ISHS Acta Horticulturae 422: International Conference on Integrated Fruit Production
IMPACT OF GROUND COVER PLANTS ON BENEFICIAL ARTHROPODS IN AN APPLE ORCHARD IN WEST VIRGINIA, USA |
| Authors: | M.W. Brown, J.J. Schmitt |
| Abstract:
A conventionally managed orchard was compared with an orchard with a ground cover of clover and rye and managed to conserve biological control organisms. In the first three years after planting the orchard with diverse ground covers had a more diverse biological control community than the conventional orchard even though the trees were less vigorous and had fewer aphids. Use of ground cover plants can enhance biological control in apple orchards but care must be taken not to reduce tree vigor. There is strong pressure from consumers and governments to reduce the amount of pesticides used in agricultural production. In this study we examined how a change in cultural management of apple orchards could affect biological control of insect pests. Diversification of agricultural systems can enhance biological controls by offering alternate sources of food and shelter. In this study we diversified the agroecosystem by planting ground cover plants under the trees. In holistic ecosystem studies such as this, effects of management changes can have far-reaching effects on apple disease epidemiology and horticultural properties of the production system. Before recommending any changes in management for pest control, ramifications in other aspects of the system must be evaluated to ensure compatibility. Two apple orchards were planted in West Virginia, USA, in the Spring of 1992, to test the effects of orchard diversification on the insect community. One orchard, conventional, was managed according to standard commercial practices, including a 2.5 m herbicide strip under the trees. The other orchard, IPM, was planted with Secale cereale (rye) and Trifolium pratense (clover) in 1 m strips underneath the trees leaving only 0.5 m of herbicide strip at the tree base. The IPM orchard also received an introduction of mite predators in a bouquet of apple branches from an unsprayed orchard and a Bacillus thuringiensis spray in May 1993 when the conventional orchard had an application of azinphosmethyl (Guthion). Fungicide applications were similar for the two orchards. Sampling was conducted monthly through the growing season with whole tree visual observation of ten randomly selected trees per orchard per sample and sweep net sampling at five locations per orchard per sample. The introduction of bouquets of branches did accelerate the establishment of biological control of Panonychus ulmi. Although mite populations never reached threshold levels, population growth was reduced in the IPM orchard before the conventional. In the year after introduction of the branches, the mite predators Leptothrips mall and Orius insidiosus were found earlier in the IPM orchard than in the conventional. Adult parasitic hymenoptera, sampled with a sweep net, were more abundant and diverse in the IPM orchard than the conventional orchard. Role of these hymenoptera in pest control is unknown because of the lack of host records. However, these results showed that the ground cover provided more habitat for parasitic hymenoptera than the conventional system. | |
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