PRIN OF WEED SCIENCE
PRIN OF WEED SCIENCE PLS 4601
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This 5 page Class Notes was uploaded by Sarai Hauck on Friday September 18, 2015. The Class Notes belongs to PLS 4601 at University of Florida taught by Barry Brecke in Fall. Since its upload, it has received 56 views. For similar materials see /class/206855/pls-4601-university-of-florida in Plant Science at University of Florida.
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Date Created: 09/18/15
Herbicides cont l Fate of Foliar Applied Herbicides A Volatilization both soil applied and foliar applied herbicides 1 Fate of foliar herbicides on soil or leaves a Herbicide may volatilize and be lost b Volatilization 1 change in chemical from liquid or solid to vapor 2 3 4 a b results in poor weed control offsite movement Example ester formulation of 24 D Clomazone B Foliar Applied Herbicide Fate 1 Dry on leaf and form crystals 2 Penetrate into leaf cuticle and remain there 3 Penetrate into inner leaf structure but not be phloem mobile a Chemical will move upward with transpiration stream and accumulate in leaf margins triazines and ureas 4 Be absorbed largely into the phloem and move throughout the plant a 5 Phenoxys and glyphosate Leafabsorption most important site for above ground plant parts Must penetrate 1 cuticle 2 cell wall 3 plamalemma 4 be released into cytoplasm Foliar absorption not complete until herbicide molecules have been released in cytoplasm a Leaf cuticle very important in foliar absorption and is in uenced by environment and species penetrates by diffusion b Cuticle thickness determined by 1 Age of plant older thicker cuticle 2 Light intensity higher thicker cuticle 3 Photoperiod daylength affects cuticle thickness sicklepod c Cuticle like a sponge when dry no water in spaces and waxes are very close together When wet cuticle expands and may form channels d Structure of leaf surface amount of wax ifany in uences absorption of chemical in addition to formulation of chemical ie esters or salts e Herbicide absorption is not complete until chemical is in the cytoplasm Plant leaf factors a Cuticle b Leaf age c Leafangle d Trichomes e Stomata Environmental factors a Any condition that promotes plant growth will improve herbicide performance b Light 1 increases metabolism required fortranslocation 2 intensive light increase cuticle thickness c Temperature 1 absorption and translocation increase with temperature and humidity 2 rainfall decreases absorption Stem absorption a not usually important in agronomic applications b important in some forestry procedures where under bark injections of herbicides are administered to weed trees 9 Bud absorption a not important in many foliar applications b foliar applications of contact herbicides may require bud absorption to give complete kill ofvegetation Example paraquat C Herbicide Translocation 1 Movement within living plant tissue a Symplast living tissue and mainly concerned with phloem b Phloem translocation since phloem is living it must remain alive to carry out herbicide movement High rates may kill phloem tissue at area of absorption and poor weed control may result important in perennials c 24 D reported to move as much as 40quot per hour in healthy phloem tissue 2 Movement within nonliving plant tissue a Apopolast nonliving tissue mainly concerned with xylem b Toxic chemicals moved through xylem tissue can be applied at high rates and not adversely in uence overall translocation c Xylem translocation usually upward in plant but under special conditions may be downward ie Dry soil high light low humidity or large leafarea d Xylem movement reported in some instances at a rate as fast as 1 foot per minute Herbicide Selectivity Text Chapter 8 A Factors affecting selectivity U39PFDN Physical factors Biological factors lnherent properties of herbicides Chemical plant protectants Pesticide interactions Physical factors soil applied herbicides 1 Selectivity of soil applied herbicides may be achieved by varying Herbicide dose Herbicide formulation Herbicide placement Protective barriers 09965 Stage of plant growth Herbicide dose physical characteristic in soil a Herbicides applied to soil are adsorbed to CM and clay particles amount absorbed is critical with regard to activity Herbicide Formulation a Soil applied herbicides that may be phytotoxic to crop in liquid form may be applied in granular form after crop emergence and good weed control b Granule de ect off foliage fall to soil avoid absorption by crop leaves Herbicide Placement physical soil a To be effective herbicide must enter plants contact roots shoots or foliage b By varying placement selectivity may be achieved 1 apply herbicide to soil surface instead of incorporation 2 shallow incorporation to prevent volatilization and movement to sensitive plants
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