If you’ve ever done a bit of gardening, chances are that you’ve come face to face with how devastating plant leaf spot diseases can be. These infections often hit vulnerable plants, more specifically – trees, and shrubs. They are at their peak when the weather is very humid or rainy and can often outlast dry, hot, or cold periods. Thanks to decades of studying them, however, there are quite a lot of ways you can deal with these infections now. Moreover, I will also give you plenty of tips on how to protect your garden against these infections.
In this article, we will go over the following aspects of these plant leaf spots diseases:
- What causes plant leaf spots
- How to identify them
We will also discuss a few fairly common leaf spot diseases individually so that you get a better idea of what they are and how to deal with them. Now, let’s start with the most important question regarding this topic…
Table of Contents
- What Causes Plant Leaf Spots
- How to Identify Them
- Tips to Limit Leaf Spot Outbreaks
- Frequently Asked Questions
- Final Words
What Causes Plant Leaf Spots
The term “Leaf Spot” is often used in gardening to describe a whole group of plant diseases. That group contains diseases from different types of pathogens, mainly fungal but also sometimes bacterial. Large clusters of plants that suffer from fungal leaf spots are often referred to as canker or anthracnose. A lot of the pathogens that cause leaf spots are often specific to the host they infect. This means that one fungus often affects only its desired host and rarely jumps or skips to other plant species. There are, however, known cases of infections skipping rapidly from plant to plant, mainly due to mutations.
In terms of susceptibility, almost every tree, shrub, flower, or grass species out there is vulnerable to a leaf spot infection. However, there are some types out there that are far more resilient and are genetically modified to resist such diseases.
Some of the most common fungal leaf spot diseases are leaf rusts, downy mildew, bacterial leaf spots and blight, shoot blight or canker. We will take a closer look at these further down the article. Now, let’s take a look at how exactly we can identify these diseases in our own garden.
How to Identify Them
While identifying the infection late when it has manifested itself is easy, spotting it early on requires a bit of knowledge and experience. The physical manifestation that you see on the leaves comes in different forms, sizes, and colors. One of the first places you have to inspect when it comes to trees is their lower inner branches. Typically, moisture is higher there and there is less sunlight. Both of these conditions are excellent catalysts for fungal infections and that’s precisely why most leaf spot diseases start there.
Since fungal and bacterial pathogens are blown into your trees by the wind or splashed by the rain, the spots will occur quite randomly. Sometimes you will be able to notice certain patterns across your yard but in most other cases, the disease won’t be bound specifically to one branch, a few leaves, or one part of your garden. Depending on the specific type of pathogen, the leaf spots can also occur on different parts of the leaf. They can be on:
- The top part of the leaf
- The bottom part of the leaf
- Both of its surfaces
In terms of their shape and form, leaf spots can be – round or angular, raised or sunken, and have their edges either smooth or fringed. Colors-wise, they range from different shades of green, through yellow and red, all the way to brown, black, and tan. Since the fungal or bacterial colonies won’t develop equally across the whole plant, you may observe different shapes, sizes, and even colors of the leaf spots on a single plant. As a rule of thumb, the smaller the leaf spot, the younger the infection is on that particular part.
Oftentimes, in the middle of the leaf spot, you can see germination structures. These represent the spore-producing centers of the pathogen and are their way of multiplying and spreading further. If your plant has had its leaves drop too early, that is another tell-tale sign of a leaf spot infection.
Leaf spot pathogens life cycle
One of the best ways to known how to deal with leaf spot is understanding better what it is and how it progresses. Since we already covered what causes it and how to identify these infections, let’s talk a bit more about the life cycle of these pathogens and see how they survive, feed, and spread.
Bacteria and fungi are one of nature’s most resistant creations. Most pathogens that are responsible for leaf spots can survive harsh winters and re-infect plants when Spring arrives. They can also infect fallen leaves and spread through them when you rake them up. Typically, though, their usual method of spreading is through the wind, from close contact, or rain splashes.
During the season in which the plants grow the fastest, fungal and bacterial infections spread the fastest. Rainy years usually give them the necessary conditions to grow and proliferate in an uncontrollable fashion. To start their infection, most pathogens will need water or high humidity around or on the leaves for around 24 hours. This is why dry weather typically works against these types of infections.
When they do infect a weak spot on the plant’s body or leaves, these pathogens require up to two weeks to fully mature. Then, they start producing spores which then leave the germination center by either flying off or by touching other parts of the plan (or even another plant). As I already mentioned, each pathogen is usually host-specific so the species-to-species transfer is often unlikely but not impossible.
When the weather is not in their favor, these bacteria and fungi are often dormant and have the potential to re-infect as soon as conditions are favorable again.
