAGEMENT OF HERBICIDE RESISTANT WEEDS IN VIRGINIA'S AGRONOMIC CROPS

Sponsoring Institution

National Institute of Food and Agriculture

Project Status

COMPLETE

Funding Source

HATCH

Reporting Frequency

Annual

Accession No.

0216921

Grant No.

(N/A)

Cumulative Award Amt.

(N/A)

Proposal No.

(N/A)

Multistate No.

(N/A)

Project Start Date

Jan 1, 2009

Project End Date

Sep 30, 2012

Grant Year

(N/A)

Program Code

[(N/A)]- (N/A)

Recipient Organization
VIRGINIA POLYTECHNIC INSTITUTE
(N/A)
BLACKSBURG,VA 24061

Performing Department
Plant Pathology Physiology & Weed Science

Non Technical Summary
Because current herbicide use patterns demonstrate increased reliance on newer compounds to which the development of resistance is likely, because introduction of genetically modified crops continues to increase reliance on a relatively limited number of materials, and because several of the newer, highly specific herbicides are also those for which genetic transformations for crop tolerance have been made, the occurrence of weed resistance will continue to increase. Research is needed, therefore, to monitor reported incidences of suspected herbicide resistance, confirm the resistance, characterize the physiological basis of the resistance, and develop alternative control strategies. Successful completion of this research will identify economically and environmentally sustainable control strategies for resistant weeds, and prevent them from becoming significant constraints to agricultural productivity.

Animal Health Component

(N/A)

Research Effort Categories

Basic

(N/A)

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
213	1510	1140	25%
213	1599	1140	40%
213	1820	1140	35%

Knowledge Area
213 - Weeds Affecting Plants;

Subject Of Investigation
1510 - Corn; 1599 - Grain crops, general/other; 1820 - Soybean;

Field Of Science
1140 - Weed science;

Keywords

herbicide resistance

herbicide resistant weeds

agronomic crops

weed management

genetically modified crops

Goals / Objectives
1) Receive reports from the field, conduct field site visits, collect seed or other propagules, and conduct initial greenhouse screening for resistance to the herbicide applied. 2) Expand greenhouse evaluations to elucidate the nature of the response of resistant and susceptible biotypes of specific weeds to a range of application rates of the herbicide to which resistance has been confirmed. Determine the response of these weeds to other herbicides in chemical families in the same mode of action group where cross resistance might be expected. 3) Conduct field research in small-plot format conducted at the site(s) where resistant weed species are identified or suspected. This research will be conducted for triazine-resistant pigweed and lambsquarters, diclofop-resistant Italian ryegrass, shattercane with resistance to ALS-inhibiting herbicides, common lambsquarters with reduced sensitivity to glyphosate, common chickweed with reduced sensitivity to ALS-inhibiting herbicides, and other species as they are identified. 4) Present findings at scientific meetings, and resulting recommendations through Virginia Cooperative Extension via the Pest Management Guide Series, other print and web-based publications, and grower meetings, field-days, and in-service training sessions for county agents and agribusiness representatives.

Project Methods
Research to confirm and characterize the nature of resistance will be performed in the Weed Science greenhouse at the PPWS Department's Glade Road Research Center in Blacksburg. In greenhouse experiments, seed or other propagules of resistant species will be planted in 10-cm pots containing commercial potting media and watered and fertilized as needed. Plants will be thinned to 1 to 3 per pot depending on the species. Herbicide applications for greenhouse experiments will be made with a CO2-pressurized track sprayer. Visual evaluations of weed vigor and height reduction will be made on approximately weekly intervals. Determination of dry weight reduction will made at the termination of the experiment, generally 6-8 weeks after treatment. All treatments will be replicated four times, and treatments arranged in a randomized complete block design. Field research to develop alternative control methods will be conducted on university land where naturally-occurring infestations of resistant weed species are present. Crop establishment and maintenance will be performed in accordance with established VCE guidelines. All field research will be conducted using standard small plot format, utilizing a minimum of four replications in a randomized complete block design. Individual plots will be 3 by 8 m and will contain a 2 m treated area located in the middle of the 3 m plot width, thereby creating a 1 m "running check" and buffer area between adjacent treated areas. All herbicide applications will be made with CO2-pressurized backpack equipment designed for small plot research. Weed control and crop vigor evaluations will be made at approximately 14 day intervals throughout the growing season. All plots will be mechanically or hand harvested. For both greenhouse and field experiments, percentage control and percentage weed or crop vigor reduction data will be subjected to arcsine transformation prior to analysis to normalize data distribution. Data will be subjected to one-way or factorial analysis of variance as appropriate to the study design and means separated using an appropriate statistical measure at the 5% level of significance. Greenhouse experiments will generally be established in a factorial design involving herbicide rates, herbicides, and resistant and susceptible biotypes as factors.

