- Browning of boxwood: Is it boxwood blight?
- What’s Killing My Boxwood?
- Shrubs With Yellow Leaves
- Small Evergreen
- Large Evergreen
- Small Deciduous
- Large Deciduous
- Yellow Fall Foliage
- Butterfly Bush Leaves Turning Yellow: How To Fix Yellowing Butterfly Bush Leaves
- Why Butterfly Bush Leaves Are Yellow
- Additional Reasons for Yellowing Butterfly Bush Leaves
- Boxwood Basics
- Local News
- What Are the Symptoms You Should Keep an Eye Open For
- How to Make Sure Of The Possible Disease
- How to Treat the Problem
- How to Prevent An Infestation
Browning of boxwood: Is it boxwood blight?
Since boxwood blight has been found in Michigan for the first time in summer of 2018, growers, landscapers and consumers alike are concerned that their boxwoods could have boxwood blight. It is a legitimate concern because the disease has been found in Michigan and 27 other states. Boxwood blight (Calonectria pseudonaviculata) is a fungal pathogen of species in the plant family Buxaceae, which includes the popular boxwood, sweetbox and Pachysandra spp.
In boxwood, often the first symptom noticed is a large amount of rapid defoliation (leaf drop), which is indicative of a severe infection. Generally, part of the plant will become chlorotic or brown, and leaves will rapidly fall to the ground, leaving bare branches behind. Initial symptoms are generally first observed in late spring or early summer when close examination of boxwood leaves may reveal round, dark or light brown leaf spots with darker borders and potentially a yellow halo. These spots eventually grow larger and coalesce before turning brown or straw-like and dropping to the ground. Black, elongated, streaking lesions may also be visible on the stem. These can occur on the stem from the soil line to the shoot tips. If the weather is humid, the underside of the leaf will have a white, frosty appearance caused by the formation of upright bundles of fungal spores. For pictures of these symptoms, see “Preventing the spread of boxwood blight in landscapes.”
However, there are numerous reasons for defoliation and browning of boxwood plants. Here are seven common aliments of boxwood plants.
Winter injury is the most common problem that affects boxwood. It becomes apparent as the snow recedes and the uppermost or outermost leaves and stems on the boxwoods are brown. Buxus sempervirens is typically hardy down to USDA Zone 5. Plants are especially susceptible to winter damage in temperatures below -10 degrees Fahrenheit, especially in locations next to pavement or siding of the house with direct sunlight that warms the tissue up too quickly. Winter damage is especially distinctive in that the growth below the former snowline is still green. As long as the damage is not overly severe, growers can just prune out or prune off the damaged foliage.
Winter damage of boxwoods on the outermost growth and growth that was above the snowline. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.
Salt used for sidewalks and roadways can cause damage to boxwoods. First, the spray of the salt water on the foliage can cause the plant to desiccate in those tissues, killing the leaves on one side of the plant. Excessive salt washed into the soil can also change the water uptake of the plant, causing salt damage. In these cases, it is most identifiable when there is a pattern where the boxwoods closest to walking surfaces show the worst damage. It is also noticed in spring.
Salt damage on boxwoods at a residential landscape. The plant closest to the stairs to the porch show the most severe injury. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.
Boxwoods, like other plants, can show drought stress by the browning of foliage. Drought stress is the most severe in newly-planted landscapes where the plants are suffering from transplant shock, those without irrigation or rainfall for a long period of time, or those grown in very warm temperatures. The symptoms of drought stress are typically browning of the center of leaves and chlorotic foliage.
Drought stress of boxwood plants can cause the yellowing and necrosis of foliage. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.
Boxwood leaves can turn brown from the boxwood leafminer. The adult leafminer (a mosquito-like fly) lays its eggs between the layers of the leaf and the developing larvae feeds on the tissue. The adults emerge from the leaves, leaving an emergence hole where they exited. The infested leaves will develop brown patches as the larvae grow and heavily infested leaves will defoliate in the late fall and early spring.
Boxwood leafminer larvae feed on the inner tissue of boxwood leaves causing the browning of leaves of boxwood plants. This is distinguishable since there is often an emergence hole or a larva of the leafminer inside the leaf. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.
