Plant Answer Line questions and answers.
Last year I had a big problem with weevils in my salal, rhododendrons and a few other shrubs. I am not sure if they returned after putting down beneficial nematodes last fall.
Weevils are tough! You are on the right track with beneficial nematodes. It might take a few seasons to make a difference. Here is a link to information by entomologist Art Antonelli of Washington State University about controlling weevils, especially on Rhododendron.
My prune tree has tons of aphids in the leaves (also a lot of ladybugs to eat them but I am not sure the ladybugs will win out). Do I need to try to rid the tree of the aphids? If so how?
The question of whether to control aphids in your prune tree really depends on how bad the infestation is and if the tree is otherwise healthy enough to outgrow them. Often infestations like aphids are a symptom of a larger problem. The tree may be stressed out by root competition from grass or too much or not enough water, too much or not enough nitrogen. A stressed out tree is attractive to aphids, who in turn attract lady bugs.
My own mature prune tree gets covered in aphids every year. The leaves get distorted, and lady bugs come in droves. Some years I get a good harvest and some years I do not. I choose not to worry about it (I have other plants to fuss over). But if you feel the need to do something, see the HortSense website from Washington State University.
I will be transporting plants from Oregon to Washington to sell to the public. Are there any restrictions, such as quarantines, that are important to know about?
You should contact the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS).
The Oregon Department of Agriculture has information on plant exports, quarantines, and permits. There are also Washington State codes about the transportation of plants that can be found in Chapter 17.24 RCW, Insect Pests and Plant Diseases. You can then click on specific sections, such as 17.24.081, Prohibited acts.
Additionally, this site makes reference to the Washington Administrative Code and includes information about standards that apply to plants and pests. See Chapter 16-402 WAC, Plant Pest Infestations and Plant Labeling standards.
You can also click on the embedded links to look at the specific standards.
Are there any tree identification guides online? In particular, I am interested in weeping birch.
For several excellent images of weeping birch (Betula pendula), go to
Oregon State University’s and click on Betula pendula. Look at all the images associated with this species of birch.
Also try Virginia Tech’s tree identification page.
Here are some other online tree identification guides:
What Tree Is It
University of Wisconsin’s Tree i.d.
Cal Poly’s Urban Tree Key
I am wondering about an environmentally sensitive way to get rid of blackberries. I understand that mowing them consistently for 4 years works, but unfortunately this is not an option because of the terrain. If an herbicide is our only option, can you recommend one that has minimal impact?
The area is quite large – a mile long and 20 feet wide.
Invasive.org has produced a document entitled Controlling Himalayan Blackberry in the Pacific Northwest. It includes manual removal, shading, grazing, biological controls, and last-resort herbicide information. (We cannot recommend any specific herbicides, as we are not licensed pesticide handlers.)
The Northwest Coalition for Alternatives to Pesticides has information on nonchemical blackberry control.
For additional information, phone the Master Gardener’s DialExtension (King County) at 206-296-3425 (or 800-325-6165, ext.6-3425) and listen to tape #1274 about removing blackberries. However, the solutions given in this tape may apply to smaller areas, rather than the larger stand you mentioned.
An interesting idea that some people are trying locally is the use of goats.
This article in the Seattle Post-Intelligencer mentions Healing Hooves of Spokane. There is at least one company on Vashon Island which offers this service as well. Another P-I article mentions Rent-a-Ruminant.
This document from Sound Native Plants contains contact information for several such services.
I’d like to hear your thoughts about the safest way to
remove moss from the north side of my roof. I do
organic gardening, and I don’t want to contaminate the
soil with runoff.
The City of Portland had a guide to safe moss removal (formerly available online) indicating that that the most common product sold for moss removal, zinc sulfate, is a pollutant and is toxic to aquatic life. They do say that zinc strips on the roof are an alternative, but they also release zinc, and are pretreated with pesticide.
