Yield loss by potato beetle, Leptinotarsa decemlineata Say and threshold value Effect of the soil separation technique in potato fields on earthworm population

“The injury caused by potato beetles is the defoliation of potato plants especially under warm and dry weather conditions. A single larva can destroy up to 40 to 50 cm’ of the leaf surface which corresponds to 1 % to 2 % of the leaf area of plants at the developmental stage appearance of blossom””. The yield loss due to one larva is approximately 0.6 %. The economic injury level is reached on average with five larvae per plant. Treatments with insect growth regulators or Bacillus thuringiensis are justified when 30 % of the plants ore attacked by young larvae (L] -L2). With other insecticides, the threshold value is reached at a defoliation rate of 10 to 20 %.”