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Psylla piri defeated by complementary control

, : Psylla piri defeated by complementary control. Mededelingen van de Faculteit Landbouwwetenschappen Rijksuniversiteit Gent 43: 527-539

The author reviews the causes (mostly excessive use of chemical pesticides) that led to the upsetting of the natural balance in apple and pear orchards in Italy and elsewhere in 1945-70, and lists the original main arthropod pests (Aphis pomi Deg., Dysaphis plantaginea (Pass.), Cydia pomonella (L.) (Laspeyresia pomonella) and Quadraspidiotus perniciosus (Comst.)) in contrast with the 8 new or acquired pests (Panonychus ulmi (Koch), Tetranychus urticae Koch, Leucoptera scitella (Zell.), Phyllonorycter blancardella (F.) (Lithocolletis blancardella), Stigmella malella (Stnt.) (Nepticula malella), Adoxophyes orana (Fisch. v. Roesl.) (reticulana (Hb.)), Argyrotaenia pulchellana (Haw.) and Psylla pyri (L.)) that occur in orchards habitually treated with chemicals against the original fungus diseases and insect pests. The history of the introduction of integrated or guided control is also reviewed, but a distinction is made between this and the concept of control measures supplementing natural control ('complementary control'), which the author considers better for the environment. In complementary control, the natural balance is restored not by introduced natural enemies but by making treatments with very selective insecticides (preferably stomach rather than contact poisons) only against the original pest species, and by allowing the 'acquired' pests to die out naturally as their natural enemies are no longer killed by chemical sprays. This was tried successfully from 1970 onwards on apple and pear in Pavia, Italy. Sprays of lead arsenate were applied against C. pomonella and of methyl-demeton or pirimicarb against aphids, after blooming; in 1972, with the gradual disappearance of tetranychids and leaf-miners, the main emphasis was on the control of Q. perniciosus with sprays of barium polysulfide in March, and after 1975 lead arsenate was effectively replaced by diflubenzuron. P. pyri still remained a problem, but from experiments in 1975-77 it was found that certain non-specific fungicides applied against apple scab were also killing a pathogenic fungus (probably a species of Entomophthora) that had previously held psyllid populations in check. It is therefore recommended that benamidazolic compounds such as benomyl or thiophanate-methyl, which are specific against scab and oidium and not against downy mildew, should be added to the complementary control schedule of diflubenzuron, barium polysulfide and methyl-demeton or pirimicarb. It is also recommended that organophosphates, carbamates and organochlorine compounds, all treatments against 'acquired' pests, and any non-essential insecticide-fungicide mixtures should be excluded from the chemical control schedule in apple and pear orchards.


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