plant information – My Chicago Botanic Garden

Pest Alert: Know Your Galls

A gall, tumor, or burl is an abnormal growth on the leaves, stems, roots, buds, twigs, or crown of a plant. In most cases, the gall is unsightly but not damaging. In small plants, the vascular flow of water and food can be restricted, causing poor growth and making the plant more susceptible to other stresses. A large tree can be weakened by an infection over many years. Nematodes, mites, and insects cause 95 percent of galls. Bacteria and fungi cause the remaining five percent. In most cases, the gall-making organism can be identified by observing the structure of the gall and the species of the host plant.

Galls on a Flower — Galls on *Rudbeckia laciniata* ‘Herbstsonne’

Fungal galls are spread by ascospores in wind and water and can be found on many common trees including oak, maple, and common privet. Black knot affects many species of the genus Prunus—particularly cherries and plums.

Crown gall is a common problem caused by bacteria. The disease is spread by infested soil, transplants, or contaminated tools. The bacteria enters the plant through wounds caused by cultivation, pruning, or insects. Easy prevention methods are to plant only healthy stock (no suspicious bumps), to clean pruners between use on each plant with alcohol or a 10 percent bleach/water solution, and to take care not to injure plant stems. The bacteria stays active in the soil even after removal of infected plants, so place new, healthy stock elsewhere. Remove and destroy all infected plants. Galls caused by bacterial and fungus are more prevalent during wet years.

A gall can form in response to toxins injected during insect feeding or egg laying, or around a feeding larva. The hackberry leaf gall is caused by psyllids, which are tiny winged insects. Galls formed by insects usually do not affect the overall health of the tree unless they experience early defoliation over the course of many years. Parasites are an important control of this pest. Many oak galls are caused by gall flies and generally are not detrimental. A severe twig infection can, however, cause severe injury and even death. Spruce galls are often caused by several species of an aphid-like insect. If only a few galls are present, they can be cut off and destroyed before the insects emerge in midsummer.

Leaf galls on maple trees form because of feeding mites. Eriophyid mites produce a gall that resembles a felt patch and may occur on the upper or lower side of the leaf. The overall health of the tree should not be seriously affected.

Nematode feeding activity can injure roots and allow gall-forming bacteria into the plant. Nematodes can also form galls on carrots, camellia, fig, gardenia, okra, potato, roses, sweet potato, and tomato. Plants can be stunted, yellow, and wilted due to restrictions on the uptake of water and nutrients. Individual nematodes are invisible to the naked eye, but egg masses can be seen as pearly objects. Roots can appear scabby, pimpled, rough, and have knots. Two important prevention methods are to rotate with nematode-resistant crops and to maintain rich organic soil.

Please contact Plant Information Service at (847) 835-0972 or at plantinfo@chicagobotanic.org for additional information.

The Warm Weather and Your Garden

The late February weather in Chicago has been a glorious time to be outside and work in the garden. But the unseasonably warm weather has also raised questions about the long-term effect on plants and what garden tasks are appropriate.

It is best to hold off on doing any detailed clean up of garden beds as the mulch and leaves in the beds will provide some protection to any early growing perennials when the weather eventually turns cold again. Raking leaves off the lawn and cutting back perennials are all fine to do now providing your garden soil is not too wet.

Early flowering bulbs like snowdrops that are in flower here at the Chicago Botanic Garden are very tolerant of the cold. Daffodil and tulip foliage is coming up; these might end up being damaged by a spell of cold weather, but this should not affect the spring flowers. You do not need to take any special maintenance steps to protect these plants.

If you have some perennials that are growing in a warm area of the garden with more pronounced growth, they might benefit from a light layer of mulch. For the most part, though, there is nothing special for most gardeners to do in their perennial beds.

This is great weather to prune but proceed with care. Spring flowering shrubs like viburnums, lilacs, and forsythia set their flower buds last year so pruning done at this time of year will remove flower buds and reduce the number of spring flowers. You can still prune—just be aware of the flower buds as you are pruning. Forsythia flowers along the stems while viburnums will have a flower bud at the ends of the stem.

