Confirmation of oak anthracnose in central Pennsylvania

I checked with our Plant Disease Clinic and they are getting a lot of samples of Chestnut oak with anthracnose this spring. I think we had perfect conditions (cool and wet) for disease development when the Chestnut oak leaves were emerging this year. I have a red oak and white oak tree in my yard that also have the disease but not as severe. It's too late to do anything this year. The leaves are already infected. This disease will not kill the trees and they will likely push out more leaves to replace the ones that are dropping this year. Fungicides can be used next year on high value trees to protect them. See the news release and additional resources below provided by my colleague, Sarah Wurzbacher.

Written by Sarah Wurzbacher
Penn State Extension Forester
Lycoming County

Have you noticed more than a few oak trees losing leaves or showing brownish, papery, or necrotic foliage lately? You may be one of many central Pennsylvanians noticing an abundance of oak anthracnose, caused by the fungal pathogen Apiognomonia quercina.

What is anthracnose?

Anthracnose on chestnut oak. B. Harding

Signs of anthracnose include brown and dead spots on leaves, curling or misshapen leaves, and loss of leaves (“defoliation”). If you look closely at the undersides of leaves near leaf veins or at twigs affected by anthracnose, you may find small, pimple-like fungal structures. Try using a magnifying glass or hand lens to see these structures more clearly.

When you observe brown and curled leaves on a tree that appeared healthy last summer, you might understandably suspect the dramatic appearance of some new disease in the woods. Anthracnose, however, was likely already present in the landscape on plant tissues affected last year. In spring, wind and splashing rainwater spread anthracnose spores that infect twigs, emerging buds, and new leaves. This is one of the reasons experts advise against pruning; a practice that introduces more potential infection sites, during springtime or in wet weather.

The observed severity of oak anthracnose has everything to do with weather; prolonged wet conditions early in the growing season spell out a worst-case scenario. While we usually observe only mild damage to oak leaves from anthracnose, this year’s notably wet spring created optimal conditions for this fungal pathogen to thrive, and, as those with affected oaks can attest, damage this season tends to be more severe.

How do I know if my tree is affected?

Brown and curling edges of leaf. B. Harding

First, look for those telltale signs: brown or misshapen leaves, early-season defoliation, and pimple-like fungal structures. Not all oaks are equally susceptible, though. White oak and other oak species in the white oak group tend to be more sensitive to anthracnose. One of the simplest rules of thumb you can use to identify trees belonging the white oak group relates to the rounded lobes on their leaves; species in the red oak group, on the other hand, tend to have bristled or pointed lobes. This season, reports of anthracnose have been on white oak and chestnut oak in particular.

Despite this year’s prevalence of anthracnose, it does not hurt to rule out other possible diseases that could be affecting your oak trees. Oak wilt involves dramatic leaf damage in a short amount of time, particularly affects species in the red oak group, and requires more aggressive management approaches to prevent further damage. A few other common oak diseases are detailed in Penn State Extension’s Oak Diseases factsheet.

For conclusive identification of a disease, you can submit a plant tissue specimen to Penn State’s Plant Disease Clinic, where the sample will be tested and diagnosed. There is no charge for this service. Submission instructions can be found online or through your local Penn State Extension Office.

What do I do if my trees show signs of oak anthracnose?

If your problem really is anthracnose, do not panic! Oaks defoliated by anthracnose are capable of growing new leaves later in the season, a process called “refoliation.” Wait and see how your oaks recover. Using energy to recover from any defoliation event is stressful to an oak tree, but one defoliation in a season is not likely to kill or seriously harm the tree.

Repeated defoliations, or additional stress events for the same tree in the same season or in successive years, can be more serious. A major anthracnose-related defoliation followed by something like drought or heavy gypsy moth pressure may stress a tree enough to cause a decline in health. Think of it this way: in a few months, you can catch the flu, fight it, and feel better, but it is much more difficult to handle the flu, a broken leg, and a hastening deadline at work in those same few months. Be on the lookout for these compounding stressors later in the growing season, when you might be able to give a leg up to a few high-value yard trees through fertilization or watering, but for now, just keep an eye on your oaks and cheer on their recovery.
 

If only a few yard trees are affected, consider raking and removing anthracnose-laden leaves to reduce future infection risk, but if your affected trees are in a woodlot, leave the litter layer on the forest floor intact. Some pruning may also be advisable in the fall or during the dormant season, but be sure to adhere to your municipality’s pruning ordinances. For now, though, a patient, “wait-and-see” approach is probably your best bet.

Resources:

Anthracnose on Shade Trees

Oak Diseases Factsheet
Plant Disease Clinic

Ten Forest Myths

I thought I would share this with my readers.  Bill Cook from Michigan State posted these.  There may be others you have heard, see what you think.  Feel free to share.  One that I have heard quite often is, “We will just cut the large old trees to let the smaller younger trees grow.”  Unfortunately, those smaller trees are often the same age and completely different species than the big trees.

