Defoliants

Defoliants 

chemical preparations that cause the fall of plant leaves. Ethylene, which—according to several investigators—forms in plants and causes leaves to fall naturally, is a defoliant. Defoliants widely used in agriculture and the rates at which they are consumed (kilograms per hectare of total product) are given in Table 1.

Table 1. Common defoliants
	Rate of consumption (kg/ha)
Magnesium chlorate ...............	6–10
Sodium chlorate-pentaborate ...............	8–15
Calcium chJorate-chloride ...............	6–10
Butifos (S,S,S-tributyltrithiophosphate) ...............	0.7–2.0
Merfos (S,S,S-tributyltrithiophosphate) ...............	0.7–1.5
Calcium cyanamide ...............	40–45
Butindiol-1,4 ...............	3–5
Arsenous acid ...............	1–3
cis-β-sodium chloracrylate ...............	2–10

Butifos and merfos are the most effective defoliants. However, their shortcomings are a disagreeable odor and comparatively high toxicity to vertebrates. Chlorates are effective as defoliants, but they are slower to act. The salts of endoxohexahydrophthalic acid (endothall) and butindiol (butine-2-diol-l,4) are used on a somewhat smaller scale.

Defoliants usually cause 70-85 percent of the leaves to fall; the other leaves shrivel.

Defoliants are widely used to cause the leaves of cotton plants to fall before harvest time.

REFERENCES

Mel’nikov, N. N. Khimiia pestitsidov. Moscow, 1968.
Stonov, L. D. Defolianty i desikanty. Moscow, 1961.
Zakirov, T. S. Khimicheskaia defoliatsiia i desikatsiia khlopchatnika. Tashkent, 1968.

N. N. MEL’NIKOV [8–511–1; updated]