The Most Common Diseases Found on Plant Leaves

Plant diseases can be a real pain to eradicate, and most of these diseases attack the leaves of the plants. In most cases, there is no way to salvage the infected plant but to remove and destroy it before it can infect the rest of the plants susceptible to that disease in the vicinity. 

The most common diseases found on plant leaves are:

1. Leaf Spot
2. Leaf Blight
3. Mosaic Virus
4. Rust and
5. Downy Mildew

Prevention is always better than cure. Most of these diseases are spread by carriers such as water, wind, and insects. Read on to learn more about each of these diseases and what causes them. Not to mention, how to treat them and how to prevent them from occurring.

Leaf Spots

Leaf spots are usually either fungal or bacterial diseases that form on plant leaves, flower petals, and sometimes on the fruit of the plant. These spots usually do not kill plants outright, but they can weaken them and leave them vulnerable to other problems such as mold and mildew.

These spots can appear in one of two ways. When caused by a fungus, they will appear as small dark spots on leaves and petals, often accompanied by some fungal growth around it, looking like tiny pimple-like structures on the leaf. If there are numerous spots close together, they might merge to form “blotches.”

When caused by bacteria, they appear as lesions on the leaf surface, dark brown with a yellow halo surrounding it. Roses are particularly susceptible to one of these type bacterial leaf spots, called “black spot.” Other types of spots include frog-eye leaf spot, Septoria leaf spot, and bacterial leaf spot.

Environmental Conditions

Leaf spots form in an environment where there are humidity and heat. But can live within the plant and survive through winter conditions. 

What to Do

Leaf spots are a challenge to treat. They’re a  problem that has to be removed at the source:

• If there are individual plants, destroy and remove all the infected plants.
• Remove the infected leaves if dealing with something like a bush.
• Place the plant in direct sunlight to dry out the humidity feeding the infection.
• Avoid getting water on the foliage by directing the water you feed the plant to the base as much as possible.
• Provide good air circulation to encourage the leaves and foliage to dry out quickly.

Leaf Blights

These are diseased sections that show up on the leaves of plants, usually larger in size than a leaf spot would be and with more of an irregular shape. The spots usually start as large yellow spots. They eventually turn brown over time.

Causes

Blight is usually formed in cool and wet weather.

What to Do

• The best way to handle blight is to remove the infected plants and destroy them. 
• Repot the remaining plants in new soil.
• If you’re going to use the same pot, make sure it’s been thoroughly cleaned and sanitized.

Mosaic Virus

Mosaic virus is an incurable disease that spreads quickly and is highly destructive. Mosaic virus will appear on leaves, as the name implies, like a mosaic of yellow or green speckled patterns on the leaves that are infected. 

Other characteristics that you may encounter are stunted growth, deformed fruits, a reduced yield of fruit, or yellowing of the whole plant. The leaves may also be distorted, cupped, curled, or knotted.

There are many different mosaic viruses, but the most common ones that a gardener might encounter are tomato mosaic virus and tobacco mosaic virus. Peonies are also commonly infected with this disease.

Causes

Mosaic virus is carried by insects that feed on perennial leaves such as aphids, leafhoppers, whiteflies, and cucumber beetles. 

The virus can also be sitting in the soil, the seed, or the starter pots.

Warm environments and high nitrogen early in the early stages of growth can also be harmful to plants susceptible to mosaic virus.

What to Do

• Mosaic virus does not have any chemical controls or cures. It can survive in dry soil for a considerable amount of time. 
• Remove and destroy infected plants at the root. 
• Avoid planting any new susceptible plants in that same soil for two years. 
• The seeds of the infected crops must also be disposed of because they could be carrying the disease. 
• Also, as tobacco is a carrier of the virus, smokers should wash their hands before handling plants in order to avoid infecting new plants.
• Get rid of noticeable pests on the plants that are susceptible to the disease by wiping these plants with soapy water or rubbing alcohol (isopropyl).

Rusts

Several different fungus species spread rust. It deforms leaves, showing as large brownish-red or golden-brown spots all along the surface of the leaf. But the damage is not as serious as most of the other diseases listed out here.

With rust, you will notice that the spots that appear are spores and that the spores form on the underside of the leaves. Usually, defoliation (which is the loss of leaves) and distortion occurs.

To identify that it is a case of rust and not a leaf spot, you can also rub the leaf surface with a white cloth. Residues of the same color as the spot should come off on to the cloth. In severe cases, the leaf of the plant can wither out and die.

Causes

Rust is caused by a fungal parasite that thrives in mild, moist conditions and is transferred by spores from infected plants to healthy plants.

The spores can be carried from plant to plant by the wind or by water. This is why the disease often spreads after the plants have been watered. The parasite needs a living plant to survive.

How to Handle 

Overcoming rust is not simple or easy; you will need to do the following:

• Remove the infected parts and destroy them. You can burn them.
• If you have a bramble fruit, remove and destroy all the infected plants.
• Clean away debris of the rust and avoid getting water on the leaves.
• Promote healthy growing conditions like spacing the plants out for circulation. 
• Dust the plant early in the season with sulfur to avoid infection. Many fungicides can be tried.

Downy Mildew

Downy mildew is one type of mildew that commonly forms on plant leaves. It will be seen on the underside of the leaf as purplish, moldy mildew. Infected leaves will turn yellow and whither dead rapidly. This type of mildew is common on small grains and gourds such as squash, cucumber, etc.

Downy mildew has shared features to powdery mildew, which is also another type of mildew that occurs. The main difference between the two types of leaf mildew is their appearance in terms of color and shape on the underside of the leaf.

Causes

Downy mildew is caused by prolonged wetness. Spores form on the surface of plant leaves when the weather is cool and damp.

What to Do

Getting rid of Downy Mildew follows the same process as the other diseases:

• Remove and destroy infected plants.
• Maintain proper air circulation by spacing plants.
• Avoid getting water on the leaves.

Final Thoughts

To conclude, these are five of the most common diseases that can show up on the leaves of a plant, whether it’s your indoor plant or something in your garden that should be noted. 

It is always advisable to work to prevent these diseases before they occur. However, if they show up nonetheless, dealing with them is expedient.