Infections your tree may be suffering from.

Just like humans, and all living creatures, trees get sick and suffer from diseases. However, due to the fact that the trees can not vocally express their stress and illness, their infection or infestation may not be obvious at a quick glance. It takes a keen eye and background knowledge to identify and acknowledge if the tree is sick and what they are suffering from. Questions such as “is my tree sick?” and “how to tell if my tree is infected” often arise with the best interest to protect the tree. To answer questions such as “how to identify a sick tree”, we have amassed a comprehensive list that contains the most common diseases (Infections and infestations) a tree can catch in North America. But just like how you should trust a doctor to diagnose you, you should consult an expert arborist to perform a diagnostic to identify the issue at hand, self diagnosing could lead to a dangerous path of improper treatment. Luckily, we have services for those types of issues.

Tar Spots

Becoming more and more common within our maple tree population, tar spots are dark splotches of infection on the leaf of the tree. Despite it being called “tar” spots, the spots do not contain tar, nor do the spots manifest because of the presence of tar. These infections are caused by the pathogen: fungi. The genus of the fungi is Rhytisma, which branches (but are not limited to) to these three common species: Rhytisma acerinum, Rhytisma americanum and Rhytisma punctatum. Despite each species exhibit black spots on the leaves of infected trees, each varying species of Rhytisma has its own distinctive spots. This disease rarely harms the tree, and is rather a question of appearance for the tree. That being said, the disease does not affect healthy human beings, but if you know of someone that has a compromised immune system, it may be your best interest to help prevent infection.

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What are the differences between the species of Rhytisma?

As stated prior, each species of Rhytisma has their own distinctive “tar spot” properties. Here are the differences between the three most common species, so you can identify them yourself. Rhytisma acerinum: these tar blobs are medium sized, about 13mm (½ inch) to 25mm (1 inch); when it comes to the shape, they are vaguely circular with rough edges, uneven edges. Rhytisma americanum: these tar splotches are the largest splotches that you will notice on infected leaves, stemming from 26mm (1 inch) and larger; while the shape remains vaguely circular with rough and uneven sides. Rhytisma punctatum has the most distinctive tar spot pattern, having speckles that are about 2mm (0.07 inch), however, their relatively small size is made up for their numbers, as a ‘colony’ of spots may contain well over 50 tar spots.

​How do they spread?

Rhytisma relies on the seasons to spread itself. Take a maple tree, for example. When autumn approaches, both infected and non-infected leaves are released and fall to the ground, creating a blanket of leaves on the floor. After winter hits and spring arises, the little tar spots on the leaves then erupt, spreading spores across the foliage and onto trees, creating the cycle anew.

Leaf Rust

Leaf rust is caused by a fungus pathogen, particularly, from the taxonomy order of Pucciniales (All genus and species of this fungal pathogen essentially all do the same thing to the plant, what differs is the type of plant they infect (Such as trees or bushes) and minor appearance changes within those plant). Leaf rust develops when the Pucciniales fungus develops on the leaf, and if the environment is moist and damp to activate the spores. Pucciniales effectively spreads after sudden moisture or water meets the infected leaf and that touches healthy, non-infected leaves, starting the life cycles of Pucciniales once more. This is also why plant rust happens to spread the quickest after watering the garden or after light rainfall.

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How can I tell if my tree is infected with rust?

Pucciniales fungus infections are easily identifiable. As the name implies, the plant rust disease is named for its rust like colours that reside on the leaf of a plant. They are yellow spots on the leaf that develop into blisters or pustules that are orange-ish in colours. Within these blisters and pustules are the spores of the plant. At the right moment, the pustules or blisters break and then the spores are released to infect other leaves (With the help of water droplets). Check the leaf surface of the tree to investigate if it is infected or not. Keep in mind that these plant rust infections do not threaten the life of the tree, which means the only sign of an infected tree is with close inspection of the leaf surface.

​Can plant rust be treated?

When it comes to treating plant rust, it is easier to prevent the disease than it is to treat it. The easiest way to control the infection of Pucciniales on your plants is to use store bought solutions, however, it may come with chemicals that will damage the soil or the plant itself. You can also just simply remove the leaves of the plant, however, for those special plants that you just can not cut the leaves off, you can use a copper spray at the first signs of rust development. That way, the copper will not destroy the plant nor the soil, and it can be used as a preventative for non rust resilient plant species. If you suspect that one rust will spread to your plants, there are some preventative measures you can take to minimize the risk of it manifesting within your plant. These include not over watering the plant, watering early in the afternoon so the plant has time to dry before night, lightly putting sulfur dust on the leaves of the plant when it starts to establish itself and allowing space when planting the plants to avoid accidental spread.

Mildew Fungus

Powdery Mildew is a fungus that primarily infects the leaves of a plant. Its genus name is Golovinomyces  and the species name oronti (However, it is important to state that there are many different genus and species of powdery mildew that affect different types of plants, and are not limited to oronti). Powdery mildew can be identified as a white powdery substance on the surface on the leaf of a tree or another plant, typically has a texture similar as powdered sugar. This fungus is also the most common infection that you will find on your plants, given that it spreads relatively easily (Through wind and contact with an infected leaf) and proliferates quickly.

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How can I get rid of powdery mildew?

