Frequently Asked Questions About Plant Diseases

Frequently Asked Questions About Plant Diseases / FAQ’s on Tree / Pant Diseases

Here are most Frequently Asked Questions About Plant Diseases.

  1. What are plant diseases and how can they be recognised?

Any abnormal growth of dysfunction found on the plant could possibly be termed as a disease. These diseases tend to disturb the normal functioning of the plant.  They can be recognised by deformations or extra growth on the plant structure like oozes, mushrooms, conks etc.

  1. What are the types of plant diseases?

The diseases occurring in the plants could be broadly classified into three categories: fungal diseases, bacterial diseases and viral diseases.

Fungal disease is due to the fungi, a multi-cellular organism which breaks the plant tissue and steals the nutrients (e.g. Mold, mildew, etc.).

Prokaryotic organisms cause bacterial disease in plants (e.g. Cankers). Similarly, viruses are extremely tiny particles that are infectious in nature and destroy the host plants (e.g. Tobacco mosaic virus).

  1. What cause plant diseases?

Diseases in plants could be caused either by living entity or a non-living entity. Diseases that occur due to the presence of living organisms like fungi, bacteria and viruses are termed as Biotic diseases and that which occur due to the environmental conditions like wind, frost, salt, soil compaction etc. are termed as Abiotic diseases.

  1. What is a plant disease pyramid and how is it connected to biotic diseases?

Biotic diseases develop only under certain conditions which means that they occur only if there is a host plant, a pathogen and environmental condition conducive to the disease development and most importantly all the three should come together at the same point of time.  When this happens, then it is perfectly called as a plant disease pyramid. The major thread relating this pyramid to the biotic diseases is that if any of the conditions mentioned above goes missing then biotic diseases do not occur.

  1. What plant diseases are caused by fungus?

Fungi can cause a variety of changes in the plant structure and some observed diseases or symptoms are damping off, leaf spots, powdery mildew, cankers, root rot etc.

  1. What are phytoplasmas and what disease can they cause in plants?

They are extremely small plant pathogens and depend on insects like leafhoppers to attack the host plants. They are mainly spread by persisting to stay within the insect vectors. Symptoms of the phytoplasmas are virescence and abnormal growth called witches broom. The most common disease caused by phytoplasmas is Aster yellows.

  1. What are parasitic seed plants?

They are just like any other plant such that they reproduce, seeds disseminate through wind and water. The major difference is that these parasitic plants lack the ability to produce nutrients and depend on the host plants for the same. Parasitic plants sometimes develop structures like haustoria to penetrate into the host plant and obtain water and nutrients. The symptoms of parasitic seed plants are less vigorous and dieback and the common parasitic plant is Mistletoe (generally penetrates into the oaks and other forest trees).

  1. What plants are commonly affected by aster yellows?

It is known that aster yellow can damage more than 300 species of broad leafed herbaceous plant all over the world. The commonly affected plants are marigolds, daisies, coreopsis, delphiniums, zinnias etc. Some vegetable plants that get affected by the aster yellows are carrots, lettuce, potatoes etc. It is worthy to note that weeds (plantain, dandelion etc.) also get affected by this disease.

  1. What causes blight and what are its symptoms?

Blight is of two types, they are early blight and late blight. Early blight is caused by the alternia solani fungus and the common symptoms of the disease are damping off, stem cankers, crown rot, leaf blight and fruit rot. Late blight is caused by pathogen like Phytophthora and common symptom of the disease are leaf lesions and change in colour of green areas into brown black.

  1. How to kill blight?

Both late and early blight can be controlled by using compost tea (4 months old compost in 5 to 8 parts of water) and baking soda (1 spoon of baking soda dissolved in 1 quart of warm water). Removing dead and infected leaves and fruits from the plants can also prevent the spread the disease.

  1. What is leaf spot and what are its causes, symptoms and control measures?

The circular blemishes on the leaves of a plant are called leaf spots caused mainly due to parasitic fungi or bacteria. The common symptoms of the disease are raised or sunken spots; colour of spots could be yellow, orange-red, brown or black; loss of leaves etc.

