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programs using insecticides are available for some, but not all, commodities. In addition, post harvest treatments are available for some commodities to meet quarantine regulations. Our present research efforts are concentrated on non-chemical approaches such as sterile insect methodology, male annihilation techniques, attractants, pheromones, and an international search for parasites. We are also striving to improve safety and effectiveness of chemical procedures including fumigation of harvested commodities.
Southern Corn blight
In 1970 scientists learned that a specific strain of a fungus, Helminthosporium maydis, could cause severe damage in most of the corn grown in the corn belt and other corn production regions. This disease was designated "Southern corn blight." Throughout the growing season of 1970 research was conducted that provided information on protecting and utilizing the affected crops.
By early 1971 experiment stations, agricultural research scientists, and industry had shifted significant additional research resources to Southern corn blight. Subsequently, the federal-state effort was substantially enlarged by a Congressional appropriation of $2 million.
It was learned that the corn in the diseased fields had one genetic entity in common, Texas cytoplasmic male sterility. With this clue, and with the rich reservoir of information pertaining to cytoplasm breeding lines available from plant breeders and plant pathologists which had accumulated through years of research, it was possible for public research agencies and the hybrid seed corn companies to shift away from the susceptible genetic trait. By the end of crop year 1971 the seed industry had produced enough hybrid corn planting seed with normal cytoplasm to permit farmers to shift almost completely away from the susceptible hybrids in 1972 and thus end the threat of potentially high yield losses from this disease.
This rapidly expanded effort not only made possible the containment of the Southern corn blight epidemic in the short run, but more significantly it provided a base of knowledge for long-term benefits. This crisis demonstrated the need for a network of research scientists that can respond rapidly and effectively on short notice.
The most destructive regional epidemics on wheat in the United States have been caused by wheat stem rust. Catastrophic epidemics of this disease occurred in 1878, 1904, 1916, 1935, and 1953-54. The spring wheat and durum crops of the north central states are especially vulnerable to this disease. Stem rust caused serious losses in these states in 16 years between 1921 and 1955, estimated at $320 million. Thus, wheat would not be a profitable crop in the north central states if effectively resistant wheat cultivars were unavailable.
Today wheat stem rust is under control through a program of pest management that grew from research at the University of Minnesota in collaboration with the USDA. The main features of this program are barberry eradication, quarantine
restrictions, disease monitoring, identification of rust races, and development of resistant varieties.
The key to producing rust-resistant cultivars is the annual identification the rust races found in the United States coupled with assessment of the various sources of resistance to those races. In cooperation with wheat breeders, the lines with effective resistance are used to develop commercial cultivars. As result stem rust epidemics have been prevented on the northern hard red spring wheats for the past 25 years by the use of cultivars with suitable multiple resistances. The cost of this identification of rust races is estimated to total $1.5 million over the 25 year period. Losses avoided by utilization of this research are conservatively estimated at $250 million.
Root rot and damping-off of vegetables
Of the many maladies that afflict our cultivated crops, nothing is more insidious and unpredictably destructive than root rot and damping-off caused by the soilborne fungus Rhizoctonia. This fungus plays a major role in the root disease complex causing root rot, damping-off, seedling blights, crown rots, root rots, seed decay, and collar and fruit rots on many important field and horticultural crops. Experts estimate that the annual losses caused by Rhizoctonia amount to $16, $25, and $130 million for cucumber, beans, and potatoes, respectively. Processing tomatoes, with a potential value of $50 million cannot even be grown in the southeast because of 15 to 70 percent fruit infection. At least 200 other plant species are attacked by this pathogen. Rhizoctonia diseases are increasing because of mono-culture and intensive cropping for mechanical harvesting. Partial control can be achieved by some fungicides, but these are environmentally hazardous, expensive, and lose effectiveness.
During the last 3 years USDA scientists have developed field technology for reliable integrated management of this important pathogen on cucumbers and beans. Plowing under plant residues of a previous crop to a depth normally obtained with regular mechanical plowing (8-9 inches), rather than disking the residues shallowly, is the basic component of this technology. This component alone reduces the disease in half. The successful reduction of this pathogen by this approach is a practical exploitation of the previous unravelling of the mechanisms of survival of Rhizoctonia in soil. The effectiveness of the basic component of this technology has recently been recommended to cucumber growers by industry, SEA/AR and Extension, and has received favorable comments from growers.
