PCA Exam Defoliants

PCA Exam Defoliants Defoliation Leaf loss or leaf absicisson. In cotton production, it usually refers to leaf loss associated with application of a chemical that injures the leaf. Defoliation can also occur through natural leaf maturation and senessence, particularly with cooling weather after boll development Desiccation acclereated drying of plant tissue Harvest Aid Chemical chemicals with various modes of action that facilitate machine harvest by influencing boll opening, reducing the ammount of foilage retained on plants at harvest, speeding tissue dessication, and controlling regrowth List reason for using harvest aids -Prepare cotton for harvest in a more predictable and timely manner -Help straighten lodged plants for better drying and picking -Reduce the number of high-moisture-content green leaves, which otherwise would lower fiber grade -Can stimulate and enhance boll opening and increase yield and quality -can reduce leaf trash and other impurities at harvest and in the gin -improve the uniformity of boll opening and maturity required for mechanical harvested cotton -reduce the chances of fiber damage due to high water content in modules of harvested cotton -Reduce lint losses associated with excessive need for cleaners during ginning when cotton has higher trash content -Promote a more uniform preperation and condition of cotton that can improve the speed of ginning -Improve efficency in use of labor and equipment for harvest -Allow havrest during more favorable conditions -Reduce the amount of time lint is exposed to late season insect pests, under certain conditions -Allow more time to prepare the ground and equipment for the subsequent crop Advantages of manipulating harvest timing -Works around growers schedule -Ability to harvest before unfavorable wesather -Cotton in CA would likely be perrenial without harvest aid How do harvest aids sustain quality -Prevent leaves from sticking -prevents staining -prevents high module moisture content Natural process of defoliation As temeperatures get cold and days get short cotton petioles create an abscission layer and shed leaves. Doesn't get cold enough in the valley to do this Cytokinin effect on defoliation Cytokinins have been implicated in delaying senesence through impacts on the promotion of nutrient mobilization and may positivley influence sink strength for photoassimilate movement Auxin The concentratio of auxin in leaf tissue decreases gradually from high levels in younger leaf tissue to uch lower levels in senescing leaves. In younger leaves , high auxin levels are thought to inhibit ethylene synthesis, while in leaves far along in the senescence proccess, auxin may actually help induce additional ethylene synthesis Ethylene Increases in tissue ethylene synthesis and cincentrations have been shown to be associated with progessive degradation of ribonucleic acids and chloryphyll, and of the solubizatio of some leaf proteins, all of which are factors that reduce th long-term viability of plant tissues. Ethylene has also been implicated as involved in promoting senesecne through impacts on activation of specific enzymes ABA Increases in ABA concentrations occur during sennescene and can be associated with changes in tissue chloryphyll concentrations and other cellular constituents leaf abscission zone at the base of the petiole petiole The stalk of a leaf, which joins the leaf to a node of the stem. leaf blade large broad part of the leaf main stem stem of plant vascular tissue inside stem and petioles young leaf vs old leaf cuticle cuticle in young leaf is thinner than old leaf. its harder to abscise younger leaves with defoliants. to get old leaves to sennesece use low rates