Keeping Your Garden Healthy (part three) "Healthy Trees, Healthy Landscape"

by: Liz Roberts

Trees are complements to any yard. They create not only relaxing groves, but beautiful finishes to lawns and gardens. Despite their apparent sturdiness trees can pick up a wealth of diseases that can destroy other trees in the garden. Be savvy about what happens in your arbor. One quick diagnosis and you can save not only your chestnut oak or elm but also your entire landscape.

Chestnut trees are the most popular in America. Every yard has at least one, either offering shade in the backyard or gracing a front wall or lawn. This beautiful, romantic looking species was almost completely wiped out in the 1930’s. The cause – chestnut blight. Unfortunately the blight continues to destroy seventy years later. Trees will get cankers (a kind of contagious sore) on the branches and then into the trunk, eventually killing the tree. Another kind of blight, twig canker affects the Asiatic variety of chestnut tree. This strain girdles the twigs and then moves on to engirdling larger branches. The disease attacks seedlings , very old and/or unhealthy trees. Sadly enough there is no chemical control for chestnut blight. The best bet is to prune and burn infected branches. Chestnuts can also catch leaf spots and powdery mildew that can be controlled by fungicides.

Oak trees are also popular in yards and gardens across the country. These majestic trees are considered the nobility of both lawn and forest. However they are not immune to disease. Be on the lookout for any number of diseases that may ruin their majestic looks. Oak and most other shade trees suffer from anthracnose.(similar to the same disease that ruins fruit and vegetable crops). This is a fungus that happens after cool, wet periods. Damage may be located on buds which are killed off once they’ve contacted anthracnose , small twigs, leaves and branches.. It will weaken them and also prime them for borer attacks and winter miseries. Premature leaf drop is another sign of anthracnose. This lessens the shade produced as well as the tree’s ornamental value. It takes three seasons to produce one strain of anthracnose. It starts first in the winter in leaves that have fallen to the ground. Some spores winter in twigs that are still attached to the oak. More microscopic spores are formed in infected tissues during April and May. These spores are then blown, splashing on buds and young leaves. The best way to combat anthracnose is to rake up and remove infected leaves now during the fall season. Leaves may be shredded, composted or burned. Prune and burn or bury any dead twigs or branches. Also prune to thin out the tree’s crown or topmost area. Remember that any thinning you do during this season will allow more air to circulate. Cool autumn breezes are perfect for drying out limbs and eliminating dampness. Getting rid of any diseased branches also allows leaves to dry faster and more evenly after a rainstorm. If fertilizer is needed, then fertilize in the fall about a month after the average date of the first frost. If fertilizing in the early spring, then do so about a month before the average date of the last frost to increase tree vigor. Also recommended is spraying with a fungicide containing mancozeb first when budding occurs and then twice again .during leaf expansion. Check with local authorities as to what can be used.

Midwestern oaks also suffer from oak tatters, a relatively recent disease that eats leaves , forming a lacy pattern on what remains. The tatters occur in the spring when new leaves start to sprout There is no cure for this however healthy trees do survive tatters. Oaks also suffer from a fungus known as oak wilt which affects leaves and bark. It can be cause from the roots carrying the disease up into the tree or insects nesting in the leaves. There is no known cure for it. Infected trees can be destroyed to prevent it from spreading or root networks can be severed.

Out of all trees, elm trees suffer the worst. The dreaded Dutch Elm Disease or DED can decimate whole forests. It is caused by the virus Ophiastoma (ceratocystus) The virus blocks water conducting or vascular systems thus. preventing water and minerals from reaching branches limbs. Here in the States ,Dutch Elm Disease comes in two strains: the aggressive and non aggressive. The aggressive strain is the one that movies in too quickly, not giving the gardener any time to treat the tree. Younger elms will die quicker than older ones. Slow growing elders can linger two to three years with DED before dying off.

Luckily infected elms exhibit symptoms soon after contacting Dutch Elm Disease. Early stages can be treatable and the tree can be saved. The first sign is sudden leaf wilting along the tree’s topmost branches. Next, the leaves will change color from green to yellow to brown before they shrivel up and die. This may look normal and be ignored if it happens during the fall months. However the following spring the first indication of DED will be smaller than average leaves. The tree will probably die around mid summer. Dutch Elm Disease can be discouraged with prevention and treatment. Have a stringent sanitation program which involves surveillance (a weekly leaf check), timely pruning and proper disposal (namely burning of all infected wood). Growing strong, sturdy trees helps eliminate and cut down the chance of elms contacting DED. For this to happen, add beneficial micorrhyzial fungus to the soil. The fungus colonizes the plant’s root system where they take in water and nutrients and pass them directly into the roots. This supplement can be bought at any local or online nursery. Put the granulated soil additive in drilled holes around elms and other plants to ensure healthy, disease resistant greenery.

Elms also suffer from Verticillium wilt that is a serious vascular disease. Symptoms include one side of the tree with wilting leaves and/or branch die back.( when young off shoots and branch tip are killed off). Other symptoms include marginal browning and leaf scorching along with abnormally large seed crops and small leaves. Infected tress will also have sparse foliage and overall poor growth. The fungus infects the elms by their roots, root tissue and wounds. From these, the Verticillium wilt spreads upwards through the vascular stream. In doing this, the disease damages vital tissues while robbing leaves and branches of their water and minerals. To prevent this fungus , keep elms as healthy as possible. Be sure trees are properly transplanted as well as proper management of watering and pruning. Pruning does help however remember that an elm can still contact Verticillium wilt since it’s a root bound disease.

Beautiful trees add to any home and landscape. In order to keep their beauty , make sure they’re maintained on a regular basis with care and concern. Be on the lookout for any changes to leaves, branches and trunks. Act immediately if trees show any unusual changes. Keep them healthy and lovely all year round.