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Plant Answer Line Question

Keywords: Insect pests--Identification, Pseudotsuga menziesii, Master gardeners

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).

Date 2019-10-10
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Plant Answer Line Question

Keywords: Whiteflies, Insect pests--Identification, Insect pests--Control, Root weevils, Rhododendrons--Diseases and pests, Dahlia

I have a line of Ward's ruby azaleas. The three weakest ones have a lot of tiny notches in the leaves. I seem to remember the notches from the root weevil as being larger than these. Are the tiny notches from something else?

I also noticed that some of my dahlias have splotched leaves and that when I disturb the leaves, white-looking insects fly off the leaves. These flies apparently have spread to tomatoes as well. Are these whitefly? Will they disappear after the winter or is there some control I should use to prevent them from taking over?


First you need to get an accurate diagnosis of your problems. If you are in King County, you can bring samples to a Master Gardener Clinic. For information about Clinic hours see their website (Plant Clinic Schedule).

Oregon State University offers this information about root weevils and Rhododendron (which includes Azaleas). It describes using beneficial nematodes as a control.

According to Washington State University Cooperative Extension's publication, How to Identify Rhododendron and Azalea Problems (1984), root weevil damage to foliage is not usually a serious problem. You can check for weevils with a flashlight at night to confirm that they are the source of the notches you are seeing. There are some Neem oil-based products that may be helpful, but they must be used at the correct times of year. See WSU's HortSense page.

As for the dahlias and tomatoes, it is important to determine exactly what the insects are before proceeding with treatment. If they are whiteflies, you can put yellow sticky traps around the plants to trap them. University of California, Davis's Integrated Pest Management site has other recommended control methods, including reflective mulch. You may not want to use insecticidal soap:
"Insecticides have only a limited effect on whiteflies. Most kill only those whiteflies that come in direct contact with them. For particularly troublesome situations, try insecticidal soap or an insecticidal oil such as neem oil or narrow-range oil. Because these products only kill whitefly nymphs that are directly sprayed, plants must be thoroughly covered with the spray solution. Be sure to cover undersides of all infested leaves; usually these are the lowest leaves and the most difficult to reach. Use soaps when plants are not drought-stressed and when temperatures are under 80 degrees F to prevent possible damage to plants. Avoid using other pesticides to control whiteflies; not only do most of them kill natural enemies, whiteflies quickly build up resistance to them, and most are not very effective in garden situations."

Date 2019-10-10
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Plant Answer Line Question

Keywords: Crassula, Insect pests--Identification, Insect pests--Control, House plants

My 100-year-old Jade plant is about 5 feet tall and recently has been producing a sap from its leaves. White and sticky. Is there anything I can do to help this? Is it normal? Or is it endangering the plant? It is in kind of a cool spot; should I move it to a warmer place? It is a succulent, right? I would also like some information about repotting if necessary.


The pests most likely to cause a white, sticky substance are aphids, whiteflies, scale or mealybugs. These are known to affect jade plant, or Crassula ovata, which is indeed a succulent. They won't destroy plants, but can weaken them and allow other problems to surface. If none of the pest descriptions below resemble what you are observing, you can take affected plant samples to a local county extension agent. Without knowing the specific pest, we can't suggest specific treatments. Northwest Center for Alternatives to Pesticides has general information on caring for houseplants. Note their description of mealybugs, which do produce a sticky substance:
"These insects look like little bits of cotton that are greasy or waxy. They are oval in shape, have a segmented body, and are about 1/4 inch long. You'll usually find them hidden between leaves and stems or under leaves. They move slowly. They make a sticky liquid called honeydew and also cause leaves to become distorted and spotted."

As for temperature and repotting, The New House Plant Expert (by D. Hessayon, 1991, p. 212), says that succulents like a difference between day and nighttime temperatures. They like to be kept cool in the winter, with 50-55 degrees F ideal, but as low as 40 is alright. Jade plants should only be repotted when essential. Repotting should occur in the spring; shallow pots rather than deep ones are preferable.

Extensive care information can be found on Succulent-plant.com. There is also excellent general information on indoor care of succulents and cacti from Brooklyn Botanic Garden.

Date 2019-05-10
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Plant Answer Line Question

Keywords: Rosa, Insect pests--Identification, Fungal diseases of plants

I have several roses that bloom just fine but one particular rose bush produces buds that never open. Why is this happening?


It is possible that your rose has a problem with insects like thrips, which can cause buds not to open. If you see tunneling in the buds (holes in the petals), it could be caused by beetles. There is also a possibility that a disease is causing the problem. Fungal infections like botrytis blight can result in buds which do not open, but you would probably notice signs of the fungus during warmer temperatures, such as gray-brown fuzzy growth, and blotched petals or drooping buds. The Northwest Center for Alternatives to Pesticides provides information describing various rose problems, and organic solutions.

Here is a description of botrytis blight from University of California, Davis Integrated Pest Management. This is a brief excerpt:
"Botrytis blight, caused by the fungus Botrytis cinerea, is favored by high humidity. Affected plants have spotted flower petals and buds that fail to open, often with woolly gray fungal spores on decaying tissue. Twigs die back and large, diffuse, target-like splotches form on canes. Reduce humidity around plants by modifying irrigation, pruning, and reducing ground cover. Remove and dispose of fallen leaves and petals. Prune out infested canes, buds, and flowers. Botrytis blight is usually a problem only during spring and fall in most of California and during summer along coastal areas when the climate is cool and foggy."

The Olympia Rose Society also has information on these potential causes of failed buds. Below is their description of thrips:
"Buds do not open, or flowers are deformed. Petals have brownish yellow streaks and small dark spots or bumps. White and pastel roses are particularly susceptible. Thrips (are) tiny orange insects with elongated bodies. Thrips feed at the bases of rosebuds and on the petals of open flowers. They seem to be attracted to light-colored blossoms."

The Organic Gardener's Handbook of Natural Insect and Disease Control edited by Barbara Ellis (Rodale Press, 1996) suggests encouraging natural predators of thrips and, if the infestation is severe, spraying weekly with a safer insectidical soap or pyrethrin-based product. This same resource suggests that if your roses have botrytis blight, you will see the buds turn brown and decay instead of opening, and you should pick off and dispose of any diseased buds. They recommend spraying with sulfur once a week during the growing season.

A few things that are always a good idea when growing rose:

  • make sure there is good air circulation around your plants
  • don't water from above the plants (keep the leaves dry)
  • always clean up around the plants--don't let leaf debris or any diseased buds lie on the ground under the rose bushes

This site has many pictures of rose pests and diseases for you to compare with what you are seeing on your plant. Since I cannot diagnose the problem without seeing the plant, I recommend that you take samples of the affected buds to a Master Gardener Clinic.

Date 2019-12-27
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Garden Tip

Keywords: Insect pests--Identification, Plant diseases--Diagnosis, Plant diseases

National Gardening Association's Pest Control Library is a pictorial guide to diagnosing pests and diseases. Every article has a color picture to help confirm if the pest in question looks like the bug eating your plant. Major plant diseases are also included and organized by the part of the plant it infects: leaf, fruit, roots or all parts.

Date: 2007-07-13
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