problem solver

Tall buttercup
Ranunculus acris

IDENTIFICATION — According to folklore, if your skin glows yellow when you hold a buttercup under your chin, you love butter. But that doesn’t mean you have to love tall buttercup!

Although it looks similar to several native buttercups, this invasive perennial was introduced from Europe, and is now widespread throughout the United States and Canada. Also known as “blister plant,” tall buttercup contains a noxious oil that can blister the skin.

Its branched stems grow 1 to 3 1/2 ft. tall, and end in branched clusters of glossy, five-petaled yellow flowers. The flowers, which bloom from May to September, are only about 1 in. in diameter.

FAVORITE CONDITIONS — Tall buttercup prefers moist soil, so you’ll rarely find it where the ground stays dry. In fact, it often grows in low spots that stay wet, such as roadside ditches and stream banks. You’re more likely to find this weed in shrub borders or established perennial beds than in heavily cultivated areas. It spreads quickly and easily, often crowding out other plants

CONTROL — Because tall buttercup spreads by seed, control is easiest when plants are young and haven’t had time to set seeds. The roots are often shallow, but dense. Dig or pull this weed out by hand, but make sure to wear gloves so the blistering sap doesn’t get on your skin. You can also remove young weeds with a sharp hoe. A thick layer of mulch will help prevent seeds from germinating.

Broadleaf herbicides like 2,4-D and Roundup^® are also effective. Apply them before tall buttercup has a chance to flower and set seeds — you’ll have a much better chance of getting rid of this pesky weed.

PHOTO: Courtesy of David R. Lance
USDA APHIS PPQ

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Brown marmorated stink bug
Halyomorpha halys

IDENTIFICATION — The brown marmorated stink bug, or BMSB, is about 1/2 in. long, shield-shaped and mottled brown. And the last two segments of the antennae have an alternating light and dark brown banding. Adult females lay clusters of 20 to 30 light green eggs on the undersides of leaves from June to August.

DAMAGE — This pest feeds on more than 70 species of ornamental plants, as well as soybeans and the fruit of many trees. And when cold weather arrives, masses of BMSB come knocking at your door. Though not harmful to people, this bug lives up to its name by emitting an unpleasant odor when disturbed.

CONTROL — It’s recently found its way to North America from Asia. First discovered in Allentown, Pennsylvania, in 2001, the extent of its range isn’t known. If you see one, contact your local extension agency or go to www.csrees.usda.gov/nea/pest/pdfs/stink_bug_pest_alert.pdf to learn more. To control BMSB use an insecticide containing bifenthrin or cyfluthrin, such as Baythroid^® or Aztec^®, and follow label directions.

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Wild grape
Vitis spp.

IDENTIFICATION — Long, twining vines wind their way into shrubs and trees. As the stems mature, the bark peels into narrow strips. Older vines produce clusters of small dark purple fruit in late summer.

FAVORITE CONDITIONS — Wild grape prefers sun to part shade in any type of soil, either moist or dry. It has an unlimited spread because the vines root wherever they touch the soil. The spread is helped by birds, which eat the messy fruit. Large thickets of vines can shade out or even kill mature shrubs and trees.

CONTROL — When the plant is a seedling, pull or dig it out of the ground. If it’s too large for this, spray the plant with a nonselective herbicide, such as Roundup^® Poison Ivy & Tough Brush Killer Plus in spring or late summer. Or cut down the tree and dribble or brush on a systemic stump killer around the edges where the sap is flowing. It’s absorbed into the wood and kills the roots. Be careful — it can kill any plant it gets on.

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Rose rosette disease

IDENTIFICATION — Rose rosette is caused by an organism similar to a virus that’s transmitted by mites. Although you usually find it in weedy multiflora rose, all roses are susceptible. And it’s becoming more common in cultivated ones.

Symptoms include increased thorniness, small red or purple leaves and rapid, dense growth of the shoots in “witches brooms.”

CONTROL — Unfortunately, there’s no cure for rose rosette disease. If you think your rose has it, remove and send it away in the trash to prevent infecting others. Get rid of any nearby stands of multiflora rose, as well.

Click image to see a close-up of the leaves.

