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Plant & Insect Diagnostic Laboratory Frequently Asked Questions

Frequently Asked Questions

Below are some of the most common questions we are asked every year. You may find an answer here. Some of these contain links outside Washington State University, which provide an option for finding further information. No endorsement of products or information at these sites is implied.

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No questions in this category.


Where can I find information about common spiders of Washington?

Hobo Spider

Numerous guidebooks provide general information about spiders. One Washington State University Internet source of information about Pacific Northwest spiders can be found at EB 1548: Spiders (pdf).

We’ve moved into a new house and there seem to be spiders everywhere. What can we do to get rid of them?

According to Rod Crawford, Curator of Arachnids at the UW Burke Museum, most of the spiders you find in your house are not the same species as those found in your yard and garden. These house spiders are adept at living with conditions found in the home, such as poor food and water supply, and most spend their entire life in and around the structure where they were born. Few pose a serious concern to humans. For more information on house spiders, please refer to the “Spider Myth” website associated with the UW Burke Museum.

Mechanical removal (vacuuming spider when observed or catching them on sticky traps) is often an effective management option for reducing spider populations in your home. Repeat as necessary.

To prevent spiders from accidentally entering the home from the outside, seal up the spider entry points of the house (e.g. around doors, windows, and pipes).

If you choose to use a fogger insecticide (commonly called “bug bombs”), follow label directions carefully and make sure that the product is labeled for home use to kill spiders. For information on foggers, read Bug Bombs: Overkill Can Be Dangerous – Pesticide Safety (pdf).

I believe I have identified the spider I caught in my house this week as a hobo spider (Tegenaria agrestis) according the picture I found at EB 1548: Spiders (pdf). Could I send you a picture and have you confirm this identification?

Hobo Spider

In order to positively identify a hobo spider, we need to use a microscope to examine several key diagnostic features. A picture of your spider might help us to provide a tentative identification of the type of spider. See How to identify (or misidentify) the hobo spider (PLS 116) (pdf) for additional information about identifying spiders.

Hobo spider bites have been associated with necrotic wounds in certain people. Thus, care should be taken around these spiders.

I have a spider I would like identified, how should I preserve it before submitting it to the WSU Puyallup Plant and Insect Diagnostic Laboratory?

The best way to preserve spiders is to place them in a vial containing 70% ethanol. Mailing such a sample through the mail, however, is illegal since alcohol is both liquid and flammable so these samples would need to be submitted in person to the clinic. See insect sampling instructions for further sample submission information.

I live in Eastern Washington and have just found a brown recluse spider in my house. What should I do about this spider in my house? I am worried because I have small children that crawl around on the floor.

Research has shown that the western United States has no local populations of the brown recluse spider (Loxosceles reclusa) so the spider you found is probably not a brown recluse. A spider specialist at University of California in Riverside, Rick Vetter, has devoted a lot of effort to dispelling brown recluse myths in the West. For more information on this work, refer to Spiders and other Arachnids at UC Riverside.

We do have other spiders in Washington that can bite. Fortunately, many spiders tend not to thrive in the dry environment of our homes. The most effective prevention technique against spiders is sealing up entry points into the home- alas easier said than done. Vacuuming regularly, especially in cracks and under furniture, will also help to reduce the number of spiders in your home. Some people have had success with glue-impregnated sticky traps placed in area of high spider traffic, but out of the way of children and pets.

I see a lot of spiders in my yard. How do I best eliminate them?

PLEASE DON’T!!! Spiders—due to their predacious nature—are beneficial, trapping and eating flies and other insects. Conserve your local spiders.

I found a shiny black spider near my home in Washington with what appears to be red “hourglass” marking. Could it be a black widow spider?

Black Widow spider

Yes, black widow spider populations are found in Washington with most found in Eastern Washington. However, there are several local populations in Western Washington, for example, on several of the San Juan Islands.

Many of “black widow-like spiders” we see are other members of the “comb-footed” spider family (Theridiidae) and are considered harmless.

I live in Texas and I found several large spiders floating in my swimming pool. Why can’t I submit these spiders to your laboratory?

The Puyallup Plant and Insect Diagnostic Laboratory is only equipped to handle the identification of certain spiders in the Pacific Northwest. We have no one on staff specializing in the identification of spiders. You would be better served by contacting your local Cooperative Extension program.

My neighbor just told me that the deadliest spider in the world has recently been introduced to our county and can be brought into home when you buy bananas. Evidently people are bit on the fingers as they peel the banana and expose the spider and their finger rot off. The story sounds fairly far-fetched to me and I wonder if there is a place I could go to find the truth about spider stories like this.

Rod Crawford, Curator of Arachnids at the UW Burke Museum has a wonderful website “Spider Myths”, which explains the truth behind many of the myths and misconceptions surrounding spiders. This website is also full of spider-friendly comments and advice.

Plant Identification

You were unable to identify the leaf I submitted for identification. Why?

Unknown leaf

The sample probably did not consist of sufficient material for identification. Samples should consist of representative parts of the plant (roots, stems, leaves, and flowers) as well as complete background information about where and how the plant grows.

