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...

  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 r...

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 bro...

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 s...

On 22 July we detected the first signs of  sooty blotch  and  flyspeck   (SB&FS) on an unknown apple cultivar fruit in Appomattox VA ( Fig. 1 ). This is visible, of course, on fruit that were not treated with any fungicides during spring or summer and likely the advanced development stage indicates that fruit exhibited these symptoms for 5 to 10 days before we detected them. Depending on your spray schedule and used fungicides, we hope you do not see this disease on your fruit. However, s tart scouting your orchard to check for absence or presence of SB&FS symptoms now to see how well was your fungicide coverage during the cover sprays. FIGURE 1. FIRST SIGNS OF FLYSPECK AND SOOTY BLOTCH ON FRUIT OF UNKNOWN APPLE CULTIVAR IN APPOMATTOX VA (PHOTO BY ACIMOVIC 2021). CLICK ON THE PHOTO TO ZOOM IN. In 2021, the weather conditions during spring and through the beginning of summer 2021 were highly favorable for Apple Blotch Disease (ABD), also known as Marssonina Le...

We kindly invite you to fill out a short survey linked below which is designed to target commercial growers of tree fruit and specialty crops in Virginia. Our goal is to learn form you by asking you to provide us with your opinion and feedback on the economic significance and thus research importance of tree fruit/specialty crop diseases in your individual operation(s). The survey has been compiled by Dr. Srdjan Acimovic and is intended to help direct and guide the tree fruit and specialty crop pathology research and extension program at the Virginia Tech's Alson H. Smith Jr. Agricultural Research and Extension Center in Winchester VA. This survey is anonymous and no personal or specific farm data will be collected. Please send this blog's link or the direct link to the survey below to any of your neighbor growers as your and their opinion matters. Please access the short survey by clicking on the following link: Virginia Tree Fruit & Specialty Crop Disease Significan...

Apple bitter rot is a disease that has been an increasing problem in the last 5 years for a lot of growers. This disease is caused by the fungi from Colletotrichum genus and is favored by warm, wet and humid weather conditions prevalent during late spring and the whole summer, but usually occurs when fungicide cover sprays are too far apart while rains are frequent and spray applications do not follow these rain events. The frequent rains we had in the last 4 weeks in northern Virginia were perfect for bitter rot infections. Infections on fruit unprotected by fungicides usually appear in the first week of July, but if conditions in May or July are extremely conducive it is know to appear even earlier (Fig. 1). Occurrence of bitter rot is prevalent in orchard but can spill over to a lesser degree into storage as a postharvest decay. Typical signs of apple bitter rot are very small light brown watery spots under the fruit skin that over time enlarge into 1/4 to an inch size rot lesions ...

In the last 4 weeks or so we have witnessed the occurrence of fire blight symptoms on apples (Fig. 1A, B; Fig. 2A, B). This is a disease caused by the bacterium Erwinia amylovora and its symptom occurrence overlapped with the emergence and we can fairly say "invasion" of periodical cicada ( Magicicada ) in landscapes and orchards. For two weeks now we can see the signs of shoot damage from laying eggs which ensues after the cicada adults mate. These notches seen in Figure 3A injure branches and impact shoots. Due to the vascular tissues in the branches being compromised by the egg laying notches made by the ovipositor of the cicada females the shoots soon start wilting and die (Fig. 3B). These symptoms on a first glance very much resemble fire blight but are not caused by this bacterium, instead these are caused by the periodical cicada. If you have not timely protected your orchards with an insecticide from this insect pest I repeat the recommendation from Dr. Chris Bergh t...