Exam (elaborations)
PCA Exam Defoliants Questions & Answers
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PCA Exam Defoliants Questions & Answers
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PCA Exam Defoliants Questions &Answers
Defoliation - answer 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 - answer acclereated drying of plant tissue
Harvest Aid Chemical - answer 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 - answer -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 - answer -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 - answer -Prevent leaves from sticking
-prevents staining
-prevents high module moisture content
Natural process of defoliation - answer 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 - answer 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 - answer 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 - answer 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 - answer Increases in ABA concentrations occur during sennescene and can be
associated with changes in tissue chloryphyll concentrations and other cellular
constituents
leaf abscission zone - answer at the base of the petiole
petiole - answer The stalk of a leaf, which joins the leaf to a node of the stem.
leaf blade - answer large broad part of the leaf
main stem - answer stem of plant
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