Floral morphology is the feature on which plant taxonomy and thus identification is based—without flowers we are often unable to identify the plant.

How can I find out what variety of apple is growing in my backyard?

We are typically unable to aid with identification of fruit varieties (or varieties of other landscape plants). The sheer number of varieties grown for plants such as apples, cherries, and rhododendrons can be staggering.

Are these mushrooms edible?

Unknown mushroom

We have no trained mycologist on staff at the WSU Puyallup Plant and Insect Diagnostic Laboratory so we are unable to identify mushrooms to species. Nor, can we comment on the edibility of mushroom species as an individual’s response to a mushroom can vary and confusion of edible mushrooms with toxic mushrooms could occur on a later picking.

Plant Problems

Where can I go to learn more about Phytophthora ramorum, the cause of Sudden Oak Death?

These links will help you learn more about the pathogen Phytophthora ramorum, commonly referred to as Sudden Oak Death.

I have a rhododendron that is wilting and dying back. What is wrong with this plant?

Bare rhododendron

Plant problems can have many causes. For example, wilting can be caused by not enough water or by too much water. Many other factors, such as environment, cultural care, and the presence of insects or disease, can affect the health of a plant.

You will need to provide adequate sample material and an extensive description of the problem in order to achieve an accurate diagnosis. See plant problems sampling instructions for information on how to submit a sample to the laboratory.

I have a lot of problems with my flowering cherry tree in my yard in Western Washington. Every winter the blossoms die after budding out and in the summer many of the branches are dead with brown leaves clinging to the plant. What is happening to the tree?

Cherry tree with symptoms of Brown Rot

The damage described sounds typical of the disease brown rot caused by the fungal pathogen Monilinia. If the problem is indeed brown rot, refer to the Hortsense site and select Ornamentals ▸ Ornamental Trees ▸ Ornamental Cherry ▸ Brown rot. You can find more information on this disease as well as management recommendations. You will want to prune the tree both to remove dead branches and twigs (also the fungal inoculum that may be present in the lesions), and to increase air circulation and lower humidity in the canopy. Prune out all affected twigs several inches below the area of injury.

Sterilize your pruning tools between cuts using 10% bleach or 70% ethyl alcohol (less corrosive to tools than bleach) to avoid spreading the problem. If possible, avoid getting the leaves wet when watering the trees. Follow label directions carefully if using fungicides making sure that the product is labeled for ornamentals in the home landscape.

Every fall, the leaves on my large Western red cedar (Thuja plicata) in my yard start turning brown and I worry that I am about to loose it. But then in spring the tree looks very healthy, what is happening?

The red “flagging” branches observed on the healthy cedars in fall is normal leaf senescence. For information on what cedar flagging looks like refer to the Hortsense site and and select Ornamentals ▸ Conifers ▸ Cedar ▸ Cedar flagging.

I planted an arborvitae hedge on my property line six years ago. The plants never really thrived and now it seems as if entire plants are dead. What could be wrong?

Failure to thrive and plant death often indicates root problems. Most arborvitae hedge problems submitted to the Puyallup Plant and Insect Diagnostic Laboratory appear to have a nonliving origin of damage (such as overwatering, poor planting technique, etc.) rather than having been caused by a disease or insect problem. Arborvitaes require excellent soil drainage and good air circulation around the plants. We would require more information, as well as a sample of a declining plant including root material, to help pinpoint the cause of your arborvitae hedge problem. British Columbia has an excellent bulletin discussing problems with “cedar” hedges. You can find this bulletin at Dying Cedar Hedges– What Is The Cause?

We recently had a large elm tree diagnosed with Dutch elm disease. We are unable to burn the tree. How can be best dispose of the plant to prevent the disease from spreading to other elms?

Cut section of hollow trunk

Chipping wood into small pieces (< 1½ inches) that will quickly dry out would probably be a suitable alternative to burning. The fungal pathogen (Ophiostoma ulmi) should die as the wood dries.

The main trunk wood should be debarked to prevent the invasion of bark beetles (carriers of the Dutch elm disease fungus). Beetles do not feed or lay eggs in or on wood chips, or other wood, once the bark is removed.

You could probably also contact your city or county and get a special burning permit since you are working to stop the spread of the disease.


I am considering putting a new lawn in front of my house and would like recommendations. I also am interested in finding out how to care for an established lawn.

WSU has a bulletin EB0482 “Home Lawns” (pdf) covering establishment and maintenance of lawns in Washington. You can order a printed copy of the publication from the WSU Bulletins Office.

My newly sodded lawn looked beautiful in the beginning of summer but now dead spots are developing throughout the yard. What am I to do?

Pile of sod

First, how much are you watering your lawn? The Diagnostic Laboratory frequently receives turf samples that have been overwatered. For example, people with a new automatic irrigation system might set it to run daily for 10 to 15 minutes. Not only does this schedule contribute to high water bills, but it probably provides more water than the lawn needs.