The disease can be controlled by some management techniques like:

  • Spacing the plants properly and avoid over- crowding.
  • Not splashing water onto the leaves and keeping the moisture levels balanced.
  • Reducing the stress on the plants.
  • Avoid fertilization of plants unless a soil test recommends correction.
  • No fungicides after the disease has occurred instead they could be used before the symptoms appear on the leaves.
  1. What is powdery mildew and what are its symptoms and control measures?

The powdery mildew is made up of spores and forms like a white fungus over the leaves. The powdery mildew disease can be identified by several symptoms like dusted flour on the leaves, change in the colour of leaves to yellow, twisting of leaves, leaves and buds getting disfigured etc. This disease can be controlled and prevented by:

  • Removing and destroying the infected plant parts.
  • Spraying fungicides on infected parts.
  • Use of organic substances like sulphur, lime-sulphur, neem oil and potassium bicarbonate.
  • Using resistant varieties of plants.
  • Avoid overhead watering.
  • Light pruning or selective pruning to increase air circulation between the plant parts and also to reduce humidity around plants.
  1. How does baking soda treat powdery mildew on plants?

1 tablespoon of baking soda with half teaspoon of liquid soap and 1 gallon of water is mixed together and sprayed over the infected area to reduce the occurrence of powdery mildew. This is useful to prevent the disease, but is less effective once the disease has started.

  1. How can one treat powdery mildew organically?

There are few organic substances which can be used to treat powdery mildew on plants. They are:

  • Potassium bicarbonate
  • Milk
  • Vinegar
  • Baking soda
  • Garlic
  • Sulphur
  • Copper based substances
  1. What is canker disease in plants and what causes canker in plants?

Canker in plants is a symptom of an injury related to an open wound that has been infected by a fungal pathogen. They are caused by fungi, bacteria, virus and Abiotic disorders like sunscald and hail.

  1. What are the symptoms of canker diseases and how does one treat cankers in plants?

Cankers on plants or trees look oval or elongated in shape and vary in size. They are sunken localized areas with discolouration and brown to reddish colour lesions from the bark. Another symptom of the disease could be pale green leaves, much smaller in size, often curled and sparse. Cankers can block the water conducting tissues, thereby causing wilt and dieback.

This disease is difficult to control and there are no authorized chemicals to treat the disease. The only way to get rid of canker is to prevent them from occurring. Some control measures are:

  • Pruning the diseased parts.
  • Planting only resistant varieties.
  • Avoid bark wounds on the plants and trees.
  • Proper mulching, watering and soil management.
  • Avoid pruning when the bark is wet and use sterilized tools for pruning.
  1. What causes damping off disease?

Damping off is caused by several fungi species such as Rhizoctonia, Fusarium and Phytophthora. The most common and major type of fungus responsible for this disease is Pythium.

  1. How does damping off spread?

This disease thrives in cool temperatures and wet soils and is mostly carried by wind from one plant to another. The fungal spores take root in the soil and spread quickly across the seedlings.

  1. What is damping off and what are its symptoms?

Damping off is a common disease of the seeds and seedlings, where the stem or root tissues rot below the soil surface. Seeds affected with this disease generally germinate and grow above the soil, but within few days get water soaked, mushy and die. The disease can be clearly identified by the following:

  • Seedlings do not emerge from the soil.
  • Seedling stems turn gray or brown.
  • Very young, tender leaves wilt and turn brown or gray.
  • Stunted roots.
  • Fluffy white cobweb like growth over the seedling.
  1. How can one treat damping off or how can damping off be prevented?

Curing damping off that has already occurred in plants is difficult, but can be prevented by certain measures like:

  • Providing proper air circulation in and around the plants.
  • Using a fungicide to treat the seeds before sowing.
  • Sterilize the soil before sowing or planting.
  • The seed starter mix should be light and fast draining.
  • Do not overcrowd the seeds while sowing.
  • No overhead watering and no water supply in the afternoon.
  • Application of a foliar spray (3 to 4 tsp per gallon of water).
  1. What is mosaic virus and what are its effects?

It is a viral infection affecting almost 150 types of plants and is spread by aphids, leaf hoppers and white flies. The disease can be identified by yellow/white/green stripes on the foliage, curled or wrinkled leaves, yellow veins, stunted growth, blistered leaves, mottled fruit with warty look etc.

