Defoliants and desiccants

Chemical harvest aids are presently used on more than 75% of the cotton acreage in the U.S.. The amount of foliage may be reduced either by the use of defoliants or the use of desiccants. Defoliants induce leaf fall and must be applied one to two weeks before harvest so that the abscission process may be complete. Desiccants cause the foliage to lose water and sometimes the leaves and stems are killed so rapidly by desiccants that an abscission layer has insufficient time to develop and the drying leaves remain attached to the plant. Desiccants usually require one to three days to act before harvest can be started. The obvious advantage of desiccants over defoliants is that they may be applied at a later date, thus gaining additional time during which the leaves continue to function and to contribute to see the fiber quality. Hundreds of chemicals have been evaluated as defoliants and desiccants. Only a few are in commercial use. 

Plant growth regulators, defoliants, and desiccants are classified as pesticides in federal laws. These chemicals are used on plants to alter normal plant processes in some way. They must be measured carefully, because they usually are effective in very small amounts. Overdosing will kill or seriously damage the plants. 

This list does not include those pesticides which are either not normally used as pest control agents (plant growth regnlators, defoliants, and desiccants) or are not directly toxic to the pest (attractants and repellents). 

Aminophon is primarily a defoliant and desiccant recommended at a rate of... 

OTHER COMMENTS used in wood preservation used as a weed killer used in the production of insecticides, herbicides, rodenticides, defoliants, and desiccants used in the treatment of syphilis, psoriasis, and as an antiparasitic agent in veterinary medicine used in the manufacture of battery grids, cable sheaths, glass, and boiler tubes. 

Sevin XLR (carbaryl) Smite (sodium azide) Tedion (tetradifon) Tetram Herbicides, defoliants, and desiccants Aatrex (atrazine) Accelerate (endothall, sodium salt)... 

Uses Acidifying, wetting agent, penetrator enhances penetration of leaf surface for many aquatic and tenestrial herbicides, defoliants, and desiccants reduces adverse effects that alkaline waters have on spray solution and provides additional wetting sprayed foliage... 

Pesticide. . any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any insects, rodents, nematodes, fungi, or weeds or any other form of life declared to be pests.. . . and any substance or mixture of substances intended for use as a plant regulator, defoliant or desiccant." Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA - 1947) DDT... 

Dimethipin. 2,3-Dihydro-5,6-dimethyl-l,4-dithiin-l,l,4,4-tetraoxide [55290-64-7] (dimethipin, oxidimethiin, UBI-N252, Harvard) (25) is used as a cotton defoliant and has been used as an experimental desiccant in potato vines. In addition, it defoliates nursery stock, grapes, dry beans, and natural mbber and is used as a desiccant for seed of canola, flax (Unutn usitatissimum), rice, and sunflower (Helianthus annuus) (10). The product has been available since the mid-1970s and the experimental work was first reported in 1974 (44). 

Pesticides are not nsnally applied close to harvest due to preharvest interval restrictions for most pesticides. Crop modifiers, however, are applied, such as defoliants to sugar beets prior to digging the beets and desiccants to cotton to aid the picking of the fibers. These products usually utilize some of the wetting and spreading surfactants to aid distribution of the products. 

Chemical Manipulation of Desiccation and Defoliation and Essential Aspects for the Application and Development of New Chemical Compounds in the Future... 

Uses Spray tank adjuvant, penetrant for pesticides, esp. with postemergence herbicide and desiccant/defoliant sprays Features Increases act. of pesticides Reguiatory DOT nonregulated SARA reportable... 

Uses Adjuvant for pesticides exc. penetrator and is esp. effective with postemergence herbicide and desiccant/defoliant sprays well-suited for use under adverse weather conditions inc. stability of some volatile herbicides Reguiatory DOT nonregulated SAFtA reportable Properties Red cl, si, viscous liq. mild polyether odor emulsifies in water sp.gr. 

Pyraflufen-ethyl is also used as the defoliant for cotton and as a desiccant for potatoes. Pyraflufen-ethyl is a novel inhibitor of protoporphyrinogen IX oxidase. Inhibition of this enzyme in chloroplasts causes accumulation of protoporphyrinogen IX, which results in peroxidation of foliar cell membrane lipids under the light and finally death of cells. 

