Pesticides for Cotton in the Tropical Americas CLYDE F. R A I N W A T E R and JOHN T. PRESLEY
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Entomology Research Branch and Field Crops Research Branch, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, Md.
Cotton is grown on approximately 8,750,000 acres of land in the continental Americas south of the United States. Insects take a heavy toll over much of this area and are often the limiting factor in the economical production of cotton. Large amounts of chemicals are imported for cotton pest control, but they fall far short of the actual needs for adequate control. In addition, chemicals offer protection against certain cotton diseases caused by seed-borne and soil-borne organisms. T h e total cotton acreage in continental N o r t h and South A m e r i c a outside of the U n i t e d States is close to one third of that i n the U n i t e d States, approximately 8,750,000 acres. T o t a l production, however, is not quite i n this ratio. B r a z i l , Ecuador, P a r a g u a y , A r g e n t i n a , and N i c a r a g u a produce less cotton per land unit than is produced i n the U n i t e d States, and they represent about 7 0 % of this total acreage. P e r u , Mexico, E l Salvador, and Guatemala, on the other hand, produce more cotton per land unit than the U n i t e d States. These figures are according to Agricultural Statistics 1953, issued by the Department of A g r i c u l t u r e , and are based on the 1952 crop. A m o n g the many factors that affect cotton production are insects and diseases. Probably no other cultivated crop is so attractive to such a wide variety of insects, and i n tropical conditions they multiply rapidly and spread. Therefore, the economical production of cotton i n these areas, as elsewhere, often depends on whether or not the insects are controlled. Principal Insect Pests M a n y of the insect pests of cotton i n these countries are common to the U n i t e d States, and certain others are closely related to species that occur here. A few of the most serious pests i n certain South A m e r i c a n countries, however, are native a n d do not occur i n the U n i t e d States. F o r example, the Colombian pink bollworm (Sacadodes pyralis D y a r ) is a serious cotton pest in Colombia, N i c a r a g u a , Venezuela, and P a r a g u a y . It is also reported from A r g e n t i n a , B r i t i s h G u i a n a , P a n a m a , and E l Salvador. T h e P e r u v i a n weevil (Anthonomus vestitis Boh.) and the E c u a dorian pink bollworm (Cataraca lepisma W l s m . ) are also native to the respective countries, but do not occur i n the U n i t e d States. Cotton pests that are common both to the U n i t e d States and tropical A m e r i c a include the cotton aphid (Aphis gossypii G l o v . ) , the cotton leafworm [Alabama argillacea ( H b n . ) ] , and certain grasshoppers and spider mites. Certain species of stink bugs, mirids, and cutworms which are closely related to species that occur here at times cause serious i n j u r y to cotton throughout Mexico and Central and South A m e r i c a . The number one cotton pest i n the U n i t e d States, the boll weevil (Anthonomus grandis B o h . ) , occurs i n Mexico, Costa R i c a , N i c a r a g u a , Colombia, and Venezuela and is probably also the number one pest i n these countries. 18
PESTICIDES IN TROPICAL AGRICULTURE Advances in Chemistry; American Chemical Society: Washington, DC, 1955.
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RAINWATER A N D PRESLEY—PESTICIDES FOR C O T T O N
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The pink bollworm (Pectinophora gossypiella Saund.), considered to be potentially the worst pest of cotton in the U n i t e d States, occurs throughout the major cotton-producing areas in Mexico, Venezuela, Colombia, B r a z i l , a n d A r g e n t i n a . It probably causes more damage to cotton in the tropical Americas than a n y other insect. Several species of lepidopterous larvae cause bollworm-type i n j u r y to bolls and squares throughout the tropics. T h e y include the bollworm [Heliothis armigera ( H b n . ) ] , the tobacco budworm [Heliothis virescens ( F . ) ] , the black bollworm (Prodenia latisfascia W l k . ) , and in Peru Mescinia peruella Schaus. The cotton leaf worm [Alabama argillacea ( H b n . ) ] and several other leaf-feeding lepidopterous larvae, particularly Anomis texana Riley and the salt-marsh caterpillar [Estigmene acrea ( D r u r y ) ] , sometimes cause total destruction of the cotton crop in localized areas. Other insects which sometimes cause serious damage to cotton i n the countries to the South include stainers belonging to the genus Dysdercus, root and stalk borers of the genus Gasterocercodes, cutworms, stink bugs, whiteflies, and leaf-cutting ants. While these are the principal cotton pests, there probably are instances where some species not mentioned cause more local damage. A complete list of a l l insects and spider mite pests which cause economic i n j u r y to cotton i n Mexico and Central and South A m e r i c a would be impressive, but no such list is available and i t would require considerable research to compile it. Cultural Control of Insects T h e control of cotton pests in the tropical Americas varies from virtually no attempt in certain areas to the strict application of the latest methods in others. M a n y people think of cotton-pest control i n terms of applying chemicals to the cotton plant. A c t u a l l y , chemical control should always be considered as secondary to f a r m i n g practices that reduce insect losses. M a n y years of experimentation have shown that most of the major cotton pests have a weak link i n their life history which can be taken advantage of by cultural practices to suppress the amount of damage. Research on the pink bollworm and the boll weevil, for example, has shown that to maintain a host-free period—that is, several months of the year i n which no cotton is allowed to grow—is the most effective method of control. T h i s has been demonstrated particularly well in the Matamoros and L a g u n a areas of Mexico and i n Venezuela. T o be most effective, however, legislation