Anthracnose Oak Anthracnose
Apple Scab Plants for Wet Sites
Arborvitae Dying Powdery Mildew
Ash Decline/Leaf Galls Propagation
Bark Splitting/Trunk Damage Pruning Evergreens
Birch Dying Rejuvenating Flowering Shrubs
Black Knot on Cherry Rhododendron Rot
Blue-Green Fungus on Trees – Lichen Rose Black Spot
Cedar Apple/Hawthorn Rust Tar Spot
Dutch Elm Disease Tree Decline
Eastern Tent Caterpillar Tree Farm
European Chafer Salt Damage
Fertilizing Trees Selecting Trees
Fireblight Spruce Galls
Japanese Beetle Viburnum Leaf Beetle/Id
Lilac Blight White Pine Weevil
Living Christmas Tree Winter Injury
Losing Leaves Wisteria
Magnolia Scale
Q. 1/13 I am going to be planting conifers to start a tree farm in Rushford. I was wondering if there is any help available in picking the location, type and time of planting. I have a catalog from the NYS dept of Environmental Conservation that pointed out you could help. I have about 30 acres of old pasture land and 70 of wooded land. I would like help in using the land to produce tree and help the environment.
A. First you need to think about your objectives for this "tree farm" - Christmas trees, timber plantation, wildlife cover. The more specific you are, the easier it will be to determine what you should plant. Two resources to help are the New York Forest Owners Association and the Master Forest Owners Program . Master Forest Owners are trained volunteers that are available to come visit your land and help you define your objectives.
Next, make an assessment of the soil characteristics. Dig test holes to determine soil drainage, texture and pH. Learn more about site assessment from Cornell's Urban Horticulture Institute (pdf).
Salt Damage
Damage to plants from roadside salt can become evident by various symptoms. Evergreens (spruce, pine) will show brown or yellow needles (see winter damage below). Look for new growth on affected branches before pruning.
On deciduous plants (trees an shrubs that loose their leaves in winter) salt spray causes buds to die and new sprouts to form right below them resulting in a witches broom effect (right). Choose plants that are tolerant of roadside salt for new plantings.
Plants for Wet Sites
Q. 2/6 Last year I purchased a piece of property which has a pulsing underground spring at the top edge of the hill. There is a field between the ditch and the bottom of the hill which is also very wet. What plants would be best to absorb much of the water on the hill?
A. There are many plants that will exist in wet sites, but you can not use plants to remove significant amounts of water, especially if you expect to control ground water anytime between October and May, when plants are dormant. to find plants suited for wet soils go to University of Connecticut's Plant Database. Under basic traits/USDA hardiness zones, select zone 4. Under Sites Characteristics/Soil Moisture Drainage, select wet. To control surface drainage try calling a contractor experienced in grading.
Fertilizing Trees
To fertilize trees, you have the following options.
1. Determine if it is needed. - Fertilizer is not a "cure-all" and in some cases can be detrimental. Check the trees vigor by measuring annual growth from the terminal bud to the first ring of bud scale scars. If growth on a standard tree is 6" or more, fertilizer would not needed.
For apple trees, none is needed if annual growth is 18-24" on a young tree, and 10-12" on a mature tree. For Inadequate growth use Ammonium nitrate (33-0-0) - 2 oz/ young tree, 4 oz/mature tree or 10-10-10 or 10-6-4 - 6 oz/ young tree, 12 oz/mature tree.
2. Take soil samples and submit to Cornell's Nutrient Analysis Lab for recommendation. The lab can determine which nutrients are lacking and can provide recommendations.
Many times inadequate growth or symptoms of dieback result from poor soil qualities (too wet, too dry, too compacted) and not lack of soil nutrients.
Black Knot on Cherry
Q. 4/4 Last year we noticed many hard black substance growing on branches of our cherry tree. Is there anything we need to do to save the tree?
