More Rain = More Apple Bitter Rot: Late Maturing Apple Cultivars Need Continued Fungicide Protection up Until Harvest (!)
Bitter rot incidence is high in some Virginia and West Virginia apple orchards as hot summer days with drought mid- summer preceded rains in August and September. Bitter rot emerged at an increasing rate where fungicide was stopped in June or July or coverage until harvest was less frequent then necessary after many small rain events that in the end summed up to 2 inches of rain or more (Fig. 1). In addition, we had a severe 3 inches of rain brought in by the hurricane Ida that were highly favorable for infections by bitter rot fungi from genus Colletotrichum . If you spray every row (full orchard coverage), your fungicide cover spray is worth 14 days or 2 inches of rain, whichever comes first. Under this spray scenario, if you do not get rain for 14 days, you can extend the spray interval to 21 days, under the condition that you do not get rain during the 7 additional days. However, if you spray every second row every 14 days ( alternate row middle) , f ruit r...