Tree Disease & Insect Control

The answer is: it depends.

Leaf spot disease is an umbrella term that covers many different diseases that affect foliage.

Leaf spot can be a bacterial or a fungal disease, though fungal leaf spot diseases are the most common.

If your tree has leaf spotting, contact Absolute Tree Service for an inspection and assessment.

It depends on the type of spots and what’s causing them.

Many spots on tree leaves are a cosmetic or aesthetic problem. However, some leaf spots result from fungal or bacterial diseases that can kill your trees over time. It's important to know the difference.

The main danger to your trees is the loss of healthy leaves. A tree’s leaves are its energy source; they provide a tree with food energy through photosynthesis. If leaf spot disease kills so many leaves that your tree doesn’t have enough energy stores, your tree can decline or even die.

Most bacterial leaf spot diseases form a yellow edge or "halo" around infected areas of a leaf. The spot's interior may be tan, brown, or black, but will always have a yellow border.

These yellow margins are less common in fungal leaf spots but do appear with some. Fungal leaf disease is more easily identified by the spores that develop within the leaf spot.

Keep Your Trees Healthy

The most effective way to reduce leaf spot diseases is to keep your trees and whole garden healthy. You'll find some helpful information about how to do that in our article on Integrated Pest Management.

Healthy trees are better able to withstand diseases and more likely to put out new leaves after they've dropped diseased ones. And having sufficient water and nutrients ensures your tree will continue growing despite the stress caused by leaf spots.

Water the Right Way

If you water your garden in the evening, you may be creating conditions for fungal diseases to thrive and spread. And cool evenings and wet foliage also attract slugs and snails, which nobody wants in their garden!

It's always a good idea to water early in the morning. This ensures that any excess water left on leaves, branches, or the soil surface will evaporate during the day.

Clean Up Well

Another important thing to do is rake up and discard fallen twigs, branches, and dead leaves as soon as they fall. Just because the leaves are dead doesn't mean that the fungus is also dead.

Infected branches and leaves can spread fungi and bacteria and create places for fungal spores to overwinter.

And remember to discard the infected material. If you rake leaves into a pile and leave them in your garden, wind and rain will carry spores back to your trees.

Plant Disease Resistant Trees and Shrubs

Prevention is always better than a cure! While you may not be able to eliminate unsightly leaf spots, you can minimize infections by planting species and cultivars with good genetic resistance to common diseases. For example, there are many excellent apple and crabapple varieties that have good resistance to apple scab.

Apply Preventative Treatments

Many leaf spot diseases cause only cosmetic damage and don’t need treatment. But some, such as apple scab, are serious enough to warrant preventive treatment with a fungicide.

Consult Absolute Tree Service to properly diagnose tree leaf issues before spraying trees yourself. If you've misidentified the leaf spots' cause, your treatment will likely do more harm than good. It's usually best to let a professional apply the necessary treatment. That way, you know that the proper treatment will be used and that it will be applied correctly and at the right time (timing is critical).

Bacterial Leaf Scorch is caused by a destructive bacterium called Xylella fastidiosa. The name Xylella comes from the Greek word xylem, the name of the vital tissue inside trees that transfers water and water-soluble nutrients from the tree's roots to its branches and leaves.

Although it looks similar to leaf scorch caused by environmental factors, BLS on leaves displays a yellowed strip of leaf tissue between the healthy green portion of a leaf and its infected brown leaf tips or edges. Different tree species show differing disease patterns on their leaves. Still, the margin of yellow leaf tissue is common to all.

Since BLS damage shows up in late summer when leaf scorch from drought stress is also present, it can be difficult to distinguish, so the yellow outline is a key identifier.

Another notable identifier is that leaf damage from BLS starts with older leaves and moves upwards to leaves at the tips of branches. In contrast, water stress typically affects new leaves first, as they are the most distant points a tree sends water to and require the most energy.

To accurately identify BLS, it must be analyzed in a lab. Rutgers University has a diagnostic plant laboratory, and you can search for BLS information on its website.

Bacterial leaf scorch will also stand out during summers that are not excessively hot and receive enough rainfall to keep trees hydrated. Healthy, uninfected trees will have full, leafy crowns and show no signs of water stress. BLS-infected trees will have scorched leaves despite the ideal growing conditions.

EAB is the most devastating threat to Virginia forests. Ash trees across the state are dying at an alarming rate, with little sign of the infestation slowing down.

The emerald green insect is tiny–less than 0.5" long–but the borer (immature phase of the EAB life cycle) does a lot of damage by feeding on the vessels that transport nutrients up and down the tree, cutting off the tree's nutrient supply.

Emerald Ash Borer was confirmed in Northern Virginia in 2008 and is most active in May-August.

You can consult with a qualified tree service with experience in treating and preventing tree pests and diseases. Absolute Tree Service is one such company, and our professional team can help your trees get and stay healthy!