A. The growth you describe is a fungus called Black Knot. This fungus grows on plum and cherry trees. All of the growths should be cut off, or remove the entire tree should be removed, if it is too extensive. Branches should be pruned 8-12" beyond the fungus. Sterilizing your pruners between cuts will help prevent infecting new wood as you cut. Do not leave a branch stub when pruning, but cut back to the next closest twig or branch. The black knot fungus gall (the hard black growth) takes two years to develop. In the first year it just looks like a swelling or split in the branch. If you do not cut these out, more galls will develop. You can still cut them out this year. Try to get to them before the leaf and flower buds open. You can also apply a protective fungicide spray in spring when the flowers are opening. Check the pesticide label for directions.
Selecting Trees
Q. 4/15 Is there a source for fast growing trees, including fast growing fruit trees?
A. What you may want to do is decide on a tree the grows fast, and is suited to the site where you'll plant it, and look for it at local nurseries. Trees must have appropriate light, drainage and space to grow. Will the tree receive full sunlight (6 hours or more) or partial shade? Is the soil well drained? Dig a hole about 12" deep fill it with water, let in drain then fill it again. Measure the depth of the water when you fill it and again after one hour. If drainage is faster than 4"/hour, drainage is OK. How much space does the tree have to grow? Are there overhead wires, buildings or pathways nearby? Answer these questions and I can give you a list of trees.
Go to selecting trees. Find recommended trees for planting on you septic drain field. More information on selected trees may be found at the following web sites: University of Connecticut's Plant Database , US Forest Service Tree Fact Sheets<
Bark Splitting/Trunk damage
Q. 4/22 I was looking at my tree closely and noticed that the trunk has split. Does that mean it's hopeless?
A. Bark splitting can be caused by wounds from pruning, insect borers, mechanical damage from mowers and line trimmers, canker diseases or planting too deep. The only thing that you can do to help is to perform basic tree care; mulch around the trunk, water when the soil is dry under the mulch (check weekly during dry periods), and do not fertilize after June, if at all. If the tree is small, it may grow around the wound. If it is a large tree, is may be wise to have an arborist look at it to determine if the tree is at risk of failing or if it can be saved.
Mulching is the single best thing you can do for your tree. Mulch prevents and alleviates compaction, keeps soil cool and moist, and protects against mower and line trimmer injury. Much can be any organic product such as hardwood, bark, pine needles, etc. Depth should be 3-4 inches, but taper to the ground at the trunk. Do not mound mulch around the bark of the tree as this can cause sites for decay and insect attack.
Spruce Gall
Cooley spruce gall adelgid causes small, pineapple shaped galls on the ends of branches. Treat mid-to-late April, before galls appear, with horticultural oil (do not use on blue spruce).
Winter Injury
Q. 5/6 I see many evergreen trees along the road that appear to be dying. Is there a blight going around killing them?
A. Trees that I've seen around the state (fir, spruce, pine, yew) are showing brown or yellow needles. While some opportunist fungi may be present, the cause is most likely the combination of last summer's ('02) drought and this cold winter. Trees going into winter under drought stress have insufficient moisture reserves so sun and wind can desiccate needles. Also, stressed trees do not tolerate cold temperatures as well. Wait for new growth to begin before removing any branches. They may still be alive. In most cases, new needles will grow past the brown needles, hiding the damage. Be prepared for the next winter by mulching under the drip line of all trees and water during dry periods.
Rejuvenating Flowering Shrubs
Q. 5/24 My Potentilla has leaves that have brownish spots appearing on its leaves. Any ideas?
A. Potentilla are susceptible to few leaf spot diseases and mildew but rarely are they a serious threat to the plant. Potentilla should thrive in sun to light shade. Many flowering shrubs become less vigorous and ragged as they become overgrown. Pruning may help to rejuvenate it. You could prune a third of the largest branches by cutting them back to the ground, or prune all branches back heavily (to the ground) late next winter. More on Minimum Effort Ornamentals.