The use of integrated management represents a considerable advance towards solving the Rhizoctonia problems on vegetable crops. More research needs to be done to see whether this approach is equally effective for the reduction of Rhizoctonia diseases of other economic crops such as crown rot of sugarbeet and fruit rot of tomato. Research is also needed to select the best biocontrol strains of beneficial fungi and to accumulate the necessary data for their registration.
The soilborne fungus Sclerotinia attacks 360 species of plants. It causes extensive disease losses on forage legumes, oil seed crops, and numerous
vegetable crops. The losses on dry and snapbeans, cabbage, carrots, cucumbers, celery, lettuce, potato, tomato, and other horticultural crops amount to at least $75 million annually. Sclerotinia white mold of beans has become a very serious problem in western Nebraska, Michigan, Washington, and New York. Bean production in New York has practically been discontinued in highly desirable locations because of repeated, heavy losses from white mold. Sclerotinia white blight and stalk rot has seriously affected cabbage seed production in western Washington for many years. Sclerotinia pink-rot disease of domestic celery not only causes economic losses, but also produces phototoxic lesions, a blistering cutaneous disorder, on the exposed skin of celery harvesters. Sclerotinia drop on lettuce is a limiting factor to production in New Jersey and other lettuceproducing areas. Throughout the United States, this pathogen causes about 10 million dollar losses on sunflower; and the losses will increase as this "new" crop advances. In North Carolina Sclerotinia caused $2.0 million losses in 1976 on peanuts alone and the disease has advanced to the peanut-producing areas of Virginia.
Control measures for the Sclerotinia diseases vary with the crop and geographical area. For example, the fungicide, benomyl, provides good control of the disease on beans in New York, but not in Nebraska. Benomyl gives good control on the disease on lettuce, but EPA has not yet registered this pesticide for use on this crop. Other control measures include long term (3 years or more) crop rotation and moving the susceptible crops to new land.
USDA research scientists recently discovered several new, unusual, beneficial mycoparasitic fungi, never studied before. Two of these new superparasites, Sporidesmium and Teratosperma, attack and destroy the dark, hard surviving structures (sclerotia) of Sclerotinia. Sporidesmium has shown considerable promise for substantially reducing lettuce drop. Application of the beneficial mycoparasite to experimental field plots in May 1978 provided 63 to 83 percent disease control in two consecutive crops in 1979, and 65 to 82 percent control in two crops of lettuce in 1980, without further treatment of the soil.
One of the present obstacles to commercializing Sporidesmium as a biorational pesticide is its poor growth on laboratory growth media. Progress has been made on the nutrition and growth of this mycoparasite, but much more needs to be done to produce large amounts of the biocontrol agent and to accumulate data for its registration. Additional research is also needed to test. Sporidesmium on other pathogens and to explore new possibilities by utilizing Teratosperma for biological control of Sclerotinia.
The boll weevil is a foreign insect pest which entered the U.S. from Mexico in 1892 and spread to the east coast by 1922. The boll weevil now infests about 7 million acres in this country and has caused an estimated loss to the nation's agricultural economy of over $12 billion since it entered the country. The boll weevil developed resistance to the chlorinated hydrocarbon insecticides in 1955; and although the organophosphate insecticides provide effective control, their use destroys beneficial insects which aid in the control of the bollworm/budworm complex and other pests and also tends to hasten the development of insecticide resistance. Economical methods of controlling the boll weevil with the least
dependence on broad-spectrum insecticides is particularly important to the continued profitable production of cotton in the higher rainfall areas of the cotton belt.
Research in recent years has resulted in the development of a number of technologies useful in dealing with the boll weevil. Included are (1) modified cotton cultures using short-season cottons, (2) pheromone traps for detection and survey, (3) insect growth regulators such as Dimilin, (4) pheromone traps for suppression of low density populations, (5) mass production of usable sterile boll weevils, and (6) improved field scouting and population prediction methods.
These new technologies have been integrated into cotton insect management programs which were placed into use on a trial basis for 3 years in an optimum pest management trial in Panola County, MS, and in a boll weevil eradication trial in North Carolina and Virginia. Both trials, completed in 1980, were highly successful as evidenced by substantial reductions of in-season use of insecticides for control of both the boll weevil and the bollworm/budworm complex. The participation of 99 to 100 percent of the producers in both trials and extensive monitoring with pheromone traps and by field scouting over large areas resulted in highly effective use of diapause control, insecticide applications and other control technologies.
