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: 309

Comment by Carl Albers on January 11, 2020 at 8:29am

Have not heard about using potassium bicarbonate for the control of apple scab.  Can you expand on this a bit?  How effective is it?  Any downsides?  Timing of application?  Sources for more information? 

Comment

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

Join CornellForestConnect

Forum

Replanting after timber harvest with climate change in mind

Started by Ben T. in Woodlot Management. Last reply by Patrik Schumann yesterday. 1 Reply

Hi Everyone,I’ve been wondering what tree species are going to thrive over the next 50+ years as the climate warms in New York and I’m curious if folks are enhancing plantings of particular tree species for future commercial harvest with warmer and…Continue

Rust Colored Hemlock Bark

Started by Carl Albers in Woodlot Management Dec 31, 2023. 0 Replies

Picture of a hemlock with rust colored bark.  When I cut a nearby tree, also with rust colored bark, it was infested with HWA.  Attached picture shows a Logrite ATV arch in use.Continue

Rust Colored Hemlock Bark

Started by Carl Albers in Woodlot Management Dec 31, 2023. 0 Replies

The hemlocks in my woodlots have been infested with hemlock wooley adelgid (HWA) for at least three years now.  Lately I've noticed some of them having a rust colored bark and I wonder if this is normal and that I just didn't notice it previously? …Continue

How to control mature white pine and hemlock to allow enrichment planting of hardwoods

Started by Peter Smallidge in Woodlot Management Nov 28, 2023. 0 Replies

I had a question about control of mature white pine and hemlock to improve sunlight for enrichment planting of hardwoods.  Following is my response, but I would like to know if anyone else has any experiences to share with control of these to…Continue

Story in Northern Woodlands Magazine on Deer Impacts

Started by Brett Chedzoy in Woodlot Management Aug 8, 2023. 0 Replies

This Spring we had an opportunity to speak with writer John Litvaitis about the big picture of deer impacts on the hardwood forests of the Northeast.  I posted the original story from the summer edition of Northern Woodlands to the…Continue

Ash blonding effect on lumber quality

Started by Jeff Joseph in Woodlot Management. Last reply by Jeff Joseph May 5, 2023. 2 Replies

Question: In Peter Smallidge's most recent "Ask a Professional" column for NYFOA's Forest Owner magazine he stated that some log buyers will reject ash that shows outward signs of "blonding" on the bark. Is this because the wood will change…Continue

The American Chestnut: A New Frontier in Gene Editing

Started by Brett Chedzoy in Woodlot Management May 2, 2023. 0 Replies

https://www.asbmb.org/asbmb-today/policy/042823/the-american-chestnutInteresting discussion the difference between efforts with the American Chestnut and other…Continue

Growing Black Locust for Pleasure and Profit

Started by Brett Chedzoy in Woodlot Management Apr 20, 2023. 0 Replies

In early March I was invited to present on the opportunities for growing black locust as a timber cash crop at the Rural Landowner Conference in Allegany County.  Ryan Trapani from the Catskill Forest Owners Association asked afterwards if I would…Continue

Badge

Loading…

© 2024   Created by Peter Smallidge.   Powered by

Badges  |  Report an Issue  |  Terms of Service