Lilac Blight
Q.5/26 My lilacs are dying. Should I cut them down?
A. Bacterial Blight of Lilac causes new growth to turn dark brown and die back quickly. Cut out and destroy infected shoots as soon as symptoms appear disinfecting tools between cuts. When severe, spray with copper fungicides once in mid-September.
Viburnum Leaf Beetle
Q. 5/27 I've noticed that many of the arrowwood shrubs, that grow in fields and forest edges are dying. What's going on?
Q. 6/9 The leaves of my snowball bush are being eaten by little worms. What can I spay them with to kill them?
A. The snowball bush and the highbush cranberry , (Viburnum opulus), are popular flowering shrubs in many home landscapes. The arrowwood, (Viburnum dentatum), is a native shrub that dominates many open fields. Both have come under attack by the viburnum leaf beetle. The grubs have riddled leaves with holes, in some cases causing them to shrivel up. In July, the adult beetle emerge and may cause further defoliation of susceptible species.
This leaf beetle feeds only on species of Viburnum. Most resistant species include Koreanspice viburnum (V. carlesii), doublefile viburnum (V. plicatum var. tomentosum), Judd viburnum (V. × juddii), leatherleaf viburnum (V. rhytidiophyllum), Tea Viburnum (V. setigerum) and Siebold Viburnum (V. sieboldii). Moderately susceptible include Hobblebush (V. alnifolium), Burkwood viburnum (V. burkwoodii), Carlcephalum viburnum (V. carlcephalum), Witherod Viburnum (V. cassinoides), Linden Viburnum (V. dilatatum), Nannyberry (V. lentago), Blackhaw Viburnum (V. prunifolium) and Lantanaphyllum viburnum (V. × rhytidiophylloides).
A number of pesticides may be effective in controlling this pest. Carbaryl (sevin) or imidacloprid are used for control. Always read the label of pesticides. Spray when larvae first appear for best results. If damage from adults is excessive, a second application in mid-to late summer may be helpful. Pruning and destroying infested twigs after egg laying has ceased in the fall, anytime from October to April, is the most effective means of control for small scale plantings.
To add to Cornell's research on this pest become one of Cornell’s citizen scientist’s, who are tracking the beetles spread and preferences.
Viburnum Identification
Q. 6/8 My friend has a Viburnum that is approximately 8' tall. It produces medium sized white round snowball flowers. It is also very fragrant. Can you help me to identify this shrub? Thanks in advance!
A. Viburnum is a very common flowering shrub with over 20 common varieties. From your description, it could be V. opulus, or V. carlesii. For clues and photos to aid in identification of viburnums, go to our Viburnum Identification page.
Apple Scab
Apple Scab appears as olive brown spots on the leaves and fruit in summer. Reduce overwinter source by removing leaves and apples from last year. Good pruning will reduce number of sprays needed. Apply a registered fungicide from tight cluster (flowers buds visible but no color) until 2 -3 weeks after petal fall. Do not apply captan within 10 days of a dormant oil spray.
Cedar Apple/Hawthorn Rust
5/31 Q. In mid-May our mature Cedar tree developed bright orange "sacks" at the tips of the branches. We also have several crab apple trees and I am concerned about cedar apple rust. What can I do to prevent this from happening? The bright orange has disappeared so should the Cedar be sprayed and with what? Also the crab apples?
A. You are correct in your diagnosis of cedar apple rust. Remove the orange growths from the cedar (juniper) as soon as they appear to prevent spores from spreading to the crabapple. Similarly, cedar hawthorn rust alternately effects hawthorns. The crabapple (or hawthorn), which would get bright orange spots on the leaves if infected, may be sprayed with chlorothalonil or mancozeb when the orange masses appear on the cedar and three times thereafter at 10-14 day intervals. When using pesticides, always read the label. More on Cedar Apple Rust.
Losing Leaves
Q. 6/4 For about a week, one of my maple trees has been dropping its leaves while they are still green. The trees are 40 years old, at least. Do you have any ideas? Thanks for any help!
