Tree Diseases: What Are They and How to Treat Them?

Posted on November 16th, 2015 by Prunin Arboriculture & Landscape

Just like humans, trees carry and transmit diseases. There are a number of factors that can bring about tree diseases such as fungi, parasites, insects, and environmental stresses. Recognizing the symptoms of the most common tree diseases will help you detect problems early and maximize your tree care routine, reducing the chance of your tree dying.

Tree Disease

While you may be well-informed when it comes to diseases which can affect your lawn and your plants, you may not have given much thought to what can harm and damage your trees. When planning your tree care, whether for residential or business properties, keeping an eye out for the more common tree diseases is essential.

  1. Anthracnose
    When a fungus attacks an ash, dogwood, maple, oak, sycamore, or walnut tree, it defoliates and disfigures the tree, significantly diminishing its appearance. During the spring, watch for twig cankers, twig dieback, defoliation, and leaf blotching.

    Use fertilization and fungicide applications as needed during the spring, and remove and rack the dead leaves in the fall. You can also prevent anthracnose by watering appropriately, maintaining proper pruning, and planting resistant cultivars.

  2. Oak worm
    Oak worm is one of California’s most damaging insects. Due to the cyclical nature of the oak worm population, some years oak worms are widespread while other years they are largely absent. Oak worm eggs are white with red centers that fade to pink right before they hatch. The worms lay their eggs on bark, leaves, and limbs. Young larvae chew through leaves completely, giving them a skeleton like aesthetic.

    Typically live oaks undergo the most damage in May and June and then July through September. Both natural and synthetic treatments are available for oak worm control. Typically treating while the caterpillars are young proves most effective for wiping out the disease.

  3. Pitch canker
    Monterey and Bishop pines are highly susceptible to pitch canker. The pine pitch canker fungus is transmitted via twig, cone, and bark beetles that spread the disease to new locations. The primary symptoms of pitch canker are new growth wilting, excessive resin at the injection sites, and branch tip browning and dieback.

    There is no biological or chemical treatment that wipes out pitch canker completely.
    You can minimize the spread of the disease by pruning infected limbs, sterilizing pruning tools after tending to each tree, and removing and disposing of any infected trees in a timely fashion.

  4. Rosaeceous Plants – Rusts
    If you have hawthorn or crab apple trees in your garden, you are probably all too familiar with rusts, and the familiar discolorations on leaves which give the disease its name. Although it appears unsightly rather than serious, twig cankers can cause plants to die back, and nearby junipers can play host to rust galls, which spore and spread infection.

    Treated with fungicides – look for triadimefon as the active ingredient – when rosaeceous plants bud, or when spore outbreaks appear on junipers, additional pruning may be needed to get rid of diseased areas.

  5. Pines – Blights – Tip and Needle
    There are a variety of blights that can affect pines, with two common problems being tip and needle blight. Tip blight can be identified by an abundance of resin, and can be treated with fungicides applied to buds.

    The active ingredient to look out for is thiophanate-methyl. Pruning can also help. For needle blight, characterized by defoliation, tree care also includes pruning and application of a fungicide; look for copper hydroxide as the active ingredient.

  6. Powdery Mildew
    A bit of an equal opportunities disease, powdery mildew can affect a variety of plants. This fungus can cause stunted growth, and cause trees to lose foliage. Flowering plants may also fail to bloom. Good tree care garden management can be most effective here – avoiding shady areas and overcrowding – although a good all-purpose fungicide will be useful.

  7. Palms – Lethal Yellow
    Affecting most palm varieties, this bacterial disease is spread through plant hopper insect transmission, and will lead to death of the plant within five months of infection if not treated. As suggested in the name, yellowing foliage is indicative of the disease, and it is treated with insecticides and antibiotics.

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