  1. How can one treat/control/prevent mosaic virus?

Any disease can be prevented from occurrence, but is very difficult to control once it infects the plants. The spread of the disease can be controlled by removing the infected plants and destroying them. Some measures to prevent the disease are:

  • Planting resistant varieties.
  • Preventing the insects from entering the farm by covering the plants with floating row cover or aluminium foil mulches.
  • Proper weeding the entire farm area.
  • Avoid farming activities when the soil is damp.
  • Disinfecting the tools to avoid contamination.
  • No fungicide or pesticide should be used because they cannot control the viral disease.
  1. What is root rot disease?

As the name indicates root rot is a disease of the roots growing in wet or damp soil conditions. It is similar to damping off in all aspects, but is a post emergence rot. The disease is recognised by poor growth, wilted leaves, early leaf drop, dieback and ultimately death of the plants. There could be dark brown lesions on roots or crown.

  1. How can the root rot disease be prevented?

This disease can be controlled by drenching the soil with fungicides, fumigating the soil, solarisation and crop rotation. Regulating the moisture content in the soil and improving drainage can also be useful in preventing root rot.

  1. What is dieback disease in trees?

Dieback is a condition when a group of trees begin to lose health and die without any obvious cause. It is believed that the soil borne mould Phytophthora cinnamomi causes the root rot in plants and trees and severe root rot leads to die back.

  1. What is Fusarium wilt and what are its symptoms?

It is a soil-borne pathogen that enters the plant through the roots and blocks the water conducting tissues of the plants. The stem and leaves when affected by the disease have restricted supply of water due to which they turn yellow or wilt. The major symptoms of the disease can be first noticed on the older leaves. It can survive in the soil for many years and is generally spread by water, insects and garden equipment. The disease is prominent during hot and dry weather conditions

  1. How can one treat Fusarium wilt in plants?

Some measures to prevent, control and treat Fusarium wilt in plants are:

  • Using resistant varieties of planting material.
  • Sterilizing the pruning clippers after use.
  • Use insecticides or traps to control garden or farm insects.
  • Too much nitrogen fertilizer can increase the risk of the disease so a slow release organic fertilizer is advisable to use.
  • Removal of weeds is essential.
  • Using a fungicide for the safety of the crop is advisable.
  • If the disease is too severe, then soil solarisation is recommended.
  1. What are the diseases caused by bacteria in plants?

Bacteria in plants can manifest in the form of different diseases such as:

  • Cankers
  • Bacterial wilt
  • Blight
  • Brown spot
  • Crown gall
  1. How does bacterial disease in plants spread?

Bacteria becomes active in plants only when the conditions like high humidity, poor air circulation, plant stress, over watering, under watering etc. are conducive for them to multiply. Soil, crop debris, weeds all act as reservoirs for the bacteria and from here they spread through seeds, crop residues, water, farm equipment, etc. warm weather and overhead irrigation are favorable for the spread of the bacterial diseases.

  1. What is bacterial ooze?

Bacterial ooze is water coming out from water soaked lesions in the form of droplets. This is caused by the malanga pathogen which creates a bacterial spot composed of bacterial cells.

  1. What causes crown gall disease and how do they first appear?

The crown gal disease is caused by the Agrobacterium tumefaciens in soil and is found to affect the woody shrubs and herbaceous plants like raspberries, blackberries, roses, etc. the disease is first observed as small overgrowths on the roots, crown and trunks. The parts of the plant closer to the soil are first affected and there is a tumor like spherical white or flesh coloured swelling that is spongy and wart like in nature.

  1. What causes rust and how does one treat leaf rust?

Rust is classified as a fungal disease that affects the aerial parts of a plant. It is caused by a fungal parasite and spreads in mild moist conditions. The spores spread the rust particles from one plant to another through wind or water. There are different forms of rust that occur in the plants and look almost like the chemical rust on iron things. In plants, it can be identified as:

  • Yellow or white spot on the upper leaves of the plant.
  • Red or orange blisters called pustules on the lower side of the leaves.
  • Streaks or spots on the lower side of the leaves.
  • Spots are formed with spores.
  • Leaf distortion and defoliation.

The treatment is a difficult task, but there are some measures to control or prevent the rust.