A. If you don't see bare branches the tree will probably be fine. Trees may put on extra foliage in the spring due to plenty of water or fertilizer. They may then shed excess leaves, once hotter dryer temperatures begin, to control moisture loss. If the defoliation continues or you see branch die back call an arborist in your area to evaluate the tree. Also, a late spring frost may have damaged some leaves to cause them to fall, or there may be an insect feeding on the leaf stem. Then again the tree could be under some kind of stress (soil compaction, drought, flood). Trees can lose 50% of their leaves without losing much vigor. More on Winter Injury or Maple Decline, See also Recommendations for Trees and Shrubs Diagnosed with Unidentified Stress Problems
Oak Anthracnose
Q. 6/11 The leaves on my English oak are turning brown and shriveling up. What can I do to save the tree?
A. Trees in the "white oak" family are susceptible to oak anthracnose caused by the fungus Apiognomonia sp. Newly expanding leaves develop brown spots and shrivel up. Severe cases can cause branch dieback but t is too late for control now anyway (June). The best thing that you could do would be to remove the fallen leaves in autumn to reduce the spread of the disease to next years leaves. In severe cases fungicides before bud break will prevent a second occurrence. Contact a New York State Certified Arborist for tree injection or sprays to large trees.
Birch Dying
Q. 6/16 We have a sick birch tree . The upper branches are drooping or wilting, and there is a relatively large patch of bark that is split on both sides of one of the branches. This tree is a favorite of woodpeckers as you can see from the holes around the bark split. Can we save it? Is it contagious? We have another birch tree that is still healthy for the moment.
A. Your birch looks like it may be infested with bronze birch borer. The larvae is a grub that tunnels under the bark disrupting the flow of water up the tree. This is likely the cause of the wilting branches. Sapsuckers and wood peckers dig into the bark to get at the grubs. Keeping European birch well watered and fertilized can sustain trees, however, this tree looks to be in poor condition and may be too far gone. Take care of the other trees by mulching around the base, and watering during periods of drought. Chemical applications can help repel egg laying by adult beetles, but only certified applicators have access to the chemicals strong enough for control. When selecting birch trees choose varieties with resistance to the borer River Birch, Betula nigra, and Japanese Birch, Betula platyphylla
Another pest of birch is the Birch leaf Minor which causes dark greenish spots expanding to blotches on leaves of birch. Mostly cosmetic injury only. Control first generation is most important. Highly visible specimens can be treated with acephate, dimethoate, and Imidacloprid (soil drench in November or March).
Rose Black Spot
Q. 6/17 Every year my rose bushes start out with beautiful green leaves and then the black spot starts. All my leaves fall off the bushes. Can you help please.
A. One way to decrease the severity of Black spot is by practicing Integrated Pest Management (IPM). When foliage is not wet, prune or remove and discard affected plant parts. In autumn, rake and discard or destroy all fallen leaves. Avoid wetting foliage overnight or for long periods of time. Use disease resistant varieties for new plantings. Some black spot resistant rose hybrids include: Hybrid teas (Charlotte Armstrong, Duet, First Prize, Mister Lincoln, Peace, Tiffany, and Tropicanna); Floribunda/Grandiflora, (Angel Face, Carousel,, Goldilocks, Love, Montezuma, Queen Elizabeth, Razzle Dazzle, and Sunsprite); Shrub roses (All that Jazz, Carefree Wonder). Available pesticides include potassium bicarbonate, mancozeb, thiophanate-mehtyl, copper, lime sulfur, and chlorothalonil; use according to label directions.
Eastern Tent Caterpillar
Eastern tent caterpillar feed on leaves of many fruit trees during the night and hide in tents during the day. Trees are not harmed unless defoliation approaches 100%. However, if trees have been stressed previously, defoliation should not be allowed to exceed 50%. If defoliation is high (especially with young trees) use a registered insecticide. Or, tents can be be pulled out with a stick and destroyed. Do not burn out or prune indiscriminately.
