Why Oak Trees Are Dying in Missouri and How to Help

Oak trees are a vital part of Missouri’s urban and rural landscapes alike. They provide homes for wildlife, shade for our homes and yards, and add character to neighborhoods across St. Louis and St. Charles Counties.

Recently, we’ve seen more oak trees dying than usual. This is worrying for homeowners and nature lovers alike. In this article, we’ll look at why this is happening and discuss ways to help our oak trees stay healthy. We’ll cover the main reasons oak trees are dying, how to spot problems early, and steps you can take to protect the oaks in your yard and community

Common Causes of Oak Tree Death in Missouri and Their Signs

What’s causing the rapid decline in oak trees across our state? There are a few factors at play.

Oak Wilt Disease

Oak wilt is one of the most serious threats to oak trees in Missouri and many other states. It’s caused by a fungus called Bretziella fagacearum, which attacks the water-carrying systems inside oak trees. There is no cure for oak wilt, so preventing it is the best way to protect your valuable oak trees.

Not all oak trees are equally affected:

• The black oak group (red, black, scarlet, and pin oaks) is very susceptible and can die within weeks of infection.
• The white oak group (white, bur, chinkapin, and swamp oaks) is more resistant but can still be affected.

The disease spreads through root connections between nearby oak trees and by sap-feeding beetles that carry the fungus from infected trees to fresh wounds on healthy trees. In some cases, it can also be spread by squirrels.

Signs of oak wilt include:

• Leaves at the top of the tree turning brown and falling off, especially in summer
• Leaves changing color from the edges inward
• Brown streaks in the wood under the bark
• Rapid leaf drop, with brown leaves staying on the tree

To prevent oak wilt, avoid pruning or wounding oaks during the growing season, especially from April through July. Don’t move firewood from infected areas, and keep trees well-watered during droughts to reduce stress and keep trees strong.

If your tree falls victim to oak wilt, removing the tree early is the best option to prevent it from becoming a safety hazard and an eyesore.

Bacterial Leaf Scorch

Bacterial Leaf Scorch is caused by a bacterium called Xylella fastidiosa and is becoming more common in Missouri’s oak trees.

This disease affects the tree’s ability to move water and nutrients. While it doesn’t usually kill trees right away, it can weaken them over time, making them more likely to get other problems.

Signs of Bacterial Leaf Scorch include:

• Leaves with brown edges and yellow margins, looking scorched
• Symptoms starting on one branch and spreading over several years
• Leaf discoloration appearing in late summer or early fall

To manage bacterial leaf scorch, keep trees healthy through proper watering and fertilizing, prune affected branches, and in some cases, the use antibiotic treatments might be necessary. Contact an arborist for professional advice and application.

Sudden Oak Death

Sudden Oak Death is caused by a pathogen called Phytophthora ramorum. It’s common and extremely damaging in western states and was recently introduced into Missouri and other midwestern states in 2019. The pathogen entered the state through infected rhododendron plants shipped to big box retailers like Walmart where they were then sold to homeowners.

More than 100 different plants can host the pathogen. It’s referred to sudden oak death once it infects oak trees. It can kill an oak tree in just a few weeks to a few years after infection.

Signs of Sudden Oak Death include:

• Cankers on the trunk or main stems, often oozing dark fluid
• Leaves turning pale green, then brown
• Entire branches dying rapidly

To prevent Sudden Oak Death, only buy plants from reputable, local sources and inspect them carefully. Keep your trees healthy through proper care and regular check-ups.

Insect Problems

Fungal diseases aren’t the only issues oaks face in Missouri. Several types of insects can also damage and kill oak trees. Two big problems in our area are gypsy moths and two-lined chestnut borers.

Spongy Moth (Formerly Gypsy Moth)

Spongy moths are invasive insects that can severely damage oak trees. In their caterpillar stage, they eat a lot of oak leaves. They can strip entire trees bare, leaving them weak and open to other threats.

Signs of spongy moth infestation:

• Egg masses on tree bark (look like tan, fuzzy patches)
• Caterpillars feeding on leaves in spring and early summer
• Thinning tree canopy
• Completely leafless trees in severe cases

When oaks lose a significant amount of their foliage, they struggle to photosynthesize, become weak, and attract other pests and diseases, putting the tree at risk of failing.

Two-lined Chestnut Borers

Two-lined chestnut borers are native beetles that often attack stressed or weakened oak trees. The larvae tunnel under the bark, disrupting the tree’s ability to transport water and nutrients.

Signs of two-lined chestnut borer infestation:

• Small, D-shaped exit holes in the bark
• Winding tunnels under the bark if you peel it back
• Upper branches dying back
• Thinning or browning leaves, often starting at the top of the tree

Other Insect Threats

While gypsy moths and two-lined chestnut borers are major concerns, other insects can also harm oak trees:

• Oak leaf rollers and cankerworms can eat all the leaves off trees
• Scale insects and aphids can suck sap from leaves and branches
• Bark beetles can attack trees weakened by drought or other stressors

It’s important to note that insects often attack trees that are already weak from other problems. If you notice any sign of pest damage on your oaks, call us at 314-322-7690 right away for the best chance of saving your trees.

How to Prevent Oak Tree Problems

Best Practices for Oak Tree Care

Taking good care of oak trees can help them stay strong and resist problems. Here are some tips:

1. Watering: During dry spells, water your oak trees deeply but not too often. A good soaking once a week is better than light watering every day. Using a soaker hose is much more effective than a standard sprinkler system.
2. Mulching: Put a layer of mulch around the base of the tree, but keep it away from the trunk. This helps keep moisture in the soil and protects the roots.
3. Fertilizing: Most oak trees don’t need extra fertilizer. If you think your tree might need it, ask a tree expert first! If your oaks would benefit, we can ensure only the necessary nutrients are applied.

Pruning Dos and Don’ts

Proper pruning can help keep oak trees healthy, but it’s important to do it right:

• Do prune dead or diseased branches promptly.
• Don’t prune oak trees during the growing season (usually April through July) to avoid attracting insects that spread diseases. In general, oaks are best pruned in winter, during dormancy.
• Do make clean cuts just outside the branch collar (the swollen area where the branch meets the trunk).
• Don’t remove more than 25% of the tree’s live branches in one year.

For best results, have the certified arborists at Mathias Precision Tree Service prune your trees with care.

Protect Your Oak Trees Before It’s Too Late

Oak trees are a treasured part of our community in St. Louis and St. Charles Counties. By taking steps to keep oaks healthy, we not only reduce the risk of pest and disease problems but also ensure our yards and streets remain beautiful under the shade of mature oaks for generations to come.

If you’re worried about the oaks on your property, don’t wait – call Mathias Precision Tree Service today at 314-322-7690 to schedule a professional inspection and keep your trees strong for years to come.