Although a number of new technologies are ready for expanded use, additional research is needed to (1) develop more effective insect growth regulators and sterile insects; (2) search for new chemicals such as feeding deterrents antifertility agents and insecticides; (3) to continue the search for resistant host plants and biological control agents; (4) to define the geographical races of boll weevils; and (5) to improve survey, detection, and prediction capabilities.
Bollworm (corn earworm) and tobacco budworm
The cotton bollworm or corn earworm and the tobacco budworm are the most destructive insect pests of American agriculture, causing losses in excess of $1 billion each year. In addition to losses to cotton, these insects are serious pests of corn, soybeans, tomatoes, sorghum, peanuts, lettuce, and other crops. The budworm, because of its development of resistance to insecticides, was responsible for the collapse of a 750,000-acre cotton industry in northern Mexico in the 1960's. Also, the cotton industry was seriously threatened in the mid-south and southern California in the mid-1970's by the tobacco budworm because effective control measures were not available. Because of resistance to three classes of insecticides by the budworm, only one class of insecticides is currently highly effective for its control. Therefore, other control methods are desperately needed to insure that crops that are attacked by the bollworm/budworm complex can be produced economically.
Progress in developing new controls have been made; some of these new controls are being utilized while others are still under development. Included are (1) resistant crop cultivars, particularly in corn; (2) attractants in traps for survey and prediction; (3) new synthetic pyrethroid and organophosphate insecticides; (4) improved formulations and new strains of microbial agents such as Bacillus thurgiensis and a nuclear polyhedrosis virus;
(5) mass production and release methods for an egg parasite; and (6) improved field scouting techniques. In addition to these new technologies that are in use at least to a limited extent, exciting discoveries of potential practical use include the hybrid sterility trait in the tobacco budworm, the identification of the components of the sex pheromones for both the bollworm and tobacco budworm, and the development of a large number of resistant breeding lines of plants.
The advances that have had the most impact on control of the bollworm/budworm in recent years have been the development of predictive population models and survey methods which have saved the farmer in Texas alone $5 million and the development of the synthetic pyrethroid insecticides. However, the future prospects for control of the boll weevil without in-season use of broad spectrum insecticides provides an opportunity for increased use of selective methods of control and of naturally occurring beneficial insects for control of the bollworm/budworm complex.
Many promising methods of control for the bollworm/budworm complex are on the horizon. However, development of practical use for these methods is complex. Since there are two species of insects involved that feed on a wide range of cultivated and wild host plants, such techniques as hybrid sterility, mating disruption with pheromones, and perhaps mass releases of parasite or predators may require a community or larger area approach
Additional research is needed in a wide range of areas including (1) search for hybrid sterility in the bollworm (corn earworm), (2) nutrition, rearing, and behavior of bollworms and budworms for use in biological control (sterility, parasites, pheromones), (3) large scale field studies on mating disruption with pheromones, (4) improved rearing of egg and larval parasites, (5) continued search for host plant resistance, and (6) survey and prediction with particular emphasis on micro-meterological factors.
Pink bollworm The pink bollworm is a foreign insect pest that became a very serious pest of cotton in the irrigated West in about 1965. Use of broad spectrum insecticides for its control led to the development of insecticide resistance in other insects such as the tobacco budworm in southern California and Arizona. The potential establishment of the pink bollworm into the San Joaquin Valley of California threatens the cotton crop in that area that is valued at over $1 billion. Improved methods of controlling the pink bollworm with reduced dependence on broad spectrum insecticides is needed to protect the cotton crop in Arizona, southern California, and Mexico and to reduce the threat to the cotton crop in the San Joaquin Valley of California.
Research advances in recent years have included (1) the commercialization of nectarless varieties of cotton that reduce populations of the pink bollworm by about 50 percent; (2) new synthetic pyrethoid and organophosphate insecticides; (3) development of the mating disruption technique using the pink bollworm pheromone; (4) rearing and release of sterile insects to prevent infestation of cotton in the Imperial Valley of California; (5) discovery of plant growth regulators for potential use in cultural control; and (6) improved survey, particularly with pheromone traps, and population prediction.