What to Watch For & How We Can Help
As spring rolls into early summer here in Southern Wisconsin, your trees are waking up—but so are the pests. Some issues are easy to overlook until they’ve already caused damage. Others can move fast, and if not caught early, lead to lasting harm or even tree loss.
At Tim Andrews Horticulturist LLC, we’re already seeing signs of three familiar threats: maple petiole borer, oak wilt, and emerald ash borer. Here’s what to know, what to look for, and how we can help protect your trees and your landscape investment.
🍁 Maple Petiole Borer – Harmless but Startling
If your sugar or red maples are suddenly dropping green leaves by the handful—don’t panic. You might be seeing the work of the maple petiole borer, a tiny sawfly larva that tunnels into the leaf stem (called the petiole). As it feeds, it weakens the stem, and eventually the leaves drop to the ground with a small stub still attached.
While dramatic, this usually doesn’t harm the tree. According to UW–Madison Extension, chemical controls aren’t recommended, and the best management is simply raking and disposing of the fallen leaves to break the insect’s life cycle.
Good news? It’s mostly cosmetic.
What to do? Clean up, keep an eye out next year, and let us know if it becomes a recurring problem.
🌳 Oak Wilt – A Real Threat to Your Oaks
Unlike the petiole borer, oak wilt is a serious and fast-moving fungal disease. It spreads through root grafts and beetles attracted to fresh pruning cuts. Once infected, red oaks in particular can die within a single season.
The most important defense? Timing.
UW–Extension and the DNR both recommend avoiding any pruning of oak trees from April through November to minimize the risk of infection.
At Tim Andrews Horticulturist LLC, we strictly follow these seasonal guidelines—but we also offer oak wilt treatments designed to help oaks resist infection before it starts. We use preventive fungicide injections, carefully timed and applied to give the tree systemic protection. These treatments are most effective when done proactively—before symptoms appear, especially in areas known to have oak wilt nearby.
In cases where trees are already infected, we can help assess the situation and determine whether removal, trenching to sever root grafts, or other measures are appropriate to help contain the disease and protect nearby oaks.
In short:
- Don’t prune in spring/summer/fall
- Call us if you suspect oak wilt
- Ask about injection treatments if you have valuable red or white oaks you want to protect
🌲 Emerald Ash Borer – Still Active, Still Dangerous
You’ve likely heard of emerald ash borer (EAB)—but if your ash trees haven’t been treated yet, they’re still at risk. EAB is now confirmed in all 72 counties in Wisconsin, and untreated trees typically die within 2–4 years of infestation.
The beetles lay eggs on the bark, and the larvae burrow inside, disrupting the tree’s ability to move water and nutrients.
What to watch for:
- Canopy thinning (especially from the top down)
- Bark cracks, epicormic sprouts
- D-shaped exit holes
- Heavy woodpecker activity
We offer targeted injection treatments, and for high-value trees, the sooner we start, the better the outcome. As the UW–Madison Extension notes, treatments are most effective before symptoms appear.
Let Us Help You Care for Your Green World 🌿
Every tree has a story—and every landscape has its own pressures and patterns. At Tim Andrews Horticulturist LLC, we bring decades of experience, science-backed solutions, and deep local knowledge to help you care for your green world.
Whether it’s a one-time inspection or ongoing health monitoring, we’re here to help you make informed choices, protect your investment, and keep your trees thriving for the long haul.
Our certified arborists and horticulturists offer:
- Tree risk assessments
- Insect & disease diagnosis
- Injection & drench treatments
- Pruning timed for plant health
- Long-term landscape care strategies
Need help identifying a pest or planning treatment?
Reach out today to schedule a consultation.