Progress 01/01/09 to 09/30/12

Outputs
OUTPUTS: OUTPUTS: Postemergence control of common chickweed, the most common weed infesting Virginia small grains, has been accomplished using the ALS-inhibiting sulfonylurea herbicides thifensulfuron-methyl plus tribenuron-methyl since their commercial introduction in the 1980's. Control of this species with this treatment has been extremely effective. During the period coved by this report, however, insufficient control of this species was observed in two Virginia locations. Greenhouse evaluation of susceptibility of F1 and F2 progeny from these collections revealed high level resistance to thifensulfuron-methyl. Normal use rates of this herbicide elicited over 99% fresh weight reduction in wild type F1 plants, while no fresh weight reduction was observed in suspect collections at rates as high as 4X. 32X rates elicited no more than 55% fresh weight reductions in suspect collections. Resistance was confirmed when greenhouse evaluations revealed similar responses in F2 progeny in all collections. This represented the first confirmation of resistance to this chemistry in this weed species in the United States. Common chickweed seedlings were also treated with 1X and 4X rates of other ALS-inhibiting herbicides including metsulfuron-methyl, prosulfuron, imathezapyr, imazapyr, and bispyribac sodium. Significantly reduced susceptibility to these herbicides was also observed in resistant populations. Field research evaluating alternative control measures for this resistant common chickweed has been conducted in each year of this project. Results indicate that preemergence applications of flumioxazin, delayed preemergence applications of pendimethalin, metribuzin, or flufenacet plus metribuzin, and postemergence applications of fluroxypyr or metribuzin provided good to excellent control of resistant common chickweed with good crop tolerance. Field and greenhouse research also confirmed glyphosate resistance in a common ragweed collection from Hanover County, Virginia in 2011. This represented the first confirmation of glyphosate resistance in this species in Virginia. Field research demonstrated effective alternative control methods in soybean. Preemergence applications of flumioxazin, sulfentrazone, or sulfentrazone plus cloransulam, supplemented with postemergence applications of fomesafen or cloransulam, afforded excellent, season-long common ragweed control. Research conducted in 2012 demonstrated excellent potential for glyphosate resistant common ragweed control in USDA-regulated field trials evaluating developing GMO technologies with dicamba-tolerant soybean. This information has been disseminated to growers, VCE field staff, agribusiness representatives, and research cooperators through field research reports, numerous county and regional meetings, and the VCE Pest Management Guide. PARTICIPANTS: E.S. Hagood, C.C. Kenley (Technician), A.N. Smith (Graduate Research Assistant), P.H Davis and W.D. Shelton (Grower Cooperators). TARGET AUDIENCES: Virginia agronomic crop producers, Virginia VCE Field Staff, Virginia agribusiness personnel. PROJECT MODIFICATIONS: This project is being terminated as of 2012 due to the retirement of Dr. Scott Hagood from the project.

Impacts
IMPACT: The infestation level of ALS-resistant common chickweed has spread such that programs for its control are being utilized in over one third on Virginia's small grain acreage. Glyphosate-resistant common ragweed infestation is still very limited, with known impacts still confined to the Hanover area. Strategies for identification, management, and control of both species have been discussed in grower meetings, field days, and in-service training sessions in all areas of the state impacted or potentially impacted by these weeds. As a result of these efforts, alternative chickweed control measures have been utilized on over 150,000 acres of Virginia small grains, and producers have become aware of the threat posed by continued spread of resistant biotypes of both species.

Publications

Smith, A.N. and E.S. Hagood. 2012. Confirmation of Glyphosate-Resistant Common Ragweed in Virginia. Proc. Northeastern Weed Sci. Soc. 65: in press.