Toxic-Free Future (formerly Washington Toxics Coalition) offers several recommendations, including physical removal of the moss, landscape planning to keep the roof clear, and the aforementioned zinc strips
Oregon State University maintains a website devoted to mosses, and one page addresses the use of zinc strips as a control. Here is an excerpt:
“Zinc strips are usually considered the long-term solution to controlling mosses […] Zinc strips and galvanized flashing are apparently relatively safe and inexpensive. They effectively kill or retard the growth of mosses and fungi and appear to have effect up to 15 feet below the zinc flashing along the length of the flashing. To use: apply the rolled zinc or galvanized flashing to each side of ridge caps along the roof peaks. Place a nail down each foot of the zinc strip. With each rain zinc is released from the strip and kills the mosses below the strip. For best results remove the existing mosses prior to treatment. The active ingredient is metallic zinc.
Effectiveness: Zinc strips are considered to be effective for up to one year for most brands. The effect of galvanized flashing (example above) can persist for decades. Success rates vary with the degree of moss development and weather. Zinc strips or flashing are most effective before mosses are well developed. Physical removal of existing moss followed by installation of zinc strips or flashing is an effective long-term strategy for suppressing moss growth.
Negative Side Effects: Direct runoff from the zinc strips or flashing to surrounding vegetation, fish ponds, or water supplies should be avoided, because some contamination by zinc is likely to occur. Zinc strips should not be used with strong acids or bases.”
The PAN Pesticides Database has an entry for one type of rolled zinc strip product.
Washington Department of Ecology has a lengthy document analyzing zinc
concentrations in industrial runoff, and you can imagine that homes with
zinc strips are simply smaller contributors to this problem.
The Environmental Protection Agency lists zinc metal strips (consisting
solely of zinc metal and impurities) as minimum risk pesticides.
I think there is no easy solution, and it is a matter of deciding on a
lesser of two evils: the physical difficulties of cleaning the moss off
the roof, which is most environmentally sound, versus the relatively
small amount of pollution from using zinc strips.
Our backyard (which is flat and no pine trees) has hundreds of tiny mushrooms throughout the grass. Our front yard (which has a slight slope and one large pine tree) has many huge mushrooms. Otherwise, we have good looking grass. We have lived here for a very long time without ever seeing this problem. I know one answer is to “sweeten” the soil with lime. Should we do this now, in the fall, or at what time of year? Should we remove the mushrooms or let them be? Any other suggestions?
University of California, Davis Integrated Pest Management has guidelines on managing mushrooms in lawns. Here is an excerpt:
“Mushrooms found in lawns often develop from buried scraps of construction lumber, dead tree roots, or other organic matter. The fungi that produce these mushrooms are beneficial because they decompose organic matter in the soil, making nutrients available to other plants. These mushrooms usually are harmless to grasses, but some people consider them unsightly or want to get rid of them because young children play in the area. Remove mushrooms growing from buried wood or roots by picking them as they appear or by digging out the wood. Many of these mushrooms are associated with overirrigation or poor drainage. Removing excess thatch and aerating the soil to improve water penetration may help in some cases.”
The website further suggests adding nitrogen fertilizer, but bear in mind that excessive fertilizer contributes to urban runoff pollution.
As for sweetening the soil with lime(making it less acidic), it is best to do a soil test before attempting to amend for soil pH. The City of Seattle’s Natural Lawn Care information says that you would only need to “apply lime in the spring or fall if a soil test shows a calcium deficiency or acid soil conditions (pH less than 5).”
We leave for about 5 months in the winter and by the time we
get back our sword ferns have sprouted and it’s hard to prune the old
fronds out without cutting off the new ones. These ferns are in a fairly
protected area, so I was wondering if it would be okay to cut off the old
fronds in October before we leave? Also would it help if we just cut the
old fronds and lay them over the plant to help protect it over the
winter?
There are some slight differences of opinion on cutting back sword ferns.
