Watch arborvitae for worsening symptoms
Many tough, reliable arborvitaes are exhibiting what appear to be an unusually high number of drought- and winter-related injuries.
Experienced gardeners may still be closely checking the beleaguered evergreens, however, to see if the symptoms get worse. Environmental stresses can set the stage for fungal diseases with similar symptoms, said Judy O'Mara, plant disease diagnostician with K-State Research and Extension.
At this time of year, for example, a disease that can cause further declines in stressed evergreens is Seiridium canker, O'Mara said. In Kansas, it sometimes affects injured baldcypress trees, as well, but arborvitae tends to be the primary host. Oklahoma State University has found it in Leyland cypresses and eastern redcedars (a juniper).
Seiridium cankers aren't necessarily easy to see, she warned. So, for most gardeners, the primary symptom for this disease is a scattered branch dieback.
Dieback occurs because a canker is the plant version of an infected sore, O'Mara said. Seiridium cankers are typically long and thin, and they ooze resin. They can form on small branches or main stems. Over time, they elongate and may also develop in multiples, which can coalesce. Then they can interfere with the branch's internal water flow.
Gardeners can't control Sieridium canker with fungicides, she said. So, the measures to help arborvitaes fight the disease become the same ones recommended to keep those plants from becoming infected in the first place:
--Take care when mowing or trimming around woody plants. Wounds can be entry points for pests and diseases.
--Remove and destroy diseased branches, to limit the amount of fungi available to infect healthy tissues.
--Irrigate through dry periods of little to no rain/snow.
"Once you've removed its infected branches, keeping the tree healthy through regular watering can help prevent a reoccurrence of this disease," O'Mara said.