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Elisabeth C. Miller Library

Keyword: Master gardeners

Speakers for a garden club

I would like to find a speaker for our garden club which meets at the Phinney Neighborhood Center in northwest Seattle. We are a small general interest club. Do you have any suggestions for resources for finding people willing to talk to our club, on topics such as winter interest in the garden?

 

Here is a link to the King County Master Gardeners Speakers Bureau, with a list of presentation topics and instructions for requesting a speaker. The Arboretum Foundation may still maintain a list of speakers; you can contact them directly at info@arboretumfoundation.org

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Passionflower winter care

I have a passion flower that I brought in for the winter. It has lost all leaves and has sticky little brown spots on it . How do I get rid of the brown sticky things? And how do I get the leaves to grow back. Would putting under a grow light for the winter help.

 

I read up on Passionflower cultivation and pests in the book Passiflora: Passionflowers of the World by Torsten Ulmer & John M. MacDougal, Timber Press (2004).

Under the section, Overwintering, it says that in winter, passionflowers suffer from lower temperatures, shorter days, and low light, and therefore this season is the most critical period for these plants. Before night temperatures drop below 10 degrees C, the more sensitive container plants, such as Passiflora quadrangularis and P. vitifolia, should be taken indoors. Depending on their resistance to cold, other species will need to be taken to their winter quarters later on; for now, though, these plants should just be cut back and thoroughly scrutinized for pests. Unlike many other decorative plants, passionflowers keep their foliage in winter, with the exception of certain herbaceous species such as P. incarnata, P. lutea, and P. bryonioides. Do you know if your plant is any of those three (so we will know if its loss of leaves is normal and not a sign for alarm)? [This is from p. 49.]

About the brown sticky spots, it is extremely difficult to make a diagnosis or suggest a treatment, sight unseen. If your plant was not supposed to lose its leaves, and the leaf drop is a sign of severe stress, then those spots could be the result of the plant’s health being poor (as in low resistance to disease). The spots could be bacteria, viral, fungal or even from some insect (although I read through the list of these and could not tell what it might be).

Your plant would be a great candidate for the Master Gardeners to whom the public can take their plants for advice and diagnosis of problems. I found a Master Gardeners of Ontario, which you can search for your particular region.

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Rhododendron won’t bloom

This is the second year in a row that my rhododendron Blue Peter has flower buds but they are dry and somewhat dark and have no flowers at all. These buds are easy to deadhead. Can you help me salvage this rhododendron, which is very old, and beautiful when it blooms?

 

In order to get an accurate diagnosis you will need to take a sample of your plant (including both healthy and affected parts if possible) to a Master Gardener clinic. If they do not know what it is, ask them to send the sample to the pathology laboratory in Puyallup. It is best to go through Master Gardeners first so you will not be charged. If you send the sample yourself there will be a fee.

Meanwhile, several sources mention frost, drought, and “bud-blast” (unlikely in the Pacific Northwest) as potential causes of bud failure. Damaged flower buds and poor bud set: It is always most disappointing when fat, healthy looking flower buds either fail to open at all or only open a percentage of their buds, the rest being black and dead. Some rhododendrons regularly abort some or even all of their buds for no apparent reason. This may be due in some cases to a deficiency, perhaps magnesium, or to drought reports from various places give mixed results from applying magnesium (usually as Epsom salts)… By far the most usual cause of bud damage is frost. Flower buds are invariably less hardy than the rest of the plant so a really hard winter is sure to cause losses to flower buds. Early autumn frosts can damage buds that are not fully hardened off. This is a very annoying type of damage that may be overlooked and may not be noticed until the buds attempt to open in spring. Rhododendrons vary greatly in their ability to harden up enough to withstand early frost. In areas very prone to spring frosts, it is better to avoid growing plants that always burst into growth at the first sign of spring. Plants that frequently loose their first growth flush (and sometimes even their second) are liable to become stunted and rarely flower.

Source: The Cultivation of Rhododendrons, by P. Cox, 1993, p. 244.