  • Destroying the infected parts and replanting resistant varieties
  • Keeping the area clean from debris to prevent spread of disease.
  • Avoid water splashing on leaves.
  • Dusting leaves with sulphur in the proper season.
  • Spacing the plants correctly would encourage air circulation.
  • Applying rust fungicides would also help control rust.
  1. What causes anthracnose disease and what are its symptoms?

It is a fungal disease of the plants generally occurring during the spring season. Anthracnose is caused by the fungi colletotrichum. The general symptoms of anthracnose are dark water soaked lesions on stem, leaves and fruits. These lesions contain pink gelatinous mass of spores in the center and occur mainly during the warm weather conditions. The disease is found to grow in wet weather and is spread by wind, rain, insects and garden or farm equipment.

  1. How does one treat anthracnose?

The following treatment measures could be adopted for anthracnose disease:

  • Planting resistant varieties.
  • Disinfect the tools used for farming after every activity.
  • Avoid composting the infected leaves in the farm area.
  • Use bio-fungicides to treat the bacteria and fungi.
  • Apply copper and sulphur sprays on newly developing foliage.
  • Applying neem oil spray during the first budding period with an interval of 7 to 14 days could be a preventive measure for anthracnose.
  1. What are scab diseases in plants and what are their symptoms?

Scab is a fungal plant disease caused by the Venturia fungi and characterised by dark sooty spots on the plant parts. The major symptoms of the disease are:

  • Dark, olive green, purple, black lesions on leaves.
  • Yellow leaf colour and defoliation.
  • Dieback of infected shoots.
  • Dark immature flower buds.
  • Brown or black scabby lesions on fruit.
  • Brown or dark rings on the leaves.
  1. How can one control scab disease in plants?

Treating or controlling scab in plants can be of two types: non-chemical control and chemical control.

The non-chemical control measures include clearing the plant area from the scab infected leaves and stems, pruning the affected shoots, providing proper air circulation around the plants and using resistant cultivars as planting material.

The chemical control measures are to be used only for non-edible crops because the treatment of scab on edible crops is not available. The chemical fungicides used for ornamental plants are tebuconazole, trifloxystrobin and triconazole. The above mentioned chemicals are a combination of insecticides and fungicides.

  1. What are some of the natural ways of treating plant diseases?

Naturally available substances can be prepared as a solution and sprayed in required amounts to protect the plants from diseases. While using these substances protection should be taken such that there is no irritation on skin and other sensory organs. Also, it is important to know the quantity of the spray required for the treatment. Such natural substances are:

  • Apple cider vinegar
  • Baking soda
  • Chive spray
  • Garlic and corn spray
  • Elder leaf spray
  • Milk spray
  • Chamomile spray
  • Seaweed spray
  • Cinnamon
  • Hydrogen peroxide
  1. What is smut disease in plants and how do we treat it?

It is a fungal disease caused by the fungus called basidimycetes phylum. The most infected parts of the plant are inflorescence, flowers, anthers and ovaries and they are generally infected during the reproductive phases. The grain or cereal that is being infected gets filled with black powder (sori) of the fungus. The seeds could be treated with hot water of temperature around 52˚C for ten minutes to prevent this disease. Other prevention methods are solar energy treatment and the use of chemical fungicides like vitavax, topsin and benlate. The most common plants affected by this disease are grasses like corn, maize, sugarcane and sorghum

  1. What is downy mildew and what are its symptoms?

This is the disease affecting the foliage of the plant and is caused by the fungus like organism called oomycete. The spores developed during the infection carry the disease to other plants when the temperature of the atmosphere is below 65˚F. The fungus grows in plant debris and in the moist soil from where it is spread by wind, insects, rain and farm equipment. The disease can be recognised by yellow or white patches on the upper surface of the leaves and white or gray patches on the lower side of the leaves. As the disease gets severe, the leaves turn crisp, brown and eventually fall off.

  1. How can one treat downy mildew?

This disease can be easily prevented by not providing the right environmental conditions that favour the disease. Some other preventive measures are:

  • Pruning the dead stalks to improve air circulation in the plants.
  • Watering the plants during the early hours of the morning.
  • Removing and destroying all the infected plants during the fall and winter.
  • Planting resistant varieties of crops.
  • Using copper based fungicidal sprays for treatment even before the disease appears during wet weather conditions.

Read: Spirulina Farming, Cultivation Practices.

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