Progress 10/01/10 to 09/30/11

Outputs
OUTPUTS: Field and greenhouse research confirmed glyphosate resistance in a common ragweed (Ambrosia artemisiifolia) collection from Hanover County, Virginia. This represented the first confirmation of resistance in this weed species in Virginia. Field research demonstrated effective alternative methods of control in soybean. Preemergence applications of flumioxazin, sulfentrazone, or sulfentrazone plus cloransulam, supplemented with postemergence applications of fomesafen or cloransulam, afforded excellent, season-long ragweed control. Field research was also continued to evaluate control methods for acetolactate synthase (ALS) resistant common chickweed (Stellaria media) in wheat. Early preplant applications of flumioxazin, delayed preemergence applications of pendimethalin, metribuzin, or flufenacet plus metribuzin, and postemergence applications of fluroxypyr provided good to excellent control of ALS-resistant chickweed with good crop tolerance. PARTICIPANTS: E.S Hagood, C.C. Kenley (Technician), A.N. Smith (Graduate Research Assistant), P.H Davis and W.D. Shelton (Grower Cooperators) TARGET AUDIENCES: Virginia agronomic crop producers, Virginia Cooperative Extension Agents, Virginia agribusiness representatives. PROJECT MODIFICATIONS: When Dr. Hagood retired in 2010, Dr. John McDowell assumed responsibility as P.I. because he was acting department head at the time. Dr. Elizabeth Grabau is currently department head and has assumed official responsibility for the project. Dr. Hagood has a part-time position in the department and continues to fullfil the objectives of the project.

Impacts
The infestation level of ALS-resistant chickweed has expanded significantly in the last 2-3 years. Programs for control of this weed species have been discussed in grower meetings, field days, and in-service training sessions in all small grain producing areas of the state. As a result of these efforts, alternative chickweed control methods have been utilized on approximately 50,000 acres of Virginia small grains, and producers have become aware of the threat posed by continued spread of the resistant biotype. At this point, glyphosate-resistant common ragweed is not widely distributed, but educational efforts will be directed towards education of growers such that this species does not constrain production.

Publications

Smith, A.N. and E.S. Hagood. 2011. Nicosulfuron-resistant Johnsongrass Exhibits Differential Sensitivity to Glyphosate. 6th Resistance International Conference. Harpenden, UK.
Smith, A.N. and E.S. Hagood. 2011. Effects of Rye and Vetch Cover Crops on Herbicide Inputs in Field Corn. 65th Northeast Weed Science Society Annual Meeting. Baltimore, MD.
Smith, A.N. and E.S. Hagood. 2011. Differential Response of Virginia Johnsongrass Accessions to Glyphosate. 64th Southern Weed Science Society Annual Meeting. San Juan, Puerto Rico.
Hagood, E.S., H.P. Wilson, R.L. Ritter, B.A. Majek, W.S. Curran, R. Chandran, and M. Van Gessel. 2011. Pest Management Guide for Field Crops: Weed Control in Field Crops. VCE Publication 456-016. 140 pp.

Progress 10/01/09 to 09/30/10

Outputs
OUTPUTS: OUTPUTS: Postemergence control of common chickweed with sulfonylurea herbicides in Virginia small grains has generally been very effective. The standard treatment for the control of common chickweed is the commercially formulated combination of thifensulfuron-methyl plus tribenuron-methyl. In the 2007-08 growing season, insufficient control of this weed was observed in two Virginia counties: New Kent and King William. As previously reported, field and greenhouse evaluations confirmed high-level resistance to sulfonylurea herbicides, as well as to other groups of ALS-inhibiting herbicides. Field evaluations conducted during this reporting period demonstrated that preemergence application of flumioxazin at 30, 14, 7, and 0 days before planting afforded excellent, season-long control of common chickweed. Further field and greenhouse experiments were initiated to evaluate the susceptibility of a Rockingham County, Virginia collection of johnsongrass that had not been controlled effectively with glyphosate in glyphosate-tolerant field corn. Field evaluations demonstrated a significant reduction in control with standard field use rates of glyphosate at this location. Greenhouse experiments are being conducted to elucidate the magnitude of this differential response. Preliminary results confirm elevated glyphosate tolerance in F2 progeny from the Rockbridge site relative to the response of wild type plants. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Virginia small grain producers, Virginia corn producers, and agriservice professionals were provided information on characterization of the nature of resistance and alternative control strategies. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
As a result of the research conducted above, recommendations for the control of ALS-resistant common chickweed were disseminated through grower meetings and via the 2010 Pest Management Guide for Field Crops. Growers with ALS-resistant common chickweed have adopted either preemergence flumioxazin or postemergence fluroxypyr as means to prevent yield loss in areas infested with this chickweed biotype. In the second year of adoption, acreage impacted was approximately 15,000. As the resistant biotype spreads, implementation of these practices will affect significantly greater acreage.

