The impact of ground vegetation on the most important plant mites (Panonychus ulmi (Koch) and Tetranychus urticae Koch) and their natural enemies associated with apple trees in Sweida, Syria

摘要

Population dynamics of the two-spotted spider mite Tetranychus urticae Koch and the European red mite Panonychus ulmi (Koch) has been studied from 2010-2012 in an apple orchard in Sweida, Syria, planted with the varieties "Golden Delicious" and "Starking Delicious". The trial orchard has been divided into four sectors: the first was left without tilling since 2008, and without the leguminous cover plants, and the second section was planted with leguminous plants (vetch and Lathyrus sp.) in lines as acover crop in the field from 2009. Then it was left without any cultivation for self multiplicatio. The third section was tilled normally annually but weeds left under the tree's crowns without tillage (mechanical cut only). The fourth sector was tillednormally annually and spring cultivation under the trees was done (as conventional treatments). Phytophagous mites and predatory mites have been counted in summer season from samples of leaves. Phytophagous mites were significantly less abundant in theno tillage sector on "Golden Delicious". There were significant differences in numbers of mites on "Starking Delicious" between the four sectors, and between the two species of mites. Two species of predatory phytoseiid mites, Typhlodromus pyri Scheutenand T. cotoneaster (Wainstein) were abundant in high numbers in the sector 1 and 2 on the two apple varieties (average 1 predator / leaf), and especially in the last year of the study. No acaricides have been used in both orchard sectors (which were leftwithout tillage) in 2012 and 2013. In comparison, acaricides have been used annually in the mid of summer in other 2 orchard sectors because of the very high numbers of phytophagous spider mites. The high population density of predatory mites in the no-tillage sectors was the highest recorded in the study area since more than 10 years after annual follow-up in apple orchards there. Our results indicate the great importance of a better understanding of habitat management to control spidermites in appleorchards.