Arborvitae are tough shrubs built to withstand our crazy winters and heavy soils. Every year they will lose about one third of their inner fan-like needles just because it is their cycle of life. The old needles turn brown and drop off and green new ones appear. That is probably what is going on inside your shrub. It can look quite scary and seem like your shrub is in deep trouble. I have to remind myself of this normal cycle every year when our big white pine tree looks all its needles are falling off.

Arborvitae are also prone to winter injury from snow load or ice forming on the fans. Freeze/thaw cycles can be damaging to local areas. Is that brown spot under a dripping eave or roof line? Water dripping and freezing would cause a spot very much like that. Chemical de-icers would also cause localized tissue damage. Could there have been a spill or splash right there?

Bagworms are a problem but not this early in the season. Fungal diseases can also infect arborvitae but again, not usually this early. Insects such as spider mites sometimes invade. I’m going to attach a bunch of links to internet resources for you to read. After doing so (they are all quite short and factual), examine your brown areas closely. Look for the black pimples of fungal disease, broken branches, or old bagworm cases from last year. Compare it to the healthiest of the shrubs to see if anything seems very different.

I think you will find that this is just localized winter damage and/or normal needle drop. If that is the case, trim away that one brown area so that light can penetrate and allow your shrub to heal itself. Watch them closely as the season progresses so that things such as bagworms can be caught and corrected early with the least amount of intervention. It is always better to pick and smash a few bagworms than to spray an infestation. The very best way to know if your landscape plants are healthy is to get to know them. Take your coffee and walk around the property every chance you get just to look at each plant or group of plants. Over a very short time you will begin to notice when things are growing well and when something looks “off.” Over the course of a year, you will know if it is seasonal needle drop or a problem. It is also a wonderful way to start any day.

Here are some links to information you will want:

Thuja / arborvitae | Conifer Genus | American Conifer Society

General information. Be sure to read the Q & A’s at the bottom.

Arborvitae | Ohio Department of Natural Resources (ohiodnr.gov)

Includes information about bagworm.

Bagworms (psu.edu)

General info. Best advice is to pick them off.

Arborvitae Diseases (psu.edu)

Table of problems including fungal diseases. Look for pimple like dark dots. Fungicide should be avoided unless absolutely certain of diagnosis.

Thuja occidentalis 'Danica' - Plant Finder (missouribotanicalgarden.org)

Information on leaf blight, canker, bagworms and more.

Pestalotiopsis Tip Blight on Arborvitae (missouribotanicalgarden.org)

Tip blight is also a fungal disease and the tiny, black, pimple like fruiting bodies should be present.

Protecting trees and shrubs in winter | UMN Extension

Yew, arborvitae, and hemlock are most susceptible, but winter browning can affect all evergreens.