Volutella stem canker
In addition to abiotic problems and insect damage from boxwood leaf miner, boxwood is also susceptible to Volutella, a fungal pathogen caused by Pseudonectria buxi. Prior to the new growth in spring, the leaves will bronze and yellow. The fungus produces salmon/pink fruiting bodies when it is sporulating on the undersides of the leaves. On infected branches, the bark can become loose and they may dieback. It often causes the complete death of part of a plant.
Moist weather is conducive to the development of Volutella infection. One distinguishing difference between boxwood blight and Volutella is that the fruiting bodies or sporangia of boxwood blight are gray-white while they are pink-salmon for Volutella. In addition, the leaves do not fall off of plants with Volutella as they do with boxwood blight.
The photo on the left shows the pink fruiting bodies on the underside of the boxwood leaf. The right photo shows the dieback of a heavily infested boxwood plant. Photo by Jan Byrne, MSU Plant & Pest Diagnostics.
Macrophoma leaf spot
Boxwoods are also susceptible to Macrophoma leaf spot caused by the pathogen Macrophoma candollei. This parasitic fungal pathogen causes red-brown lesions on leaves and when sporulating has black fruiting bodies on the undersides of leaves.
Macrophoma leaf spot on boxwood leaves. Photo by Margery Daughtrey, Cornell University.
Phytophthora root and crown rot
Phytophthora root and crown rot can also cause the wilting and browning of the foliage on boxwood plants. The fungi Phytophthora spp. can cause plant stunting, yellowing of leaves, upward turning of leaves, death of root tissues and discoloration on the stem of the plant near the soil line. Leaves of plants infested with Phytophthora root rot do not have any fruiting bodies.
Dieback on boxwood plants from Phytophthora root and crown rot. Photo by Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org.
When looking at the boxwoods in your nursery or landscape, examine if there are any patterns to the damage and consider sending in a sample to get a confirmation by a diagnostic lab, such as Michigan State University Plant & Pest Diagnostics. These problems are often confused due to their similar symptomology. Diagnosticians will be able to help identify which of these common problems could be causing the plant damage.
For more information, check out “IPM Series: Boxwood” from University of Maryland Extension.
To learn more about preventing boxwood blight in commercial nurseries, check out “Preventing boxwood blight in nurseries” from MSU Extension, and for more information for landscapers and homeowners, check out “Preventing the spread of boxwood blight in landscapes.”
What’s Killing My Boxwood?
Don’t you wish you had boxwoods like these at Montrose Gardens in Hillsborough, North…
Boxwoods are supposed to be green, 24/7, 365 days a year. So it’s no wonder that when boxwoods turn brown, people get upset and demand answers. Why is this awful thing happening?????? As always, Grumpy knows.
The Two Main Culprits Absent a hobo who lives in your bushes and regularly relieves himself on their foliage, the probable cause of brown boxwoods is one of two soil-borne diseases — Phytophthora root rot or English boxwood decline. The first attacks American boxwood (Buxus sempervirens), English boxwood (B. sempervirens ‘Suffruticosa’), and littleleaf boxwood (B. microphylla). The latter attacks English boxwood. Above ground, the damage from either looks like this.
Image zoom emA diseased boxwood. Photo by Steve Bender./em
Healthy, deep green leaves first turn light green, then brown or yellowish, then straw-colored. Whole branches die and the foliage drops.
Dig up the afflicted plant and you’ll see why the leaves turned brown. Most of the roots have rotted away. Boxwoods can’t grow without roots.
What Can I Spray to Cure My Boxwoods? Both diseases are present in the soil, so spraying won’t help. Infected boxwoods are going to croak — it’s as simple as that. Some fungicides exist that you can drench the soil with to possibly protect your healthy boxwoods, but only professionals have access to them, so forget that. And while some new selections of English boxwood are said to be resistant to boxwood decline, unless you belong to the American Boxwood Society (a lively group), you’ll likely never see one.
So How Can I Prevent These Diseases? Healthy plants seldom get sick. Stressed plants do. It makes sense, therefore, to give boxwoods the proper growing conditions to keep them happy.
Boxwoods like full sun or light shade. Most important, they like loose, moist, fertile soil that drains quickly. Plant them in heavy, clay soil that stays wet and you might as well dip them in lava. So don’t plant in low spots where water pools after a rain or at the foot of a downspout. That invites Phytophthora root rot. And water them deeply during summer droughts. Drought stress promotes English boxwood decline. Don’t wet the foliage when you water. Splashing water can spread disease.
