VIRGINIA TREE FRUIT DISEASE UPDATES

  I.  APPLE SCAB If apple scab was not controlled timely last year and primary and secondary infections on leaves were visible at any time during the season, you should aim to reduce overwintering scab inoculum residing in leaf litter on the orchard floor. Especially conducive for apple scab fungus overwintering are numerous late summer and fall infections visible as small lesions on the underside of the leaves (Figure 1). Figure 1. Late summer and fall scab infections on the underside of apple leaves (Photo by S. G. Acimovic, 2009). These fall scab lesions are the most productive places where apple scab fungus will grow into the tissue of leaves after they reach the orchard floor and form initials of pear-like fruiting bodies of the fungus called pseudothecia (Figure 2). The pseudothecia facilitate release of apple scab ascospores in the spring with each wetting event.  Figure 2. Round-like pseudothecium of apple scab fungus harbored in the dead leaf tissue visible under the mic

  The preliminary efficacy trial results conducted at AREC in 2021 can be downloaded via this link: Preliminary Report on Efficacy of Gatten and Parade Fungicides in Control of Apple Powdery Mildew at AREC in Winchester VA Figure 1. RIMpro apple powdery mildew output for April 2021 in Winchester, VA.

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 rots will be or have

In order to better serve the Virginia tree fruit industry and you the growers we strive to visit in 2021 any fruit farm that is experiencing both minor to major tree disease problems. Even if you see a little bit of apple bitter rot, fire blight or brown rot please do not hesitate to contact me, your plant pathologist, via  phone 540 232 6037 or via e-mail acimovic@vt.edu , as we are actively working in the lab at Virginia Tech's Alson H. Smith Jr AREC to isolate the causal pathogens of these diseases in Virginia and build up as large as possible collection of pathogen strains which will allow us to better help and serve you now and in the future. Of particular importance to us is collecting a geographically distant and plant host- & cultivar-diverse collection of strains of the following tree pathogens:  Erwinia amylovora , the fire blight bacterium, Colletotrichum species, the fungi that cause apple and peach bitter rot, Monilinia species, the causal fungi of peach brown ro

First signs of apple bitter rot disease on fruit of apple cultivar ‘Wolf River’ have been found in the Shenandoah Valley, more exactly in Martinsburg WV, Berkeley County ( Fig.1 ). Rot started from the fruit side ( Fig. 1 bottom ) indicating that it probably started as an established quiescent Colletotrichum infection at bloom or petal fall, that then expressed recently. We found that bitter rots were almost always on fruit in dense clusters with many fruit together indicating on the conducive moisture conditions on these clusters and lack of fungicide coverage on fruit penetrating in between the fruit ( Fig. 1 top ). Bitter rot fungi can infect any fungicide-uncovered areas on fruit, especially when warm wetting events occur, and we had severla of these in the last 15 days. Extreme heat and the rain that "came" back this week has and will extremely favor this disease in the weeks preceding harvest. Start scouting for bitter rot symptoms to make sure you are free of th

On 26 July we visited a classic training system orchard in south part of Winchester, VA, with trees of apple cv. 'Ginger Gold' and detected symptoms of  Apple Blotch Disease (ABD), also known as Marssonina Leaf Blotch (MLB). The symptoms were found on the lower scaffolds in the canopy and are visible in Figure 1 . This disease primarily expresses on apple leaves and is  caused by a pathogenic fungus  Diplocarpon coronariae . Even though we  recently  experienced dry weather periods in the Shenandoah Valley, e xcessive rains we received in May and June 2021 favored the development of ABD.  Leaf symptoms express as grey to brown large round spots (blotches) that can merge. This leads to  leaf yellowing.   Figure 1. Apple Blotch Disease (aka Marssonina Leaf Blotch) on apple cultivar 'Ginger Gold' in Winchester, VA.  If effective fungicides are not applied timely, continued infections by  D. coronariae  can occur during summer and until the leaves are present on the trees.