Category Archives: Plant pests and diseases

What’s That in the Tree? Fall Webworm

Fall turns up all kinds of pests and diseases in the garden. You may be noticing what looks like stretched pantyhose in your trees now.  Look closely and you will see that these are webs with small caterpillars inside. Each caterpillar is marked with parallel rows of black spots on the back. The fall webworm (Hyphantria cunea) is very noticeable now but at this stage, the caterpillars stay in the web and feed inside on the leaves of the tree. The web is unsightly but their feeding will not kill the tree. However, this would be a good time to cut the branches and bag the webs, caterpillars and all. Close up the bags tightly and dispose the bags in the trash.

Later, after the last molt, they leave the web and crawl all over the tree. They spin cocoons, pupate, and emerge as white moths. If you are not able to bag the web don’t despair, there are many natural enemies of the fall webworm. Another tactic is to spray the first generation in the spring with horticultural oil, Bt (Bacillus thuringiensis), or insecticidal soap before they create the web. Don’t try to burn them out though, it is too dangerous to the tree. For more information on plant pests and diseases, check out the Plant Pests and Diseases tab on


Problems in the Garden? Ask These Experts

virus “aster yellows” deforming blossoms

Summer is here and by now you are seeing a host of issues in your garden. If it isn’t Japanese beetles eating your roses, it’s leaf hoppers spreading aster yellows and bagworms covering your evergreens. But don’t worry, there are plenty of resources for help in our DC metro area. One of the first places you should go to is your local Master Gardeners group and county extension agents.

Help in Northern Virginia

In Northern Virginia, there are two Master Gardener groups. People who live in Arlington and Alexandria are probably familiar with the Master Gardeners of Northern Virginia. They have an excellent website with plenty of resources. If you have a gardening question, you can contact the Extension Master Gardeners Help Desk via phone, in person at their office, or via email at This is a service for the public. You do not have to be a master gardener, live in those areas, or pay anything. The people answering the questions are volunteer Master Gardeners and County Extension Agents.

Japanese beetles are notorious for decimating rose bushes

The second option is to contact the Fairfax County Master Gardeners Help Desk by calling or e-mailing at This is a service of the Fairfax County Master Gardeners but again, you do not have to be a master gardener, you do not have to live in Fairfax County, and you do not have to pay anything. The reason why there are two Master Gardener groups in Northern Virginia is because the demand for the Master Gardener program is so high. This group also has an informative website.

Master Gardeners staff plant clinics at libraries and farmers markets. Here is the schedule for 2023. Again, free service, visit them and bring a diseased plant and they will help you. They also will help with any gardening question or issue.

Help in Maryland

In Maryland, there is the Home and Garden Information Center (HGIC) which is managed by the University of Maryland Extension. You can e-mail via a form and questions are answered by horticulturists. In the form, describe the problem and attach photos, if needed. The website lists a few suggestions: include an object to indicate scale for insects; attach both a close-up as well as the entire plant; send a photo of the entire weed plant with flower or seed head; and, if seeking a plant disease diagnosis, send photos showing the transition from healthy to diseased. This is a free service and the HGIC will assist Maryland and DC residents. This website also has a lot of great gardening information.

Leaf hoppers can spread viruses from plant to plant

Plant clinics are by county so just enter “plant clinic” and the county name to see if there is a schedule. Or the county name and “master gardeners” to see if they provide this service in another format. For example, here is the 2023 schedule for Montgomery County, Maryland.

There is a DC Master Gardener program but they do not provide plant diagnostics which is why DC residents are encouraged to contact the HGIC.

Other Options

One other option is the “Ask Extension” website, which is a portal for the Cooperative Extension System. Your question would be sent to the appropriate extension office within your state. (If you type in Washington DC you will be redirected to the Maryland HGIC.) Questions are answered by cooperative extension/university staff and volunteers within participating land grant institutions across the United States. In Maryland the land grant institution is the University of Maryland and in Virginia it is Virginia Tech. Again, a free service to the public across the country. Complete the form by entering your state, gardening question, e-mail, the county and state where you live, and the images, if needed.

bagworms are little “houses” for worms that will decimate foliage

At many independent garden centers, such as Merrifield Garden Center, there are help desks with staff horticulturists who can help you with your gardening issues. Call your local nursery to see if they have available, professional staff.

