Elisabeth C. Miller Library logo Miller Library Home UW Botanic Gardens Home UW Botanic Gardens Home book graphic

3501 NE 41st Street, Seattle, WA 98195 | (206) 543 0415 | Open: | Library Schedule

Gardening Answers Knowledgebase

Plant Answer Line Question

Keywords: Rosa, Mosaic diseases, Pests

My roses were diagnosed with both rose slug and rose mosaic. I would like to know your thoughts about treatment of these conditions, as it was suggested that I just remove affected leaves, and I am looking for a more effective solution.


I will summarize what Christine Allen's Roses for the Pacific Northwest (Steller Press, 1999) says about these two problems:

Mosaic virus:
This disease infected the roots of your rose when the plant was grafted; the symptoms do no show up for a year or two. The problem is widespread anywhere that rootstocks are developed from cuttings (rather than seed). (In Canada, apparently, most rootstocks are grown from seed, so they have far less of a problem with the disease.) The disease is incurable, and affected plants will have yellow patterning on their foliage. Other plants in the garden cannot "catch" the disease. Sometimes the symptoms disappear by midsummer, but recur the following spring.

Rose slug:
The greenish-white worms are actually sawfly larvae, and they can skeletonize leaves. They aren't caterpillars, so controls that are used for caterpillars (such as Bt) won't help. Insecticidal soaps can kill them, but only by making contact, so this means repeated spraying. It is best to do this in early evening when the larvae are most active, and may be seen on the top surfaces of the leaves. Pyrethrins are effective, but they also are acutely toxic to aquatic life, moderately toxic to birds, and may kill beneficial insects such as honeybees [my comments, not the author's], so they should be a choice of last resort. The Environmental Protection Agency has additional information on pyrethroids and pyrethrin.

To prevent or mitigate rose slugs, clean up leaf litter and other debris several times a season to eliminate pupae and interrupt the life cycle. Hoe the soil gently and not deeply, and apply annual mulch early in the year.

Date 2018-06-27
Link to this record only (permalink)

Plant Answer Line Question

Keywords: Mosaic diseases, Tomatoes--Diseases and pests

My unripe green tomatoes ('Old German' variety) have developed a very weird appearance: lots of lumps and bumps, and nooks and crannies, plus strange discolored blotches. What is causing this? And will I be able to salvage (and eat!) them?


There may be more than one problem here. I definitely see a physiological disorder called cat-facing in the photo you sent us. University of Massachusetts Extension provides this information about it:
"Cat-facing is a physiological disorder of tomatoes. Cat-face originates in the early stages of flower bud development and is the result of abnormal development of plant tissue between the style and ovary which results in misshapen fruit. Other impediments to flower bud development can also result in cat-facing. The syndrome is related to unfavorable growing conditions, in particular several days below 60 F when the plants are young. High levels of soil nitrogen and excessive pruning aggravate the problem. Accidental exposure to phenoxy herbicides can also lead to malformed fruit. Cat face is more prevalent on large-fruited, fresh market tomato varieties. Good growing practices, especially temperature control, should be followed in greenhouse production of field transplants. Excess nitrogen, aggressive pruning, and accidental exposure to hormonal herbicides should be avoided."

The book Epic Tomatoes by Craig LeHoullier (Storey Publishing, 2015) says that catfacing occurs more often in large varieties that also have large blossoms. Some older varieties (heirlooms) have this tendency. Plants put out in the garden when it is too cool can also develop this appearance later. And too much nitrogen worsens it. As early as the 19th century, plant breeders were attempting to breed out this characteristic in favor of more uniform, smooth-looking fruit, but many heirloom tomatoes much-sought for their flavor tend to have this bumpy look. A little bit of catfacing shouldn't render your tomatoes unusable. I have grown Cherokee Purple tomatoes that often have some cat-facing, but they are still delicious.

Depending on the cause of the spots, the tomatoes may or may not develop to the point of ripeness and if they do, there may be some parts that rot and some parts which are still edible. Also depending on the cause, you may decide to pull out any affect plants and dispose of them.

It's possible that those discolored spots are due to sunscald, but the pattern of the discoloration looks more like a virus. LeHoullier says that plants which are heavily pruned or have lost a lot of foliage are more vulnerable to sunscald. However, the discoloration on your tomatoes resembles a mosaic virus, such as tobacco mosaic virus. If you are growing Nicotiana in your garden, debris from that plant as well as tomato plant contact with any tobacco products (cigarettes, or the hands that have held them, etc.) could introduce the virus to your tomatoes through any small wound—such as a pruning wound or accidental damage to plant tissue.

Washington State University Extension’s HortSense webpage has useful information on mosaic viruses as does University of Minnesota Extension.

Still, the best thing to do is bring samples to your local Master Gardener Clinic. Many tomato problems look similar (viral, bacterial, stink bug damage, hornworm feeding). There is a good visual guide from Missouri Botanical Garden but an in-person diagnosis is best.

Date 2017-08-15
Link to this record only (permalink)

Didn't find an answer to your question? Ask us directly!

Browse keywords

Search Again:

May 31 2018 13:14:08