Plant protection in organic arable and horticultural production: A summary of research conducted under the German Federal Programme for Organic Agriculture and other forms of Sustainable Agriculture

Summary

Plant protection in arable and horticultural production was one of the central topics for research in the Federal Programme for Organic Agriculture. Since 2002, 53 projects have been carried out on this subject. After several status quo analyses (2002-2004), methods for control and prevention of pests and diseases were further developed and adapted to organic farming conditions. Focus areas included copper replacement, resistant varieties and improved cultivation methods. Plant health issues were also addressed in various speciality crops where pests and diseases often lead to the need to import produce from other European countries (e.g. Brussels sprouts), as domestic production cannot cover the ever-increasing demand; in this area, several projects were set up to improve growing conditions and establish new methods for plant protection. One important focus was the control of downy mildew, particularly in organic onion cultivation. In this case insights from conventional farming were adapted to organic farming conditions, e.g. in the control of downy mildew in summer onion cultivation. The growing risk of the occurrence of downy mildew in organic onion cultivation could be further reduced through the use of new, mildew-resistant varieties. New alternatives to the use of copper, such as plant extracts of sage and liquorice or microbial preparations with Aneurinibacillus migulanus demonstrated a significant reduction of infestation in onion and cucumber. In organic potatoes, primary stem infection by late blight (Phytophthora infestans) was significantly reduced by seed dressing using small amounts of copper (120 g/ha, compared to higher amounts that would be needed for a foliar treatments in the field); this led to yields increases by up to 55%. Alternative pesticides were tested against the pea moth (Cydia nigricana); here, a pyrethroid formulation showed variable effects and Spruzit-Neu® was unable to reduce pest infestation at high insect densities. The use of beneficial insects and other cultural methods was extensively studied. Covering Brussels sprouts with fine-meshed nets from the time of transplanting until the end of October achieved a 77% reduction in the infestation with cabbage whitefly (Aleyrodes proletella) during the main infestation period in September. In field trials with point releases of the parasitic wasp Encarsia tricolor, parasitism was up to 50% higher than in the reference without release; bringing the first release forward in time resulted in a significant pest reduction by about 60%. Studies on the control of carrot fly (Chamaepsila rosae) showed that a major risk factor for infestation is the distance to fields where carrot had been grown in the previous year, and thus field selection offers a major control option. In addition, the research showed that infestation can be limited by growing either early or late sets of carrots. Another project dealt with the natural control of the grain weevil (Sitophilus granarius) by a continuous release of the ectoparasitoid Lariophagus distinguendus in grain stores. This method is intended to be an affordable, easy-to-use and effective alternative to existing release methods. Further results from the BÖLN research on pest management in Crop Production are regularly published at www.bundesprogramm-oekolandbau.de.