is required and enforcement of specified planting and plow-up dates and maintenance of an absolute host-free condition between these dates. N o amount of cultural control, however, no matter how rigidly followed, has ever completely eliminated insect damage to cotton over a wide area. Chemical control is still the only means of reducing losses when the insects are actually damaging the plants. Fortunately there are chemicals available which, when properly applied at the right time, will give effective and economical control of most cotton pests. It is a mistake, however, to rely on them entirely. Good f a r m i n g practices should be given first consideration, a n d they should be followed by the application of carefully selected insecticides where and when needed. Chemical Control of Insects Most insecticides kill good as well as bad insects. T h e good insects, the p a r a sites and predators, often hold destructive insects i n check. Sometimes the application of an insecticide, while giving satisfactory control of one pest, may destroy the natural enemies of another pest, causing it to increase to such a degree that it will do more damage than the one being controlled. F o r example, the use of arsenicals for leafworm or boll weevil control has often caused the cotton aphid to increase to such proportions as to offset any good from leafworm or boll weevil control. M a n y of the lepidopterous larvae which cause bollworm-type i n j u r y to cetton are held i n check d u r i n g most of the growing season by other insects that feed on the eggs and young larvae. A n insecticide applied during the main f r u i t i n g period kills off these predaceous insects and an enormous " b o l l w o r m " population often r e sults. It is sometimes better to take a small loss during the m a i n f r u i t i n g period than to apply insecticides, although, i f severe damage is being done at any time, the
PESTICIDES IN TROPICAL AGRICULTURE Advances in Chemistry; American Chemical Society: Washington, DC, 1955.
ADVANCES
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only recourse is to use insecticides. Correct timing, however, is just as important as using the correct insecticide or applying it correctly. M a n y insecticides are effective against cotton pests, but no one insecticide will control all of them. Sometimes a mixture of two or more is required to do an effective job. F o r control of the boll weevil alone aldrin, calcium arsenate, dieldrin, endrin, B H C (benzene hexachloride), heptachlor, and toxaphene are effective. F o r control of both the boll weevil and the bollworm D D T may be added to any of these except calcium arsenate, endrin, and sometimes toxaphene. W h e n the complex of boll weevil-bollworm-spider mite is to be controlled, sulfur may be added to a l l of these except calcium arsenate. D D T , endrin, or toxaphene m a y be used for the control of other bollworms except the pink bollworm. F o r pink bollworm control, D D T is the only insecticide recommended. A p h i d s and spider mites together are controlled with parathion and demeton. B H C is effective against the cotton aphid under certain conditions. A r a m i t e will also control certain spider mites. Other insecticides that have shown considerable promise against many cotton pests under experimental conditions are methyl parathion and chlorthion, although neither is effective against the bollworm or the pink bollworm. The insecticides and miticides mentioned are not the only ones known to be effective against cotton pests, but they include most of those used for that purpose in the U n i t e d States. M a n y of them are imported in considerable quantities into L a t i n A m e r i c a n countries and have proved their effectiveness there. Approximately 44,000,000 pounds of technical organic insecticides ( D D T , B H C , toxaphene, aldrin, dieldrin, parathion, etc.), 3,600,000 pounds of calcium arsenate, and 82,000 pounds of nicotine sulfate were exported from the U n i t e d States to these countries d u r i n g 1953. Some insecticides are exported f r o m E u r o p e , particularly Folidol (methyl parathion) f r o m Germany. E v e n though these imports represent considerable quantities of insecticides, they are still f a r short of the minimum needs for adequate cotton-pest control. Cotton Diseases and Control In addition to the many insect pests of cotton, there are certain diseases which are also amenable to control through the use of chemicals. T h e diseases are caused by organisms that attack the seed or seedlings and i n severe infections will destroy the stand. Xanthomonas malvacearum, Glomerella gossypii, a n d sometimes Ascochyta gossypii cause bacterial blight, anthracnose, and wet weather blight. T h e seedling infections m a y c a r r y over to mature plants, causing leaf spots, cankers, and boll rots. Certain soil-borne organisms m a y also cause damage, particularly Rhizoctonia, Pythium, Fusarium, and Diplodia. In some areas Sclerotium bataticola, Sclerotium rolfsii, and Thielaviopsis also cause trouble. Seed treatment is the most practical method of controlling seed-borne diseases and it offers some protection against the soil-borne diseases. Although information on seed treatment i n the tropical Americas is meager, such treatment is practiced. Several seed-treatment chemicals are known to be effective in the U n i t e d States when used as recommended, and it is reasonable to suppose that they will also be effective i n the tropics. Conclusions There are approximately 8,750,000 acres of cotton grown in the tropical A m e r i cas. T h i s means that under average planting conditions about 127,000 tons of seed are required, which i f adequately treated would require about 265.5 tons of protectant chemicals. A s the cost of seed treatment is reasonable, the farmers could well afford the extra cost as an added insurance of a uniform stand f r o m the first planting. In general, the highest yields are obtained in areas of the tropics where there has been an active research program. RECEIVED
S e p t e m b e r 17,
1954.
PESTICIDES IN TROPICAL AGRICULTURE Advances in Chemistry; American Chemical Society: Washington, DC, 1955.