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Siberian elm
Ulmus pumila

IDENTIFICATION — Remember American elms? The leaves of this 50- to 70-ft.-tall, 30- to 50-ft.-wide woody weed look similar. However, they’re usually smaller and riddled by insects. In spring, before the leaves even open, you’ll spot clusters of pale-green flowers on the branches. Later, usually by early summer, large quantities of small papery disclike seeds begin to fall. They are spread by the wind, sprout and grow very quickly. Siberian elm trees have weak wood, so you’re constantly picking up the fallen twigs and branches.

FAVORITE CONDITIONS — You’ll find Siberian elm growing in full sun to part shade in moist to average soil.

CONTROL — When the plant is a seedling, pull or dig it out of the ground. If it’s too large for this, spray the plant with a nonselective herbicide, such as Roundup^® Poison Ivy & Tough Brush Killer Plus in spring or late summer. Or cut down the tree and dribble or brush on a systemic stump killer around the edges where the sap is flowing. It’s absorbed into the wood and kills the roots. Be careful, it can kill any plant it gets on.

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Black-legged or deer tick
Ixodes scapularis

IDENTIFICATION — Not all garden pests are found on plants. Some are actually on the gardener! Unfortunately, this pest is hard to spot. The black-legged tick (or deer tick), the main culprit in infecting humans with Lyme disease, is tiny. Brick-red adult females are about 3/25 in. long, and the black males are a little smaller. After feeding, females can be two to three times that size. During the immature nymph stage, they’re only about the size of the head of a pin and translucent with a gray tinge. This is the phase during which they’re most likely to attach to humans or pets and transmit disease.

Only 1 to 5 percent of black-legged ticks carry Lyme disease, most commonly in Canada and the northern United States.

CONTROL — The best control for black-legged ticks is to avoid them. They’re found in wooded areas or tall grass, so stay on paths and keep your lawn mowed. Keep pets in mowed areas, as they can bring ticks indoors or be infected with Lyme disease themselves. Mowing grass short raises the temperature and lowers humidity at ground level, which causes ticks to dehydrate and die.

Wearing long-sleeved, light-colored shirts and long pants helps keep ticks away and also makes it easier to see any that might have made it onto you. Tuck your pants into your socks to keep the little critters from crawling up your legs. Repellents with deet also keep ticks at bay.

After coming indoors from brushy areas, check for ticks, especially in your hair and around your waist and inner thighs. They need to be attached for a couple of hours to transmit disease, so removing them promptly is important. It’s best to use tweezers. Grasp the tick’s head and body and pull carefully.

For more information on Lyme disease, go to the American Lyme Disease Foundation Web site at www.aldf.com or the Centers for Disease Control and Prevention Web site at www.cdc.gov/ncidod/dvbid/lyme/.

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Bacterial leaf scorch

IDENTIFICATION — You wouldn’t be surprised to find a few brown leaves on a tree near the end of summer. But take a close look: Do the leaves have an irregular pattern of browning with a pale yellow or red band between the brown and healthy green leaf tissue? If so, it could be bacterial leaf scorch. This disease, caused by the bacterium Xylella fastidiosa, clogs the plant’s water-conducting tissues. It’s spread by spittlebugs, leafhoppers and treehoppers as they feed and is mostly confined to the Eastern and Southern United States. Sycamore, mulberry, maple, dogwood, American elm and several species of oak trees are affected.

DAMAGE — Symptoms start showing up in early summer and get worse by autumn. Each tree species is affected a little differently, but generally you’ll notice premature browning, or scorching, of leaves first. As browning spreads toward the middle of the leaf, the edges curl in and the leaf may drop off the tree. Each year more leaves turn brown. Then twigs and whole branches start to die and growth is stunted. Once weakened by this, the tree becomes vulnerable to other infections or infestations. It can take as long as five to 10 years for the whole tree to die.

CONTROL — There’s no cure for bacterial leaf scorch. It can usually be diagnosed by symptoms alone but for a definitive diagnosis, check with your local extension agency. If you need time to select and plant a new tree, you can keep the old tree going by hiring an arborist to administer trunk injections to suppress the symptoms. Or delay the development of the disease by removing infected limbs and avoiding drought stress. Mulching around the tree and watering during dry spells will help keep moisture even. Whatever treatment you choose, the tree will eventually need to be removed.

