Common Plant Diseases

Just as humans get sick, plants get diseases. Unfortunately that is a fact of life. But if you familiarize yourself with the possible diseases your plants may get, you can take immediate action and minimize the damage.

Every type of plant in your garden is at risk, including your lawn, shrubs, perennials, herbs, annuals and even your indoor houseplants. If you go to this useful gardening resource you will find some invaluable information, together with photographs that will help you to diagnose some common diseases that plants suffer from.

This web site gives you various options in terms of “host” plants that may be affected. All you do is click on the type of plant, and then you choose the host – and then the part of the plant that is affected (for example the leaf or roots).

In the meantime, here are some common diseases to look out for in your vegetable garden, and the vegetables they are mostly to affect.

Angular leaf spot (fungus)

Alternaria Cercospora, more commonly known as leaf spot, results in angular spots on the leaves of various plants including carrots and parsnips, where the foliage quickly turns yellow and then goes brown. When it attacks cucumbers and members of the cucumber family (including melons, pumpkins and squash), the spots become quite gummy and the leaves dry out and then drop off.

Anthracnose (fungus)

A type of fungus, anthracnose starts out looking like little angular lesions on the leaves of plants. The veins in the leaves start turning black and then the leaves turn brown and they wither. It also appears on pods in the form of tiny brown spots that darken and seem to sink into the pod. In damp weather, the fungus often produces masses of pink, sticky spores. When it affects fruit, lesions are tan or gray in color and they appear to have tiny pink dots. Although the disease begins when fruit is green, you won’t normally notice it until the fruit ripens.

This plant disease affects all members of the bean family including lima and snap beans and peas, as well as the cucumber family (cucumbers, gourds, melons, pumpkin and summer squash). It also affects peppers and tomatoes.

Aster yellows (phytoplasma)

This plant disease leaves plants yellow and stunted, with their leaves small and thickened. It affects lettuces, as well as carrots and parsnips.

Bacterial spot (bacterium)

This plant disease shows up as irregular water-soaked spots on leaves which start to look ragged. They then turn yellow and drop. You may also find brown, raised crusty, scab-like spots on fruit.

Peppers and tomatoes are affected by bacterial spot.

Bacterial wilt

When plants get this disease, they literally wilt and die. The disease is transmitted by the cucumber beetle that settles in the stems of plants, and so it is no surprise to discover that all members of the cucumber family are at risk.

Blossom-end rot

Blossom-end rot is basically a physiological problem that occurs when the fruit becomes water-soaked near its blossom-end. The tissue of the fruit then collapses and the fruit dries out leaving a white, papery area where the water was. Fungi often invade these areas turning the fruit black.

Blossom-end rot is common in peppers and tomatoes.

Common blight (bacterium)

A type of bacteria, common blight appears as water-soaked spots on the leaves of plants. The area around these spots usually turns yellow and the leaves may turn brown and become brittle. Pods also develop watery spots that become dry, brown, sunken blotches.

This plant disease affects all members of the bean family including lima and snap beans and peas.

Downy mildew (fungus)

Downy mildew is a fungal disease that appears as yellow angular spots on the upper surface of leaves together with a white to purple downy growth on the under-surface of leaves. Leaves usually curl, turn brown and, quite simply, die. Whole plants may also become dwarfed and yellow.

It affects members of the cucumber family including summer squash, pumpkin and melons, as well as the onion family, specifically onions, garlic and leeks.

Drop (fungus)

Drop can first be identified by soft water-soaked spots on the stem of plants. It spreads both upwards and downwards and you will soon see a cottony mass of sclerotia (embedded brown to black bodies) on the stems.

Drop affects lettuce.

Early blight (fungus)

Early blight, which is quite common in tomatoes, starts with dark-brown round spots or rings on the leaves. The area around these spots turns yellow and then the leaves wither and dry.

Fusarium wilt (fungus)

This fungal disease causes vines to turn yellow and wilt just when they are about to fruit. Stems often ooze sap. It is most prevalent in muskmelons and watermelons, but sometimes affects cucumbers and summer squash as well. It also affects tomatoes.

Fusarium basal rot (fungus)

Although you probably won’t realize it until the plants wilt and die, Fusarium basal rot causes the bulbous roots of onions, garlic and leeks to turn a dark color as they rot. Sometimes the roots dry out and then literally shrivel up.

Gummy stem blight (fungus)

Leaves of plants with gummy stem blight have water-soaked lesions and their stems turn dark brown. It doesn’t take long for them to wilt. It generally affects members of the cucumber family.

Leaf blight (fungus)

Leaf blight is a fungal disease that appears in various forms. For instance, it causes gray-green to a tan-brown color lesions to form on the leaves of sweet corn. Alternaria leaf blight causes yellow lesions to form on the leaves of vegetables in the cucumber family, including gourds, melons, pumpkin and summer squash. These lesions go brown as the leaf starts to die.

Neck rot (fungus)

Neck rot appears in the form of dry, sunken lesions around the neck of bulbs in the onion family. The bulb itself also tends to go gray and it looks as if it is covered with a powdery mold.

Root-knot nematodes

This plant disease stunts the growth of plants as small to large galls form on the roots. It commonly affects carrots and turnips which will appear to be getting too little water and nutrients to allow them to grow. It also affects tomatoes.

Root and crown rot / Phytophthora blight (fungus)

This fungal disease appears in the form of water-soaked black lesions on the stems, leaves and roots of plants and causes the leaves to wilt and die. The fruit also gets infected and invariably rots.

This plant disease affects peppers.

Rust (fungus)

Rust is a type of fungus that shows up as small red or reddish brown pustules that form on the underside of leaves and sometimes on pods as well.

Rust affects members of the bean family, particularly pole beans, as well as sweet corn.

Seed decay and damping off

This plant disease results in root and stem rot. It affects all members of the bean family including lima and snap beans and peas.

Soft rots (bacterium)

This bacteria causes onions to become wet and slimy as they mature. Soft rots creates a foul smell – which should draw your attention to it – and it starts in the neck area and moves downwards.

Various viruses

Members of the bean family, including peas, suffer from bean common mosaic, bean yellow mosaic and cucumber mosaic. Symptoms vary, but usually leaves get patchy in color and often pucker or curl. Plants very often are stunted and sometimes turn a sickly yellow color.

Members of the cucumber family, including melons, pumpkin and summer squash, get cucumber mosaic, watermelon mosaic and squash mosaic viruses. These result in distorted leaves, stunted plants and misshapen fruit.

Peppers and tomatoes suffer from tobacco mosaic and cucumber mosaic that causes their leaves to go yellow or become mottles and streaky. Leaves are also often distorted and stunted like those of other vegetables affected by viruses. Tomatoes also get tobacco streak which has similar symptoms.

Click the link to find out how to treat plant diseases, as well as a lot more information about diseases that affect these and other vegetables.