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
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
