The Development of Sustainable Weed Management Practices for Florida Citrus

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
213	0999	1140	80%
111	0999	1140	20%

Progress 12/17/98 to 09/30/04

Outputs
Predicting herbicide efficacy is influenced by environmental conditions at the time of application, herbicide rate, weed emergence, weed seed bank, and interactions with other herbicides. Soil-applied pre-emergence herbicides (PRE) prevent seed germination and reduce early weed growth to a certain extent. Application of PRE and POST herbicides reduces weed competition with citrus trees, but at a high cost because of repeated use of herbicides at very high application rates. Furthermore, repeated high application herbicide rates increase the risks of tree safety and environmental contamination. In recent years, low rate technology herbicides have become increasingly popular for weed control because of reduced environmental risks. Weed competition is more severe in young citrus groves which need more attention to protect from vagaries of weeds. Studies were conducted on new low rate technology herbicides which have potential to be available as additional tools for weed management in citrus for better and economic weed management. A new compound trifloxysulfuron from Syngenta seems to have activity on some of the hard to control weeds. The new formulations of glyphosate also hold promise as they are added with adjuvants to improve weed control efficacy and improve rainfastness. Several experiments were conducted with both pre-and post-emergence herbicides with adjuvants to increase efficacy which will reduce rate of application and reduce the cost to the growers, hence improve the environment. Herbicide mixtures and sequential application has exhibited the added advantage in improving the weed control efficacy and may be helpful in the long run in avoiding shifting weed flora to hard-to-control weeds. The work is being conducted to reduce leaching of herbicides. Leaching studies of several herbicides are continuing to establish the database. A new plant was studied with an alleopathic potential. The plant material showed suppression in growth of both grasses and broad leaf weeds. Two formulations (EC and GR) of Ridomil Gold fungicide applied alone and in combination with Admire (Imidacloprid) insecticide were evaluated under field conditions for optimal rates to avoid injury symptom to young citrus trees.

Impacts
Evaluation of new herbicides, formulations and their increased efficacy will shape the composition of weed flora in the citrus groves of Florida. Interactions of herbicide mixtures, their sequential use and improved efficacy with adjuvants will provide effective weed management and improve the economy of citrus growers. Herbicide leaching studies are aimed to protect groundwater contamination with the use of new molecules (adjuvants). Biological and allelopathy studies on weeds will provide an important aspect of integrated weed management.

Publications

Futch, S. H. and M. Singh. 2004. Florida Citrus Pest Management Guide, Co-Operative Extension Service, IFAS SPA43 2004.
Sharma, S. D. and M. Singh. 2003. Allelopathic effect of basil (Ocymum sanctum) materials on the germination of certain weed seeds. Indian J. Weed Sci. 36(1&2):99-103.
Singh, S. and M. Singh. 2004. Evaluation of some adjuvants for improving glyphosate efficacy. ASTM STP 1460 (in press)
Singh, S., A. Yadav, R. S. Balyan, R. K. Malik and M. Singh. 2004. Control of ragweed parthenium (Parthenium hysterophorus) and associated weeds. Weed Technol. 18:658-664.
Singh, S. and M. Singh. 2004. Effect of growth stage on trifloxysulfuron and glyphosate efficacy in twelve weed species of citrus groves. Weed Tech. 18:1031-1036.

Progress 10/01/02 to 10/01/03

Outputs
During this year, work was concentrated on efficacy enhancement of existing herbicides, evaluation of new herbicides, their formulations and integrated use for the control of citrus weeds. Field experiments at different locations were conducted by using herbicide mixtures and adjuvants for increased spectrum of weed kill and lowering the application rates of herbicides. Evaluation of new adjuvants tank mixed with glyphosate was done for grass and broadleaf weed species. Effect of sequential and tank mix application for season-long weed control was demonstrated under field condition. Effect of adjuvants on herbicide leaching and allelopathy effect on weeds species was carried under greenhouse conditions. Importance of stage of weeds on the efficacy of CGA 362622 and formulations of glyphosate (Roundup, UltraMax, and Touchdown IQ) were studied for the hardy weeds of citrus groves both under field and glass house conditions. Tank mix application of burndown herbicides with glyphosate was evaluated both under field and greenhouse conditions. The project is intended to generate useful information on the bioecology of weeds for their effective management and avoidance of resistance by adopting varied strategies of weed management for long-term efficacy. Use of herbicides mixtures and adjuvants will enhance the efficacy of herbicide and lower their application rates with out taxing environment.