Of course, there are always gardening books at the local public libraries. Below are suggestions of helpful books. Remember, do not get stressed about your garden. This is all part of the process. Figuring out what is wrong with a plant is part of gardening because gardening is a learning experience.

  • Bug Free Organic Gardening: Controlling Pests and Insects Without Chemicals by Anna Hess, Skyhorse Publishing, 2019
  • Pests and Diseases by Andrew Halstead and Pippa Greenwood, DK Publishers, May 2018
  • Home Gardener’s Garden Pests and Diseases:  Identifying and Controlling Pests and Diseases of Ornamentals, Vegetables, and Fruits by David Squire, Creative Homeowner, 2016
  • What’s Wrong with My Plant (And How Do I Fix It?) (2009); What’s Wrong with my Vegetable Garden (2011); What’s Wrong with my Fruit Garden (2013), What’s Wrong with my Houseplant (2016) by David Deardorff and Kathryn Wadsworth, Timber Press
  • The Gardener’s Guide to Common-Sense Pest Control: Completely Revised and Updated by William Olkowski, Helga Olkowski, Sheila Daar, Taunton Press, 2013
  • The Practical Encyclopedia of Garden Pests and Diseases: An Illustrated Guide to Common Problems and How to Deal With Them Successfully by Andrew Mikolajski, Anness Publishing 2012
  • Good Bug, Bad Bug by Jessica Walliser, St. Lynn’s Press, 2011
  • The Organic Gardener’s Handbook of Natural Pest and Disease Control: A Complete Guide to a Healthy Garden and Yard The Earth-Friendly Way by Barbara W. Ellis, Fern Marshall Bradley, and Deborah L. Martin, Rodale Press, 2010
  • Rodale’s Vegetable Garden Problem Solver by Fern Marshall Bradley, Rodale Press, 2007
  • Better Homes & Gardens Garden Doctor Advice from the Experts, Meredith Corporation, 2005
  • Garden Insects of North America by Whitney Cranshaw, Princeton University Press, 2004
  • Reader’s Digest, Gardener’s Problem Solver, Miranda Smith, 2004
  • Insect, Disease and Weed ID Guide: Find-it-Fast Organic Solutions for Your Garden by Linda Gilkeson, author; Jill Jesiolowski, editor; Deborah L. Martin, editor, Rodale Press, 2001
  • Pests and Diseases: The Complete Guide to Preventing, Identifying, and Treating Plant Problems by Pippa Greenwood, Andrew Halstead, A.R. Chase, Daniel Gilrein, American Horticultural Society, 2000.
  • Weeds of the Northeast by Richard H. Uva, Joseph C. Neal, Joseph M. DiTomaso, Cornell University Press, 1997

Garden Battles: Cabbage Worm

cabbageworm butterfly on kale

cabbage worm butterfly on kale

I was harvesting my lettuce when a flash of white flitted by the kale. My heart stopped: it was the dreaded cabbage worm.

Last year, I spent an enormous amount of time fighting imported cabbage worm. The white butterflies, the adult form, are attracted to members of the cabbage family. In my garden, that means mustard and kale. The small, white butterflies lay yellow, bullet-shaped eggs under the leaves. Within a few weeks, the larva, the disgusting green worms, decimate leaves and stems. They then pupate and more adults emerge so within a growing season there are several generations. Surprisingly, they can continue all year long on my property in Northern Virginia.

cabbageworm butterfly near lettuce

cabbage worm butterfly on lettuce

At first, I tried picking the worms off but quickly concluded that: first, it’s gross; and second, it’s easier said than done. It is difficult to pick them up on a continuous basis because we are all busy.  It seems eggs are always hatching, larvae are always present from very tiny to very large, and the green color of the worm blends in with the green leaves.

I know the other recommendation is to use row covers but I live in a traditional suburban home and my kale and mustard plants are in pots on the deck or tucked in the landscape, not in rows. I do not have the type of vegetable garden where there are rows of one crop.

