plant disease

Black Knot of Plum & Cherry: Prune Now!

By Joan Allen

Originally published by the UConn Home & Garden Education Center

black knot of plum and cherry trees
Photo: UConn

Black knot of plum and cherry, caused by the fungus Apiosporina morbosa, may be overlooked during the growing season when the leaves are hiding the galls, but this time of year they are hard to miss, especially when they are as abundant as they are on the tree in the photo below.

This is a serious disease of these trees and can eventually kill susceptible varieties. Management options include sanitation, resistant varieties and properly timed fungicides.

Where manageable, prune out all galls during the dormant season and dispose of them off-site, burn or bury them. This is because even removed galls may still produce spores that can cause new infections. Prune  6″ below the visible edge of the gall because the fungus can be invading the wood in that area prior to gall development.

This disease can affect both orchard and ornamental varieties of plum and cherry but some of the tart cherries are less susceptible. Native wild cherries are hosts of the disease and provide a reservoir of inoculum for orchards and ornamentals. It’s helpful to remove those nearby where possible. For new plum plantings (fruiting/orchard), ‘President’ is highly resistant. Moderately resistant options include ‘Methley’, ‘Milton’, ‘Early Italian’, ‘Brodshaw’, ‘Fellenberg’, ‘Shiro’, ‘Santa Rosa’ and ‘Formosa’. ‘Shropshire’ and ‘Stanley’ are considered quite susceptible.

Here’s how disease develops: Infections occur in the spring on new growth from spores produced on the surface of 2+ year old galls. Spores are produced and spread during rainy weather and shoots must remain wet for a period of time for the spores to germinate and initiate an infection. Infections can occur at temperatures of 50°F or higher when water is present for the required period of time. Over the course of the first summer, a small greenish brown swelling develops. By the end of the second summer, the gall or knot becomes hard, rough and black. These galls begin producing spores the following spring. Galls expand in size each year until the branch is girdled (killed all the way around) and then they die. Once a twig or shoot is girdled, the portion beyond the gall can’t get any water or nutrients and dies as a result. Sometimes, larger branches and trunks can become infected, presumably through wounds.

What if you have a susceptible tree and want to prevent this disease? If you know you have a source of infection (hosts with galls nearby, either wild or on a neighboring property) and you’ve had some infections, keep up with the monitoring and pruning, fertilize and water as necessary to prevent stress, and use preventive fungicides, such as lime sulfur during dormancy (organic option) or chlorothalonil or others labeled for this disease. Other than lime sulfur, applications should be made as directed on the label beginning at bud swell and until new terminal growth ceases.

Become a First Detector

late blight
Late blight. Photo: Joan Allen

By Joan Allen

The National Plant Diagnostic Network (NPDN) was formed along with the National Animal Health Laboratory Network (NAHLN) in 2002.

The mission of the NPDN is to enhance national agricultural security by quickly detecting and identifying introduced pests and pathogens.

This is accomplished through the creation of a nationwide network of diagnostic laboratories at land-grant universities (UConn in Connecticut) and state agriculture departments, training for diagnosticians and First Detectors, and the establishment of pro- cedures to be followed when a suspected exotic introduction is discovered.

Introduction of a damaging exotic pest or pathogen can be either acciden- tal (such as the Asian Longhorned Beetle [ALB] or the Emerald Ash Borer [EAB]) or intentional (such as an act
of bioterrorism).

Who can be a First Detector? Anyone who spends time with plants and would like to learn how they can help protect them from exotic pests and pathogens. The group includes professionals that work with plants in areas such as re- search, extension, agriculture, forestry, landscaping and the green industry.

But professionals aren’t the only ones who can play an important role in the early detection of an introduced pest or pathogen that has the potential to cause significant and damaging impact. Gar- deners, hikers, campers and anyone who spends time enjoying the outdoors all make great First Detectors.

By becoming familiar with the common plant pests and problems in your area, you can learn to recognize some- thing unusual and follow the established protocol to have it identified and, if needed, acted upon.

Free training is available online at https://firstdetector.org or by attending a local in-person training session. In-person training sessions can be organized for groups at no cost by contacting joan.allen@uconn.edu

The online training consists of six modules that can be completed one at a time at your convenience. Module topics include Mission of the NPDN, Monitoring for High Risk Pests, Diagnosing Plant Problems, Submitting Diagnostic Samples, Photography for Diagnosis and Disease & Pest Scenarios.

Each module is followed by a short quiz. Once all six are successfully completed, you will be a certified First Detector and can download your certificate.

The training includes information on what to do and who to contact if you come across an unusual pest, pathogen or plant. Certified First Detectors become part of a national network and may receive email communications including alerts about pests and pathogens that are a threat to plants in their area along with an electronic newsletter.

Plant Diagnostic App

pdlThe UConn Plant Diagnostic Lab has partnered with other university diagnostic labs led by Purdue University to create a plant diagnostic app for the iPhone and iPad.  The app is now available and the download is free.  Users select the diagnostic lab of their choice (usually the closest geographically), complete sample information forms and submit up to six diagnostic images.  When complete, the submission is sent to the selected diagnostic lab via email.   Once a lab is selected, it will become your default lab unless changed.
Submissions may include plant disease or insect problems and plant or insect ID.   There is currently no fee for image diagnosis at UConn but this varies depending on the lab selected.  If an accurate ID or diagnosis cannot be made from the information and images submitted, additional information, images or a physical sample may be requested. 
To find the app, search for ‘plant sample submission’.   Check it out and try this new tool! 

Spring Bedding Plant Meetings

Extension word markLeanne Pundt of UConn Extension hosted two Spring Bedding Plant meetings in February for Connecticut growers. One was held in Vernon and the other in Torrington so that all growers were offered a convenient location.
The Meetings began with a discussion on the greenhouse issues of 2012, including downy mildew on garden impatiens.  Leanne offered tips on how to manage pests on ornamentals, vegetables and herb bedding plants.

Extension Educator Jude Boucher presented a virtual tour of how some Connecticut growers are growing vegetables in the greenhouses, a tour of some of the All America Sweepstakes (AAS) winners and losers at the UConn Department of Plant Science Research Farm plus give us updates on late blight on tomatoes

UConn Plant Science Department Head Rich McAvoy covered updates on plant growth regulators, reviewed the best management practices for Plant Growth Regulators (PGR’S) and gave tips on how to hold plants if sales are delayed.   He also gave some tips on nutritional monitoring using the pour thru method and how to calibrate your injector.
Wade Elmer, Plant Pathologist at the Connecticut Agricultural Experiment Station covered emerging diseases such as downy mildews, powdery mildews, botrytis,  leaf spots, root rots and others plus highlighted what diseases to expect on some of the shade tolerant species growing in 2013. 
Overall, both meetings were well attended and very successful. It should be a very successful year for bedding plants.