Impacts
Evaluation of new herbicides, formulations and their increased efficacy will shape the composition of weed flora in the citrus groves of Florida. Interactions of herbicide mixtures, their sequential use and improved efficacy with adjuvants will provide effective weed management and improve the economy of citrus growers. Herbicide leaching studies are aimed to protect groundwater contamination with the use of new molecules (adjuvants). Biological and allelopathy studies on weeds will provide an important aspect of integrated weed management.

Publications

Singh, M., W. Mersie, and R. H. Brlansky. 2003. Phytotoxicity of the fungicide metalaxyl and its optical isomers. Plant Disease 87(9):1144-1147.
Singh, M. and S. Singh. 2003. Response of some important citrus weeds to two formulations of glyphosate applied at three growth stages. The BCPC International Congress - Crop Science and Technology 2003. Vol. 2:1053-1058.
Singh, S., A. Yadav, R. K. Malik, and M. Singh. 2003. Rhizotron study on soil moisture and plant population effect on root competition of cotton and mungbean with Trianthema portulacastrum and Echinochloa crus-galli. The BCPC International Congress - Crop Science and Technology 2003. Vol. 2:1059-1064.
Singh, M. 2003. Weed Management in citrus. Proceedings IX International Citriculture Congress. Vol. 2:370-376.
Chandramohan, S., R. Charudattan, R. M. Sonoda, and M. Singh. 2003. A novel strategy to manage weedy grasses on the citrus orchard floor. Proceedings IX International Citriculture Congress. Vol. 2:380-382.
Singh, M. 2003. Efficacy enhancement of herbicides with adjuvants. Proceedings of the IV Asia-Pacific Crop Protection Conference & Exhibition 2003, New Delhi, India, 18-19 Sept. 2003, Pp. 308-314.

Progress 10/01/01 to 10/01/02

Outputs
During this year, work was concentrated on bioecology of weeds and efficacy enhancement of existing herbicides, evaluation of new herbicides and their integrated use for the control of citrus weeds. Field experiments at different locations were conducted by using herbicide mixtures and adjuvants for increased spectrum of weed kill and lowering the application rates of herbicides. Evaluation of new adjuvants tank mixed with glyphosate was done for grass and broadleaf weed species. Effect of stage of weeds on the efficacy of CGA 362622 and formulations of glyphosate (Roundup UltraMax, and Touchdown IQ) were studied for the hardy weeds of citrus groves both under field and glass house conditions. Bioecology study on seeding depth, artificial flooding on weed seed germination, effect of temperature, pH and osmotic potential on germination of a range of citrus weeds was undertaken. Effect of late application of glyphosate and gramoxone on fruit drop of Hamlin citrus variety was studied at farmer field.

Impacts
The project is intended to generate useful information on the bioecology of weeds for their effective management and avoidance of resistance by adopting varied strategies of weed management for long-term efficacy. Use of herbicides mixtures and adjuvants will enhance the efficacy of herbicide and lower their application rates with out taxing environment.

Publications

Singh, M. 2002. Efficacy enhancement of pre-seeding herbicides under zero tillage system. International Workshop on Herbicide Resistance Management and Zero Tillage in Rice-Wheat Cropping System, CCS Haryana Agricultural University, Hisar, India, 4-6 March, 2002, pp. 88-92.
Singh, M. and Sharma, S. D. 2002. Benefits of Triazine herbicides and other weed control technology in citrus management, in H. M. LeBaron, eds, Triazine Herbicides (in press).
Singh, M., Tan, S., and Sharma, S. D. 2002. Effects of adjuvants on wetting and water infiltration of soils. Environ. Contam. Toxicol. 68:692-698.
Singh, M., Tan, S., and Sharma, S. D. 2002. Adjuvants enhance weed control efficacy of foliar applied diuron. Weed Technol. 16(1):74-78.
Singh, M., Tan, S., and Sharma, S. D. 2002. Leaching and sorption of norflurazon in soils as affected by cationic surfactants. Bull. Environ. Contam. Toxicol. 68:901-907.
Chandramohan, S., Charudattan, R., Sonoda, S. M., and Singh, M. 2002. Field evaluation of a fungal pathogen for the control of seven weedy grasses. Weed Sci. 50:204-213.
Singh, M., Tan. S. and Sharma, S.D. 2002. Adjuvants influence the activity of diuron and Norflurazon. Pesticide Formulations and Delivery Systems: Meeting the Challenges of the Current Crop Protection Industry. STP 1430:173-182.