Publications

Hagood, E.S. 2010. ALS-Resistant Common Chickweed (Stellaria media): First U.S. Report. Pan-American Weed Resistance Conference. 1:N20.
Hagood, E.S., H.P. Wilson, R.L. Ritter, W.S. Curran, R. Chandran, and M. Van Gessel. 2010. Pest management Guide for Field Crops: Weeds: Grain crops, Soybeans, Forages. VCE Publication 456-016. Section 5. 160 pages

Progress 10/01/08 to 09/30/09

Outputs
OUTPUTS: Postemergence control of common chickweed with sulfonylurea herbicides in Virginia small grains has generally been very effective. The standard treatment for the control of common chickweed has been the commercially formulated combination of thifensulfuron-methyl plus tribenuron-methyl. In the 2007-08 growing season, insufficient control of this weed was observed in two Virginia counties: New Kent (NK) and King William (KW). Two collections of mature common chickweed plants were made at each of these locations, and designated NK1, NK2, KW1, and KW2. Susceptibility of F1 progeny derived from these collections was evaluated relative to the susceptibility of wild type (WT) F1 progeny. Thifensulfuron-methyl was applied to 3-4 cm common chickweed seedlings at 0, 0.25, 0.5, 1, 2, 4, 8, 16, and 32 times the labeled use rate of 0.026 kg ai ha-1. At 28 days after treatment (DAT), vigor reductions in WT common chickweed ranged from 91 to 99 percent in response to thifensulfuron-methyl rates from 0.5 to 32X. In NK and KW common chickweed, no vigor reduction was observed in response to thifensulfuron-methyl rates up to 4X, and vigor reductions of 0 to 11 percent were observed in response to rates ranging from 8 to 32X. Fresh weight of WT common chickweed at 30 DAT in response to 0.5 to 32X thifensulfuron-methyl rates was reduced by 98 percent or greater. Fresh weight reductions in response to this range of thifensulfuron-methyl rates were 11 to 26 percent, 13 to 30 percent, 11 to 40 percent, and 20 to 55 percent for NK1, NK2, KW1, and KW2 collections, respectively. In subsequent experiments, common chickweed seedlings were treated with 1 or 4X rates of other ALS-inhibiting herbicides including metsulfuron-methyl, prosulfuron, imazethapyr, imazapyr, and bispyribac-sodium. Significant differences in susceptibility were observed on the basis of herbicide, rate, and collection at 28 DAT. In field experiments, preemergence applications of flumioxazin provided 73 to 100 percent common chickweed control. Delayed preemergence treatments of pendimethalin, metribuzin, or flufenacet plus metribuzin provided 93 percent or greater common chickweed control. Postemergence treatments of thifensulfuron-methyl plus tribenuron-methyl provided no common chickweed control, while 2,4-D plus dicamba, pyrasulfotole plus bromoxynil, and the lower application rate of metribuzin provided fair control. Good to excellent control of common chickweed was observed in response to applications of fluroxypyr and the higher rate of metribuzin. No treatment resulted in a significant reduction in wheat vigor. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Virginia small grain producers and agriservice professionals were provided information on characterization of the nature of resistance and alternative control strategies. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
As a result of the research conducted above, recommendations for the control of ALS-resistant common chickweed were disseminated through grower meetings and via the 2010 Pest Management Guide for Field Crops. Growers with ALS-resistant common chickweed have adopted either preemergence flumioxazin or postemergence fluroxypyr as means to prevent yield loss in areas infested with this chickweed biotype. In the first year of adoption, acreage impacted is expected to be less than 1000. However, as the resistant biotype spreads, implementation of these practices will affect significantly greater acreage.

Publications

Hagood. E.S., G.A. Hite, and D.D. Ganske. 2009. Response of Virginia Collections of Common Chickweed (Stellaria media) to Sulfonylurea Herbicides. Weed Sci. Soc. Amer. Abstr. 49:237.