I have about 20 arborvitae trees along my driveway and all are browning. I'm a new homeowner and do not know the trees' history. What sort of issue do the below pictures exhibit? Thanks.

I am in Long Island, NY. I am pretty sure the browning was already present when I moved in in March.

Browning arborvitae 1 Browning arborvitae 2

Update: 1.5 months after applying two rounds of Bayer mite treatment, here is the same set of trees:

Greening arborvitae 1 Greening arborvitae 2

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    I am in Long Island, NY. I am pretty sure the browning was already present when I moved in in March. We've had sufficient rain this month, though I don't think our sprinklers include this strip of trees. – Ken Feyl Jun 4 '17 at 3:38
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    You say winter burn -- can you rule out spider mites? – Ken Feyl Jun 4 '17 at 5:43
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    OK, I did the white paper test and, while I'm no expert, it does appear to be spider mites. I see the telltale tiny dots on the white paper, and I see webbing in the branches. Should I try to treat with Bayer? Do the trees look recoverable or are they already in a death spiral and will have to be replanted anyway? Thanks. – Ken Feyl Jun 6 '17 at 1:03

Arborvitie (Eastern White Cedar) when used in the landscape have a few problems:

  1. Low salt tolerance. Road salt is particularly obnoxious.
  2. Winter sunburn. In spring they are getting a double dose of sunlight from direct sun, and reflection off the snow. This dehydrates the needles. But the roots are still frozen, so they can't replace the water. This is made worse if they are immediately south of a house or solid fence, as this creates a warm pocket, and adds another source of reflected sunlight.
  3. Insect pests. In addition to spidermite, there is at least one scale insect that troubles them. If you feed your resident bird population in winter, they will help with this. We feed year round, and as a result have about a metric tonne of chickadees that spend their summers gleaning spydermites, and aphids off our trees.

The needles don't live forever, so brown needles and twigs in the interior of the tree are common. Trimming off the occasional external ones comes with ownership.


Another alternative approach can be to use predatory mites.

This is an excellent article about spider mites and methods of control including predatory mites.

Spider Mites: A Beginner Guide to Understanding and Controlling Mites

Thankfully, spider mites have many natural enemies that help reduce infestations and limit population overgrowth. Some of these natural predators include:

Phytoline P (Phytoseiulus Persimilis)
Amblyline cu CRS (Predatory Mite)
Anderline aa (Predatory Mite)
Exhibitline sf ( Predatory Thrips)

In many cases, the predators take care of entire infestations without the need for human intervention. Due to chemical spraying and the loss of beneficial insects, spider mites may have less predators to worry about in the area. However, the mites may also run rampant in greenhouses and interiorscapes where workers prefer not to use chemical pesticides. These areas have less natural predators, providing a safer breeding ground for mites to grow in numbers.

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