Finally, I resorted to Thuricide®, a liquid form of Bacillus thuringiensis (Bt), thinking that I would just have to spray once or twice. Bt is a bacteria that kills the larvae so it is a non-toxic, biological insecticide. However, it got to the point where I felt that all I was doing was spraying instead of growing and eating.

By the end of the year, I was fed up and vowed not to grow kale and mustard again. Then I thought what if I grew the colored mustards as a winter annual in a container? For sure the cabbage worms could not be active in the winter.

But yes, Virginia, they were very active in the winter and ate the mustard as if it were a summer delicacy. Do you have this problem in the garden and if so, what do you do to battle the cabbage worm?

Deformed Flowers? It May Be Aster Yellows

Lately I have seen a lot of chatter on Facebook about distorted Echinacea and Rudbeckia flowers in the garden. I too noticed this in my Virginia garden, so I looked it up.

Sure enough, my plants have “aster yellows.” Aster yellows is caused by a phytoplasma, a small bacterium. This is a disease that affects more than 300 species of plants, including asters, coneflowers, zinnias, marigolds, heleniums, and chrysanthemums. And it is not just ornamental plants but edibles such as garlic, lettuce, carrots, tomatoes, and celery. Continue reading

Wanted Dead or Alive: Spotted Lanternfly

Spotted lanternfly (Lycorma delicatula) is a non-native, invasive insect first seen in September 2014 in Berks County, PA, when a shipment of stone arrived from China with the eggs attached. The insect is native to China, India, Japan, Korea, and Vietnam. By 2017, the insect moved to 13 Pennsylvania counties and a single county in both Delaware and New York. It is highly invasive, has a wide host range, and lacks natural, native enemies. To date, spotted lanternfly, also known as SLF, has been identified in 11 states: New York, Maryland, Virginia, West Virginia, Pennsylvania, Massachusetts, Ohio, Connecticut, Delaware, Indiana, and New Jersey. Continue reading

Wanted Dead or Alive: Spotted Lanternfly

Recently an article appeared in (Fairfax County local news) with the headline “One of the world’s most wanted insects has landed in Fairfax County.” I immediately contacted Adria Bordas, Fairfax County’s Virginia Cooperative Extension (VCE) agent for horticulture. Spotted lanternfly is one insect I do not want in my garden. If you think a downpour of 17-year cicadas is gross, try looking at a tree dripping with spotted lanternfly. Continue reading

Remove the Bagworms in Your Shrubs and Trees

Bagworms are common pests in the Washington DC metro area. Usually we do not see the actual worms (Thyridoptery x ephemeraeformis), we see their “homes,” which are 2-inch long “bags” they have spun from silk and plant debris. These bags are hung like small, brown ornaments on shrubs and trees. At this time of year, they are prominent and should be removed.

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Got Deer? Try These Tactics in the Garden

deerNewcomers to this area will eventually see deer standing on the roadside or venturing out of the woods at dusk. At first, they admire the lovely bucolic sight, gentle deer, twitching their tails, flicking their ears back and forth. But as the newcomers settle down and try their hand at gardening, they learn that the deer are not as cute as they once thought. Continue reading

Gardening Questions? Ask These Experts

cucumberSummer is here and by now your Victory garden is planted. Dreams of fresh red tomatoes and lush green cucumbers are dancing in your head. But wait, what are those green caterpillars? What are those brown spots? Answers to these gardening questions and more are available from your local Master Gardeners and county extension agents. Even during this pandemic, they are standing by to help you with your gardening issues. Best of all, this is a free service for the public. Continue reading

Herbs Attract and Support Beneficial Insects in the Garden

Small thyme flowers

The herbs in my garden live among the annuals, perennials, vegetables, and shrubs. I do not have a separate, formal herb garden.  Every new herb plant gets tucked in any space I can find. I harvest them to use them fresh in the kitchen and for floral arrangements. By summer, many of my herbs are blooming along with everything else but that’s okay, they still serve a purpose. Even if I didn’t get to harvest them, they are helping the rest of the garden by attracting and supporting beneficial insects. Continue reading