What Is Leaf Spot, And Is It Wreaking Havoc On Your Plants?

What Is Leaf Spot, And Is It Wreaking Havoc On Your Plants?

Leaf spot is a common problem that affects both indoor and outdoor plants. It can cause unsightly blemishes on the leaves of your plants, ranging from small black and yellow dots to larger brown or white patches. Fungi are the main cause of this problem, and they leave their signature in various colors like rust red, inky black, sunshiny yellow and pale white. Some bacteria also cause leaf spots that appear as brown or black streaks on the leaves. Each blemish is like a battleground, where your plant’s defenses fight against the enemy.

To treat leaf spots, you need to use effective herbicides that can kill the parasites. However, the fight against leaf spots is not just about using herbicides. You also need to adopt proper gardening practices such as watering your plants correctly and spacing them strategically. These practices not only help to prevent leaf spot attacks but also aid in the recovery of plants already affected by the disease. By embracing these practices, you can become a horticultural hero and conquer leaf spots, restoring your garden or houseplants to their former glory.

The contributing factors and symptoms of leaf spots

plant with spotted leaves


Fungal pores are the culprits behind the infamous fungal leaf spot disease. When these microscopic freeloaders secure themselves onto leafy territories, they go on a reproductive spree (scientifically known as sporulation), leading to the dreadful, unsightly spots. What begins as small individual circles soon link arms, metamorphosing into a blotch. It’s a horrifying spectacle as the once vibrant leaf turns into a shade of brown or black before dropping on the soil.

High air moisture levels and ineffectual air circulation set the perfect stage for the leaf spot disease drama. Other miscreants aiding and abetting those pesky fungi include the seemingly harmless routine of over-misting foliage and inadvertent splashing of water on leaves. Adding to the suspense is another plot twist, the bacterial leaf spot with its damning evidence of dark brown, slightly concave, and moist spots.

The plot thickens beyond fungi and bacteria. Smaller pests with a knack for making plants their home are part of the conspiracy, too. These sly little creatures pierce or scrape leaves, leaving behind diminutive spots mainly toward the leaf edge or one section, like a secret signature of their tiny transgressions. This case often demands sleuthing for evidence with a magnifying glass and a Sherlock Holmes-esque acumen. Mealybugs and whiteflies trigger white spots, while spider mites turn the leaf canvas into an eyesore of yellow or brown spots. Thrip invasion manifests in silver spots underneath the leaf.

How do you treat leaf spots on your plants?

Spraying herbicide on spotted leaves

Andrii Salomatin/Shutterstock

Multiple physical and chemical options stand out in leaf spot treatment. Start with carefully trimming and disposing of leaves heavily stained with the disease. In addition, put some distance between your afflicted plant and your other green pals. After all, you don’t want this to become an epidemic. Regarding how to control leaf spot disease without chemicals, good old baking soda will suffice. Concoct 2 tablespoons with either 2.5 tablespoons of vegetable oil or 1 teaspoon of liquid soap in 1 gallon of water. The oil and soap help the mixture adhere to the leaves. Please note that baking soda might cause some issues, so apply the mixture to a few leaves first and monitor.

If the pantry staple isn’t cutting it, neem oil or a copper or sulfur-based fungicide might save the day. Seeking an all-rounder weapon against fungal and bacterial issues on plants? Serenade ASO Biological Fungicide, listed for $132.90 at ARBICO Organics, is a worthy contender. But what if insects or spider mites are behind your leafy woes? A broad-spectrum insecticide such as Sevin Insect Killer Concentrate on Amazon does the trick for insect invasion. For spider mites, try insecticidal soaps, neem oil, or a natural miticide like Grower’s Ally Spider Mite Control Concentrate on Walmart. Fostering air circulation around your plants and steering clear of the leaves when watering, complemented by regular treatments, will help fortify protection against leaf spot disease.

✿ Read More About Flowers.

Dr Heidi Parkes

By Dr Heidi Parkes

Senior Information Extension Officer QLD Dept of Agriculture & Fisheries.