It might be fine to cut the old fronds this fall and leave them as
protection over the winter, but it isn’t really necessary to cut them
back until early spring, if at all. The local web site for Great Plant
Picks recommends cutting sword ferns to the ground in late winter, or
only cutting back every 3 years or so on plants growing in poor soil:
Paghat’s Garden, another local gardening site recommends only cutting away dead fronds. Excerpt:
It was once believed it was necessary to cut all the fronds off in
February immediately before new growth begins, but it is now the
recommendation to only trim dead fronds. By April when the fiddleheads
are thickly erupting, any of last year’s fronds that have lost their
beauty should be removed, but only for looks’ sake, removing up to as
many as all of them. They’ll soon enough be replaced by new. Just don’t
remove the fronds before winter’s final frosts, as the reason this fern
adapted itself to keeping its fronds green at least until winters’ end is
to shelter & protect the humping crown from excessive cold or from
sunlight in winter when deciduous trees might not adequately shade the
rootcrown.
Since your plants are in a protected area, you might be able to go ahead
with your October trimming, but really the main reason to trim is an
aesthetic one, so it isn’t absolutely necessary.
A landscaper planted a River birch next to our house 9 years ago. The roots are everywhere. We heard that this is one of the worst trees to plant next to a house. We have a basement. What should we do?
River birch (Betula nigra) is rated as having moderate root damage
potential by the Urban Forest Ecosystems Institute.
The following, from University of Saskatchewan’s “Guide to Birch Trees,” supports what you have heard about planting this tree near a structure, but takes the approach that it is not good for the tree, rather than a danger to the foundation. Excerpt:
“On a healthy birch, the roots will spread to a distance of at least twice
the tree’s height. This means that the roots of a mature tree may cover
an area about one third the size of a football field. To permit proper
root spread, trees should be planted as far as possible from any
obstruction that may interfere with root development. Sidewalks,
driveways, patios and building foundations will all limit root
development. Where a tree is growing on heavy soils, aeration holes will
help maintain root vitality.”
Tree roots are not likely to infiltrate a solid foundation, but if there
are cracks, it is certainly possible, and if tree roots expand
sufficiently over time, they may begin to exert pressure on the
foundation. However, birch roots are shallow, as indicated in this USDA
Forest Service guide to growing birch trees.
It is not a good idea to plant any tree right next to a house, if only
because the tree will undoubtedly require pruning to keep it out of the
way of windows, doors, and so forth. If you like the tree and would like
to move it to a better spot, you should consider contacting a certified
arborist. Here are links to referral services.
Pacific Northwest Chapter of the International Society of Arboriculture
I have grown runner beans in the center of England for
several years, with good crops and healthy plants, but this year my
plants have some sort of disease. The leaves have brown spots which seem
to spread along the leaf veins and then over the whole leaf. Some plants
are still producing healthy beans, but on some plants the beans have shrivelled
and turned yellow. I don’t know if these are the same plants with the
worst leaf problems as the plants are tangled together too much. I have
looked at various websites, but am not sure that any diseases shown
correctly match my problem. I would be very grateful if you have any
idea as to what it is and how to deal with it.
While I cannot diagnose the problem remotely, your description does sound
quite a bit like anthracnose, which is a fungal disease. According to The
Organic Gardener’s Handbook of Natural Insect and Disease Control by
Barbara Ellis (Rodale Press, 1996), this disease thrives in wet, humid
conditions. You would see leaves with dark streaks, and black petioles
and veins on the underside of the leaves. If this is indeed the problem,
plants may be sprayed with sulfur, or you can seek out resistant
cultivars next time around (‘Espada,’ ‘Marbel,’ Morgane,’ and ‘Rocdor’
are a few).
On the other hand, the yellowing of the seed pods sounds more like
bacterial blight, also encouraged by warm, damp weather. If your plants
are not forming any new pods, remove and destroy them. Next time you
plant, be sure there is adequate space between plants, and perhaps
rotating the crop to a different location might help.
Just to give you some basis of comparison, here are links to sites with
information about diseases affecting beans:
Cornell University Vegetable MD Online
University of California, Davis Integrated Pest Management
Royal Horticultural Society lists several problems affecting runner beans. There is a fungal disease of broad beans called chocolate spot which sounds a little like what you describe.