Common Signs of Fungal Infection in Plants

Fungi are nature’s ultimate recyclers. Without fungi, our world would drown in dead matter that cannot decay on its own. While we rely on fungi to keep our world’s cycle of life and death moving, there are some species that negatively affect plant growth. In fact, fungi cause the majority of issues we see in our plants–about 85% of all known plant diseases. Since we often cannot see the fungus the way we can spot insect pests, it can be difficult to diagnose the issue as fungal infection.

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How Does Fungi Infect Plants?

Fungi, like animals, are unable to produce their own food. They must consume other organisms for nutrients. While some species grow symbiotically with plants to obtain sugars and share nutrients and most others will only target dead plant and animal matter, some pathogenic species will infect plants while they are still alive. Spores and mycelium (thin white strands that comprise the main body of fungi) can enter through open stomata, roots, or penetrate directly through cell walls. After entering, they cause plant stress that manifests in different ways, depending on the type of fungus.

Symptoms of Fungal Infection

Powdery mildew: This is a white film that grows on most plant parts, and is extremely common because, unlike most fungi, powdery mildew can grow even in warm, dry conditions.

Leaf rust: Rusty-colored pustules will develop solely on the underside of leaves. As the fungus spreads further, you will observe pale discoloration on the top of the leaf as well. Eventually, the leaves will completely fall off.

Black spot: The name says it all. Dark spots form on the top of leaves, but never on the bottoms. They will grow until the entire leaf is yellow and spotted with black or brown dots. Black spot forms because there is standing water on a leaf. Overcrowding, wetting leaves while watering, and poor air flow will encourage black spot growth.

Botrytis blight: This disease affects flowers and buds, causing them to decay and become covered in a white fuzzy film.

Chlorosis: This is the term for when leaves become pale or yellowed due to a lack of chlorophyll. Some fungal infections cause chlorosis as they steal nutrients from the host, though the most common causes of chlorosis are some form of nutrient deficiency from the soil.

What Should You Do?

Most remedies to protect your plants from fungal growth are proactive, not reactive.

  • When choosing planting sites, avoid cool, stagnant, moist conditions, as these encourage fungal growth.
  • Allow soil to dry out between waterings
  • Grow plants in areas that receive ample sunlight and drainage.
  • Do your best to water close to the ground–wet leaves and stems are much more susceptible to fungi than dry ones.
  • Water early so that the soil has time to dry out before night, when fungus is most active.
  • Select plant varieties that are naturally resistant to disease
  • Avoid overcrowding when you plant, and prune diligently so that air can flow between the leaves and dry them off
  • Pruning sickly leaves and stems can stop disease spread, so inspect your plants often and remove any parts that look infected. Be sure to sterilize your pruning shears with a disinfectant wipe between cuttings when removing infected parts.

Pro Tip: When cultivating indoor plants, keep them away from vents blowing cold air to prevent fungal infection.

If you have a particularly stubborn problem with fungal infection, you may wish to get professional assistance. Visit one of Big Earth Landscape Supply‘s 4 area locations to speak with a gardening and lawncare expert about fungicides which can assist in keeping your garden healthy and strong.