Advice for the Home Gardener from the Help Desk of the UC Master Gardener Program of Contra Costa County
Help Desk: Thank you for contacting the UC Master Gardener Program Help Desk with your concerns about your ailing Italian Cypress trees in Central County.
Italian cypress Cupressus sempervirens thrive in full sun in the dry, Mediterranean-type climate of California, but it does poorly and can become stressed and diseased in a wetter or cooler climate and if it is planted where it gets too much water or in partial shade or if it is exposed to cold winter temperatures. As we discussed on the phone, the very wet winter last year after years of drought may not have helped your trees.
Based on what was recommended to you by a tree service, they may have been attempting to treat for root rot. As its name implies, root rot happens when the tree's roots are too wet for extended periods, causing branches to wilt, turn yellow or brown and eventually die. A fungicide applied to the soil as directed might halt the rot. As discussed, this may or may not help your trees. There is more information on root rots in the included pest link below.
The irrigation requirement for Italian Cypress in at your garden in Central County is ‘Low Water', so your established trees would need no irrigation during the winter months, minimal irrigation in the Spring and Fall (no more than .5 gallons per month per tree) and 2 gallons per month total irrigation per tree in the hottest months of June – August. With this information you can calculate how long to run your drip irrigation depending on the drip emitter output you are using. Be careful not to overwater!
You may also want to do a close examination of your trees to help determine an appropriate course of action. I've attached information below on various pests and diseases of cypress trees: http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/cypress.html
Below are links to UC Pest Note information on several common pests of cypress that you'll want to look for:
Cypress tip miner—Argyresthia cupressella: Browning tips may be caused by cypress tip miners, the larvae of a tiny, silvery tan moth: Argyresthia cupressella. The females lay eggs on the green tips. The eggs hatch into larvae that feed on the twig tips. http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/INVERT/cyptipminer.html
Cypress canker -Seiridium cardinale: This fungus attacks trees in the cypress family by entering through cracks in their bark and producing toxins that wreak havoc with the flow of sap, limiting the supply of water and nutrients. The cracks in the bark could be caused by pruning cuts, boring insects, or weather damage. The spores spread by wind and water splash. Symptoms include dieback beginning from the top of the tree or branches browning and dying throughout the canopy. A branch can change color over a period of days. http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/cyprcanker.html
Spider mites: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html
As we discussed, your trees should be provided with the best possible cultural care: full sunlight, good drainage, moderately fertile soil, and enough moisture to prevent summer drought stress to help them resist pests and diseases. UC does not have any specific recommendations about feeding programs for these trees, so our discussion about improving the soil around the trees with compost may be a better course of action rather than feeding with general fertilizers.
While we are unable to recommend a specific arborist in our area, we can refer you to the International Society of Arboriculture (ISA) ‘Find an Arborist' website. This website has a search feature that allows you to find certified arborists based on where you live. When you call, explain your situation and ask if they specialize in cypress problems. https://www.treesaregood.org/findanarborist
Please call us again if you wish to discuss more specifics.
Good luck with your trees.
Help Desk of the UC Master Gardener Program of Contra Costa County (SLH)
Notes: Contra Costa MG's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: email@example.com, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.edu/HortCoCo/ You can also subscribe to the Biog.