Progress 10/01/00 to 10/01/01

Outputs
During this year the work was done on weed biology/ecology, efficacy enhancement and non-chemical alternate mathods of weed management in citrus. Also, the work was continued on the downword movement of herbicides in soil. Advance trials were conducted on CGA-362 to optimize the rate of application for maximum weed control without any phytotoxicity to young citrus trees. A new herbicide Broadstrike from Dow Agrisciences was evaluated for wweed control and tree safety. The herbicide has potential to be used as an additional tool for weed managemnt in citrus. Preliminary experiments were conducted on allelopathiy, a non-chemical method of weed management. Allelopathic effect of basil (Ocymum sanctum)was examines on the germination and growth of hairy beggerticks, pigweed and guineagrass. The work on difficult to control vines and some broad leaf weeds indicated that higher rates of diruon and simazine can minimize their germination and growth.

Impacts
This project will provide the information on best management practices for weed control in Florida citrus to maximize the profit to the growers by reducing the the overall cost of produtcion. Additionally, the project will provide the infromation on environmentally safe appliaction of herbicides to prevent the ground water contamination.

Publications

Sharma, S. D. and M. Singh. 2001. Environmental factors affecting absorption and bioefficacy of glyphosate in Florida beggarweed (Desmodium tortuosum). Crop Protection Journal, 20 (6): 511-516.
Sharma, S. D. and Singh, M. 2001. Surfactant increase toxicity of glyphosate and 2,4-D efficacy to Brazil pusley. HortScience 36(4): 726-728.
Sharma, SD and M Singh. 2001. Susceptibility of Florida Candler Fine Soil to Herbicide Leaching. Bull Enviorn. Contam. Toxicol. 67: 594-600.
Sharma, S. D. and Singh, M. 2001. Influence of nonionic surfactants on glyphosate formulations. Proc. Intl. Sym. on Adjuvants for Agrochemicals. 519-524.
Singh, M. and S. D Sharma. 2001. Effect of ethoxylated alcohol surfactant series on the bioefficacy of glyphosate and fluazifop-P. Proc. Intl. Sym. on Adjuvants for Agrochemicals. 531-536.
Singh, M. and S. D. Sharma. 2001. Bioecological factors affecting germination of weed seeds. Proc. BCPC-Weeds: 277-282.
Sharma, S.D., M. Singh and R. H. Brlansky. 2001. Adjuvant affect cuticular waxes and penetration of glyphosate. Proc. BCPC-Weeds: 689-694.
Singh, M., S. Tan and S. D. Sharma 2001. Adjuvants enhance weed control efficacy of foliar applied diuron. Weed Technol. (In press).
Chandramohan, S., Charudattan, R., Sonoda, R.M., and Singh, M. 2002. Field evaluation of a fungal pathogen mixture for the control of seven weedy grasses. Weed Sci. 50:___(In press)
Singh, M., S. Tan, and S. D. Sharma. 2001. Effects of adjunvants on wetting and water infiltration of soils. Bull. Env. Contam. Toxicol. (Accepted)
Singh, S. Tan, and S. D. Sharma. 2001. Leaching and sorption of norflurazon in soils as affected by cationic surfactants. Bull. Env. Contam. Toxicol. (Accepted)
Sharma, S. D. and Singh, M. 2001. Different adjuvant types and glyphosate efficacy on some weeds. Proc. Fl. State Hort. Soc. (Accepted in refereed section).