Can I Replace My Dead Boxwood With Another Boxwood? Sure. But since these two diseases live in the soil, your new boxwood will probably die of them too. Then you’ll get really peeved. So plant something else.
More Info on Boxwoods For additional reading on using and caring for boxwoods, check out these articles:
- “Boxwood Basics”
- “Boxwoods for Every Landscape”
- “Transplanting Boxwood Step-By-Step”
- “Boxwoods: Perfect For Pots”
Why are my Boxwood’s Leaves Turning Brown? I have not done anything different to my front boxwood hedges, but this year they are not fully green and healthy looking. I tried fertilizer but that did not help, what is the problem?
There are several different problems that could be affecting the health of your Boxwoods. For a true and accurate diagnosis, we would have to send a Plant Health Care Technician to your property to inspect, but for now, we will take some time explaining the few issues that we see quite often.
Boxwood Blight is a fairly new fungal disease that was originally identified in North America in 2011. Signs of this include lesions or dark streaking on the stems, brown spotting on the leaves, and defoliation (leaves falling off the branches). These warning signs should not be ignored, because if left untreated, Boxwood Blight will completely kill your shrub and can rapidly spread across a group hedge.
When looking at your boxwood, if you notice the outside leaves appear yellowish in color and smaller than the green ones, as though they have shrunken, you probably have Leafminers. Leafminers are fairly noticeable to the common eye. If you look closely you will see little yellowish-orange larvae. They tend to chew a tunnel through the top layer of the leaf, and then feed on the inside. As the larvae mature, they grow into reddish-yellow flies that will swarm around your boxwoods awaiting new growth. As new growth develops, they lay their eggs on the healthy leaves and so the cycle continues and your leafminer problem exponentially gets worse.
Winter burn is a condition that occurs during cold winter months when the leafs of a plant have lost their water and the roots are completely frozen and unable to replenish. Despite the fact that boxwoods are a very hardy evergreen, they are particularly susceptible to winter burn. Signs your boxwood is damaged because of winter burn include: the damaged portions of your shrub face the area the wind blows from (usually South or Southwest), foliage is damaged and dried out, and in severe cases, the stems are cracked.
In most cases, your Boxwoods can be revived and will bounce back to the hardy green shrubs you remember by next season. Unfortunately, in some instances, as with Boxwood Blight, if the disease has spread significantly, we may recommend removal of the infected plant. The goal with Boxwoods and all your precious greens, is preventative care. This is the number one reason why we created our Plant Health Care Program. Rather than always getting the calls to fix the problem, we want to help ensure the problem never happens. Spraying your shrubs with Horticultural Oils several times a year will help ward off diseases and insects. Also, ensuring your shrubs are nutritious and strong entering the winter season can greatly decrease the chances that cold weather will result in Winter Burn. These services and more, are all part of our Planet Health Care Program. Custom designed to meet the needs of your property and keep your plants healthy all year round.
For more info or to sign up today, please call us at 914-725-0441.
Shrubs With Yellow Leaves
When you think of adding color to the garden, perennials and annuals usually spring to mind. However, some shrubs offer color and visual interest with more than just their blossoms or berries. Evergreen shrubs with yellow foliage add a splash of color year-round, and the green leaves of some deciduous shrubs turn yellow in the autumn, providing a fall show. Plant yellow-leaf shrubs in moderation, as too many can distract from other plants, according to the Iowa State University Extension.
Gold Coast juniper (Juniperus chinensis Gold Coast) and Old Gold juniper (Juniperus chinensis Old Gold) both grow up to 3 feet tall and spread up to 6 feet. These compact shrubs have golden yellow foliage.
Rheingold arborvitae (Thuja occidentalis Rheingold) and Golden Globe arborvitae (Thuja occidentalis Golden Globe) have bright to deep golden-yellow leaves. The Rheingold grows up to 5 feet and the Golden Globe to 4 feet tall. Both produce more attractive foliage in sites with full sun exposure.
