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Plant Answer Line Question

Keywords: Cupressus, Moths, Trees--Diseases and pests

I haven't been able to find much about control of cypress tip moth on true cypress (Cupressus). I'm looking for a non-toxic control instead of the WSU recommendation of Orthene. Would Neem possibly work? Spinosad? Both are registered for leaf miners (fly larvae), but this is a moth larvae. Bt won't work because the larvae are inside of the foliage. What's the best timing for a non-toxic? WSU recommends controlling the adults in July-August.


University of British Columbia Botanical Garden's forum has this to say:

"In the west, cypress tip moth sometimes infests cypress (Cupressus and Cupressocyparis) and false cypress (Chamaecyparis); those are also sometimes called cedars. In the east, cedar often refers to Juniperus (red cedar), Thuja or Chamaecyparis (white cedar); all are subject to bagworm infestations and various tip-miners. In the west, timely shearing is the most effective way to control cypress tip moth, and this may also be a tactic in other parts of North America.

"In many cases, infestations occur because there are few natural enemies about to reduce pest levels. Sometimes, pests are attracted to plants that are already weakened by stress. Healthy plants and diverse plantings, together with a reduction in pesticide use, will over time, increase beneficial organisms which will in turn reduce pest levels. Spraying to reduce pests generally affects beneficials to a greater degree than the actual target pest. This is because pest species often have a greater capacity to rebound -- they often reproduce faster, have a greater tolerance for pesticide residues and have a greater capacity to become resistant to pesticides."

Oregon State University's IPM site only mentions chemical controls.

From an online forum, 'Horticulture Guy:'

Q. I have a row of 16 - three year old "Emerald Green" arborvitaes. I suspect they have arborvitae leafminer (cypress tip moth). I have noticed the moths before, but now there are more and I just recently noticed brownish-yellow tips on a couple of the trees. All of them have lots of needles falling from the interior. My problem is that I have received conflicting reports about the proper time to spray for them, and is there anything I can do in the meantime to lesson the damage? Thank you! Linda Brieger - Tacoma, WA

A. The way to gain control over any pest population is to know its life cycle. Spraying is geared toward eliminating the adult form of the insect, which is a moth as the second of the two common names indicates. The most likely reason you may see conflicting reports on when to spray the moths is because of varying times the moth may emerge in different regions where they are present. They are generally active in our area from April to June with a peak of activity in May. The moths lay their eggs during this period and the eggs hatch and then burrow into the needles of the host plant. According to the WSU extension the adult moths are silver-tan and approximately 1/4" in length. External sprays won't have an effect on the larvae once they burrow so you need to spray weekly during this period to catch the larvae as they hatch. Systemic insecticides are able to kill the larvae once they are in the host. You can limit systemic insecticide spraying to one application near the beginning of the activity since they generally remain effective for some time (see labels for instructions). As far as "in the meantime" a sprayless solution is to prune out and destroy infected parts of the host now so that there are less moths in the spring. You can also keep an eye out in the spring for the white cocoons that form after the larvae exit the host to become adult moths. You can remove these as well.

University of California Integrated Pest Management suggests that proper cultural care and removal of susceptible plants is the answer. Excerpt:

Provide proper cultural care to keep plants vigorous. Prune out and dispose of foliage infested with immature leafminers to restore the plant's aesthetic appearance and provide some control. Consider replacing plants especially susceptible to the cypress tip miner. High populations and damage can be reduced on established plantings by applying a broad-spectrum, persistent insecticide such as acephate on susceptible varieties when adult moths are active. Beginning in early spring, examine foliage tips for the cocoons. When these appear, vigorously shake foliage and watch to see if silvery tan, tiny moths fly up then settle back on the foliage. One application to foliage can be made when a large number of tip moths appear, between March and May in California. This reduces browning next season.

You could try using the Neem oil (instead of the more toxic alternatives) although I did not find any information specifically suggesting this as a control for cypress tip moth. The WSU book, Pacific Northwest Landscape IPM Manual (2002) suggests natural parasites which attack this species of insect, but they do not specify the identity of these predators. They state that there are no "biorational pesticide management options" for this pest.

Date 2019-05-09
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Plant Answer Line Question

Keywords: Cupressus, Tree planting, Transplanting, Soil amendments, Conifers

I am going to take my 6-foot tall Wilma Goldcrest out of the giant pot it is currently in, and plant it in the ground. I am seeking some sort of consensus on how to prepare the hole into which the tree is going. Someone said that I should not put compost in the hole because that will encourage the roots to just stay in the area of the hole. If that's the case, then shouldn't the "no compost" rule apply to all new plantings (which, of course, it does not)? Also, when should I fertilize the tree and what kind of fertilizer should I use? I always use organic fertilizers. What about putting some bone meal in the planting hole to feed new root growth?


I refer you to the following information from Washington State University Extension horticulturist, Professor Linda Chalker-Scott, who discusses planting procedures in her book, The Informed Gardener (University of Washington Press, 2008). She says that the planting hole need only be the depth of the root system, but should be twice the width. She advises against amending the planting hole in any way: Backfill the hole with native soil, not a soil amendment. The idea is not to 'spoil' the plant by putting rich compost just in the hole, which will deter the roots from spreading out into the surrounding area.

Her debunked gardening myths may also be found online. This one addresses soil amendments and planting. She also addresses the use of bone meal as a planting amendment.

'Wilma Goldcrest' is a cultivar of Cupressus macrocarpa, or Monterey cypress. The University of California's Garden Information publication on "Pines and Other Conifers"(including Monterey cypress)says:
"Pines and conifers require less fertilizer than most other trees and shrubs. Heavy fertilizing can promote rank, unsightly growth, destroying their natural, symmetrical, picturesque form." If you do wish to use fertilizer, a dilution of something like seaweed or fish fertilizer would probably not be harmful.

Here is more about fertilizing conifers from University of Minnesota Extension Horticulture.
"Why Fertilize?
The plant itself will often indicate when it needs fertilizer. If growth rate and needle color are normal for a particular variety, fertilization is not necessary. If new growth is sparse or slow, or the needles are not a healthy color, or are shorter than normal, you should probably fertilize. Keep in mind, however, it is not unusual or abnormal for newly transplanted evergreens to exhibit slow growth until they're re-established.
Regular fertilization may be recommended if you are trying to grow evergreens in a less than ideal site, such as very sandy or heavy clay soil, or if the plant has suffered damage from insects or disease. You might also wish to fertilize to encourage more rapid growth in relatively young evergreens."

Local garden writer Ann Lovejoy says the following in her book, The Handbook of Northwest Gardening (Sasquatch Books, 2007): "I rarely feed plants directly, preferring to feed the soil with what are called 'feeding mulches,' made of materials such as compost, seed meals, kelp, and fish meals."

Date 2019-09-11
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