What Are the Most Common Plant Diseases?
This summer, we've had way more rain than I can ever remember here where I live in upstate NY. We've had record flooding and some of our neighbors have had catastrophic damage as a result. Fortunately, we've had zero problems besides a super soggy lawn - and some very sick garden plants.
That's why this guest post by my friend Jessica R. really struck a chord when it came into my inbox this week. I wanted to make sure to get it posted so that I could share these tips with any of you who might find yourself in a similar boat!
This article will focus on the most common plant diseases. We’ll also cover how to tell what plant disease you’re facing in the garden and how to find a treatment option so the disease doesn't destroy your garden.
Read on to learn all about plant diseases in today's guest post!
**J&R Pierce Family Farm is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to allow sites to earn advertising fees by linking to products on Amazon. I often link to Amazon when recommending certain products, and if you choose to purchase, I may earn a small percentage of the sale. It costs you nothing extra, and all recommended products are ones that I personally vouch for.**
What is the Most Common Type of Plant Disease?
Having a garden can be such a rewarding experience, especially when you can provide your own fresh food on the table. However, when plant diseases strike, it can be extremely frustrating. Some of the most common are:
Powdery mildew
Downey mildew
Black spot
Rust
Root rot
Damping off
Mosaic virus
Fusarium wilt
Verticillium wilt
Sooty mold
Snow mold
Canker
Leaf spot
Soft rot
Curly top virus
Spotted wilt
Angular leaf spot
Black rot
Bacterial blight
Bacterial canker
Bacterial speck
Bacterial spot
Plant diseases can be caused by bacteria, viruses, and fungi. Knowing the most common diseases and what they look like is essential to be prepared to combat them. You’ll have a better chance of identifying them early and saving your plants.
For now, if you want to get more information on plant disease, you can watch this video:
What Are 10 Diseases Caused by Bacteria in Plants?
Many plant diseases are caused by bacteria. They affect many different types of plants, can often overwinter, and can cause significant damage, if not death.
You don't need to have a flooded garden to be concerned about these, either. Here’s a look at ten common bacterial diseases.
Black Rot
A bacterial disease that affects the plants in the Brassica family, black rot is highly persistent. It’s caused by Xanthomonas campestris pv campestris bacteria and tends to do the most damage to kale, broccoli, cauliflower, and cabbage.
One of the most common entry points to your garden or farm is through infected seed or weeds. Once you treat black rot, it can persist in residues. Plants of all stages of maturity can be affected.
Black rot starts as a yellowing of the leaves’ edges, which quickly turns into v-shaped lesions, which are characteristic of the disease. As the disease progresses, the plant can experience blackened vascular tissue and head rot.
Bacterial Soft Rot
One of the most damaging plant diseases worldwide is bacterial soft rot. Actually, a group of diseases, soft rots, are not picky about the plant types they affect, damaging plants from nearly every family.
These diseases damage the plants’ softer parts, including fruits and bulbs. Crops can be affected in the field or in storage and over a broad range of temperatures.
Soft rot bacteria cause the molecules that hold the plant’s cells together to degrade. Eventually, the structure collapses.
Bacterial Wilt
Bacterial wilt commonly affects plants like potatoes, tomatoes, and geraniums. Cuttings or other propagative plant material typically introduce it to a new area.
While the bacterium responsible for the disease can exist in plant material, it can also survive in soil, planting material, irrigation, and wastewater runoff. It can be moved from field to field through runoff or equipment.
Infected plants will wilt on a section or in total. This is followed by the leaves turning yellow. Eventually, the affected leaves will die, and growth will be stunted.
Bacterial Blight
Generally seen in the early season, bacterial blight can overwinter on plant residue. The disease spreads from this residue to the newly planted crops through splashes of water that carry the bacterial cells to the leaves.
Once the bacteria enter the plants, they release a toxin that inhibits the production of chlorophyll. Additionally, infected leaves can transmit the bacteria to unaffected leaves through contact.
Plants affected in the early growing season typically show brown spots as symptoms. Young plants often have stunted growth.