The common boxwood (Buxus sempervirens) has oval foliage with dark green tops and bright yellow bottoms. This hardy shrub grows between 10 and 15 feet tall. Boxwoods can grow in full sun to heavy shade but require well-drained soil to thrive.
The Aureo-variegata cultivar of common boxwood has variegated yellow and green foliage. This dense shrub can grow up to 20 feet tall and prefers moist, cool soil and full sun.
Goldflame spirea (Spiraea x bumalda Goldflame) and Goldmound spirea (Spiraea x Goldmound) both grow from 2 to 3 feet tall and produce pink blossoms in early summer. Goldflame has copper to orange spring foliage that turns yellow-green in summer. Goldmound has golden yellow leaves.
The Tiger Eye sumac’s (Rhus typhina Tiger Eye) golden-yellow foliage turns orange to red in autumn. This spreading plant can grow up to 6 feet tall and, unlike many other yellow-leaf shrubs, prefers light to partial shade.
Golden privet (Ligustrum x vicaryi) can grow up to 12 feet tall. When grown in full sun, this hardy shrub has bright yellow leaves. Plants grown in shadier spots have yellowish-green foliage.
Several cultivars of hybrid witchhazel (Hamamelis x intermedia) offer yellow foliage. These include Arnold Promise, which can grow up to 20 feet tall and produces yellow blossoms in summer as well as bright yellow to orange fall leaves.
Yellow Fall Foliage
The Rocky Mountain maple (Acer glabrum) grows up to 10 feet tall. The foliage on this multi-stemmed, deciduous shrub turns brilliant yellow in fall.
The red twig dogwood (Cornus sericea) and red osier dogwood (Cornus stolonifera) both display yellow to red autumn foliage. These deciduous shrubs grow up to 10 feet tall and can tolerate some shade.
Butterfly Bush Leaves Turning Yellow: How To Fix Yellowing Butterfly Bush Leaves
Butterfly bush is a common ornamental specimen, prized for its long flower spikes and ability to attract pollinators. This plant is a perennial, which dies back in fall and produces new foliage in spring. When it defoliates in autumn, the leaves change color naturally; but during the growing season, yellow leaves on my butterfly bush can signal other problems. Cultural or insect issues are likely the cause for leaves turning yellow on butterfly bush. Here are some potential causes so you can triage your yellowing butterfly bush leaves.
Why Butterfly Bush Leaves Are Yellow
Butterfly bush is aptly named because it draws bees and butterflies but also emits a strong scent in the evening which attracts moths. This plant has beautiful 6- to 12-inch long flower spikes but ashy green unremarkable foliage. If butterfly bush leaves are yellow, it might be due to plant stress or it might be an insect invasion. These vigorous growers are not subject to many disease or insect issues and are resilient enough that they don’t need regular babying. That being said, occasional problems do occur.
Cultural Issues for Yellowing Butterfly Bush Leaves
If you notice leaves turning yellow on butterfly bush, it’s time to investigate the possible causes. Buddleia prefers well-drained soil and full sun for best flower production. Wet roots can cause the plant to decline and the roots may rot in overly soggy conditions.
Soil pH is important to plant health and helps with uptake of nutrients. Butterfly bush should be grown in a pH of 6.0 to 7.0. If soil is overly acidic, phosphorus ions react with aluminum and iron to form less soluble compounds. That means that those micro-nutrients are not readily available to the plant.
If iron availability is low, the leaves will fade to yellow, leaving intact the green veins in the foliage. When butterfly bush leaves are yellow with green veins, this is a sign of iron chlorosis and can be treated by sweetening the soil with lime and fertilizing the plant to start it on the road to recovery.
Insects and Butterfly Bush Leaves Turning Yellow
Spider mites are common pests of Buddleia, especially when the plants are stressed. Dry conditions bring on infestations of these tiny sucking insects. It is this feeding method which saps the energy of the plant and results in symptoms like leaves turning yellow on butterfly bush.
There are several other sucking insects that might plague the plant, but spider mites are the most prevalent. Look for webs in amongst the fading leaves. This will be the clue to which insects are the culprits. Buoy the health of your plant by watering it deeply and regularly, giving it a foliar feed and spraying it with horticultural soap to combat the tiny pests.
Nematodes in sandy soil can also foul the health of the plant. Purchase beneficial nematodes as a solution. Avoid pesticides, as Buddleia attracts many beneficial insects that could be killed.