The shallow daily watering regime fails to promote development of the roots deep into the underlying soil. In addition, frequent irrigations keep the leaf blades and thatch layer damp, which can promote development of disease problems.

We would require a sample and detailed information on the lawn care to further identify the problem. See lawn sampling instructions for further directions on sampling for lawn problem diagnosis.

Moss is growing all over my lawn. What moss killer can I use to kill it?

Moss in turfgrass

Moss killers (you can find them at your local hardware, home & garden store, or nursery) can only temporarily get rid of the moss problem. In order to achieve management of the moss problem, you need to address the underlying reasons as to why the turf is not thriving and the moss becomes established (shade, wet conditions…etc.).

Visit the Hortsense site and select Lawn and Turf ▸ Moss, or you can check out the Oregon State University website on Controlling Moss in Lawns for more information.

We have this unwelcome grass in our yard. The grass seems to die out every summer but then grows again in fall. The grass creeps along and often forms tufts at the top of the plant- it can be very difficult to mow. It feels like you are walking on a padded surface, unlike regular grass. What is it and how can we manage it?


Without a sample of the grass in question, we are unable to confirm the identity of your problem grass. Your description of walking across the grass suggests one of our native bentgrasses that often grow some distance horizontally before putting out green blades.

Unfortunately there are no “magic bullets” herbicides available for removing one unwanted grass species from the desired types without hurting the wanted turf. So typically to get rid of a weedy grass, we recommend carefully spot spraying a broad spectrum herbicide, for example glyphosate sold under names such as Roundup, on the grasses in the weedy areas.

Follow label directions carefully if herbicides are used. After killing the grasses in this area, you may need to reseed with a desired turf mix to fill in the open spots.

A weedy grass out competing the desired grass species is often an indication of turf management problems. Examples of management problems include growing sunloving species in the shade, over or underwatering, and mowing at the wrong height. For turf management information, see EB0482: Home Lawns (pdf).

I need information on craneflies in lawns.


Whatcom County Extension has developed an informative website covering craneflies and their management in the Pacific Northwest—Cranefly Pest of the Pacific Northwest.

As you will read, if you are concerned about cranefly injury to your lawn, you should be monitoring cranefly population within the turf and watching for damage. Additional management recommendations can be found at the Hortsense site by selecting Lawn and Turf ▸ European Cranefly.

Moles seem to be taking over my lawn. What can I do about them?


Haven’t you always wanted a “pet” mole? Mole management can be very difficult. Most of the “home remedies”, such as juicy fruit gum, mothballs, sonic noisemakers, will not help to remedy the situation. Scissor traps, one of the most effective management strategies against moles, are not currently legal to use in Washington State. For more information on management of moles, refer to these websites: Moles (pdf).

After fertilizing our lawn this spring, we noticed that the flowering plum growing in the middle of the lawn developed abnormal looking leaves and twisty branch ends. What is going on?

The plum may have been damaged by application of a growth regulator herbicide. Are you using a lawn fertilizer product that also contains herbicide for weed control (e.g. Weed n Feed)? These mixture products typically contain a hormone mimic herbicide, such as 2,4-D or dicamba. These growth regulator herbicides target broad leaved plants (such as dandelions) but can cause damage to other broadleaf trees and shrubs growing in, or alongside, the lawn. Injury occurs either from drift of the herbicide in the mixture, or from absorption of the herbicide by the tree or shrub roots that are growing beneath the lawn.

Avoid using such herbicides near this tree. Remember that the rooting zone of trees and shrubs typically extends beyond the drip zone of the canopy—the diameter of the root system is typically about 1.5× the height of the plant. Once the herbicide is out of the environment, the tree should grow normally.

Other Testing

I see that the WSU Puyallup Plant Clinic does not provide soil testing. Where I can I send my soil for such testing?

Lists of analytical laboratories serving the Pacific Northwest can be found at two websites:

Be sure to call several companies for information on services and fees (as these can vary widely) before deciding on a laboratory to use.

Remember that the results of a soil test are only as valid as the quality of the sample submitted.

For interpretation of results, Oregon State University provides a Soil Test Interpretation Guide (pdf).

I need to have my horse’s hay analyzed for nutrient content, where can I find information on laboratories providing this type of testing?

Animal nutrition analysis is provided by many of the companies listed in EB1578e: Analytical Laboratories and Consultants Serving Agriculture in the Pacific Northwest (pdf).

I am thinking about starting a nursery operation specializing in growing maples and would like to have the soil tested for the presence of the Verticillium wilt pathogen. Does your laboratory provide this testing?

At this time, we are not equipped to handle soil testing for the pathogen Verticillium. The Plant Clinic at Oregon State University runs such tests. You will want to contact them for additional information.

I recently observed my neighbor spraying several plants in my yard with an unknown pesticide. The plants rapidly turned black and started dying back. What should I do?

Roses next to white house

The Washington State Department of Agriculture is best equipped to handle pesticide misuse questions and situations. You can contact them at 360-902-2040. Please leave a message and they will respond to your question.