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leaf drop in Dogwoods

I have a couple of dogwood trees, both are about 40 years old. In the front yard is a pink dogwood approx 25 ft tall and in the backyard a white one, approx 50 ft tall. Each year in the spring for the past few years the leaves have been browning and falling off the white one. Now the pink one is beginning to develop the same symptoms. Is there anything I can do?

There are several possible causes of leaf drop in Dogwoods. Below, please find referral information for the Master Gardeners and two websites that contain information about pests and diseases of Dogwoods and methods used to control them.

To know for sure what is causing leaf drop in your trees, you may wish to consider bringing a bagged sample of the leaves to the Master Gardeners Diagnostic Clinic here at the Center for Urban Horticulture or another of the many Clinic locations. You can locate a Master Gardener Clinic within King County on this website (Plant Clinic Schedule).

You mentioned that the leaves of your trees turn brown and then drop. These symptoms are commonly found when Dogwoods have been attacked by Anthracnose.
The Washington State University Cooperative Extension’s “Dogwood Anthracnose” page may be of use in helping you determine whether your trees have this disease.

Hopefully, this information will get you started. If you would like more information or have any other questions, please be sure and let us know.

I hope that your trees recover!

diseases that affect rhododendrons

My rhododendrons have a problem. What appears to be a white powder covers the buds and spreads up the leaves. What is it, and what can I do to stop it?

I cannot be absolutely certain without seeing the plants, but it sounds as if your rhododendrons could have powdery mildew.

Here is an article from the Washington State University Cooperative Extension which describes this disease. One preventive measure you should certainly take is to clean up all the fallen leaves and twigs under your rhododendrons, because the fungus which causes powdery mildew can overwinter there.

You could bring in a sample to a Master Gardener Clinic, and ask if they can diagnose the disease as well (they are at the Center for Urban Horticulture and other locations–see their website.

Douglas fir insect pests

I have some large second growth Douglas firs in my yard that were topped about 20 years ago. The last several years, almost all of them have developed pitch oozing down their sides from up high. What might be wrong with my trees, and what do you think I should do now?

Disease and pest diagnosis is impossible without actually examining the affected plant. However, based on the symptom of oozing pitch you described, these Pseudotsuga menziesii (Douglas fir) could be suffering from one (or more) of the following pests:

Fir Beetle

Pitch Moth

Twig Weevil

For a proper diagnosis you could hire an arborist. The Pacific Northwest Chapter of the International Society for Arboriculture has a directory of certified arborists.

You could also take many photos and a plant sample to a Master Gardener clinic. This is a free service run by volunteers trained by WSU faculty. Clinic locations and times can be found at this website (Plant Clinic Schedule).

common maple problems

I have an uncommon maple (Acer ukuruduense) that I planted two years ago, and which one year ago started sending out long stems from the base, so that now it has a vase shape. One month ago the main (original) stem turned black almost to the ground (the bottom two feet or so are still green), and all its leaves turned brown and fell off. Some of the buds still seem viable, but it seems to be dying at the tips. The rest of the plant is so far showing no signs of trouble. I have not been able to figure out what is going on.

Questions:

1. What is causing this?

2. What, if anything, did I do wrong, and what can I do differently?

3. Might this problem spread to other trees: I have several other small maples in the vicinity.

Other information: The tree is so far just surrounded by bare dirt. This year I watered it frequently with a soaker hose throughout the summer, but last year I was not watering it regularly. It is in full sun, which it is supposed to like.

 

 

 

pine needles turning yellow and dropping

Recently we noticed that one of our evergreen trees has a lot of needles that are turning yellowish brown and dropping off. I would say about 25% of the needles are affected, some in the middle of the branches, some at the ends. The needles are about 3 1/2 inches long and are in bunches of five – I think it is a pine.

Is this normal for that type of tree? Or is it more likely the tree is stressed for some reason and we need to deal with it?

This will be a lengthy answer and I will assume you live in the Pacific Northwest—the following information will not apply to other areas.

In order to get an accurate diagnosis you will need to take a sample of your plant (including both healthy and affected parts if possible) to a Master Gardener clinic.

