Plant Diseases – What Do They Mean?

Conditions that disrupt normal plant growth are called plant diseases. These diseases disturb the growth, function, normal structure, and other activities in plants. Usually, some casual agents cause these disturbances in plants. These agents can be infectious or noninfectious.

Infectious Plant Diseases:
Pathogenic organisms such as bacteria, fungi, mycoplasma, viruses, viroid, nematodes, parasites, etc., cause Infectious plant diseases. These agents can reproduce inside or on their hosts multiple times. They also can spread from one host to another.

Noninfectious Plant Diseases:
Generally, unfavorable environments cause noninfectious plant diseases. Some of these cases include extreme temperatures, toxic atmospheres, contaminated soils, and mineral deficits. These agents cannot reproduce within a host. Hence, they do not transmit from one host to another.

In some cases, multiple disease-causing agents may infect a plant at a time. Pathogens readily infect plants suffering from a nutrient deficiency or soil moisture-oxygen imbalance. Plants infected with one pathogen are often susceptible to being attacked by other secondary agents.

The combination of multiple pathogen attacks increases the complexity of the plant disease. Therefore, the study of the climatic condition, soil, growth environment, etc. is necessary to recognize a plant disease. Reputed pathologists can help find/diagnose these cases.

Infectious Plant Diseases (Biotic Diseases)

Eeshie, Bacterial wilt, CC BY-SA 3.0

Generally, bacteria, fungi, or viruses cause Infectious (biotic) plant diseases. We have briefed some common causative agents and major plant diseases below:

Bacterial Plant Diseases:

Aster Yellows,
Bacterial Wilt,
Blight (Fire Blight, Rice Bacterial Blight),
Canker,
Crown gall, Rot (Basal Rot),
Scab

Fungal Plant Diseases:

Anthracnose,
Black Knot,
Blight (Chestnut Blight, Late Blight),
Canker,
Clubroot,
Damping-off,
Dutch elm disease,
Ergot,
Fusarium Wilt (Panama Disease),
Leaf blister,
Mildew (Downy Mildew, Powdery Mildew),
Oak Wilt,
Rot (Basal Rot, Gray Mold Rot, Heart Rot),
Rust (Blister Rust, Cedar-Apple Rust, Coffee Rust),
Scab (Apple Scab),
Smut (Bunt, Corn Smut),
Snow Mold,
Sooty Mold,
Verticillium wilt

Viral Plant Diseases:

Curly Top,
Mosaic,
Psorosis,
Spotted Wilt

Non-Infectious Plant Diseases (Abiotic Diseases)

Photo by Scot Nelson CC0

Non-living causes contribute to non-infectious (abiotic) diseases in plants. Unlike infectious diseases, they cannot spread abruptly from one plant to another. Some of the common factors causing these diseases include nutritional deficiencies, unfavorable environmental conditions, and chemical imbalances in the soil.

Nutrient Deficiencies:
In general, plants need a wide range of nutrients to survive. Nutrient deficiencies can cause yellowing leaves, stunted growth, and poor production of flowers or fruits.

Plants suffering from Iron deficiency may have normal-looking green veins. But their leaves turn yellow or pale yellow. Similarly, magnesium deficiency causes the lower leaves of the plants to turn yellow and then brown. Finally, the infected leaves fall off from plants.

Nitrogen-deficit plants have stunted growth and produce fewer fruits or flowers. They may also have pale green or yellow leaves. Calcium deficiency may lead to blossom end rot disease. A sunken, leathery area forms on the bottom end of the fruits like peppers or tomatoes.

Sun Light:
Plants need optimal light conditions to thrive healthily. Exposure to heavy or low lighting conditions can stress off the plants. This may result in stretched stems, leaf scorch, or poor blooming.

Leaf scorch is a common non-infectious Plant Disease. Excessive light or heat exposure causes these types of plant diseases.

Temperature Extremes:
Extreme temperatures, both hot and cold, can hinder normal growth in plants. Heat stress can lead to leaf scorch, wilting, and stunted growth. Similarly, cold stress can cause cell membrane damage. This can also lead to discoloration, wilting, etc., and eventually kill the plants.

Watering:  
Both overwatering and underwatering can cause plant stress. This may lead to diseases like edema, wilting, root rot, and stunted growth.

Soil Engagement

Lack of organic matter, compaction, poor drainage, etc., are some of the soil problems that can hinder plant growth. In some areas, salt layers build up on soils. This condition is also called salt injury. This can cause leaf burn, stunted growth, and wilting.

Non-infectious diseases may pose a serious threat to farmers and gardeners. However, understanding the causes can help prevent these diseases.

Diagnosing Plant Diseases

It is important to diagnose the plant disease systematically. It helps in treating the disease and future prevention of the disease. There are many ways to achieve this.  However, we have elaborated on the most common and easy two-pronged approach below:

1.) Inspect the Symptoms for Plant Diseases

Halvard : from Norway., Aceraceae-Plant-diseases, CC BY-SA 3.0

Meticulous Visual Examination:
Examine the whole plant visually including stems, leaves, roots, fruits, and flowers. Look for any signs of wilting, discoloration, spots, abnormal growth patterns, lesions, or the presence of some insects or plant mites.