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Bull thistle
Cirsium vulgare

IDENTIFICATION — Common throughout much of North America, bull thistle is a biennial that reproduces only by seed. The seeds sprout in fall or spring. First-year plants are a low rosette of leaves that can grow as large as 3 ft. in diameter, although they’re usually smaller.

A second-year bull thistle is from 2 to 6 ft. tall by midsummer when it blooms. The flowers are 1 to 2 in. in diameter, deep purple to bright pink and fuzzy. There are spines along the stems, the edges of the long leaves and the midrib of each leaf. And the underside of the leaf is silvery-white.

After the blooms fade, the flower head seems to close up and a white fuzz appears at the tip. Soon, the “bud” reopens to release the seeds. Each tiny, brown, striped seed has a bit of white fluff attached that helps it drift on the wind to a new location.

FAVORITE CONDITIONS — This is an aggressive weed with a long taproot that will grow in almost any soil. It needs a place where it can complete its two-year life cycle undisturbed, so you rarely find it in areas that are regularly cultivated, such as vegetable gardens or annual beds. Lawns, shrub and perennial borders, as well as fencerows, ditches and garden edges, are where it grows best.

CONTROL — The easiest control method is to cut the entire plant down to the ground just before it blooms. If you cut first-year rosettes or older plants too early in the season, the root can resprout and flower. Even flowering stems that are cut and lying on the ground can produce viable seeds, so burn or bury them. For serious infestations, glyphosate or 2,4-D herbicides are effective if you spray first-year rosettes in the spring or fall.

Take care of lots of weeds with the Handy Weeder/Cultivator at right!

PHOTO: © Mary Howell Williams

problem solver

Spotted cucumber beetle
Diabrotica undecimpunctata howardi

IDENTIFICATION — Adult beetles are 1/4 to 1/3-in. long and yellow to green with 11 black spots on their backs. The wormlike larvae are yellowish and start out about 1/8 in. long.

DAMAGE — Spotted cucumber beetle will attack most any type of flower, but also eats beans, tomatoes, cucumbers, melons and other edibles. Adults chew irregular holes in flowers, leaves and fruit from July to fall. The larvae (known as Southern corn rootworm) feed on corn roots in May, June and July, often transmitting bacterial wilt disease.

CONTROL — Beneficial nematodes can help. Buy them at local garden centers or mail-order sources, such as Gardens Alive. Mix the powder with water and water them into the soil late in the day in midsummer to control the larvae. For beetles, grow plants to attract natural predators (purple coneflower, hydrangea or Shasta daisy to attract soldier beetles, or angelica, thyme or yarrow to attract parasitic wasps). As a last resort, mix up and spray tops and undersides of leaves with horticultural oil or insecticidal soap (on overcast or cloudy days) as soon as you notice damage.

problem solver

Clematis magnesium deficiency

Clematis leaves can turn yellow when they get too much moisture. But if your clematis is growing in well-drained soil, yellow foliage is likely a symptom of magnesium deficiency, which usually affects the oldest leaves first. One cause is using too much fertilizer that’s high in potassium. The illustration shows how the areas between the leaf veins and around the edges turn yellow in early summer. Without enough chlorophyll, the plant becomes stunted and weak and may even die.

To treat your clematis, mix 1⁄4 cup Epsom salts (magnesium sulphate) into a gallon of water and spray the leaves in summer. You may need to treat it several times before you see improvement. Or sprinkle the dry Epsom salts right on the soil (1⁄4 to 1⁄2 cup per 10 sq. ft.) around the plant. This can be done once, at any time of the year.

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Hemp dogbane
Apocynum cannabinum

IDENTIFICATION — Like an alien in a science fiction movie, the roots of hemp dogbane keep spreading as if they’re going to take over the world. Their long horizontal roots can spread more than 20 ft., eventually forming colonies that will squeeze out other plants.

The red-brown stems of hemp dogbane, sometimes known as “Indian hemp,” “bitterroot,” “rheumatism weed” or “Choctaw-root,” can grow up to 6 ft. tall. While young, the plant looks a bit like a milkweed. If you break the stem or leaves, you’ll discover a milky white sap, which is toxic if ingested. Small bell-shaped pale-green flowers bloom in clusters near the tips of the stems from June to August. Later, two 2- to 4-in.-long seed pods replace each flower. These pods are filled with tiny brown seeds that have tufts of white fuzz to help them float on the wind.

