Yil

772 doses? These aspects should be considered not only for the pest complex but also with respect to the beneficial insects in the system and thus require knowledge of the specificity of action, stability, and possible side effects of the insecticides. (5) Are suitable cultural procedures available? (6) Are resistant strains of the crop available? (7) Do the farmers already have the resources, human and technological, to adopt the new strategy? (8) Will the new strategy be acceptable to farmers, both economically and socially? Culture, tradition, and religion are important factors in determining farming practice. Thus, changes in planting and harvesting dates may be resisted if they interfere with other customs. Likewise, a suggested change in the cultivars used may not be acceptable if the new cultivars' taste, texture, or yield is different. It will be apparent from this sample of questions that IPM is interdisciplinary in nature and may require the collaboration of experts in widely different areas, for example, entomologists, plant breeders, chemists, toxicologists, meteorologists, computer modelers, economists, anthropologists, and sociologists.

Many examples of pest management might be cited that differ in complexity, geographic location, and crop pest being controlled. In its simplest (and rarest) form, pest management involves only one method of control and, strictly speaking, cannot be described as IPM. Thus, biological control is entirely satisfactory for control of sugarcane pests in Hawaii and coconut pests in Fiji (DeBach and Rosen, 1991). More often, two or more control methods are employed. For example, at the height of the pesticide syndrome, apple growers in Nova Scotia used a battery of fungicides and insecticides (especially broad-spectrum synthetics) against apple pests. Far from achieving the desired effects, this led to even greater problems. By about 1950 earlier pests such as codling moth (Cydia pomonella), eye-spotted bud moth (Spilonota ocellana), and oystershell scale (Lepidosaphes ulmi) had become even more serious, and other species, for example, European red mite (Panonychus ulmi) and fruit-tree leafroller (Archips argyrospilus) had become pests because of destruction of their natural enemies. The need to reduce the escalating costs of this program stimulated intensive study of apple orchard ecology, including the effects of pesticides on the natural enemy complex. The outcome of this work was the development of an integrated control program that utilized fewer but more specific insecticides (as well as different fungicides, some of which had killed some natural enemies) and allowed for recovery of many of the natural enemies. By 1955 the mite and scale insect had practically disappeared, and the density of the eye-spotted bud moth had fallen significantly.

As a final example, the IPM program for cotton pests in the San Joaquin Valley, California, will be outlined (van den Bosch et al., in Huffaker, 1971; Anonymous, 1984; El-Zik and Frisbie, in Pimentel, 1991, Vol. 3; P. B. Goodell, pers. comm.). This region produces about 10% of the cotton grown in the United States. The usual picture emerges. As with many other crops, cotton growing was initially a small-scale agricultural activity, not requiring an organized program of crop protection. With the development of synthetic insecticides, a massive increase in acreage devoted to cotton growing occurred. Insect pest outbreaks were easily dealt with through the regular but infrequent application of an organochlorine insecticide. With time, however, it became necessary to increase the application frequency and dose of insecticide to combat population resurgences and increased resistance in the two major pests, the corn earworm (Helicoverpa zea) and the western tarnished plant bug (Lygus hesperus), as well as outbreaks of secondary pests such as cabbage looper (Trichoplusia ni), beet armyworm (Spodoptera exigua), salt-marsh caterpillar (Es-tigmene acraea), pink bollworm (Pectinophora gossypiella), tobacco budworm (Heliothis virescens), and spider mites (Tetranychidae) following destruction of their natural enemies.

As the use of organochlorines was discontinued, growers changed to using organophos- 773

phates or carbamates, but insect resistance to these also developed rapidly. At the peak of this

INSEj CTS AND

"crisis phase," almost 50% of all insecticides applied to field crops across the United States cumans were being used on cotton, and control often required 10-20 applications of insecticide per growing season. Not surprisingly, at this point cotton could no longer be grown profitably, many marginal farmers went out ofbusiness, and overall there was a massive decline in the acreage devoted to this crop. It was only then that development of a cotton IPM program began.

Early in the development of the integrated program, it was realized that no reliably established economic injury thresholds existed for either of the major pests and that, for Lygus, time of insecticide application was critical. For Lygus, it was determined that the generally accepted injury threshold of 10 bugs/50 net sweeps was invalid; rather, the major period of importance was June 1-July 20 and only if the density exceeded 10 bugs/50 net sweeps in this period should insecticides be applied. After July 20, Lygus densities of 20 or more bugs/50 net sweeps would not affect the quantity or quality of cotton produced, provided that the plants had flowered normally in June and early July.

It was noted that corn earworms seldom became pests except in fields treated for Lygus outbreaks (using the old value for economic injury threshold) where the corn earworms' natural enemies (the bugs Geocoris pallens and Nabis americoferus and the lacewing, Chrysopa carnea) were destroyed by insecticide. With the new threshold for economic injury due to Lygus, tied in with the plant's seasonal development, the use of insecticides was reduced, especially after late July, and the earworms' natural enemies survived. Further reduction in insecticide usage came about with the raising of the economic injury threshold for corn earworms from 4 earworms/plant to 15 treatable earworms (first- and second-instar larvae)/plant. This arose, in part, from realization that larvae often feed on surplus buds, flowers, and small bolls that are not picked. Thus, by the 1980s only one or two applications of insecticide per season were required. This has since grown to three or four applications per season, due to the emergence of new pests and the inclusion of new, narrow-spectrum insecticides in the spray regime (see below). Somewhat offsetting the higher costs of these applications has been a switch in the type of cotton grown: Pima (Gossipium barbadense), worth about US$2.20 per kilogram, has replaced the traditional Acala Uplands (G. hir-sutum) (US$1.30 per kilogram) in about 25% of the San Joaquin Valley cotton-growing area.

Cultural control is also used to reduce the effects of Lygus on the cotton crop. Lygus prefers alfalfa (Medicago sativa) to cotton and will remain on the former plant when given a choice. Traditionally, however, alfalfa fields were solid cut (all of the field cut at once) provoking mass migration of Lygus into adjacent cotton fields. Alfalfa growers were persuaded to practice strip cutting to prevent such a migration, particularly following the discovery that strip cutting also reduces pest problems in the alfalfa itself by favoring Aphidius smithi, a parasitoid of the pea aphid (Acyrthosiphon pisum). Also, because alfalfa is cut at 28-day intervals, it is possible to stagger the cutting cycles in adjacent fields. An earlier proposal that cotton growers plant strips of alfalfa through their fields did not become practical because of difficulty in managing both crops. Currently, GIS technology is being used as part of a landscape-management program, designed to characterize areas with a high potential for Lygus outbreaks.

It was also noted that safflower could be a major source of Lygus, the bugs moving into cotton as the former plant began to flower. Careful monitoring of the bug populations in the

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

Get My Free Ebook


Post a comment