Unlike the oak wilt, trees and other plants can be rid of a powdery mildew infection. By simple removal of the infected leaf, or perhaps the whole branch if the infection is rampant, getting rid of powdery mildew is a doable task that does not demand elaborate procedures to remove infection. If you suspect your plant to be infected by a mildew fungus, you can do a home remedy that consists of 4 parts water and 1 parts milk, or simply apple cider vinegar then apply that mixture on the leaf. Additionally, you can purchase a bottle of mildew removal to quicken the results. Keep in mind that if a tree is infected, clearing a section of infected leaves may not be enough to completely clear the tree of the fungus, which you may have to leave to an expert arborist to deal with it.

Is powdery mildew dangerous for the trees and humans?

When it comes to the danger factor of Golovinomyces orontii (or their other fungal relatives), it does not directly threaten the tree’s health, nor does it seem to be severely damaging to the integrity of the leaves of deciduous trees (As shedding off all the infected leaves is usually enough to self rid of Golovinomyces orontii). However, because tree branches are easily rocked and swayed by the wind, Golovinomyces orontii spores are easily distributed to other trees and possibly other plants as well. If the trees host a powdery mildew that can also manifest itself on the leaf surface of another plant, such as your vegetables, it can wreak havoc on developing vegetables and prevent mature plants from growing fruit.
In regards to impacts powdery mildew has on the health of humans, they are relatively harmless unless ingested, which may cause stomach aches and diarrhea. If you or someone you know of have respiratory complications, it may cause coughing and breathing difficulty if the spores are inhaled. Though it may not directly affect you, mildew affects the plants around you, which may include vegetables within the fridge or fruits in a fruit bowl, making them inedible. 

Oak Wilt

Oak wilt is a dangerous disease that can decimates the life of an oak tree. As the name suggests, this disease most commonly infects oak trees, primarily the red oaks. Caused by a fungus pathogen, Ceratocystis (genus) fagacearum (species), oak wilt mostly resides within the northern United States and has not yet been confirmed in Canada. Because a heavy population of oak trees happen to reside within the great lakes, it is becoming more and more a possibility that Canadian oak trees may become infected with Oak wilt, so it is important we keep a keen eye on the condition of our oak trees.

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How does oak wilt spread?

Ceratocystis fagacearum spreads by the root system of the tree, infecting healthy roots in the network of oak roots. Additionally, Ceratocystis fagacearum can be spread by beetles that feed on the sap of the oak. For example, when an infected red oak reaches the end of its life, fungal mats develop and sap beetles who consume oak sap transport Ceratocystis fagacearum from the vascular system (The system where sap flows within the tree) of one tree to the vascular system to another tree, starting the cycle again.

How does Oak wilt affect the tree and is Oak wilt treatable?

When Ceratocystis fagacearum infects an oak tree, the fungus targets the vascular system of the tree and essentially blocks the flow of nutrients. Similar to strokes and heart attacks, blocking the vessels of nutrients (Such as the blood vessels) prevents that particular area of the tree from blocking nutrient flow. Because Ceratocystis fagacearum mostly resides in the middle of the trunk, it essentially prevents sugars from the leaves from flowing to the roots, and it also prevents water from the roots to flow to the leaves. This in turn causes the whole tree to be wilted, hence the diseased being named Oak Wilt. Unfortunately, when an oak tree is infected, there is little we can do to save the tree itself. However, we can take preventative measures to ensure that the fungus does not spread from tree to tree. This can be done via careful root pruning, sap beetle control or, if an immediate solution is required, complete tree removal.

Ash Borer

The emerald ash borer (EAB) may be the most infamous invasive species in Ontario Canada. Their impacts on the ash trees are even placed on watch to make sure these insects do not damage more than they do. The genus name, Agrilus and the species name, planipennis, the emerald ash borer are small green beetles that are about 12mm (½ inches) in length and mostly reside around an ash tree. One could say that there is a miniature war going on to protect the ash trees. Here, you will find the basics when it comes to the Agrilus planipennis.

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How can I identify the ash borer and how do the ash trees get affected by the insects?

The emerald ash borer is dark green in colour, with a somewhat rectangular body shape that curves at ends (Think of a very thin shield). The larva of these insects are also milky white in colour and are about 29mm in length (1.14 inches) and have little black appendages.
The Agrilus planipennis, as you may have guessed, primarily attacks the ash trees. For these insects, they affect both healthy trees and compromised trees, which you can identify if your ash tree suddenly loses its leaves or it starts to lose its integrity (Suddenly easily sways due to the wind). The adult and mature insects normally are found within the foliage, but are also commonly found on the trunk of the tree so keep a keen eye on those areas. A sure sign of adult ash borer activity is if you notice a D shaped hole on the trunk. However, these D shaped holes are difficult to notice, an inspection may be required Additionally, if you notice removed bark and strange maze-like or S shaped patterns on the tree trunk, that is a sign that an ash borer larva has already done damage to the tree. While the mature ash borer does not directly harm the tree, it is their larvae that destroys the tree from the inside.

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Why should arborists take action to stop the ash borer?

In Ontario, the ash borer is a deadly invasive species that can whittle down the ash tree population. The mortality rate of the ash tree when infected by an ash borer is nearly 100%. Because they are invasive species, there are no predators that target ash borers, which allows them to multiply their population at an alarming rate. Losing ash trees to these insects means losing the homes of small mammals and birds, loss of biodiversity in the rural and urban landscape and erosion of the soil.

How can I help?

When tending a tree or a plant, it can become difficult if you are relying on online sources to guide you through. You may spend more money that you need for materials and tools that might not even be effective to clearing out the issue. Additionally, you may accidentally do more harm than good if not properly conducted. It is important to let a professional arborist inspect and then act accordingly. That way, you do not accidentally spend money on expensive products and are helping preserve and expand the tree population.