Preventing Anthracnose and Apple Scab

Crabby Apples and Other Complaints

We waited a long time for summer to arrive this year, so it is unfair that some flowering crabapples are turning yellow and brown and shedding their leaves already. Mountain-ash, serviceberry, and hawthorn are also affected by the same disorder. Here and there a few maples and other species are also dropping random leaves, which are for the most part still green, often with patches of black or brown. The latter situation has a different origin, but both are rooted in the record-wet spring weather of 2019.

A common pathogen called apple scab (Venturia inaequalis) affects apple trees of course, but quite a few other members of the rose family, including flowering crabapples.  Venturia inaequalis is a fungus that overwinters in the fallen leaves of previously infected trees; its spores are released from the old leaves to begin a new infection cycle by the impact of spring rains. Obviously more rain means a greater number of spores in the air and a more severe case of the disease.

Symptoms of apple scab are small brown or olive-green spots on leaves as well as fruit. In a drier season there may be little harm done, but in wet years it often results in many leaves being killed. Sometimes they show a bit of orange or yellow before dropping, though dead leaves may also stay on the branches for the whole season. Apple scab seldom kills trees, but it weakens them. In commercial apple orchards it can lead to blemished fruit that are prone to splitting open.

One of the easiest ways to help minimize apple scab is to rake up and destroy fallen leaves each autumn. Fungicides can reduce symptoms if applied in early spring when buds are just opening. One of the better products is potassium bicarbonate, an organic compound. However, if you have a susceptible flowering crab, it will always be an uphill battle, one which gets worse over time. The very best way to deal with this problem is to replace it with a disease-resistant cultivar. Today there are more than 20 gorgeous cold-hardy crabapples resistant to apple scab. A complete list can be found at http://www.hort.cornell.edu/uhi/outreach/recurbtree/pdfs/~recurbtre...

Anthracnose is a general term for a group of related fungi which infect leaves of many herbaceous plants and hardwood trees. The pathogens are host-specific, so walnut anthracnose is caused by a different organism than maple anthracnose, even though the symptoms are similar. Look for brown or black lesions, usually angular, and bounded by leaf veins. As with apple scab, anthracnose is highly weather-dependent, being far more severe in wet years than dry. Another similarity is that the disease overwinters in leaves that were infected the previous year.

It is harder to control anthracnose because spores can overwinter on twig and branch tissue as well. While fungicide applications may help, shade trees are often too large for a homeowner to effectively reach all the foliage, and it is very expensive to have large trees sprayed with a boom truck. Affected leaves should be raked up and destroyed. In addition, take measures to increase air circulation and sunlight penetration around affected trees. It may be necessary to thin out trees planted too closely.

While both these disorders have been around for centuries, more frequent weather extremes in recent years have made them harder to control than ever. Though there are anthracnose-resistant vegetables, to my knowledge there are no resistant trees other than mango and dogwood, so increased planting distance and better sanitation are essential now. But the number one way to prevent crabby crabapples is to plant only disease-resistant varieties that are happy even when the weather is miserable.

 

Views: 30

Comment

You need to be a member of CornellForestConnect to add comments!

Join CornellForestConnect

Forum

Norway Spruce stump treatment

Started by Alicia Rose in Woodlot Management Nov 4. 0 Replies

A urea application of a freshly cut Norway spruce stump surface. This treatment has been implemented as a management strategy to prevent the future crop and adjacent trees from Heterobasidion annosum infection. This is not common practice in Welsh…Continue

Beech control with triclopyr versus glyphosate

Started by Peter Smallidge in Woodlot Management. Last reply by Peter Smallidge Oct 23. 2 Replies

[I'm pasting from a recent email thread]Question - I'm working on a couple beech regen and mid story control projects.   I have been using Garlon 4 in oil.   Works good, but sometimes I want it to move through the roots and the Garlon doesn't do…Continue

Why don't evergreens drop their leaves in the fall?

Started by Brett Chedzoy in Woodlot Management Oct 22. 0 Replies

Hmmm, a timely question for the fall foliage season and a lesson that I don't remember being taught at forestry school (though I admit that I may not have been paying attention!) …Continue

Verticillium Wilt

Started by Carl DuPoldt in Forest Health Jul 9. 0 Replies

Verticillium Wilt - https://mailchi.mp/unl.edu/nebraskas-forest-health-report-july-2019 Symptoms of Verticillium wilt are now becoming apparent in infected trees in…Continue

Silvopasture in Wisconsin: Goals, Challenges, and other Fodder for Thought

Started by Carl DuPoldt in Agroforestry May 9. 0 Replies

Silvopasture in Wisconsin: Goals, Challenges, and other Fodder for ThoughtWednesday, May 29, 2019 at 11:00am (CDT)Diane MayerfeldSustainable Agriculture Coordinator, UW-Extension, Center for Integrated Agricultural Systems (CIAS) -…Continue

Small acreage logging project

Started by WJ Rodenhouse in Woodlot Management. Last reply by Lew Ward Apr 22. 1 Reply

A friend asked me what types of protections he should include in agreement with logger when having his 10 acre forest logged. I thought maybe some of you could provide insight. Logger stated Workman's comp wasn't needed in a family business.Thanks!Continue

Western Larch Question

Started by Alex Harmon in Wildlife Management. Last reply by Pamela Dallaire Mar 30. 2 Replies

Would a Western Larch (tree) NOT lose its needles during fall and winter if it was kept indoors? / what causes it to lose its needles(temperature change, change in length of days)? IF YOU KNOW THE ANSWER PLEASE REPLY!!!!!! NOT KNOWING IS KILLING ME!!Continue

How tree diversity affects invasive forest pests

Started by Brett Chedzoy in Woodlot Management. Last reply by Brett Chedzoy Mar 27. 1 Reply

A long-standing tenet in forestry is that healthier and more diverse woods are typically more resilient to stress factors and pest.  This holds true in most cases, but there are the notable exceptions like EAB.This article from the "Morning Ag…Continue

Badge

Loading…

© 2019   Created by Peter Smallidge.   Powered by

Badges  |  Report an Issue  |  Terms of Service