In later growth stages, angular lesions appear. These appear as small yellow to brown spots, and their centers change color to reddish-brown before drying out. Eventually, the lesions fall out of the leaves, leaving a ragged appearance.
Bacterial Brown Spot
Bacterial brown spot symptoms are characterized by ovoid spots with necrotic tissue in their centers. These spots are surrounded by a narrow area of light-green or yellow tissue. The spots have the potential to grow together, and the centers may fall out.
Leaf Spot
While most leaf spot diseases are caused by fungi, there are some caused by bacteria. In any situation, these diseases affect trees and shrubs by limiting the process of photosynthesis. Generally, only a small portion of the overall surface area of leaves will be affected.
However, if there is considerable leaf loss for two to four years in a row, it should be taken seriously. When leaf loss continues for multiple consecutive growing seasons, it places the plant at risk for stunted growth and increased susceptibility to other problems.
Because of the range of leaf spot diseases, there is no uniform appearance. Spots can be nearly any shape or texture and have a range of colors. Additionally, you may find more than one type of spot on a single plant.
Bacterial Speck
Another disease that has no uniform shape or size is bacterial speck. It will appear as dark brown to black lesions located on the stems, leaves, and fruit. Lesions on the leaves are typically located near the margins, resulting in extensive tissue death.
The disease is persistent, surviving in the soil, on seeds, and in debris coming from diseased plants. It can be easily spread through irrigation.
Bacterial Canker
Bacterial canker is a disease that affects the Prunus tree genus, including cherry, peach, and plum. When a tree is first infected, it may show no symptoms. The first thing you may notice is branch dieback.
In some cases, subtle symptoms may appear before the dieback. For example, infected flowers may open only to collapse, while infected leaves will spot and then turn yellow.
The bacteria that cause the disease can overwinter in cankers, buds of susceptible trees, and asymptomatic, systemically infected branches.
Fire Blight
Fire blight is a disease that affects trees and can kill blossoms and shoots. Severe cases can cause the death of the entire tree. Heavily affected trees may give the appearance of having been scorched by fire.
These bacteria can overwinter in the cankers on infected trees. As the weather warms in the spring, the bacteria multiply and ooze out of the canker, spreading via pollinators that are attracted to the sticky sweetness of the bacterial ooze.
Crown Gall
Affecting trees and shrubs, crown gall causes the growth of rough and woody tumor-like galls on the roots and trunks. These galls can disrupt the flow of water and nutrients throughout the plant’s system, reducing growth and overall vigor.
Young plants or those where galls have completely encircled the main stem are susceptible to dying. The bacteria enter the plant through the root system via wounds that were received through various means.
What Are Common Plant Viruses?
Viruses can also cause plant disease. They’re harder to tackle and can cause significant losses to your crops. Here’s a look at some common plant viruses.
Tobacco and Tomato Mosaic Viruses
While there are many forms of mosaic viruses, the two most commonly faced by gardeners are the tomato mosaic virus and the tobacco mosaic virus. The virus causes mottled yellow and green leaves. Additionally, you may find they are curled or distorted.
Some plants may also have stunted growth, reduced yields, and malformed fruits. This virus is more common during hotter temperatures.
The virus can survive in dry soil for an extended period. When you identify an affected plant, it must be removed entirely, including all roots. Susceptible plants should not be planted in the same area for two years.
Tomato Yellow Leaf Curl Virus
One of the most damaging viruses affecting tomatoes is the tomato yellow leaf curl virus (TYLCV). The primary symptom is leaves that become yellow between the veins. They then curl upward toward the middle of the leaf.
The TYLCV is spread over short distances by the Bemisia whitefly. Over long distances, it’s primarily transported through the movement of plants, especially tomato transplants.
Brome Mosaic Virus
The brome mosaic virus largely affects grasses, especially cereal crops. Infection frequently leads to stunting in the affected plant. Transmission can be achieved through accidental human intervention in the field, such as by using farming equipment.
Plum Pox Virus
A viral disease of stone fruit, the plum pox virus is transmitted by grafting, budding, or insect interactions with diseased trees. It can be carried long distances in infected plant materials.
