5 Plant Diseases Every Gardener Should Know
June 30, 2025

5 Plant Diseases Every Gardener Should Know

What is a Plant Disease?

So, you’ve made it this far! You’ve planted, watered, and tended your garden for weeks and now a strange  spot on a leaf is threatening your sanity. But what could it be and what do you do about it? It could be a disease of some kind. A plant disease is a condition that impairs a plant's normal functions, typically caused by pathogens. But, don’t worry. If caught early on, many plant diseases are easily treated. It is even better to prevent them, of course! We will get to that too.


There are many plant diseases that plague gardens across the world but below are the five most common. If none of these seem to match up to what you’re seeing, it could be a pest, a nutrient deficiency (see below), or a different disease. If you want to read more about various plant diseases, check out the UCANR IPM page or the University of Minnesota’s webpage to get started. I also recommend talking with your local extension office if the problem still eludes you; they are usually more familiar with local problems. A local extension office is a community-based resource, often connected to a university, that offers expert advice and support on gardening, farming, and other horticultural issues. Let’s dig into the top five most common garden diseases and how to handle them like a pro.


Most Common Plant Diseases in the USA

 

Powdery Mildew

  • Identify: This looks like someone dusted your plant leaves (top and or bottom) with white flour. It can show up on either side of the leaves and can be devastating if left unchecked. It is spread by water and is more prevalent in humid, high rainfall areas.
  • How to Help: Improve airflow and avoid getting water on the leaves (water directly at the base of the soil). Spray the leaves down with neem oil every 2-3 days to control the spread.

Blight

  • Identify: Typically seen on tomatoes and potatoes, blight causes black or brown spots on the leaves and stems, which eventually lead to plant collapse.
  • How to Help: Remove affected foliage immediately and avoid overhead watering. Practice crop rotations. When you’re planning a garden with your quality heirloom seeds, consider organizing your planting so tomatoes and potatoes don’t follow each other in the same spot each year.

Leaf Spot

  • Identify: Brown, black, or yellow spots on vegetables, flowers, and shrubs. Leaf spot is caused by various bacteria and fungi, depending on the region and time of year. It is spread by leaves brushing against other leaves and sometimes by water as well.
  • How to Help: Remove spotted leaves and avoid watering in the evening. Keep plants spaced out to allow air to circulate.

Root Rot

  • Identify: Wilted-looking plants even when the soil is wet. Slow growth. Brown, slimy roots. More common in potted plants, but it can happen in the garden as well if the drainage is poor.
  • How to Help: Avoid the problem by not overwatering and always having plants in well-draining containers and soil. If a plant already has root rot, dig it up, remove the affected roots, and replant it in well-draining soil. Water thoroughly, but allow the top few inches of soil to dry out before each watering.

Rust

  • Identify: Rusty-orange spots on the undersides of leaves. Especially prevalent in damp, humid weather. Starts very small and escalates with improper watering practices.
  • How to Help: Remove affected leaves and avoid splashing water on foliage. Fungicidal sprays can help if it spreads.

Nutrient Deficiencies

If none of the above diseases seem to describe the problem your plants are having, it could be a nutrient deficiency. If your leaves are looking pale, have discolored veins, the new leaves are looking unhealthy, or something similar to this, you may need to improve the fertility of your soil. Get a soil test done through your local extension office and fertilize with a high-quality fertilizer (there are organic options too!). Compost is the best option when possible. Check out the Royal Horticultural Society’s fantastic resource about nutrient deficiencies for more information.


IPM: Your tool kit

With any disease, a wide variety of prevention and control measures will always be your best bet. Integrated Pest Management (IPM) is a term used in the horticultural and agricultural industries to describe an all-inclusive approach to managing plant problems. While this term is most often used in conjunction with preventing and treating plant pests, the same principles and many of the same tactics apply to diseases, too. For the typical home gardener, this looks like:

  • rotating crops

  • using neem oil

  • using row covers

  • having good watering practices

  • not overcrowding plants

  • removing garden debris

  • inspecting new plants before planting

  • utilizing companion plants

  • fertilizing appropriately

  • testing and enriching the soil

  • having proper drainage 

  • having good airflow in the garden


All of these things (and more) will help to keep your garden pest- and disease-free. Prevention is the best defense! Keeping your garden healthy isn’t about perfection; it’s about being observant, curious, and proactive. With a little know-how and the right prevention tools, you’ll be well on your way to a thriving, disease-free garden. Happy growing!

About This Expert:

Lara Wadsworth is a freelance horticulture writer with a Bachelor's degree in Horticulture and over three years of experience creating engaging content about gardening and plant care. As a wife, mom, and dog lover, Lara understands the importance of balancing a busy life with a thriving garden. She values practical advice and effective strategies that empower beginners and experienced gardeners alike to grow with confidence. Through her writing, she aims to inspire others to enjoy the rewards of gardening, no matter their skill level.

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