Question 1

What is Oak Wilt and is it in Maryland?

Accepted Answer

Oak Wilt is a deadly fungal disease (Bretziella fagacearum) that has been spreading through Maryland. It is transmitted by sap beetles attracted to fresh pruning wounds and through root grafts between neighboring oaks. Red oaks can die within weeks of infection; white oaks are more resistant but still susceptible. Never prune oaks from April through July in Maryland.

Question 2

What is the Emerald Ash Borer and what does it do to trees?

Accepted Answer

The Emerald Ash Borer (EAB) is an invasive beetle that has killed hundreds of millions of ash trees across North America. It is now widespread throughout Maryland. EAB larvae feed under the bark, disrupting the tree's ability to transport water and nutrients. Infected trees show canopy dieback, S-shaped galleries under the bark, and D-shaped exit holes. Untreated ash trees in infested areas will die.

Question 3

Can a tree with Emerald Ash Borer be saved?

Accepted Answer

Yes, if caught early enough. Systemic insecticide treatments (emamectin benzoate injections or soil-applied imidacloprid) can protect ash trees from EAB when applied before or in the early stages of infestation. Trees that have lost more than 50% of their canopy are generally not good candidates for treatment.

Question 4

What causes mushrooms to grow at the base of a tree?

Accepted Answer

Mushrooms or shelf fungi at the base of a tree indicate internal wood decay caused by fungal pathogens. Common culprits include Armillaria (honey fungus), Ganoderma, and various bracket fungi. The visible mushrooms are the fruiting bodies of decay that may already be extensive inside the trunk or root system. Have the tree assessed by a licensed tree expert.

Question 5

Why are my tree's leaves turning yellow or brown in summer?

Accepted Answer

Summer leaf discoloration has many causes: drought stress (most common in Maryland summers), verticillium wilt, bacterial leaf scorch, iron chlorosis, or root damage. The pattern of discoloration matters — yellowing between veins suggests nutrient deficiency; browning at leaf margins suggests drought or salt damage; random brown patches may indicate disease.

Question 6

What is bacterial leaf scorch and which trees does it affect?

Accepted Answer

Bacterial leaf scorch (Xylella fastidiosa) causes progressive browning of leaf margins in late summer, typically starting on older leaves. It affects oaks, elms, maples, sycamores, and other hardwoods in Maryland. There is no cure, but proper tree care (watering, mulching, avoiding stress) can slow progression and extend the tree's life.

Question 7

How do I know if my tree has a pest problem?

Accepted Answer

Signs of pest infestation include: unusual holes in the bark (borers), sawdust-like frass at the base (carpenter ants or borers), sticky honeydew on leaves or surfaces below (scale insects or aphids), webbing in the canopy (tent caterpillars, spider mites), and premature leaf drop. Early detection is key — many pest problems are treatable if caught before significant damage occurs.

Question 8

What is sudden oak death and is it in Maryland?

Accepted Answer

Sudden Oak Death (Phytophthora ramorum) is a water mold that has devastated oak populations on the West Coast. It has been detected in nursery plants in Maryland but has not established in Maryland forests as of 2025. The primary concern is purchasing infected nursery stock. Buy trees from reputable local nurseries and inspect new plants before planting near existing oaks.

Question 9

Can I treat a diseased tree myself?

Accepted Answer

Minor issues like aphids or scale insects can sometimes be managed with homeowner products. However, serious diseases (Oak Wilt, Dutch Elm Disease, EAB) require professional diagnosis and treatment. Misidentifying a disease and applying the wrong treatment can accelerate decline. For any significant health concern, have a Maryland Licensed Tree Expert assess the tree first.

Question 10

How can I improve the health of my trees?

Accepted Answer

The most impactful things you can do: mulch the root zone (3–4 inches deep, keep away from the trunk), avoid compacting soil over roots, water during drought, avoid wounding the trunk with lawn equipment, and prune at the right time of year. Healthy trees are far more resistant to disease and pest problems than stressed trees.

Tree Health & Disease Questions Answered

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