In Vitro, in Vivo and in Field Sensitivity of Venturia inaequalis to Anilinopyrimidine Fungicides with Different Types of Scab Management and Degree of Control

Abstract

The sensitivity of Venturia inaequalis to anilino-pyrimidine (AP) fungicides (pyrimethanil and cyprodinil) was studied on populations sampled from apple trees with different fungicide and APs histories: 1) apple trees in uncultivated areas never exposed to fungicides (wild types), 2) commercial orchards with many years of good scab control with APs (well-controlled); 3) populations in experimental Centre where an initial good activity decreased after several years of intensive use (poorly controlled). The in vitro sensitivity tests were performed on monoconidial isolates, while those in vivo with curative or preventive applications on populations inoculated on apple seedlings. In the field, the infection on apple trees was assessed as severity of attack on leaves. The results evidenced that the sensitivity in vitro to pyrimethanil and cyprodinil showed a progressive lower reduction from wild types to well controlled, ending with poorly controlled populations. In vivo tests the same moderate decrease of sensitivity and activity (with a wide range) was more evident with curative, respect preventive applications, as noticed also with an important DMI (difenoconazole). In field trials, the populations intensively treated with APs showed, after some years, a reduction of control, that was confirmed in the following years. These activity reductions were sensibly less strong respect those evidenced by strobilurins, both in field and in vitro tests. The particular characteristic of resistance to AP fungicides is discussed.