Concepts and methods in biological control of diseases in apple orchards¹

Abstract

The project ‘Promotion of Biological Methods in Apple Growing’ which started in Switzerland in 1985 concentrates on the control of Venturia inaequalis (scab) and Podosphaera leucotricha (powdery mildew). The project considers the selection of suitable cultivars resistant or only slightly susceptible to fungal diseases and the assessment of tolerable economic loss. It also includes curative treatments with sterol‐synthesis‐inhibiting fungicides, according to scab infection periods, as well as applications of plant extracts (proposed by the Institute of Biological Husbandry) and suspensions of antagonists or their culture filtrates as plant‐protecting agents. Screening experiments on apple seedlings showed that root extracts of Rumex obtusifolium significantly reduced powdery mildew infections under greenhouse conditions. In field experiments treatments with R. obtusifolium extracts at intervals of 7–10 days were less effective. Saponin‐containing extracts of different plants gave satisfying control of scab on seedlings in the growth chamber but were not very effective in the field. Applications of spore suspensions and culture filtrates of the phyllosphere fungi Chaetomium spp. reduced scab and mildew infections on apple seedlings to some extent. It was found that in the last 2 years even primary infections of P. leucotricha were severely parasitized by Ampelomyces quisqualis. Preliminary studies showed that the lack of efficacy of this biocontrol system is due to the delayed spread of the hyperparasite.

Assessment of phylloplane microorganism populations in Canterbury apple orchards

“…These factors include leaf age, external nutrients, the interactions between populations of different microorganisms (Blakeman 1985), temperature, relative humidity, duration of leaf wetness, light intensity, wind speed and the presence of air pollutants and pesticides (Dix & Webster 1995). Pesticides in particular, have the potential to reduce population diversity and to give competitive advantages to some species, including foliar pathogens (Bosshard et al 1987).…”

Variations in the Community Structure of Fungal Microbiota Associated with Apple Fruit Shaped by Fruit Bagging-Based Practice

“…Therefore, it was very likely that various apple pathogenic fungi were enriched in the peel tissues of the bagged apple fruit. However, it has also been reported that many fungal species of this class play an important role as biological control agents against pathogenic fungi associated with various plant hosts [ 105 , 106 , 107 , 108 ], including apple [ 109 , 110 , 111 , 112 , 113 ]. Several taxa observed on the peel of the bagged fruit have been shown to be potential biocontrol agents ( Table S2 ), suggesting that the peel is a favorable habitat for beneficial fungi.…”

Management of post-harvest diseases of fruits, vegetables and tuber crops /

“…Several investigators have reported better control with integrated strategies. Control of apple diseases with a combination of natural compounds, plant resistance and by the use of antagonists is commonly practised (Bosshard et al 1987;Pathak 1997). The common methods include the following.…”