Tree Diseases

Don’t worry, it is a very common thing to get yellow or black spots on your maple tree leaves.  This is caused by a fungal disease (Rhystisma acerinum), also known as tar spot. Tar spot is rarely harmful enough to affect the health of trees, but makes trees look unpleasant. Heavy infections can also cause early leaf drop.  The best way to help control the fungus, is to rake and destroy leaves in the fall.

What is Tar Spot Disease?

Tar spot is a fungal leaf disease that does occur on several plants, but it is most common on maple trees. It does not cause permanent damage to the tree.

Tar spot is an unsightly condition on the leaves for maple trees. It starts with small yellow spots on growing leaves, and by late summer these yellow spots expand into large black blotches that look like tar has been dropped on the leaves. This is because a fungal pathogen, Rhytisma acerinum has developed on the leaves of the maple.When the fungus initially infects a leaf, it causes a small 1/3 cm (1/8 inch.) wide yellow spot to form. As the summer weather progresses, that spot spreads, eventually growing up to 2 cm (3/4 inch.) wide. The spreading yellow spot will also change colour as it continues to grow, slowly turning from a yellow-green to a deep, tarry black.  That is why it is referred to as a tar spot.

A variety of factors contribute to the spread and recurrence of this fungal infection. Some factors, such as weather, are not able to be controlled. However, there are some ways in which you can help to prevent infection. Proper garden and yard sanitation will help reduce the spread of tar spot. Overwintering in fallen leaves, one of the best practices is the removal of all your maple’s fallen leaves and bagging or composting them to eliminate the closest source of tar spot spores. If you leave the fallen leaves on the ground until spring, the spores on them will likely reinfect the new foliage and start the cycle again.

Trees that have trouble with the fungal disease year after year may also be struggling with excessive moisture. You’ll do them a great favour if you increase the grade around them to eliminate standing water and prevent moisture build-up.

Young trees may require treatment, especially if other trees have had a lot of their leaf surfaces covered by fungal disease in the recent past. If you’re planting a younger maple in an area prone to the fungal disease, though, applying a fungicide, Safer Defender Garden Fungicide 1L Ready-to-Use or Safer 3-in-1 Garden Spray 1L Ready-to-Use, at bud break and twice again in 7- to 14-day intervals is recommended. Once your tree is well-established and too tall to easily spray, it should be able to fend for itself.

Oak wilt is a disease caused by a fungus. It starts with fall colouring out of season—the leaves are wilting and browning, and within a few weeks, the tree is dead. Once a tree has been infected, there is nothing you can do other than remove it promptly to prevent the disease from spreading to nearby healthy oak trees. That’s why it’s so important to know the symptoms of the disease.

Health effects

The first sign of oak wilt is a rapid wilting and browning of the leaves in late spring to early summer, followed by the leaves dropping. This starts at the top of the tree, which is not easy to inspect in tall trees.

The browning of the leaves starts at the margins of the leaf at the apex, which is the tip of the leaf. From there it progresses downwards along the margins towards the midrib and the leaf stem. The browned leaves drop to the ground. Another symptom are vertical cracks in the bark with mat-like fungal spores underneath. The bark swells and eventually ruptures from the pressure created by the growing fungus.

In the following you might also notice sap beetles. While feeding on the sweet-smelling fungal mat, these beetles, about one-quarter to one-eighth of an inch, pick up the spores and thereby spread the disease further.

What homeowners can do to control Oak Wilt

Oaks that belong to the group of red oaks (pin oak, black oak, northern red oak) are more susceptible than white oaks (white oak, bur oak, swamp white oak). There is no way to save an infected oak tree; the only way to deal with oak wilt is prevention. Since the fungus enters the tree through wounds, avoid injuring oaks between April and August. That means no pruning during those months, and careful maneuvering around oak trees with your lawnmower and other power tools.

Scale is an animal that appears to have no resemblance to an insect. It has no legs, no eyes, and no readily apparent antennae; and it is hidden under a shell made of its own cast “skins”. Magnolia scale is white and ‘fluffy’.

Magnolia Scale lifecycle

Magnolia scale is our largest soft scale insect, reaching ½ inch in length.  This scale spends the winter on small twigs as tiny, dark-coloured nymphs.  In the spring, the scales begin to feed, mature, and change colour.  The males, which turn white, are smaller than the females, about 1/8 inch in length, and emerge as tiny, gnat-like insects.  The males mate with the females and then die.  The females turn white to brownish-purple in colour and continue to enlarge through July.

Magnolia scale eggs hatch internally and the crawlers emerge from the mother insect. Crawler emergence occurs late summer into early fall.  Insect life cycles are dictated by heat so emergence of crawlers will vary from year to year.   On average crawler emergence occurs from late August through the end of September.  The crawlers move around until they find a suitable feeding site, usually on branches, where they settle down and remain through the winter.  The adult female dies after reproducing, but may remain attached to the stem for many weeks, making the population seem larger than it really is.

What homeowners can do to control Magnolia Scale

Survey your property for egg masses and scrape them off surfaces into soapy water to destroy them.

1.  Place your catchment container below the egg mass
2. Use your scraper tool to remove the egg mass from the surface. Ensure that all eggs are scraped. Try not to leave any residual eggs in bark ridges or crevices.
3. Empty the contents of your catchment container or bag into a bucket of soapy water
4. Leave the eggs sitting in the bucket for a day or two, then dispose of the contents

Egg masses can be located high up in trees. Care needs to be taken if trying to access anything aloft, especially if using ladders. Some private tree care companies can be hired to provide this service at heights.