The dormant season, and in particular late winter, is the best time of year to complete rejuvenation pruning, which is the aggressive pruning of overgrown shrubs to bring them back into scale with the garden. Shrubs like hydrangea (except oak leaf hydrangea), potentilla, and spirea that flower on new wood respond well to pruning now too. For instance, I cut my Annabelle hydrangea back to the ground each spring.

Any plants installed last summer or fall should have been mulched when they were planted. If they were not, then mulch them now to help mitigate the temperature swings in the soil and prevent frost heaving of any plants in spring. The freezing and thawing of the soil can push recently installed small plants such as 1-gallon perennials or ground covers that were grown in containers out of the soil as the weather transitions to spring.

If we receive a good covering of snow, the snow itself will not harm plants unless it builds up on them and breaks branches. It is a good idea to brush plants off during a storm if you observe them getting weighted down. Later snowstorms are more likely to come in wet and heavy. Leave the plants alone if the snow has frozen on them to avoid breaking branches during the removal process.

Enjoy the warm weather and the early blooms, both at the Chicago Botanic Garden and in your own backyard.

The Plant Doctor Is in the House

A couple years ago, in early spring, I got the kind of call that puts a “plant doctor” like me on edge. “Come look at the roses right away,” someone said. In my 25 years at the Chicago Botanic Garden, no one has ever called me to say, “Hey, Tom, come look at the roses; they look great today!” I’m in charge of plant healthcare at the Garden, so when I pick up the phone, there’s usually a problem.

I got the call about the Krasberg Rose Garden following a string of very damp nights that meant trouble—a white fuzz had spread over all the roses. The fuzz was a destructive pathogen that produces mycelium, or fungal spores. It can happen pretty much overnight. We ended up managing the problem, but it was scary to start off a season like that. Roses are tricky, prone to a lot of diseases and insect problems. Our friends at the Missouri Botanical Garden lost all their roses to a virus called rose rosette disease.

I don’t just get calls about diseases or pests such as the emerald ash borer. I get called to the Butterflies & Blooms exhibition if the staff is worried about a larva or to the Elizabeth Hubert Malott Japanese Garden if there’s a raccoon problem. I like to say that I’m sort of like a CSI detective when it comes to plants. If a plant is failing, I try to find out why and what it needs. I look at the buds, the stem, the trunk, the root flare, the soil, and the plant’s history over the years.

PHOTO: Tom Tiddens poses with a cardboard coyote cutout, used to deter varmints from veg. — Tom Tiddens and a plant healthcare specialist’s best friend head out to play fetch.

I also work with the horticulturists on preventive care, including watering, pruning, weeding, and fertilizing. When I see a problem in the early stages, I’m very patient and tolerant. I like to see if Mother Nature might take care of it—maybe a hard rain will wash away any aphids or the ladybugs will get rid of the pests, for instance.

People ask me how I track the health of more than 2.6 million plants here. I have two great plant healthcare specialists who work with me, and I really rely on the horticulturists—they’re my eyes out in the field—and my volunteer team, which includes a lot of master gardeners. Every week, I give the volunteers a map and checklist marked with target plants and pests. So a typical volunteer assignment, for example, would be to check the spirea bushes in the Sensory Garden for aphids.

PHOTO: Bagworms infect a pine. — From bagworms…

PHOTO: Rust infects a fruit and leaf. — …to rust…

PHOTO: Black spot infects rose foliage. — …to black spot on roses, Tom Tiddens treats them all.

The average home gardener doesn’t have to be so methodical. Gardening shouldn’t be a chore. I like to keep things simple at home. I don’t like weeding, and I avoid using a lot of perennials or groundcovers. I like having a nice woodchip mulch bed and a mulching lawnmower. It’s the same thing with fall leaves. Everyone bags up all the leaves. Nope. I raise my mulching lawnmower, and I just grind them into the lawn.

Register now for a certificate class with Tom Tiddens, plant health care supervisor and certified arborist. From July 21 to August 28, he will teach Plant Health 2 with Kathie Hayden, the Garden’s manager of plant information service.