Comparison of Integrated and Conventional Production of Young Nonbearing Apple Orchards

The large number of pesticide applications in apple orchards creates serious problems with pesticide residues and their side effects on beneficial organisms, the environment and human health. This is the reason behind the search for new systems for apple protection. The investigations were made in apple orchards of the Institute of Agriculture at Kyustendil, during the period from 1997-1999. Three scab resistant cultivars grafted on rootstocks MM106 were planted in 1996. The orchard was divided into four plots. Two plots were treated as „conventionally” and the other two were treated as „integrated” according to the general principles, rules and standards of integrated apple production. The key disease during the experimental period was powdery mildew, which can be controlled only with pruning of infected clusters and shoots during the first three years after planting. The key pests in the orchard during the nonbearing period were the green apple aphid and San Jose scale. In the integrated plant protection system, it is possible to reduce the number of insecticide treatments depending on the density of the main pests.


INTRODUCTION
The soil, climatic and topographical conditions in many regions of Bulgaria are favorable for apple growing and production of high quality fruits.It is impossible to grow trees and have high quality and quantity production without plant protection practices.The large number of pesticide applications (10-16 in a growing season) creates serious problems with pesticide residues and their side effects on beneficial organisms, the environment and human health.This is the reason for the search for new environmentally-friendly systems for apple protection.These new systems are e.g.integrated and organic production systems, which are being investigated in the case of apple diseases, pest and weeds (van der Scheer, 1980;Alston, 1989;Dickler and Schaffermeyer, 1993;Blommers, 1994;Sutton, 1996;Grauslund and Bertelsen, 1996;Holb and Heijne, 2001;Holb et al., 2001).Several points of integrated and organic production systems are well qualified (Anonymous, 1989;Dickler, 1990;Dickler and Schaffermeyer, 1991;Cross and Dickler, 1994;Avilla, 1996;Grauslund and Bertelsen, 1996;Berrie and Cross, 1996;El Titi et al., 1996;Holb et al., 2003b), however, further development of plant protection is still needed for both environmentallyfriendly production systems in apple growing (Cross, 1993;Cross et al., 1996;Holb et al., 2003b).
The aim of our study was to compare the effect of conventional and integrated plant protection systems on incidences of several plant diseases and pests.Investigations were made in three consecutive seasons on three apple cultivars.
Incidences of all apple diseases and pests were assessed in all of the three growing seasons.Assessed diseases and pests, their economic threshold levels and number of treatments during the examined periods can be seen in Table 1.

Incidence of plant diseases
Permanent disease on the three cultivars was powdery mildew (Podosphaera leucotricha (Ell.et Ev.) Salmon).Cultivars Prima, Florina and Erwin Baur were slightly infected with powdery mildew in both plant protection systems during the examined periods (Table 2).The results were similar to results of Borovinova (1994) made in Kyustendil during 1992-1994.Holb et al. (2001) also found low disease incidence in Hungary in integrated apple orchards on six apple cultivars, including two resistant ones.In other studies, van der Scheer (1980) and Holb et al. (2003a) found low disease incidence of apple scab on scab susceptible apple cultivar Jonagold in a Dutch integrated apple orchard.Moreover, strong relationships were shown between disease incidence and severity measurements and predictive models were given to forecast scab on leaf and fruit (Holb et al., 2003a).In our study, disease was controlled with five fungicide applications in the conventional systems and with pruning of infected clusters and shoots in the integrated systems.Regardless of absence of treatments in the integrated system, the damage by powdery mildew was under the economic threshold level on all the three cultivars (Table 2).Other apple diseases were not found on the investigated apple cultivars.These results were similar to those of van der Scheer (1980) and Holb et al. (2001).
The presence of aphids in the conventional production system was low, but the density was over the accepted threshold level in the integrated plant protection system.
In the first year, aphids had to be controlled by approved insecticides in the integrated orchard.A few separate trees were attacked and severely damaged by leopard moth (Zeuzera pyrina L.) and they were uprooted.During the second year, five insecticide treatments were applied against aphids, leaf miners and San Jose scale in order to reduce their number under the economic threshold level.In the third year, seven insecticide treatments were applied in the conventional and six in the integrated production systems against aphids, San Jose scale, leaf miners and leaf rollers.The presence of separate flowers and fruits led up to a special treatment against codling moth (Cydia (Laspeyresia) pomonella L.).In the three years, one treatment against leaf rollers was saved in integrated plant protection because their density was below the economic threshold level.Similar results of damage caused by pests were obtained in several other European integrated orchards (Bloomers, 1994;Berrie and Cross, 1996;Grauslund and Bertelsen, 1996).

CONCLUSIONS
The key disease during the experimental period was powdery mildew, which could be effectively controlled when fungicide treatments were combined with pruning of infected clusters and shoots during the first three years after planting.
The key pests in the integrated orchard during the nonbearing period were the green apple aphid and San Jose scale.These pests could be controlled by integrated plant protection methods.In the integrated control system, it is possible to reduce the number of insecticide treatments depending on the density of the main pests.