Arborvitae Dying
Q. 6/22 My arborvitae (white cedar) is turning brown.
A. There can be many causes for arborvitae foliage turning brown. Two possibilities are listed below.
Arborvitae Leaf Minor - Damage starts in tips of shoots causing leaves to be yellow or brown. Hold up to light to look for larvae within the leaf. If not too severe, prune off brown foliage. Insecticides may be applied Early May and mid August.
Spruce Spider Mite - Damage occurs to oldest (interior) leaves appearing as yellowing or stippling of foliage. Tap branches over a white piece of paper, mites will appear as dust-like specks moving about. White fast moving mites are predacious, feeding on the pest mites. If these are seen, do not spray. They will control the pest. If you find 10 or more mites and no predators, spray with horticultural oil or insecticidal soap.
European Chafer
Q. 6/26 I have several trees in my yard, most are evergreens and a pear tree too. At dusk I noticed thousands of bugs/beetles settling into the trees. The bugs are light brown/gold in color and are about 1/2 inch long by 1/4 inch wide. Do you know what these bugs are and if they are dangerous to my trees? Is there a way to get rid of them?
A. Most likely you are seeing a scarab beetle called the European Chafer. The beetle does not harm trees but the grub, which will be hatching from eggs in August (the adults are mating now), can cause damage to the roots of grass. You can check for the grubs in late August or early September by peeling back a layer of sod. If you see 8-10 grubs per square foot, then you may want to treat the lawn with an insecticide for grubs. Contact your local Cooperative Extension or nursery for recommended chemicals.
Ash Decline/Leaf Galls
Q. 6/26 I have noticed that a few of the white ash trees in my woods have lost all of their leaves.The trees are 6-8 inches in diameter with one about 12 inches and seems to be sporadic.Just today, I found a small ash with wilting leaves and upon inspection there were small pods wrapped up in the leaves. These pods were about an inch long, a pencil diameter and very hard. I took three pods off and opened them up. I found them full of very small grubs about an eighth of a inch long. Looking at them under a magnifying glass they had a thin brown strip running along the length on top. Could these little grubs be my problem or whatever laid them?
A. The gall on the leaf of your ash is called the Ash midrib gall and is caused by a small fly-like insect called a midge. Leaf galls exist on many different trees species and do not harm the tree.
The decline of your ash my be caused by a disease called ash yellows. This disease affects ash under stress. Ash is an intermediate shade intolerant species which means that they can grow well as saplings in shade but as they mature, they will die if not in full sun. To save the trees or regenerate Ash, first identify crop trees. A crop tree would be one that has favorable characteristics that coincide with your woodlot goals. In the case of ash, the goal may be timber production or wildlife food source. For wildlife, select female trees. Ash are dioecious - trees are either male or female. You can look now for flowers or the beginnings of the small seeds called samaras. Remove all other trees around the ash that have crowns touching or within 6'.
Tree Decline
Q. 7/1 I have a Maple that has major branches that have lost their leaves. This phenomena started last year and I cut the affected limbs back severely. The remaining trunk has lost 50% of the bark. This year another branch has lost it leaves. The rest of the tree appears healthy. This tree is over 15 years old. The site has not changed; has not been disturbed or treated.
A. This type of tree decline may have several factors influencing it; drought, poor soils, mechanical injury, and fungus. Leading causes of tree decline, that I see, is soil compaction/poor drainage and trunk injury. Soil compaction is heavy, hard soil that does not allow water and air to filter through and may impede root penetration. Compaction may occur naturally in clayey soils or be created by vehicles or even foot traffic. Remediation of compacted soil can be complicated and is best addressed when choosing and planting new trees. Check soil (pdf) pH to be sure that it is adequate. Create a mulch ring (minimum 2' diameter, maximum to the drip line) around the base of the tree to retain soil moisture and avoid lawn mower or line trimmer damage. Water when the soil under the mulch is dry. Avoid over fertilization or fertilizing after July 4th - this makes the tree more susceptible to winter damage and frost cracks.