Additional Reasons for Yellowing Butterfly Bush Leaves
Disease is another concern when you see butterfly bush leaves turning yellow. Buddleia is a hardy, tough plant that is rarely attacked by any diseases, though they do happen.
Downy mildew causes a coating to form on leaves, diminishing their effectiveness at photosynthesis and eventually causing leaf tips to fade and the entire leaf to die. It is most common when plants experience cool temperatures and extended leaf wetness.
Herbicide injury from drift is another possible cause for yellowing leaves. Spraying non-selective herbicides in windy conditions will cause some of the poison to float on the air. If it contacts your butterfly bush, the infected areas will die. This is most often the leaves at the outside of the plant. If you are using a systemic herbicide, the poison will transport into the vascular system of your Buddleia and can kill it. Use caution when spraying and avoid applying in windy conditions.
Follow these tips to keep your plant happy. Van Chaplin, Tina Cornett
A healthy, green boxwood looks about as dignified as a plant can be. It adds an air of formality and permanence to the landscape, taking center stage in winter when trees are leafless and then receding gracefully into the background in summer when flowers dominate. Its tidiness and ease of maintenance make it a favorite just about everywhere it grows. But if yours appears more sickly than stately, one or more of the following factors may be to blame.
- Poor drainage–Boxwoods can’t take standing water and heavy, wet soil. Poor drainage leads to root rot, which in turn causes parts of the shrub to become light brown and die. You can prune out the dead stuff, but unless you improve the drainage by redirecting excess water or amending the soil with lots of organic matter, the whole plant will eventually croak.
- Fungus–When a shrub is sheared to produce denser outer foliage, dead leaves and stems can accumulate, unseen, in the center of the plant. This creates an incubator for fungal diseases that can cause potentially fatal dieback. To stop this, prune back all dying branches to healthy wood (as indicated by the green cambium layer just under the bark). Remove all debris from the center of the plant, and thin out some of the outside growth so that air and light can reach the center.
- Fluffy and Fido–When scent-marking pets pass by your plants, yellow and brown leaves soon follow. Repeated dousing can kill entire branches. Applying a product such as Lambert Kay Boundary or De-Fence Dog and Cat Repellent will discourage return visits.
- Exposure–Boxwoods thrive in full sun or light shade, but they don’t like exposed, very windy sites, particularly in winter. They’re generally cold hardy everywhere in the South. But if you live in the Upper South, seek out an especially hardy selection, such as ‘Winter Gem,’ ‘Wintergreen,’ ‘Green Beauty,’ ‘Green Mountain,’ or ‘Green Velvet.’ As a bonus, these selections also remain green throughout the winter. Many others turn bronze during this season.
- Location–Boxwoods won’t grow in the Tropical South, so don’t waste your time. In the Coastal South, Japanese boxwood (Buxus microphylla japonica) seems better adapted than other types.
- Nematodes–Common in moist, warm, sandy soils, nematodes are microscopic worms that feed on plant roots. They are a serious problem for the plant in Florida, causing large sections of foliage to yellow, wilt, and die. There is no easy cure. To put it simply, if your soil has nematodes, don’t plant boxwoods.
So what should you do if your plant is ailing? Some can be saved, while others aren’t worth the trouble. If 3 feet tall or less, prune back the dead branches to live wood now. Also, open up the center of the plant. New growth will sprout this spring. At that time, sprinkle one or two cupfuls of a slow-release, natural fertilizer, such as cottonseed meal or Plant-Tone 5-3-3, around the shrub, and water it in. Eventually, the plant will fill out.
But if you have a huge boxwood with big dead spots and it’s a slow grower such as English boxwood (B. sempervirens ‘Suffruticosa’), it’s time to face the music. By the time the plant grows back, you’ll be pushing up daisies. Replace it with a new one.
Boxwood is a beautiful bush – until you shear it and shear it some more. Over time, all that shearing transforms boxwood into a ball of green veneer with a dead center.
“This was sheared because you can see the repeated action inside the plant,” says York extension agent Jim Orband, pulling back branches among American boxwoods – Buxus sempervirens – in the sunken garden at the Nelson House in Yorktown. Orband recently used those boxwoods to show volunteers at the Nelson House how to selectively prune the plants so new foliage will fill in. Pruned properly, those fatigued boxwoods will return to their glory. Here’s what he taught the volunteers.