FAVORITE CONDITIONS — Hemp dogbane can be found in fields, thickets and open woods all over North America. It prefers moist soil, but once it’s established, the extensive root system makes it quite drought tolerant. In home gardens, you’re most likely to find it in shrub borders, low areas, like ditches, and in fence rows. You’ll rarely see this weed in garden areas that are regularly cultivated.

CONTROL — Working the soil repeatedly will help control hemp dogbane. Till young plants under before they reach 10 in. tall and have a chance to become established. If you can turn the soil and expose the roots during hot and dry weather, those roots will be less likely to resprout. You’ll need to till the area several times a year, and over a period of years, to eradicate all of the roots.

Because it’s such an aggressive spreader, hemp dogbane is most quickly controlled with herbicides, such as 2,4-D or Roundup^®. Apply them in the spring when the plant is just beginning to bloom or in late summer before the leaves turn yellow.

problem solver

Tar spot
Rhytisma spp.

IDENTIFICATION — There’s nothing more frustrating than having the beauty of maple tree foliage marred by big black spots. If your tree looks like it’s been splattered with black paint, it probably has tar spot, a fungal disease. There are several different species of this fungus, but the most common are Rhytisma acerinum and R. punctatum.

DAMAGE — Tar spot starts out as 1⁄8-in.-diameter pale yellow spots in late spring to early summer. By mid- to late summer, you’ll notice black spots inside the yellow ones. The “tar” is raised above the leaf surface, giving it a three-dimensional feel. Spots caused by R. acerinum grow to about an inch while spots caused by R. punctatum stay much smaller. Tar spot doesn’t kill the tree, but it just doesn’t look good, and heavy infestations can cause premature leaf drop.

CONTROL — The fungus that causes tar spot overwinters on leaf debris, and spores are spread by the wind in spring. There are fungicides available but they’re difficult to use and don’t work very well. Your best bet for controlling this fungus is to rake up the fallen leaves in the fall and send them away in the yard waste.

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Cabbage looper
Trichoplusia ni

IDENTIFICATION — Now’s the time of year to be on the lookout for a small 1 1/2-in. green caterpillar with white racing stripes and a voracious appetite each spring in North America. The cabbage looper can eat three times its body weight every day! And with two to seven generations each year, depending on the length of your growing season, that’s a lot of plant damage.

The moth has mottled brown wings with a single silver spot in the center and most often lays a single pale yellow to green egg on a leaf. But clusters of six or seven eggs aren’t uncommon. Cabbage looper’s favorite egg hosts are cruciferous vegetables, such as cabbage, turnips, kale and others, but it’s not picky. About three days after the egg is laid, a caterpillar emerges and starts eating.

DAMAGE — Yes, a cabbage looper loves to eat cabbage, but it also munches on broccoli, cauliflower, potatoes, lettuce, tomatoes and cucumbers. Ornamental plants, such as mums, carnations, snapdragons, geraniums and hollyhocks, are also on the menu. Avoiding the veins of the leaves, the cabbage looper eats irregular holes and can defoliate a plant in no time. This can stunt growth or even kill the plant. Be sure to check the centers of broccoli and other plants, as a cabbage looper will sometimes bore its way into the heads.

CONTROL — You can hand pick any caterpillars that you find. Or encourage predatory wasps and ground beetles to live in your garden by avoiding insecticides and leaving leaf debris or mulch around for hiding places. In turn, they’ll do you the favor of eating these hungry caterpillars. For serious problems, try a spray product containing neem. This organic pesticide stops the caterpillar from eating and disrupts its growth so much the insect dies.

Click image to see a close-up.

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Yellow woodsorrel
Oxalis stricta

IDENTIFICATION — If yellow woodsorrel has something to lean on, it can grow to be 20 in. tall. But it’s usually more mounding to sprawling. It has tiny yellow flowers almost all of the growing season. Each leaflet is shaped like a small heart and folds up at night. When touched, the ripe seed pods explode to shoot the seeds great distances.

