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.
N. N. MEL’NIKOV [8–511–1; updated]