Get to know your plant. It’s easy to confuse yaupon holly with common boxwood because the two look so much alike. Each has nice small evergreen leaves. But, there is a distinguishing difference – look at the leaves and how they grow. At left, you see the alternate leaf pattern on yaupon holly; the leaves are arranged in an alternate leaf pattern, meaning they appear singly on alternate sides of the stem, not in pairs.
Boxwood, on the other hand, grows with an opposite leaf pattern, meaning leaves are arranged in pairs along a stem or shoot.
Use the proper tool. Bypass pruners make clean, sharp cuts on many kinds of wood, including boxwood stems. Slant your pruning cut so water sheds off the stem, away from the remaining bud. Disinfect your pruning tools between plants, using rubbing alcohol, Listerine or Lysol. Place the alcohol in a plastic container with cotton balls; retrieve a cotton ball periodically to clean the pruning tool and then simply return it to the container with the alcohol when done. Virginia Tech does not recommend household bleach to disinfect any pruning tools because it’s corrosive and potentially harmful to the user.
Create “windows.” Identify browning or yellowing foliage and selectively remove it; prune back about six to eight inches so side buds (lateral) can emerge and develop. This type of pruning removes the tip-end bud (terminal bud), causing growth hormones in the plant to push out the side buds. Do this throughout the plant to create areas – or “windows” – where light and air can penetrate the plant.
Take it to the ground. In some instances, it’s best to use a pruning saw to remove old, thick branches that are diseased, dying or dead. Use the thumbnail test to determine if plant wood is healthy; scratch the bark with your nail, going down the stem until you find green wood.
Here, Orband takes dying trunks back to the base of the plant. You can use this method of pruning to allow a “bay window” of light to enter the plant. Eventually new foliage will emerge at the base of the plant and along the sides of nearby stems.
When you remove an entire trunk, cut at the collar, or the swelling where a branch joins the main trunk. You do not need to use any wound dressing paint, glue or tar on freshly cut limbs or branches, according to Virginia Cooperative Extension; research shows wound dressings trap harmful fungi and/or bacteria. Woody plants naturally seal wounds within 12 hours to prevent pathogens from doing damage.
Creating these big windows of light may seem drastic, but it’s a cultural practice that improves the plant’s overall health and good looks, says Orband.
Once you get boxwood rejuvenated, avoid snipping only the outer edges or you will be back where you started – having only a green veneer and no good interior growth.
It’s way too soon to dig gardens or apply fertilizers, but plump magnolia buds and bright yellow willow branches invite us to one of the first steps in spring land care. It’s time to inspect woody plants for winter damage, diseases and insects.
According to Jeremiah Green, an arborist with The Care of Trees, an affiliate of the Davey Tree Company based in Hamden and Norwalk, a lot of people call their offices about evergreens this time of year.
“They see browning on the needles and worry the tree is dying,” Green said. “In reality, some browning is completely natural — while other times it’s a cause for concern.”
He says that winter weather makes it difficult for evergreen trees to supply their needles with enough water, which leads to drying and browning. Most evergreens naturally drop some needles in fall and winter.
“White pines, for example, drop about one-third of their needles during the dormant season. That’s their cycle,” he said. “But if you see an entire side of the tree turn brown, and it is in direct sunlight or has a lot of wind exposure, the tree may have winterburn.”
Winterburn results when intense winter sun heats needles and leaves above the ambient temperature, and it can affect broadleaf evergreens such as rhododendrons and boxwoods as well.
If the needles or leaves are already dry, the problem is worse. Damage usually appears on the southwest side, where sun is hottest. Sometimes only the tip of the needle turns brown while the base remains green.
Prevention of winter damage begins in the prior growing season, according to Green.
“Keep trees evenly watered throughout the growing season and into the late fall, particularly young trees,” he said.
As for expensive or highly visible landscape plants, “Anti-desiccants can be helpful. They put waxy coating on leaves, which helps shield leaves from moisture loss.”
Green says people often call this time of year about spruce damage, particularly Colorado blue spruces.