Ten Forest Myths

By Bill Cook, Michigan State University Extension

April 2, 2018

Forests, forestry and the forest industry are among the most environmentally friendly of human activities, contrary to common perspectives. Our popular culture seems to perpetuate many incorrect assumptions and perceptions about forests and how humans depend upon forests. Do not believe everything you read. Look it up and learn, it can end up being pretty fun stuff!

1. Trees provide the air we breathe.

Most of the Earth’s fresh oxygen is produced from the oceans, which makes sense when you understand that three-quarters of the Earths’ surface is covered with water. For terrestrial systems, non-forest biomes are the most common. So, oxygen from trees? Meh. Okay, they produce some, but it is not a particularly high value attributable to trees or forests.

2. We should plant two trees for every one we harvest.

In the Lake States, planting is typically unnecessary. Our forest management systems are tailored to the various forest types to create environmental conditions that encourage natural regeneration. This management is quite successful. So, why plant a few trees when nature will successfully produce billions? This said, there are circumstances where tree planting is needed and useful.

3. A tree grows one ring per year.

If a tree grew only one ring, how could you tell where last year’s ring ended and the next year’s ring began? In fact, our northern temperate trees grow two annual rings each year. The wider, light-colored ring grows in the springtime, followed by the narrower, dark colored ring in the summertime. Then, the tree stops growing wood for about six months.

4. Forests are disappearing.

This is not true in Michigan or across the Lake States, although it is true in some regions around the world. As of 2017, Michigan has more acres of forestland than any time since the 1930s, when statistical forest inventories began. Now, if you live in an urban area and see sprawl gobbling up the countryside, it might be easy to get this impression. However, statewide, we now have a bit over 20 million acres of forest, and that covers a little over half the state.

5. Clearcutting is deforestation.

Deforestation, by definition, is a land use change from forest to something else. The overwhelming amount of deforestation is for agriculture, and then, secondly, for building human infrastructure. Clearcutting is a forest regeneration practice designed to stimulate the reproduction of sun-loving tree species, such as the aspens, red pine, jack pine and others. Natural clearcutting happens through wildfire, windstorms, insect and disease outbreaks and similar events. While clearcutting is not quite exactly the same thing, it’s far more benign than natural occurrences.

6. Planting a tree will save the planet.

This is a popular promotional campaign and has some value in raising awareness, but in ecological terms it is nonsense. Even if every Michigander planted a thousand trees every year, that amount would not come close to annual natural regeneration. However, planting trees does have strategic value in filling-in where nature missed a beat, to change forest type compositions, or to achieve a visual quality objective at a residence or in a city. So, planting trees is a great thing, it is just not going to save the planet.

7. Mother nature knows best.

Nature knows nothing. It is not sentient. Benign neglect is not a fruitful strategy. The predictable paths of natural succession lead to places most people are not going to be happy with. First, the forest legacy following the historic logging era left forests in an unnatural condition, which is the forest that we see today. Second, ecological forest processes alone are unlikely to meet all the demands that society places upon forests. Third, forest health challenges and exotic species place additional pressures on forests. The solution to these problems is active forest management. We don’t manage forests for the forests’ sake. We manage forests for people, by working with natural processes.

8. Timber harvest destroys wildlife habitat.

Harvest, natural disturbance or forest succession creates habitat changes. These changes benefit some species and do not benefit others. Therefore, any particular timber harvest will have wildlife winners and losers. The same is true without the harvest. More likely, critics of timber harvest react to the change in visual quality, which is an especially poor measure of ecological integrity.

9. Government owns most of the forest.

Nearly two-thirds of the Michigan forest is privately owned. Of that, families own nearly three-quarters. The State of Michigan owns about 21 percent and the federal government owns about 17 percent. Ownership has a huge impact on how a forest is managed. However, regardless of ownership, all forests provide benefits to everyone.

10. Forest industry is a destructive, extractive industry.

It is counter-intuitive to many, but the forest industry provides the financial incentive for forest management. No markets leads to no management. With an unmanaged forest, there is a road of troubles. Additionally, there is no greener industry. Thousands of daily products, made from the most environmentally friendly raw material at our disposal, come from forests. Forest products also include clean water and a diversity of wildlife habitat. In contrast to the myth, the forest industry supports a wide range of goods and services, including a healthier environment. Wood use is not a choice, it is essential to our survival. Every U.S. resident uses an average of three to four pounds of wood every day.

Michigan is a big state. It can be misleading to assume that what may be seen in a particular area or along highway corridors is what occurs across the state. Our forests currently produce an amazing array of benefits and unmet opportunities. The potential for increases in quality and quantity of these benefits is huge.