Elm bark beetles and Dutch Elm Disease: tests of combined control

Abstract

The possibility for the combined control of Ophiostoma novo-ulmi and Scolytus multistriatus was tested in Italy. Two elm clones [U. pumila × U. minor (clone B) and U. glabra var. pendula grafted onto U. pumila × U. minor pollards (clone A)] were treated by stem injection of different blend or concentrations of fungicides and insecticides. Then, adults of S. multistriatus, either loaded with spores of two isolates of O. novo-ulmi (H328 and 182) or provided of their natural load of conidia, were forced to feed in twig crotches of the treated trees. After 48 hours all insects were checked (dead or alive). One month later, the same twigs were cut off and brought to the laboratory. From each twig, three discs almost 1 mm thick were then taken (0, 3 and 6 cm over the point where the insect fed). The wood discs were inoculated in selective substrate and stored until the development of O. novo-ulmi colonies. All thesis containing insecticides give good results against S. multistriatus. Similarly, all thesis containing fungicides show a good fungus control independently from the fungal isolated. The percentage of fungal transmission obtained from insects carrying the natural load of conidia was lower than percentages obtained from beetles artificially loaded. Both beetle sex and position on the foliage never influence insect mortality or O. novo-ulmi infection. The best results were obtained injecting the Carbendazim + Acephate blend in the clone A. High chemical concentrations did not improve the general results.