It affects the Prunus genus, including almonds, cherries, peaches, apricots, nectarines, and plums. While it does not kill the trees, it dramatically reduces the yield and makes the fruit unmarketable. Additionally, it does not affect humans or animals.
What Kinds of Fungal Disease Might Affect My Plants?
You were probably right if you’ve ever noticed what you thought was mold on one of your plants. Many fungal diseases also affect plants. Here are a few common fungal diseases.
Rust
One of the most common fungal diseases is rust. As its name indicates, it leaves spots on the plants that resemble rust in the colors of red, orange, yellow, and brown. While it’s an eyesore and takes away from the beauty of the plants, it rarely causes significant damage.
Sooty Mold
Many plant-sucking insects leave behind honeydew, a sticky, sweet deposit. Sooty mold is a type of fungus that readily grows on these deposits. When it grows on leaves, it doesn’t just cause a decrease in attractiveness–it impedes photosynthesis and stunts plant growth.
To stop the mold growth, you’ll need to get rid of the insects. The mold won’t grow without the honeydew.
Verticillium Wilt
This fungal disease affects hundreds of species of plants, from trees to edibles to ornamentals. The pathogens can live in the soil for years and eventually make their way into the plant’s system through its roots.
They block the vascular system, causing wilting branches. The foliage turns yellow and prematurely falls off. You may also notice stunted growth in your affected plants.
How Do I Know What Disease My Plant Has?
You’ll need to evaluate the symptoms when you notice your plant isn’t doing well. Look for any tell-tale spots, cankers, lesions, or molds. This will help you start the process of identifying the disease.
Once you find identifying characteristics, you’ll need to take in all the details, including the following:
Size of spots/lesions
Shape of spots/lesions
Color of spots/lesions
Texture of spots/lesions
Location of damage
Color of affected leaves
Presence of mold
If you are unfamiliar with what you are seeing, you’ll need to research. You can use an app on the internet or download one to your smart device. They offer an immeasurable wealth of information.
In addition to identifying the disease your plant is facing, they’ll also provide information on how to treat it as well as preventative measures.
How to Treat the Most Common Plant Diseases
The first thing you’ll need to decide before you treat any diseases is how you want to do it. Do you want to use eco-friendly options, or are you okay with using chemicals? This will determine which course you take when planning your treatment.
In most cases, plant diseases can be treated by some of the following measures:
Pruning affected foliage to open airflow around the plant and prevent further spread
Staking or caging plants that might be sagging to the ground
Using a chemical fungicide, miticide, bactericides, or nematodes (nematicides)
Wiping plants with soapy water or rubbing alcohol to remove pests
Remove infected plants and throw them in the trash (do not compost)
Adjust watering practices
If you have certain types of mold, they often grow because of insect activity. Some of these will also not respond to fungicide treatments. Instead, you’ll need to remove the insects creating the sticky, sweet deposits causing the mold to grow.
Once you remove the insects, you can gently clean the leaves of mold and honeydew, removing the problem.
In extreme cases with some diseases, you’ll need to remove the entire plant to prevent the spread of the problem. When this is the case, you must ensure you get every part of the plant, including the roots. Many diseases can survive on plant parts, waiting to infect other plants.
While this might not necessarily help if you're already dealing with plant diseases, I also recommend the following for the future:
Planting in raised beds - keeping your garden beds elevated off the ground reduces the likelihood of poor drainage
Mulching around plants to adjust soil moisture
Rotating your crops each season to reduce the likelihood of mold spores, bacteria, viruses, and other diseases from lingering until next year to re-infect your plants
Final Thoughts
Plant diseases can be devastating to your garden or farm, especially when they’re not caught early. Unfortunately, many can be spread from seeds or transplants, causing damage from planting.
If any plants were infected at the end of the growing season, debris left in the field can also be a source of disease the following season. Many diseases can overwinter in this debris, waiting to infect new plants in the spring.
Staying on top of your plants’ health is essential to combatting diseases as they arise. You’ll need to be ready to take action if any of your plants start to go downhill so that you can protect the rest of your garden.
Want to learn more about farming? Be sure to check out these featured articles!
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