Based on the mind-blowing number of boxwood samples that arrive daily at our Wilmette store and are being seen by our landscape team, there’s a big, post-winter problem. The damage is largely attributable to two things- an insect (Boxwood leafminer) and record-breaking low winter temperatures.

If you’re fortunate enough to spend the winter in southern climes and only heard about Chicago’s record-shattering -20 F. you’re one of the lucky ones. Our Zone 5 hardy landscape plants had to endure Zone 3 winter temperatures. While plants only recognize actual temperature, wind chill factors just this side of -60 F. are devastatingly dehydrating.

Let’s talk first about winter damage, whose symptoms can be easily be confused with Boxwood leafminer. Let me set the stage. The ground is frozen rock solid. The plants may or may not be somewhat buried in snow. This is a good time to point out that snow is wonderful insulation and therefore a plant’s best friend. Many evergreens, boxwood included, in the path of open, unbridled northwest or southwest wind simply lost water faster than root systems could replace it. It’s a case of plant “freeze drying”, if that analogy helps. 

• The plants looked green and healthy last fall and throughout the winter.
• The discoloration symptoms only appeared since March or later.
• The leaves are totally bleached on the newest growth tips (little or no green on the leaves) and stems are brittle and snap, rather than being flexible or having any moisture in them.
• The discoloration often shows first on top or windward sides of the plants, but can completely cover the plant.

• The plants were symptomatic last summer and fall. Leafminer symptoms include: individual orange-brown “blisters” that are visible on upper and lower leaf surfaces, especially on foliage at the branch tips.                                 
• For those with a scientific bent (and a strong stomach undeterred by wriggling larvae) the top layer of leaf can be carefully removed to reveal the feeding larvae.          
• If populations are high enough the blisters can coalesce and consume a large portion of the leaf, very often leaving some aspect of green tissue on individual leaves, but not always. 
• Boxwood leafminer can be controlled with topical sprays or soil drenches.

To add insult to injury (pun honestly not intended) in the Boxwood brouhaha it’s common for some plants to be victims of both. Right now “wait and see” seems to be a smart, measured course of action.