PCA Exam Defoliants (actual 2025) Latest Rated A
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
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
Water Stress
Not too much not too little. Enough stress to encourage
sennesacnce, not so much plant cant phsiologically respond to
dessicant
Defoliants vs Dessicants
Defoliants are used for leaf removal, sennesece leaves,, form
an absiccion layer whilw still having enough leaf weight to
break the abscission layer and drop off plant. under high
humidity and warm temps they can be more injurious to
leaves while Dessicants are used for quick kill and
dehydration, lower humidity leads to faster dessication
, Crop cycle of Cotton in California
Annual crop that is planted in the spring and harvested in the
fall
Seed germination to emergence is 5-14 days
Emergence to harvest is 150-200 days
Squares
Flower buds at all stages of development
Bolls
Developing fruit (including seed, developing fiber and walls
of the fruit)
Describe how defoliant efficacy is impacted by the perennial
nature of the cotton plant
Indeterminant growth habitat of cotton means that as long as
some water and nutrients are available the plants will put out
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
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
Water Stress
Not too much not too little. Enough stress to encourage
sennesacnce, not so much plant cant phsiologically respond to
dessicant
Defoliants vs Dessicants
Defoliants are used for leaf removal, sennesece leaves,, form
an absiccion layer whilw still having enough leaf weight to
break the abscission layer and drop off plant. under high
humidity and warm temps they can be more injurious to
leaves while Dessicants are used for quick kill and
dehydration, lower humidity leads to faster dessication
, Crop cycle of Cotton in California
Annual crop that is planted in the spring and harvested in the
fall
Seed germination to emergence is 5-14 days
Emergence to harvest is 150-200 days
Squares
Flower buds at all stages of development
Bolls
Developing fruit (including seed, developing fiber and walls
of the fruit)
Describe how defoliant efficacy is impacted by the perennial
nature of the cotton plant
Indeterminant growth habitat of cotton means that as long as
some water and nutrients are available the plants will put out