White Pine Weevil
Q. 7/6 The top of my white pine is dying. Will it spread to the entire tree?
A. White pine weevil will cause the top of white pine or spruce to turn brown and wilt over like a shepherds crook. Prune out and destroy the brown, crooked leaders before late July before the larvae emerge as an adult beetle. Other pines and firs may also be attacked.
Fireblight
Q. 7/8 This tree obviously has a problem. Leaves died back quickly and blackening of the bark around area of missing bark. Do you have any thoughts on this one?
A. This looks like a disease called fireblight that affects trees and shrubs in the rose family (rosacea), particularly ornamental apples, pears and MT Ash. Carefully remove and dispose of infected branches as soon as they appear. Cut at least 6-12" below signs of infection. Prune out any remaining cankered branches during dormant season. Avoid high rates of nitrogen. Where severe, apply fungicide containing copper at bloom.
Anthracnose
Q. 7/9 Have you noticed that all sycamore trees in our area have not leafed out this year? I hope this condition will not damage these magnificent trees. I thought that these trees were late with the new growth of leaves. Here is is July, and they are still not fully leaved. Do you have any information on why leaves have not formed this year. Cold spring?
A. You should be seeing a second flush of leaves. A leaf disease known as Anthracnose hit susceptible trees early stopping development of young leaves. The trees responded by setting out new leaves. A similar thing has happened to some oaks. In most cases it is going to be OK. But I always say that with a bit of hesitation because you just never know.One defoliation and the tree will bounce back. Two in a row could cause dieback or death of the entire tree. Trees already in a stressed condition, along a roadside, damaged by construction, etc., may not come back.
Wisteria
Q. 7/10 I have a wisteria that has been planted for many years. It has taken over the tree I planted it next to but has never bloomed what can I do?
A. Wisteria need to be mature to flower, sometimes 10 years or longer. To encourage them to flower earlier there are a few things that you can try. Avoid nitrogen fertilizer. Wisteria are in the pea family and make their own N. Too much N encourages vegetative growth. Feed with triple super phosphate, 0-60-0, in the fall. Prune twice a year. Thin after flowering, removing crowded stems leaving only one or two buds on a branch. Cut back in fall after growth stops. Remove the weakest shoots in dense clusters at end of branches. Also, remove bean-like seed pods so more energy goes into flower bud production. Rejuvenate every three years. Cut back the most vigorous stems to about 3" from the main stem.
Japanese Beetles
Q. 7/13 Japanese Beetles love the leaves of my plum tree & mutilate it every year. We spray it and that seems to help some (until it rains, then we redo). Do you have any other suggestions for these annoying critters?
A. Japanese beetle feeding on leaves does not substantially hurt the tree. You can try Japanese beetle traps to lure the beetles away from your plum. Using the traps actually increases the number of beetles in an area, so place them 100 yards or more away from the plants your protecting. Controlling grubs in the lawn may help if you have a large lawn. But check for grubs in late August by pealing back sod and counting grubs. 5-8 grubs/sq ft indicate a high population however they may not be Japanese beetle grubs so you may need to have them identified at your local Cooperative Extension. Lawn insecticides should be applied in late August to September. Preventative applications, such as imidacloprid may be used where high populations of grubs have been found in the past and need to be applied in June.
Propagation
7/20 Q. I have been trying to root a nice sized cutting from a forsythia bush for over six weeks. It stays green, but no roots yet! I have changed the water every week or so. What is the matter? Thanx!!
A. Forsythia, and many flowering shrubs, may be propagated by taking softwood cuttings. That is the soft, light green growth on the tips of the branch that you would find in June. Just cut off this new growth, dip it in rooting powder, place in moist perlite and cover the pot and cuttings with a plastic bag. In 3-4 weeks you should have a mass of roots. Alternatively, bend a lower branch down so that it is in contact with the ground and secure it. Cover with soil and mulch and it should form roots over the season. Next year cut the branch off of the parent plant, below where new roots have formed.