Marking Locations:
Pay attention to the affected locations and note them down. Determine whether the symptoms appear on older leaves, new growth, or specific areas like root bases, stems, etc., Check if the damage is localized or widespread. Also, look for specific patterns like wilting more on one side, spotting in one area, etc.,

2.) Distinguish Cause: Infectious Plant Diseases (Biotic) or Non-Infectious Plant Diseases (Abiotic)

After understanding the symptoms, try to find the type of disease. Biotic diseases have more specific indicators. Try to find signs of disease-causing agents like, insect droppings (insect frass) or fungal spores.

Analyze recent developments in environmental conditions. This may include watering practices, temperature, and sunlight exposure. Imbalances, deficiencies, or extremes in these factors can cause abiotic diseases.

Online Resources:
Many online resources help to diagnose plant diseases. They usually have detailed symptom checkers or photo guides, using which you can narrow down the diseases yourselves. Some facilities also allow you to upload photos of infected plants and provide details so that they can help in the diagnosis.

Professional Assistance:
If you are unsure of the disease or need a definitive diagnosis, you can always get assistance from your local Cooperative Extension office, nearby plant pathologists, or nurseries. This is recommended especially, if the infection is severe. They may ask for samples of infected parts for lab testing.

In this way, you can get a picture of what is happening to your plant. Then, take further steps as per the professional recommendations to cure your plant.

Treating Infected Plants

After diagnosing plant diseases, the next step is to treat them. Depending on the infection, there are many ways to cure it. We have briefed a common, simple two-pronged approach to achieve this.

1.) Isolate the Plant

Isolate the infected plants from others. This helps prevent the spreading of the disease or pests. This can be very simple in the case of container plants. Just keep the containers away in a safe place, the job is done! For other plants, the isolation process can differ.

2.) Treating the Infection

Here are some of the common treatments for most common plant diseases:

Pruning:
Prune the infected portions of the plant and dispose of them carefully.  Make sure to sterilize the pruning shears before, after, and also in between the pruning process.  This helps prevent spreading/transmitting the plant diseases to other healthy plants.

Adjusting Care:  
Generally, lack of basic amenities like adequate sunlight, improper watering, competing weeds, etc., make the plants vulnerable to infections. Hence, provide them with basic necessary needs in all cases. Make sure to fertilize them at regular intervals as per the recommendation.

Natural Remedies:  
You can treat mild infections with natural remedies. They include neem oil spray, insecticidal soap, and baking soda solutions. In most cases, this treatment cures the disease.

Fungicides or Insecticides:
In case of severe infections, you can use fungicides or insecticides. They prove to be effective on almost all diseases. However, make sure to follow the safety precautions and expert recommendations.

Other Measures

In some cases, you may have to dispose of a diseased plant. While doing so, make sure to follow the recommended procedures. Otherwise, the disease may quickly return.

Compost:
If your plant is infected with less persistent diseases, you can simply remove the infected portions. Then, turn the removed portions into compost in a safe area of your garden space. You can also make use of your local government bodies’ nearby green waste center for this purpose.

Burial:  
In some cases, a portion of infected plants may rot. This includes fruits, flowers, vegetables, and leaves. You can simply bury them in a hole about 1-2 feet deep. Depending on the disease, some experts may recommend adding solvents with these rotten parts in the holes.

Bonfires:
You can use bonfires to dispose of dry garbage, including wooden debris. Even some seriously infected plants need bonfires for professional disposal. Make sure to use non-windy spaces, free of dry items, to set fire. Otherwise, the fire may spread to other areas.

Household Trash:
You can dispose of Small wooden pruning, infected bulbs, collapsed seedlings, etc., using normal garbage cans in your home. However, make sure to throw the garbage in appropriate areas, as recommended by your local management.

How to Prevent Plant Diseases

Preventing plant diseases is a crucial step in successful gardening. Some of the common precautions are listed below:

Start with Healthy Plants:
Reputed nurseries and garden centers sell disease-resistant varieties of plants. These plants are especially bred to resist infections. So, whenever possible, choose these types of plants to grow in your garden spaces.

Practice Good Sanitation:
Clean your gardens regularly. Maintain the cleanliness and tidiness of your gardens by removing fallen leaves, weeds, and other debris. In this way, you can reduce the hiding places of harmful pathogens. Also, make sure to sterilize /clean garden tools before, after, and in between usage. It stops diseases from spreading among plants.

Watering:   
Avoid overwatering. This can lead to various fungal diseases, including root rot. Allow soil to dry in between the watering schedule. Make sure to water deeply at a time. If possible, water in the early mornings. This allows plants to cool off and dry themselves as the sun rises.

Provide Adequate Air Circulation:  
Prune the plants at regular intervals. Make sure there is enough air passage between plants. This reduces moist conditions, thereby preventing most fungal diseases.

Mulching:  
Mulching has various advantages including weed suppression, moisture retention, and soil temperature regulation. This also helps prevent splashing up of fungal spores to other plants.

Monitor your plants for disease symptoms regularly. Upon identification, act immediately. This helps reduce the severity of the damage. Dispose of the diseased fruits, leaves, flowers, etc., professionally. By following the above steps, you can maintain your garden plants healthy.

Curious Contemplations
Powdery Mildew
Aphids