FAVORITE CONDITIONS — You’ll find yellow woodsorrel in flower beds, lawns and even containers. It grows in most any kind of soil, but tends to be less aggressive in fertile soil. And it tolerates both sun and shade.

CONTROL — The stems break easily, making it difficult to pull. But if you do it when the soil is moist, it’s much easier and you’re more likely to get all of the roots out. It’s easier to hoe out the shallow roots, and large areas of it can also be controlled by herbicides. This perennial spreads by seeds and underground rhizomes.

PHOTO: John Holtorf

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Ground ivy
Glechoma hederacea

IDENTIFICATION — Ground ivy, also known as creeping Charlie, is a perennial weed that spreads by seeds and above-ground runners. Each runner can be several feet long, with many leaf nodes along the stem. Wherever these nodes touch the soil they take root quickly to form thick, dense mats.

In midspring to early summer, purple flowers completely cover the plant. The foliage is small with a scalloped edge and if crushed, it gives off a strong minty smell.

FAVORITE CONDITIONS — You’ll find ground ivy’s at home in lawns or areas that are occasionally tilled. Moist, shaded spots are perfect for it, but it’ll tolerate almost anything, from full sun to dry, compacted soil.

CONTROL — In flower and vegetable gardens, pulling and hoeing are effective. Just make sure to pick up all of the pieces. Any part that’s left behind can grow a new plant. Once you get ground ivy under control, you’ll want to keep it from creeping back into gardens from neighboring areas. It’s a good idea to maintain a strip of bare soil around your garden where you can patrol occasionally and remove runners before they spread.

Since ground ivy can’t grow as fast in tall grass, set your lawn mower blade high. You can also use selective herbicides that won’t harm your lawn. Look for products containing dicamba, such as Acme Trimec ^® or Weed-B-Gon Lawn Weed Killer2 ^®. Read the instructions, but in severe infestations you may need to make at least two applications about 10 to 14 days apart to get rid of ground ivy.

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Foxtail barley
Hordeum jubatum

IDENTIFICATION — Growing up to 3 ft. tall, this upright grassy weed has wispy seedheads that look iridescent in the sunshine. Foxtail barley spreads by seeds and roots. Each seed has wiry bristles with tiny barbs that grip onto clothing or fur to help it travel to new locations.

FAVORITE CONDITIONS — Foxtail barley can grow almost anywhere with full sun and well-drained soil.

CONTROL — Dig this perennial from the soil or apply a non-selective herbicide in the spring as the flower heads begin to show.

PHOTO: Courtesy of Bradley Higbee,
Paramount Farming, Bugwood.org

from the wild side

Big-eyed bug
Geocoris spp.

IDENTIFICATION — These insects may not be pretty, but they’re good to have around. The appropriately named big-eyed bug is a predator other bugs steer clear of. There are 19 different species of big-eyed bug in North America, all with similar habits and life cycles. One of the most common, Geocoris punctipes, is shown above. Adults are about 3⁄16 in. long with transparent wings and a broad head as wide as the oval-shaped body. They have piercing-sucking mouthparts that they use to stab prey.

Big-eyed bugs usually eat whiteflies, aphids, mites, small caterpillars and even insect eggs. A single nymph can eat 150 tobacco budworm eggs while in this stage and an adult, up to 80 mites per day! They’ll occasionally feed on plants when prey is scarce, but damage is minimal.

LIFE CYCLE — Big-eyed bugs only live about 30 days. They emerge in spring to feed and lay eggs. These eggs hatch in about a week into tiny juveniles that look just like the mature bugs. What makes this insect so helpful is that males, females and all stages of juveniles eat insects — mostly those you don’t want around. Late-season adults spend the winter in leaf litter, turf thatch, under loose bark or any place they can find. Insects like big-eyed bugs that overwinter as adults have a chemical in their system to prevent ice from forming, almost like anti-freeze. Once the body temperature reaches 55 degrees F in spring, they start waking up.

Big-eyed bugs are so abundant you don’t have to do anything to attract them to the garden — they’re probably already there. But to encourage more of these hungry predators, avoid spraying insecticides.

Click image to see lookalikes.