Rhododendron Rot
7/ 24 Q. I have several Rhododendron that look dead and a number of them are starting to dry up. They start drying up underneath, then a week or so later, the whole plant has dried up. I didn't see any rodent damage. The plants were planted in July of last year and were mulched with landscape fabric when they were planted. The hole they were planted was fixed with peat moss because the original soil is chunky and gray.
A. I believe that there are a number of factors at work here:
- soil incompatibility - You mention a peaty soil and a "chunky" soil. This may be the result of amending the planting hole with peat moss. Any time that there is a transition in soil texture, peaty to clayey or even peaty to sandy, the hole will retain water until it becomes saturated. If the soil layer below is poorly drained then the hole stays wet. This creates a "tea cup" effect where the amended hole becomes a container drowning the roots.
- Poor drainage - even if the planting holes were not amended, the soil may be poorly drained. Check soil drainage by digging a hole about 12" deep, fill with water and measure the depth. Measure the depth of the water 15 minutes later to see how much the water has drained. Multiply the figure by 4 to get inches per hour. < 4"/hr = poorly drained, 4-8"/hr = moderately drained, >8"/hr = excessively drained.
- Gas exchange - Plants conduct photosynthesis to manufacture food and respiration to grow. Photosynthesis requires CO2 and respiration requires O2. Roots function like our lungs. They absorb oxygen and give off CO2, just the opposite of leaves. Landscape fabrics restrict the exchange of these gasses to the point that roots suffocate due to build up of CO2. (I just thought of another possibility - natural gas leaks can cause similar effects. Any possibility that gas lines are near this area?)
- Rain - July '04 was one of the wettest on record. This with the possibility for poor drainage and evaporation could have been the last straw.
Dutch Elm Disease
Q. 7/26 We have 3 elm trees that are around 25yrs to 50yrs old. Two of the elms have just died. Is there a disease going around in them? The trees are in open land. We notice the problem this spring. The leafs started turning brown then the tree died.
A. Dutch elm disease was first seen in the US in the '30's. It still kills elm trees. Isolated trees may live for many years before becoming infected with the disease. The dry summer may have caused the disease to progress quickly and kill the trees. Trees infected with the disease can not be cured. The only control is preventing the disease from becoming established. The elm bark beetle spreads the disease so control should be targeted at them. Dead elm trees should be cut down and all bark removed to kill over wintering beetles if the wood is to be stored for firewood. Restricted use pesticides are available to control the beetles but can only be used by a certified pesticide applicator and arborists.
Tar Spot
Q. 8/16 My maple has big black spots. It seems fine otherwise. Do I need to spray it with something?
A. Tar spot of Norway maple (including Crimson King that is mistakenly called "red" maple) cases large black spots on leaves and may cause early defoliation. In severe cases, the leaf also shows a wilting or scorching. This disease of the foliage does not harm the tree so control is not warranted. Remove leaves or mulch them to reduce occurrence of the disease next year.
Magnolia Scale
Q. 9/2 The sidewalk beneath my magnolia is covered with a blackish mold. Could this be coming from the tree?
A. The black substance is called sooty mold. It is from a fungus that forms on the secretions (honeydew) of an insect called the magnolia Scale which also causes the leaves to yellow. The insect appears as a brown "bump" on the twig. The young black crawlers of Magnolia scale will soon be present (early October) signaling the next opportunity to control this insect. Apply horticultural oil, insecticidal soap, acephate, carbaryl, or Malathion, as crawlers appear. Imidacloprid (soil drench), or dormant oil could be used in early spring (April). Always read the pesticide label. Scale insects may also be removed by hand in July before crawlers emerge.
