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Greenbugs and other cereal aphids

Aphids continue to cause heavy reductions in wheat and barley production. In addition to causing losses by direct feeding, aphids transmit diseases such as barley yellow dwarf which cause serious reductions in wheat and barley yields. One of these aphids, the greenbug, also severely reduces yields of grain sorghum. When injurious aphid populations occur, widespread applications of insecticides are required for control.

Plant resistance in sorghum to aphids represents a real success in reducing losses and in reducing the number of situations calling for pesticide application. Plant resistance has virtually eliminated losses which could have exceeded $200 million from 1976-1980. However, a new strain of greenbug has recently appeared that can attack this "resistant sorghum." SEA/AR researchers have discovered other effective sources of resistance which, it is believed, can combat the new greenbug strain. Research to develop additional resistant varieties is underway but should be increased to counteract other new greenbug strains which are certain to develop. Research will also be initiated to develop management systems to suppress the total aphid populations and prevent their spread throughout the central U.S. as soon as resources permit.

Corn rootworms

Corn rootworms are serious pests of corn in the mid-west and at a cost of $6.00/acre. More than 20 million acres of corn are treated with insecticides each year to control these pests. In spite of these insecticide applications, rootworms cause an estimated $200 million loss in corn production each year on top of the $120 million expended for control.

More effective control methods and management techniques to incorporate into integrated pest management systems have been the recent objectives of our research. Also, SEA/AR scientists have discovered and identified the sex pheromone of the rootworm, identified and defined many of the ecological factors which cause fluctuations in corn rootworm populations, and have developed methods to increase the effectiveness of insecticides.

corns.

Additional resistant corn germplasm is propably available in tropical For climatic reasons, these tropical corns cannot be tested for rootworm resistance in the U.S., consequently cooperative research programs are contemplated with corn scientists in Latin America to accelerate the incorporation of resistant germplasm into corn varieties adapted to temperate America.

Information on control and management of corn rootworms is now available to allow the development of pest management systems. Future research should emphasize the practical development of the above control techniques and the development of even more effective pest management systems.

Grasshoppers

More than 50 species of grasshoppers cause serious losses of rangeland, cultivated forages and crops. Twenty three percent or more of rangeland forage is consumed by grasshoppers each year and heavy populations not only

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consume the forage needed for livestock and wildlife, but so overgraze the range that they cause long-lasting ecological damage.

Researchers have developed the use of effective insecticides and are developing biological control agents to be incorporated into grasshopper management systems. Nosema locustae, a grasshopper disease organism, has been registered and research on other pathogens is also underway. New research thrusts will include the development of integrated grasshopper management systems which can be effectively used by private producers and APHIS to keep the number of grasshoppers below economic levels and prevent devastating outbreaks.

Corn borers

The European corn borer and the southwestern corn borer combined cause an estimated $300 million loss in corn production each year. Without corn

varieties that are resistant to the first generation of European corn borer these losses would be much greater. Scientists have recently developed germplasm with resistance to both first and second generation of European corn borer and to the southwestern corn borers.

Additional research is needed to further develop resistant germplasm, develop the use of the sex attractants and develop additional chemical and biological control agents.

Mediterranean fruit fly

The Mediterranean fruit fly is potentially one of the most destructive insect pests ever to threaten American agriculture. World-wide it attacks more than 200 different kinds of fruits and vegetables making them unfit to eat. Should this pest become firmly established in the continental United States it could conceivably spread to most of the southern United States.

The cost to American agriculture and to American consumers in case of such spread would be measured in hundreds of millions of dollars annually. These tremendous costs would take several forms: (1) direct losses of marketable production to fruit and vegetable growers; (2) increased cost of production due to cost of control measures; (3) increased cost of transportation and marketing due to mandated commodity treatments, and (4) increased cost to consumers at the market place. Additionally, the U.S. balance of payments could be adversely affected due to the necessity to treat exported commodities. It is conceivable that some foreign markets could be lost entirely if our country's horticultural crops become infested with the Mediterranean fruit fly. Of equal concern is the fact that if we experience a wide geographical spread of this insect, a significant increase in the use of insecticides for control would result. This could lead not only to additional environmental pollution but could also upset the delicate balance of nature that many of our growers of today are depending upon for control of other pests.

Through research we have developed the basic technology necessary to eradicate incipient infestations. This technology consists of highly effective attractants to detect and delimit infestations, a selective toxic bait which does not attract other species, and the sterile male method. Field control

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.

Wheat rust

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.

Sclerotinia diseases

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.

Boll weevil

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

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