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Poison ivy
Toxicodendron radicans

IDENTIFICATION — Just about every gardener’s least favorite weed! Not only does poison ivy grow and spread rapidly, but it gives many people an itchy, sometimes painful, rash. This woody weed can have an upright form up to 7 ft. tall or appear as a climbing vine, hanging on to trees or fences with dark aerial roots.

The three leaflets, which are sometimes shiny, have a wavy edge and a reddish cast and stem. Insignificant green-white flowers appear in late spring, followed by fruit that ripens about the same time the leaves turn red in fall.

FAVORITE CONDITIONS — Poison ivy prefers moist, rich soil in full sun to part shade. You can find it along roadsides, in wooded, moist or wet areas.

CONTROL — To pull or cut back the plant, be careful to keep urushiol, the sticky oil that is present in all parts of the plant, off your skin. Wear long pants, long sleeves and double gloves. If you don’t want to handle it, spray the plant with a systemic herbicide like Roundup^®, but it’ll take time and several applications to eradicate it. You can also dab or spray the cut ends of the vine with a systemic brush killer (again, a herbicide that contains triclopyr is best.)

LOOKALIKES — Another sneaky thing about poison ivy: It has some lookalikes. You’ve probably heard the old saying, “Leaves of three, let it be.” That’s good advice — poison ivy doesn’t really stand out in a crowd, but it always has three leaflets on each leaf.

However, small box elder (Acer negundo) seedlings look similar, and they tend to grow in the same places you’ll find poison ivy — along the fence, behind the garage, and other places where you may not do a lot of cultivating. The clues? Boxelder stems often have a grayish “bloom” on them.

Another lookalike is Boston ivy (Parthenocissus tricuspidata), especially small, new growth. Unfortunately, it has a red stem, just like poison ivy, so it’s a little harder to tell apart. Usually the leaf edges are a little more jagged, and the leaves are slightly smaller. But when in doubt, it’s best to be careful!

problem solver

Sooty mold

IDENTIFICATION — Have you noticed a coating that looks like chimney soot on your plants, trees or even the deck or sidewalk? More than likely, it’s sooty mold. This harmless fungus grows on honeydew, a clear, sticky substance secreted by sucking insects, such as aphids, scale, mealy bugs and whiteflies. When these insects attack plants, the honeydew appears on the leaves and sometimes also on nearby surfaces, as well. The sooty mold doesn’t penetrate the leaf, bark or any other surface.

DAMAGE — While most of the damage caused by sooty mold is purely cosmetic, a thick layer on leaves or evergreen needles can reduce a plant’s ability to perform photosynthesis, or feed itself. This weakens the plant, making it more susceptible to other diseases or insects. It’s a particular problem for shade or understory plants, such as rhododendrons, hostas or hydrangeas, which already grow in low light.

CONTROL — To keep sooty mold from coming back, you’ll need to eliminate the insects producing the honeydew. Take a good look above the area where you see sooty mold. The most common sap-sucking culprits you’ll find are aphids and scale. Aphids are easily dislodged with a good strong spray from your hose. Use horticultural oil on scale insects to suffocate them. Some oils should be applied in late winter and others in summer. Also, some plants are sensitive to these oils, so be sure to check the label before you spray.

Once the insects and the honeydew they produce are gone, the mold will gradually wear away from leaf and stem surfaces. To remove stubborn spots on hardscaping, a little scrubbing with soapy water does the trick.

Click to see a foliage detail.

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Pennsylvania pellitory
Parietaria pensylvanica

IDENTIFICATION — Growing 6 to 18 in. tall, Pennsylvania pellitory has leaves with slightly fuzzy undersides. Click the image to see a foliage detail. At first glance, this spring weed’s narrow upright form looks broader because the plant often grows in dense colonies. The green flowers along the main stems have no petals and are barely noticeable.

FAVORITE CONDITIONS — Although it prefers part shade, you’ll find Pennsylvania pellitory in full sun if the soil never dries out. It reseeds rampantly, especially in areas that are tilled annually.

CONTROL — The shallow, fibrous roots are easy to pull or hoe out. (Check out our favorite hand hoe.) If you miss pulling a few weeds, red admiral butterfly caterpillars will enjoy eating the leaves. But herbicides are effective if you need to eradicate large stands of this annual.

Read about more spring weeds in the April issue of Garden Gate magazine. On newsstands now!