What types of diseases can occur in plants?

Angelo’s interest in plants has led him to work in a variety of fields, including research, grounds management, technical training, design, and nursery management.


How to Identify and Treat Plant Disease

Protect your plants from debilitating diseases by learning to recognize the symptoms and practice prevention. A wholistic approach includes first identifying the pathogen. Next, choose a therapy approach that is safe, effective, and accountable. Continue reading and save this page for plant disease detection.

Black Spot 

Black spot is a frequent disease affecting roses, but it may also affect other ornamental and garden plants. This fungus develops black, circular patches on the top surfaces of the leaves. Lower leaves are frequently the first to get affected. Infested leaves become yellow and fall off the plant in severe infestations. Black spot is a concern after prolonged periods of rain or when leaves have been moist for 6 hours or longer. Spores of black spot overwinter on fallen leaves.

Tips for Controlling Black Spots on Leaves

  • Plant in soil that drains well. Regular feedings of organic fertilizer will keep your plants healthy. This will aid in the prevention of fungal disease in plants.
  • Spores of the fungus survive the winter in plant detritus. Remove any dead leaves or diseased canes from around the plants and dispose of them in the garbage. Make no additions to the compost pile.
  • After each usage, disinfect your pruners with a household disinfectant. Ethanol or isopropyl alcohol can be used straight out of the bottle.
  • Avoid spraying water on the leaves because water (not wind) spreads fungus spores. Apply water straight to the roots while watering. Water plants that are susceptible to the illness using a soaker hose.

Other Leaf Spots

Fungal leaf spot disease may be seen both inside and outdoors on houseplants. This happens in hot, humid weather. The fungus patches get big enough to touch each other as the illness advances. At this time, the leaf surface resembles blotches rather than dots. Leaf spot may cause plant defoliation. Follow the same guidelines as for controlling black spot.

Powdery Mildew

Powdery mildew is a fungus that wreaks havoc on many of our landscaping plants, flowers, veggies, and fruits. Powdery mildew is easily identified. Infected plants will display a white powdery substance that is most visible on upper leaf surfaces, but it can appear anywhere on the plant including stems, flower buds, and even the fruit of the plant. This fungus thrives in low soil moisture circumstances with high humidity levels on the plant’s top surface. It affects plants stored in gloomy locations more than those kept in full sunlight.

Tips for Controlling Powdery Mildew

  • When buying plants from a greenhouse, inspect them for mildew (and insects).
  • Wiping off the leaves is not an effective powdery mildew treatment since it returns within days.
  • All contaminated material should be removed since spores overwinter in it. Trim and remove infected plant parts.
  • Do not incorporate the trash into the soil or compost pile.
  • Plants should be spaced far enough apart to promote air circulation and minimize humidity.

Downy Mildew

Because downy mildews differ from powdery mildews, it is important to understand the differences between the two. Powdery mildews are real fungal infections that appear on the top leaves as a white powdery material. Downy mildews, on the other hand, are more related to algae and produce grayish fuzzy looking spores on the lower surfaces of leaves. Look for light green or yellow patches on the top surfaces of older leaves to diagnose downy mildew. The fungus will have a white to grey downy material on its bottom surfaces. Downy mildew grows in chilly, wet conditions, such as early spring or late autumn. Temperatures below 65°F and high relative humidity promote spore development.

Tips for Downy Mildew Treatment

  • Water is required for downy mildew to live and spread. The illness cannot spread if there is no wetness on your leaves. Keep as much water off the leaves as possible.
  • Downy mildew need water to live and spread. If there is no water on your leaves, the illness cannot spread. Keep as much water as possible off the leaves.

*Some fungicides used to combat powdery mildew are ineffective against downy mildew. Earth’s Ally’s fungicide will control both powdery and downy mildew.


Plant blight is a widespread disease. Remember the 1840s potato famine? One million people perished as a consequence of the blight. Nevertheless, blight affects other plants, including tomatoes, in addition to potatoes. Blight is a fungal disease that spreads by windborne spores. As a result, spores may cover wide surfaces and transmit the virus quickly. Blight can only spread under warm, humid circumstances, such as two consecutive days with temperatures over 50°F and humidity levels exceeding 90% for eleven hours or longer. There is no treatment. The only alternative is to prevent.

Tips for Preventing Blight

  • Grow early variety of potatoes since blight comes in mid-summer and you may harvest your crop before the blight.
  • Grow early types of potatoes since blight develops in the middle of summer and you may harvest your crop before the blight.
  • Discard any plant portions that have been affected with blight. Keep the area clean of fallen debris from your diseased plants and discard in the trash. Do not add anything to your compost pile.


Canker is often identified by an open wound that has been infected by fungal or bacterial pathogens. Some cankers are minor, while others are fatal. Canker is most common on woody landscaping plants. Sunken, bloated, cracked, or dead regions on stems, limbs, or the trunk may be symptoms. Cankers have the ability to girdle branches and destroy vegetation. Cankers are most common on stressed plants that have been weakened by cold, insects, drought conditions, nutritional imbalances or root rot. Pathogens may also be transferred by rodents.

Tips for Controlling Canker in Plants

  • Remove diseased parts in dry weather.
  • Grow resistant varieties whenever possible.
  • Prevent overwatering and overcrowding, as well as mechanical wounds caused by lawn mowers.
  • Wrap young, freshly planted trees to protect them from sunscald. Sunscald creates dead patches that form on trunk and limbs of young trees if the trunks have been shaded, then transplanted to sunny areas.
  • Plant in good soils and provide nutritional needs to keep plants healthy.

Tips to Control Plant Fungus and Diseases

Prior to planting, create a well-drained soil with lots of organic matter. If required, raise the beds and fill them with a professional potting mix that drains properly. Too much water in the soil might cause rotting. Keep water away from the leaves. Water the root zone by hand or with a soaker hose. Fertilize plants as needed to maintain them in optimal health.

  • Choose resistant varieties whenever possible.
  • To increase air circulation, prune or stake plants, avoid crowding them, and eliminate tall weeds.
  • Plants in containers may be planted in places with poor air circulation.
  • Remove any infected debris to keep the disease from spreading. Severely affected plants should be removed and discarded (not composted).
  • Water during early morning hours so the plants can dry out and avoid getting water on the leaves. Water later in the day if downy mildew is present as it favors morning moisture. Avoid getting water on the leaves in any case. A soaker hose will retain water at the root zone, preventing spore dispersion.
  • Examine all plants for disease signs and pests before buying from your local greenhouse.
  • After cutting unhealthy plant sections, disinfect pruners.
  • Get yourself a hand lens. A 10x hand lens is ideal for detecting fungal and insect concerns. Besides that, a hand lens allows you to see thing in nature difficult to see with the naked eye.

Keep all parts of the plant protected by using a fungicide for plants. Plant-based environmentally friendly fungicide spray Disease Control is a contact fungicide and bactericide that has been OMRI Listed® for use on houseplants and in organic gardens. Formulated with food-grade citric acid, Earth’s Ally is highly effective at treating and preventing the common plant diseases outlined in this article.

These steps will build a healthy immune system and help avoid disease (and insect) problems. Diseases and pests like to target stressed or weak plants. Consider your immune system. The better it is, the more effectively it will battle illness.


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