As pointed out earlier, all U.S. cotton in commercial production is now harvested by machines. The application of harvest-aid chemicals to cause the plants to shed their leaves (defoliation) or to kill and dry the plant (desiccation) are common practices in many areas. Chlorates and organic phosphates are popular defoliant materials and arsenic acid is commonly used as a desiccant. 

Chemical compounds classified as pesticides (fungicides, herbicides and insecticides) total over 500. Others used as rodenticides, desiccants, defoliants, etc., increase that number. Agricultural uses include all crops and livestock on farms, plus those used as seed treatments, in greenhouses, parks, golf courses, nurseries and lavms in urban areas. Chemicals are applied by farmers, industry, or institutional employees, commercial applicators and individual citizens. 

Arsenic trioxide finds major use in the preparation of other compounds, notably those used in agricultural applications, The compounds monosodium methylarsonate. disodium methylarsonate, methane arsenic acid (cacodylic acid) are used for weed control, while arsenic acid, H3ASO4, is used as a desiccant for the defoliation of cotton crops, Other compounds once widely used in agriculture are calcium arsenate for control of boll weevils, lead arsenate as a pesticide for fruit crops, and sodium arsenite as a herbicide and for cattle and sheep dip. In some areas, arsenilic acid has been used as a feed additive for swine and poultry. Restrictions on these compounds vary from one country and region to the next. 

The best known of these defoliants are sodium chlorate which has the danger of starting fires, tributyl-phosphorotrithioite (merphos, Folex) its oxygenated relative tributylphosphorotri-thioite (DEF), and endothall (Accelerate). Recent research reports claim that amino methyl phosphonic acid and certain of its relatives were found to be more active than current commercial products. The best known desiccant used for defoliation of cotton is paraquat (1,1 -dimethyl-4,4 -bipyridinium) (8). 

Uses herbicides/insecticides pre- or post-emergence control of broadleaf weeds in cereals, maize, lucerne, clover, trefoil, grass leys, potatoes, peas, onions, garlics, peas, leeks, soya beans, orchards, groundnuts, strawberries, vineyards and other crops for control of strawberry runners and raspberry suckers and overwintering forms of insect pests on fruit trees also used as a desiccant for leguminous seed crops destruction of potato haulms as a pre-harvest hop defoliant, etc. 

Uses Paraquat is a colorless, odorless, white or pale yellow crystalline solid that is hygroscopic. Paraquat is a quaternary nitrogen herbicide that is widely used for broadleaf weed control. It is a quick-acting, nonselective compound that destroys green plant tissue on contact and by translocation within the plant. It has been employed for killing marijuana in the United States and Mexico. It also is used as a crop desiccant and defoliant, as well as an aquatic herbicide. Paraquat is highly persistent in the soil environment, with a reported field half-life of greater than 1,000 days.5-7,17... 

Agricultural uses for ammonium thiosulfate take advantage of both the sulfur and ammonium content by blending with other nitrogen fertilisers such as urea (71). Some foliar-spray fertilisers contain ammonium thiosulfate together with other metal micronutrients (72,73). Ammonium thiosulfate or mixtures with ammonium nitrate can also be used as desiccants and defoliants in crop-bearing plants such as cotton (qv), soybean, alfalfa, rice, and peppers... 

Current uses of arsenic are in pesticides, cotton desiccants, and wood preservatives. Arsenic is also used as a bronzing and decolorizing agent in the manufacture of glass, and in the production of semiconductors (Tanaka, 2004), as a desiccant and defoliant in agriculture, and as a byproduct of the smelting of nonferrous metals, particularly gold and copper, from coal residues (Hall, 2002). 

A considerable number of organometallic species of arsenic, antimony and bismuth have been detected in the natural environment in different manners. A number of these are nonmethyl compounds which have entered the environment after manufacture and use [e.g. butyltin and phenyltin compounds for antifouling paints on boats, and arsanilic acid (Figure 2, 5) and phenylarsonic acids (Figure 2, 6-8) for animal husbandry]. Only a few methyl compounds are now manufactured and used (e.g. methyltin compounds for oxide film precursors on glass and methylarsenic compounds for desiccants or defoliants). 

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