Progress 10/01/99 to 09/30/00

Outputs
Research on the use of new and old adjuvants formulated with glyphosate was continued and information has been generated on its efficacy to control weeds in of citrus groves. In an experiment, effect of an ethoxylated alcohol surfactant (C6-C18) series with ethylene oxide (EO) contents varied from 3.5 to 30 was examined, which confirmed the choice of EO or carbon chain for glyphosate. Results from this study and other experiments with adjuvants indicated that the effect of various adjuvants on herbicide enhancement was complicated, specific to active ingredient, type of adjuvants, weed species and environment conditions. In another study, effect of air temperatures (16, 22, 35 C) or relative humidity (RH, 45, 70, 95%) on 14C-glyphosate distributions in Florida beggarweed was examined. Absorption of 14C-glyphosate were significantly higher at 22 C or 95% RH than other test values. These results indicated that temperature or RH influenced the absorption process of glyphosate and hence the control of weeds. In a study, surveys of Florida and Brazil pusley in 14 citrus counties indicated more of Brazil pusley. Bioefficacy study of different glyphosate formulations, Roundup Ultra, Landmaster II and tank mix glyphosate +2,4-D, and 2,4-D (with or without surfactants) on Brazil pusley indicated that application of glyphosate alone had only marginal affects on Brazil pusley, but addition of surfactant significantly increased percent control. Application of Landmaster II/tank mix glyphosate + 2,4-D (with or without surfactants) controlled 96-100% of the plants. No regrowth of shoots occurred in the tank mix treatment. These results suggest that 2,4-D could be used either as a component of formulation or a tank mix product with glyphosate to control Brazil pusley. Preliminary studies on new, low rate technology herbicides (Milestone and CGA362622) indicated that these low rate technology herbicides could be effective, economic and environmentally safe in citrus groves for best weed management. In a study, effect of glyphosate with or without surfactant applied to dayflower a difficult-to-control weed was examined and compared with black nightshade, an easy to control by glyphosate. Glyphosate absorption and control of dayflower were best under shade than under light and was significantly higher with surfactant. Uptake and translocation values of 14C-glyphosate were consistent with percent control of weeds. Relative comparison of scanning electron micrographs also showed that the presence surfactant disrupted or dissolved the waxes present on the leaf surface thus allowing increased penetration of glyphosate into the plant. Besides these, experiment on allelopathic effect of basil (Ocymum sanctum) materials indicated significant germination inhibition of certain weeds. Effects of various bio-ecological factors, temperature, photoperiod, light intensity, pH, osmotic potential, planting depth and flooding duration, on the germination of phaseybean and guineagrass seeds were examined, indicated that mechanical manipulation e.g. flooding and burying seed by deep and cross plowing might effectively reduce the emergence of weed seeds.

Impacts
The project will provide citrus growers to optimize herbicide application rates for weed control. Based on the results, citrus growers will be able to control weeds at lower cost and environmentally safe. This project will provide the information on difficult to control weeds, influence of bioecological factors on germination of weed seed, reducing herbicide leaching and impact on the environment.

Publications

Chandran, R. S. and M. Singh (2000) Antagonistic effect of thiazopyr on azafenidin to control yellow nutsedge (Cyprus esculentus). Weed Technology 14: 556-561.
Chandran, R. S. and M. Singh (2000) Depletion of an artificial weed seed bank during the dormant period via heating and subsequent chilling of soil. HortScience, 35: 1092-1094.
Futch, S. H. and M. Singh. Field evaluation of chemical weed control in Florida citrus. Accepted in FSHS 2000 meeting Peer Reviewed section
Futch, S. H. and M. Singh. 2000. Field evaluation of chemical weed control in Florida citrus. Proc. Fla. State Hort. Sci. (in press)
Futch, S. H. and M. Singh. 2000. Weeds. In: 2000 Florida Citrus Pest Management Guide. J. L. Knapp, ed. University of Fla., Coop. Ext. Serv., IFAS. SP-43. pp. 33.1.1- 1.11.
Sharma, S. D. and Singh, M. (2000), Optimizing foliar activity of glyphosate on Bidens frondosa and Panicum maximum with different adjuvant types. Weed Research 40: 000-000 (in press).
Sharma, S. D. and Singh, M. (2000) Surfactant improves glyphosate and 2,4-D efficacy on Brazil pusley (Richardia brasiliensis) control in Citrus. Accepted HortScience Journal.
Sharma, S. D. and M. Singh. 2000. Efficacy enhancement of glyphosate by adjuvants and N-fertilizers. Proc. Southern Weed Sci Soc., 53: 144
Sharma, S. D. and M. Singh. 2000. The effect of adjuvants on foliar activity of glyphosate on hairy beggerticks (Bidens frondosa L.) and guinea grass (Panicum maximum (Jacq)). Proc. WSSA meeting , Toronto, Canada. pp. 80-81.
Sharma, S. D., M. Singh, and R. S. Chandran. 2000. Survey and control of Florida/Brazil pusley in Florida citrus. Proc. FWSS meeting, Ocala, FL.
Singh, M. and Sharma, S. D. Effect of Glyphosate Formulations on Some Difficult to Control Weeds. Accepted in FSHS 2000 meeting Peer Reviewed section.
Singh, M. and S. D. Sharma. 2000. Effect of glyphosate formulation on Brazil pusley (Richardia brasiliensis (Moq.) Gomez.) control in Florida Citrus. Proc. Third Intl. Weed Sci. Cong., Foz do Iguassu, Brazil. pp 113.