Meanwhile, to learn about diseases common to pines in the Pacific Northwest, go to the Pacific Northwest Plant Disease Management Handbook and search using the term pine. There are several possibilities with good photos. Remedies are included with each disease.

Insect information is more difficult to get, so following are the most likely-sounding pests:

1. Pine (Pinus) – Black pineleaf scale (Nuculaspis californica)

Pest description and crop damage
Mature scales are almost circular, 1/16 inch in diameter, and yellowish brown to black. Young hatch in spring and
summer. Scale feeding is restricted to the needles and results in their becoming splotched with yellow patches. Heavy infestations cause premature needle drop and may result in death of the tree. Affected trees often display a thin crown, yellow or reddish coloration, and a shortening of the needles. This insect attacks various species of pine, ponderosa most commonly, as well as Douglas-fir and hemlock.

Biology and life history
This scale overwinters as an immature. The crawlers start to disperse to fresh foliage in spring. There may be one to three generations per year.

Management-cultural control

Trees under stress tend to be particularly susceptible to attack, as are trees growing in dusty conditions. Avoid creating these types of conditions.

Management-chemical control (home)

Dormant season:

Apply with enough water to cover the entire tree thoroughly.

1. horticultural oil. Apply during delayed-dormant period.

Growing season:

insecticidal soap

2. Pine (Pinus) – Eriophyid mites (Trisetacus spp.)

Pest description and crop damage
Eriophyid mites are tiny, wormlike, whitish or tan mites which feed under bud scales or in the needle sheaths, often
between the needle bases. Symptoms of eriophyid mite infestations include yellowing, distortion, and stunting of new needles, and development of numerous buds where a bud has been infested (rosetting). Severe infestations
may kill needles and cause needle drop, leaving naked branch tips. Rosettes may develop into witches’ broom growths. Two-needle pines, particularly lodgepole or shore pine, are affected.

Management-cultural control

Prune out heavily infested growths.

3. Pine (Pinus) – European pine shoot moth (Rhyacionia buoliana)

Pest description and crop damage
Adult moths are reddish-orange with silver markings on the wings. The mature larvae are about 5/8 inch long and
reddish-brown with black heads. The larvae of the European pine shoot moth feed on tips of branches, boring first into needles or bud bases, then into the shoots. Infested tips are covered with pitch-covered webbing, often develop a characteristic “shepherd’s crook” shape, and may die back. Infested needles are yellowed near the twig tips and eventually turn brown and die. All pines are susceptible, especially two- and three-needle species.

Biology and life history
The insect overwinters as larvae in the mined buds, covered with resin-coated webs. The adult moth lays eggs on new shoots near leaf bases in the late spring. The larvae hatch and bore into the needles, which turn brown by summer. By midsummer, they are mining in the buds and cease feeding by August. There is one generation per year.

Sampling and thresholds: Check for yellowed leaves at shoot tips in midsummer.

Management-cultural control

Prune and destroy infested tips in spring, before adults emerge. Be sure to prune far enough down the branch to remove the insects.

Management-chemical control (home)

1. azadirachtin (neem extract)

pests affecting currant trees

We moved into a new house which has a large currant or gooseberry bush. Now that it has leafed out there are numerous caterpillars eating the leaves. I know they are not tent caterpillars, but I cannot identify them. They are whitish-green with yellow bands across the top and bottom, with many black dots or bumps. The head and first six legs are black. It would be nice to learn more about them.

 

I cannot make a conclusive pest identification remotely, but there is a possibility these caterpillars are currant sawfly, or imported currantworm. Here is some information about this pest from the Pacific Northwest Pest Management Handbooks.

If this pest is the culprit, the book, The Organic Gardener’s Handbook of Natural Insect and Disease Control edited by Barbara Ellis (Rodale Press, 1996) recommends using Pyrethrin spray, spraying into the center of the bush. Bees are severely affected by this pesticide, so follow the guidelines shown on this University of California, Davis Integrated Pest Management page. Also see this guide to reducing bee poisoning from pesticides.

For a definitive pest identification, you may want to bring a sample of the pest and its damage to a Master Gardener Clinic.
Using the following link, you can locate a Master Gardener Clinic in your part of Washington State.