“The tree is native to high altitudes and a drier climate,” he said. “Outside of its native range, it can get a disease called cytospora canker.”
The problem appears as cankers on the on the lower limbs and trunks, accompanied by white sap droplets. The lower branches lose needles and die in an irregular pattern. “There’s no treatment for cytospora other than encouraging the overall health of the tree,” he says. Early identification makes a difference.
March is also a good time to look for insects.
“Some signs include small holes in the bark and sawdust in the branches and on trunks,” Green said.
He recommends the use of “spring dormant oil,” a name that refers to the dormancy of the plants, not the oil. This horticultural spray can reduce the populations of spider mites, aphids, scales, several types of adelgids, lace bugs and more.
“It’s an old practice that has stood the test of time,” he said. “It has extremely low toxicity and it doesn’t hurt beneficial insects because, for the most part, they haven’t emerged yet.”
Green’s definition of good tree care includes the possibility of selective pruning to remove dying branches. A steady water supply makes a big difference, especially to young trees.
It is helpful to keep lime and lawn care treatments separate from tree areas. Lime raises pH, which is good for grass but not for most of our regional trees. Lawn fertilizers can burn the roots of young, newly planted trees.
It is also helpful to spread one-half inch of finished compost under branch drip lines, and cover with two to three inches of mulch. No mulch or compost should ever touch the trunk.
“Pine needles or leaf litter are great sources of mulch,” Green said, “but not gravel, rubber or dyed mulch.”
Gravel adds no organic matter, and according to Green, dyed mulches sometimes have a lot of termite pesticide, which can be bad for the trees.
If you decide to get help with pruning or spraying, remember that arborists are licensed in this state. The Connecticut Tree Protective Association provides a searchable database as well as a list: ctpa.org/find-arborist/.
Kathy Connolly is a landscape designer, speaker, and writer from Old Saybrook. Contact her or view her speaking schedule at www.SpeakingofLandscapes.com
Aphids, mites, lace bugs, borers and leafminers attack many species of woody plants, including boxwood, privet, Indian hawthorn, holly and evergreens. These insects suck vital juices from the leaves, stems and branches, causing leaves to turn partially or completely yellow. The leaves may die or drop off the plant prematurely. Leafminers hatch inside leaves while the larvae of borers burrow beneath the bark to feed. Some insects that do little damage to the plant themselves can transmit often deadly diseases as they feed. Use a forceful spray with the garden hose to knock insects off the hedge and repeat two or three times. If the hedge is still infested, you can use horticultural oil or insecticidal soaps to smother the insects. Prune infested areas of the hedge and burn the cuttings. Gather all fallen leaves and other plant debris from around the hedge and burn that, too. If the infestation is severe, treat the plant with insecticide, but make sure the product is formulated to kill the type of insect infesting the hedge and is safe to use on the plants forming the hedge. Japanese beetles and other large insects may also attack the foliage and cause the leaves to yellow. Pick off beetles and other large insects by hand and drop them into a bucket of soapy water to kill them.
Despite being one of the easiest to maintain greenery in your garden, your own private hedge still needs care and attention. Besides the basic watering, weeding and occasional compost, you need, as you might have guessed, to keep an eye open and combat any possible disease that may affect it.
The plants of your privet hedge can be affected by numerous types of diseases, among which the most common are the honey fungus and the wilt.
What Are the Symptoms You Should Keep an Eye Open For
For starters, you should know that the wilt is, in fact, a form of fungus that attacks the plants in the privet hedge as well as other types of greenery. The fact that a plant has been affected by wilt can be seen at the leaves. These at first curl, then will gradually turn yellow or a tone of reddish and then die and fall off.
The honey fungus attacks at first the root of the plant. This in turn will affect the overall state of health of the plant, with clear signs being late leaf sprung in spring or healthy green leafed branches beginning to die.
How to Make Sure Of The Possible Disease
Now, the symptoms are quite clear for both diseases, but, it is highly recommended that you carefully analyze whether or not the disease is correct, so that that you can effectively combat them.
In case you suspect that you hedge has been infected by wilt, in order to make sure you need to carefully peel off a piece of bark. If the wood seems to present a discolored tone, then this means that wilt is the cause.