Progress 10/01/98 to 09/30/99

Outputs
Excellent progress on the effect of adjuvants in weed control efficacy of glyphosate has been made. Information has been generated on several new and old adjuvants for their effect on the efficacy to control weeds in Florida Citrus groves. In general, it was observed that the role of adjuvants in herbicide enhancement is complicated, specific to active ingredient of herbicide and surfactant, weed species and environment conditions. A number of broadleaf and grass weeds were treated with 14C-glyphosate alone and formulated with different nonionic, organosilicone, vegetable oils to determine the distribution pattern of 14C. It was observed that contact angle and 14C-distribution were significantly affected by the presence of different waxes on the leaf surface and adjuvants in glyphosate. The surface tension values of L-77 alone and when added to glyphosate were minimum and so as contact angle values when measured on Teflon slide. Over a 48-h time course, it was observed that >50% of applied 14C-glyphosate was absorbed within 15 min in Spanish needle with L-77. At 6h and thereafter, 14C absorption was significantly higher with methylated seed oil as compared to X-77 applications to Spanish needle. When treatments were applied to guinea grass, uptake and translocation were increased with adjuvant addition within 48h of treatment except with L-77. Adjuvant L-77 did not show any improvement in absorption, rather there was a significant reduction in the 14C absorption as compared to no adjuvant in guinea grass; similar results were obtained in bioefficacy studies. In another study significantly higher control of grasses (nutsedge, Johnson and guinea) and broadleaf weeds (black nightshade, wild mustard, hairy beggarticks and lambsquarters) was achieved with glyphosate + Priowet 2001 (P2001) than glyphosate alone. Improved efficacy of surfactants possibly may also be due to co-penetration or humectant action of these surfactants possibly because of their differential chemical component and characteristics. Weed competition study was also conducted. Effective preemergence herbicides like bromacil, simazine, norflurazon and diuron used for weed management in citrus are suspected to leach into groundwater because of their high soil mobility in the coarse soils of Florida. Our research to date indicated that adjuvants possess the potential to reduce leaching of herbicides in soil. Laboratory work showed that it increased the surface tension of the herbicide solution thereby reducing the chance for preferential flow of herbicides, a mechanism suspected to promote ground water contamination. Some of the adjuvants tested increased sorption of the herbicide by the soil, which not only abates herbicide movement into water systems but also enhances its efficacy. We screened forty-five commercially available adjuvants using soil-leaching columns. Our results indicated that the leaching of bromacil and simazine was not reduced significantly through the use of adjuvants. However, the adjuvants Gum Ghatti, Monazoline-T, E-17-2, E-18-5, Monazoline-O, and Emcol CC-55 were effective in reducing leaching of the herbicide norflurazon in a sandy soil.

Impacts
The project will provide citrus growers to optimize herbicide application rates for weed control. Based on the results from this project, the citrus growers will be able to control weeds at much lower cost. Also, this project will provide the information on difficult to control weeds, reducing herbicide leaching and impact on the environment.

Publications

Sun, J. and Singh, M. 1998. Correlation of adjuvant physico-chemical properties and glyphosate efficacy. In: Pesticide Formulations and Application systems. Nalewaja, J.D.; Goss, R. and Tann, R. S. (eds), 18:273-280.
Singh, M. 1998. Adjuvants and post-emergence herbicides for weed control in citrus. Proc. 5th Intl. Symp. Adjuvants for Agrochemicals. 330-335.
Chandran R. S. and M. Singh. 1999. Reduction of norflurazon leaching in a sandy soil by adjuvants. Bull. Environ. Contam. Toxicol. 62:315-323.
Chandran R. S., M. Singh and S. Salihu. 1999. Thiazopyr stimulates hairy beggarticks (Biden pilosa) germination. Weed Technology 13:576-580.
Chandran, R. S. and M. Singh. 1999. Effect of adjuvants to reduce norflurazon leaching in a sandy soil. Proceedings Southern Weed Science Society. 52:193
Chandramohan, S., R. M. Sonoda, and M. Singh. 1999. Biological control of woody grasses in citrus with a pathogen mixture. Proc. Florida State Hort. Soc. Nov.2, Stuart, Fl.
Futch, S. H and M. Singh. 1998. Use of soil columns as a method to simulate herbicide movement in soil at various rainfall rates. Proc. Southern Weed Science Society. 51:96
Futch, S. H and M. Singh. 1999. Herbicide mobility using soil leaching columns. Bull. Environ. Contam. Toxicol. 62:520-529.
Futch, S. H. and M. Singh. 1999. Economical approach to analyzation of weed control data. Proc. Florida State Hort. Soc. Nov.2, Stuart, Fl.
Sharma, S. D. and Singh, M. 1999. Effect of two adjuvant types on the distrbution of 14C-glyphosate applied to model weed species. Proc. Brighton Crop Protection Conference- Weeds.