VIRGINIA TREE FRUIT DISEASE UPDATES

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...

1. Some locations are reporting occurrence of Rusty Spot of Peach, a usually rare disease in most orchards. This is a fungal disease developing on peach fruit only thus leading to losses and it is caused the same pathogen causing apple powdery mildew - Podosphaera leucotricha . The fungus either probably overwinters in peach buds, or trees get infected from nearby apple trees as the source of infection (conidia i.e. spores of the fungus are spread to peaches by wind, dew droplets, and rain). Critical timing for application of fungicides is from shuck split through 3rd cover (pit hardening) In other words young peach fruit are susceptible and get infected if protection is not timely applied. However, the infections can start as early as petal fall. If you are scouting orchard frequently, finding the first white or rusty patch spot of this disease should be the trigger for an immediate fungicide application. The most effective fungicides are Gem, Luna Sensation, Merivon, Fontelis, Tilt,...

1. Fire Blight. If 1 to 5% or more fire flight symptoms are visible, you have active infections taking place on actively growing shoots. If you see fire blight strikes (flags) in 2021, assume that in the next 3 years from 2021 the bacterium will be probably be present for a long time and your orchard will be at high risk from when the first flower open until terminal bud set on shoots, thus will require protection each spring when models like Maryblyt or EIP in NEWA predict infections risks. If you see fire blight symptoms do not apply streptomycin as the bacterium is in the tissue, so it cannot be reached by the antibiotic, and there is a risk that if you do you will promote streptomycin resistance acquisition in the fire blight bacterium Erwinia amylovora . This will reduce efficacy of this antibiotic, or even worse lead to the loss of its efficacy.   At this moment, if symptoms are visible, apply plant growth regulator (PGR) prohexadione-calcium (Apogee, Kudos) to reduce su...

Welcome to the  Acimovic Lab's Tree Fruit Disease Updates blog. Acimovic Laboratory is located at the Virginia Tech's Alson H. Smith Jr. Agricultural Research and Extension Center (AREC) in Winchester, VA. As a branch of Virginia Tech's School of Plant and Environmental Sciences and  Virginia Agricultural Experiment Station (VAES) our program involves research and extension focused on diseases of fruit tree crops with emphasis on apple, pear, peach and cherries. We investigate all components of the disease triangle: pathogen, plant, and the environment in order to better understand their interactions that serve as a necessary basis to develop new disease management strategies. As a part of the VAES , AREC in Winchester is a valuable source of cutting edge research-based information that is constantly provided to Virginia farmers through extension meetings, presentation, educational programs and field days organized by the Virginia Cooperative Extension and participat...