While there is no cure for your plant once it is infected, there are a few methods that you can use in order to slow down to stop the infection from spreading. Some of the most common ones include sulfur sprays and copper-based fungicides. These are applied at the first sign of the disease. The way they work is by preventing the fungal or bacterial spores from germinating. That way, they stop the infection dead in its tracks. There are also other broad-spectrum fungicides that will kill most bacterial and fungal leaf spot infections. Most of them are bee-safe but double-check that with the manufacturer before going forward with a particular model.
On the market, you can also find garden dust solutions that contain copper and pyrethrins. These provide both insect control and can deal with fungal infections on your plants. They are, however, quite hard to apply since you will have to cover both sides of the leaves in order to protect them.
As a whole, fungicides are often viewed as a last resort. They are typically applied only on a tree that has lost its leaves for a few years in a row. Fungicides also have a protective effect. However, their biggest side effect is that they may help in the spreading of resistant bacterial and fungal strains. The process behind this is that the fungicide will stop all of the vulnerable pathogens, leaving the resistant ones to spread. That potentially gives them space and time to proliferate and spread around, making them the now dominant strain.
Now, let’s take a look at a few great tips on how you can limit and even prevent potential leaf spot outbreaks in your garden…
Tips to Limit Leaf Spot Outbreaks
There are quite a lot of things you could do in order to protect your garden from leaf spots. Some of the most important tips I have for you are:
- Choose resistant tree and shrub varieties when buying new ones.
- Keep the soil under your trees clean. If needed, sanitize it after you rake the fallen leaves.
- Rake up any fallen fruits and leaves and gather them.
- Destroy the fallen fruits and leaves before the first snowfall to prevent re-infection upon the next season.
- Regularly prune your shrubs and trees to improve air circulation and light penetration. This will prevent inner branches and leaves from experiencing lesser temperatures and higher moisture levels.
- Do not plant your plants too close to each other. This will make them transfer infections from one another easier.
- Use mulch to cover any raked soil. Mulch will prevent the growth of weeds and will prevent pathogens from splashing onto your plants from falling droplets.
- Always disinfect your equipment when you prune or work on your plants, especially if they have signs of leaf spots. Using a solution of 1 part bleach and 4 parts water on your tools after every cut is highly advised.
- If you get new seeds, make sure they come from a leaf spot-free batch.
- Absolutely never use fertilizers on plants that have leaf spot disease. This will only make it worse for the plant and other nearby plants.
- If you can’t deal with the infection, call a specialist (arborist) to help with larger outbreaks or large trees.
- Avoid having sprinklers around your trees. This will splash water onto their leaves, giving bacteria and fungi good conditions to grow and proliferate.
Additionally, you should water your trees at the base only. Water them only once the soil is dried up. This will prevent your trees from being stressed too much, which decreases their natural resistance to pathogens. To further protect them, you can have a 3-inch mulch layer around the tree. However, remember to never mulch too close to the tree trunk. Try maintaining a 2-inch distance from it, as that will promote better air circulation to the stem. Check and add more mulch each year.
If you’re now starting to plant a grass lawn for your home, I highly recommend checking out my full Buyer’s Guide on some of the best grass seeds for this year. Additionally, you can check my article on how to plant grass seeds where you will find tons of tips and detailed instructions!
Frequently Asked Questions
Do leaf spots kill plants?
Leaf spots are always caused by different types of bacterial or fungal infections on the plant. While older plants such as established trees can handle them, newer less established trees or plants might take a lot of damage. Whether or not it gets to the point where it kills the plant is up to early and late treatment and the plant’s own defensive mechanisms.
What kills leaf spots fast?
While there are plenty of homemade leaf spot-killing solutions, fungicides work the best. They are highly effective and usually target the specific culprit behind your plant’s leaf spots. Such fungicides often contain propiconazole which is a highly effective treatment agent for these diseases.
What is a natural leaf spot solution?
Since some people don’t like using fungicides in their gardens, there are some homemade recipes out there. One of the most common remedies is mixing 1 drop of ivory dish soap with 2 tsp of baking soda and 4 cups of water. Spray that on your plants once a day and monitor the progress of the disease.
Can leaf spot go away on its own?
While leaf spots can make your plants and/or turf look sick, they are seldom permanent in terms of the damage they do. All types of leaf spots typically die out with the change of seasons but that doesn’t mean that they can’t cause a ton of damage to your garden before they naturally disappear. Moreover, recurring infections with leaf spots are common in untreated plants year over year.
Is leaf spot contagious to nearby plants?
Yes, these plant fungal infections are highly contagious. What accelerates their rate of transfer even further is the moist and warm conditions surrounding them. Typically, plants from the same cluster suffer from these infections together.
Plant leaf spot diseases are becoming more and more common across the whole country. Their nature is one of fungal or bacterial origin and these infections can spread through the wind, contaminated plants, or even rain. This makes them incredibly hard to protect against but knowing how to deal with them is typically the only preparation you will need. Raking up fallen leaves, keeping a healthy distance between your plants, pruning your shrubs, and using fungicides are all effective ways of preventing and treating these diseases!