Plant & Pest Advisory» All Fruit Articles


As I See it: Powdery Mildew, New Apples-Fireblight and Thinning, Tree Training

Win Cowgill - Professor and Area Fruit Agent
This weekend brought high temperatures and peaches are starting to grow and size in response to the warm weather. Peaches like warm!

Powdery Mildew and Dry Weather
The hot humid weather this weekend was ideal for powdery mildew. While primary infection is over PM can still spread of the original infections in terminals was not controlled. The protectant fungicides (Captan, Mancozebs) are not effective on PM. The Strobilurin’s are not as effective normally as the Sterol Inhibitors (SI’s) like Rally, Procure, etc. If you have already used 2-3 applications of an SI this spring, consider the use of Sulfur if you are have a powdery mildew outbreak that has not been controlled. Sulfur is an excellent mildewcide. Caution, Do NOT use if the temperatures are forecast to be 80F or higher which means the next few days. Microthiol sulfur is one brand and is OMRI approved for organic growers at 5lbs/Acre. On pumpkins sulfur is one of my preferred choices of materials for PM control.

New Apple trees and Fireblight
The NEWA fireblight forecaster is calling for high or extreme infection periods all this week if you have any open blooms. Be sure to check newly planted trees for flowers! Strep is only good 24 hours before and after an infection. Streptomycin should not be used on the shoot blight phase as it is infective and will hasten resistance buildup. The exception is if we have a hail event this week, then strep must be applied within 24 hours. Growers should be keeping an eye open for fire blight strikes and remove them ASAP if they appear. Several south Jersey orchards are reporting infections appearing. The only chemical control of the shoot blight phase is a combination of copper plus mancozeb. This can help to dry up infections but it will russet the fruit! 

Apple Thinning
It is too late to chemical thin apples at this point; hand thinning should be completed as soon as possible for maximum benefit. Peaches need to be done first as apples will get a size response at any time, peaches start to not respond after pit hardening.

Apple Tree Training and Stripping Leaders
Next week we will have a full article on tree treeing but for now focus on singling out the leaders to one on 1-3 year old trees. Remove competing shoots down 4-8 inches below the start of the new terminal growth (singling to one leader). On new tall spindle trees tie down all feathers to below horizontal, this is essential.