If you suspect that honey fungus is the cause of your problems, then you need to carefully inspect the roots of the plant. Check whether or not you can identify cream colored fungi, yellow mushrooms or a strange production that is very similar to black boot laces.
How to Treat the Problem
In order to treat the wilt problem, you need to use fertilizer that has a high concentration of potassium and a low concentration of nitrogen. When you use the fertilizer, take note to sterilize the gardening tools before and after use. If you cannot see any significant improvement, remove the plant with the root intact and avoid planting another plant in its place.
Unfortunately, in case of honey fungus there is no actual treatment, and the plant needs to be dug up with the roots intact and removed.
How to Prevent An Infestation
To prevent an infestation with wilt, we recommend that you seek privet species that have a high resistance to the disease.
To prevent honey fungus we strongly recommend that you use well drained soil and clean wood mulch in your gardening.
Courtesy Bob Morris Japanese privet do better when planted in wood mulch, rather than rock mulch.
Q: We have had these trees in our backyard for 15 years. I don’t know what they are. All of a sudden, one has a bare spot. What might this be? I enclosed a picture.
A: From your picture, the plant looks like Japanese or Texas privet. Privets are notorious for looking bad, leaf drop and twig dieback, when they are not watered frequently enough or not given enough water.
They usually do nicely in lawns or when surrounded by other plants with a similar water requirement.
Typically they do not perform well when planted by themselves in rock mulch or if the soil becomes excessively dry between irrigations. I would like to see the rock mulch replaced with wood mulch or other plants located around the base of the plant that require a similar watering frequency.
These extra plants provide some additional water to the soil and help keep it from drying too much.
Q: Every year about this time my grapevines become infested with gnats or some form of small flying bugs that swarm. Because I have my grapes trellised over a walkway, the gnats are a real nuisance when walking or sitting under the vines. What are these bugs, and how do I get rid of them?
A: It is a bit difficult to suggest a control without knowing which insect this might be.
Gnats are not a common problem on grapes this time of year or actually any time of year. Leafhoppers and whiteflies are, however.
Leafhoppers are small insects that “hop” from grape leaves but do not fly. They do hop off leaves in large numbers when you get close to the plants and can get in your face, nose and mouth. They are a nuisance, but flying does not fit their description.
We occasionally get whiteflies in grapes but as their name suggests they are “white.” They swarm, are small and also a nuisance. Gnats feed off decaying matter and small feeder roots of plants and do not normally feed on grape plants. They are more typically a problem during cooler times of the year or infesting houseplants.
Approaches to controlling leafhoppers and whiteflies are different from each other if, in fact, one of these is your problem. Leafhoppers leave tiny black specks on the leaves (their poop) and feeding damage makes the leaves have a bronzy appearance, speckled or appear off-color.
Whiteflies may also cause leaves to discolor but usually leave behind a sticky residue on leaves from their feeding. Since gnats don’t feed on plant leaves, they do not cause damage to the leaves but can be a nuisance.
Spinosad, applied in May and June, will usually reduce leafhopper numbers and help prevent their populations from escalating. Applied later than this has little control on adult insects.
Whiteflies are difficult to control but repeat applications of soap sprays, followed by Neem sprays, usually reduce whitefly numbers.
Q: Why are the leaves on my roses turning black?
A: There is quite a bit of shade on the leaves in the picture you sent. Is that typical? Too much shade could cause leaf drop.
One of your pictures has yellow leaves with green veins, typical of iron chlorosis, a lack of available iron. Otherwise these leaves look like they are dying back from the edges, a problem called leaf scorch.
Leaf scorch can be caused by a lack of water, salinity that is high levels of salts in the soil, rose cane borers that are disrupting the flow of water to the leaves, root dieback from root rot, disease such as collar rot, soil mineralization from a lack of organic matter in the soil and probably a few I didn’t think of.
Make sure these roses are getting adequate sunlight, soil amendments and wood mulch, watered appropriately and not excessively, fertilized appropriately including iron fertilizer once a year.
Roses have a life expectancy of about 10 years for most gardeners or a bit more if you care for your plants. Many homeowners hold on to roses much longer than they should and have difficulty replacing them when they should.
If these are in bad condition, replace them. Do not put roses in these locations if there is not at least six hours of full sunlight.
Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com. Send questions to [email protected]