Powdery Mildew
Q. 9/14 I have 2 small lilac bushes. First the leaves started to appear a powdery white. Now, they are turning black. I recently mulched them with pine chips. Could this be the problem? There do not seem to be insects on the leaves. Thanks.
A. The white powder is powdery mildew. As the fungus matures and sporulate they turn brown.
It will not effect the long term health of the shrubs. To reduce the occurrence in the future, be sure the shrubs are in full sun and get good air circulation - thinning pruning of over head trees and thinning the shrubs themselves can accomplish this.
Pruning Evergreens
Q. 10/10 My husband tried pruning the junipers in front of our house into neat little rectangle shapes. Unfortunately they look more like a moldy block of swiss cheese. Can we cut them back low and let them re grow? I have done this previously with yews with good results.
A. Juniper is not as easy to rejuvenate as yew. You will not be able to cut them back to bare branches and allow them to re-grow. You can only try to manage the new growth in a more natural form. This means that you can not keep the shrubs the same size indefinitely. They will have to grow up into their new form. If there is only a few inches of green foliage around the top and sides, You will have a difficult time. Shearing branches year after year results in a witches broom - branches ending with many short twigs that hold the living needles. Ideally you want long branches arising from the interior of the plant with living foliage along the entire length. In March or April, start thinning the branches reducing the number of shoots off of each broom-like branch. Touch up the plant in mid-June for symmetry by removing long shoots of new growth. Repeat that every year. Maybe in 5 years they'll begin to look respectable again.
Blue-Green Fungus on Trees - Lichen
Q. 10/28 I recently purchased a new home that has several trees in the landscaping. All of them are covered with a blue-green fungus. Some are much worse than others, to the point that some are severely stunted and infected.
A. The blue-green fungus is a lichen. It would not be responsible for the problems that you are seeing on your trees however. Lichen are non-aggressive to plants and colonize after the plant is under stress in humid shaded locations. The slow growth of stressed plants give lichen a foothold to start growing. Lichen are formed by a symbiotic relationship between a fungus and an algae. The algae produces sugar through photosynthesis which feeds the fungus and the fungus collects moisture and nutrients for the algae. Removing lichen from a plant causes more harm than leaving it.
Living Christmas Tree
Q. 12/12 What kinds of evergreen trees make a good living Christmas tree?
A. If you are considering a living Christmas tree, your choice of trees could be as wide as when choosing a cut tree; Spruce, Douglas Fir, Balsam fir, concolor fir, would all make good choices for a live tree and a landscape specimen. The first thing to be aware of is that a live tree will be dormant this time of year, and needs to remain dormant. So keep live trees in the house for about 2 weeks. Longer if it is in a cool part of the house, shorter if it will be in a warm room. You may also spray the tree with an anti-desiccant to prevent moisture loss. Bring it indoors in stages. One day in the garage, one day in a cold basement or entry way, then in the home. While in the house, keep it away from heat and direct sunlight, and water it with cold water. Keep the roots moist, but not soggy. After 2 weeks you need to plant the tree outdoors, so you should dig the hole where you plan to plant it NOW, before the ground freezes. If the tree is not planted the roots will freeze and a good portion (if not all) of the tree will die. Roots are not as cold hardy as the above ground portion. The soil that is removed should be kept unfrozen so that you can use it to fill in the voids around the root ball when planting. Water the tree well after planting and place mulch over the roots for added insulation. If in a windy location you will also need to stake it.
Using Pesticides Safely
Indiscriminate use of pesticides introduces unneeded chemicals into the environment, puts yourself at risk of contamination, possibly kills beneficial insects and could lead to pesticide resistance in pest insects. Before choosing an insecticide, ask yourself how much damage you can withstand. If the damage to the plant is only aesthetic, your first option is always to do nothing. To choose the appropriate insecticide, look for the name of the pest and the host plant on the label. Always read the label and follow the directions for application methods.
This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registrations, some of the suggestions given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Cornell Cooperative Extension assume no liability resulting form the use of these guidelines.