green thuja - Knowledgebase Question

Parsons, Ka
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Question by jgbow4751
October 15, 2010
I have 3 green thuja about 5 ft tall and all 3 are now (after 2 years) turning brown on the interior along the main trunk. I thought these were disease resistant. What should I do? Thx

Answer from NGA
October 15, 2010
Thuja are disease resistant but not necessarily insect resistant. A population of spidermites feeding on the foliage can turn the inner foliage brown. Look carefully for webbing on the foliage or for tiny spider mite insects. These pests love dusty, dry locations and the inner areas of arborvitates are their favorite places. Even if you don't find spidermites you might want to regularly hose off the interiors of your evergreen shrubs during the summer months. A strong stream of water will dislodge any spidermites and discourage them from taking up residence.

If you do not find spidermites in your thuja's foliage, the browning may simply be the natural shedding of the oldest foliage. All evergreens retain their foliage for 2-3 years but then the foliage dies and drops off, leaving bare branches. You can camouflage the bare centers by pruning the tips of the branches of your arborvitaes on an annual basis. A light trimming will encourage a flush of new growth which will make the foliage thick enough to cover over the bare centers of the plants.

Good luck with your landscape.

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