EMERALD ARBORVITAE Thuja occidentalis has dry brown dead tips over most of it's exterior - Knowledgebase Question

Roseville, CA
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Question by jeffhanrahan
August 31, 2006
Purchased Monrovia #7301m EMERALD ARBORVITAE Thuja occidentalis 'Emerald' (T.o. 'Smaragd'). We planted 28 trees as a fence line about one year ago (late September). Was recommended by local nursery to plant after the heat spell we were going through during August 2005. After initial planting and watering, we got lucky and only lost two to yellowing at the tips and looking real sick. Nursery said that was a highly successful number to survive. We were good with that information and thought well on our way to a succesful planting.

A good wet winter in our area and a very pleasant spring. No need for watering over the winter with very steady rains. Plants looked absolutely gorgeous and fully green into early spring. As the thermometer moved upwards in June and July, we noticed the tips turning brown. Not yellow like the first two we lost, but brown and dried out. Brush your hand up it and the dry tips would just fall off. Then we hit our real hot spell of 100+ temps in July for about two weeks and then it came back down into the high 90s for the remainder of July and August. Was back at the nursery and they said make sure you are watering regularly for about 40 minutes on a drip irrigation system twice a week during the hot spell and then tapper it back to once a week once the temps come back down to normal in the 80s- 90s. They do not seem to be getting any worse at this point but the brown tips are completely covering the exterior shell of the trees top to bottom, front and back.

I bought one of those moisture meters which is about a foot long metal spike you stick in the ground to take moisture readings. Has a scale of 1-10. 1 is dry, 10 is wet. After the 40 minute soaking from the drip emitters, an hour later the meter spikes at 10 showing high moisture content. 3 days later before the next cycle for watering, I take a reading and the meter shows a 3 on the scale showing the soil is draining and some mositure retention is there. It's not bone dry. Readings are taken at the root ball and also 1-2 feet from the drip emitters. Pretty solid readings around the entire base of the tree. Trees get almost full sun all day long. Have not applied any fertilizers yet.

Questions here are:
-Am I over/under watering?
-Does going from beautiful lush green, straight to brown with no yellowing before going brown at the tips indicate something else going on?
-WIll sheering away the dead brown tips be advisable?
-And best time to sheer if needed?

Answer from NGA
August 31, 2006
What you report RE: soil moisture sounds like it's right in tune with the needs of your plants. Brown tips are probably showing some root stress, but if it occurred at any other time of the year, I'd chalk it up to a late frost. You might want to inspect the dead areas with a magnifying glass. Look for webbing or spider mites (tiny as a flake of black pepper). Extensive feeding can cause the kind of dieback you describe.

At this point I'd continue with the watering schedule and shear the dead tips from the plants. No new growth will emerge from the dead tips and shearing them off will make the plants look more attractive as well as prompting new growth lower down on each stem. Spring is the ultimate pruning time but you should be able to do it now and the new growth will still have time to harden off before cold weather arrives.

Next spring you can lightly fertilize your plants to encourage healthy new growth.

Best wishes with your landscape!

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