Black Spot Management Guide

Fungal diseases can be harmful to plants, often discoloring and weakening them. Black spot is a common fungal disease that primarily affects roses. It is most likely to infect roses grown outside, but it can still be found on indoor roses as well. We’ve gathered information to help you control and prevent black spot on your plants. 

Black spot (Diplocarpon rosae) is a fungal disease that is spread via water. Spores are released from infected plants. When water splashes, it transfers the spores to other plants. This can occur during rainfall or when watering your plants. While this disease most often attacks roses, other plants could be affected by the disease. Black spot begins as a purple or black spot on the upper surface of leaves. These spots will grow and may develop yellow halos around them. Symptoms typically start lower on the plant and work their way up. This disease can weaken the plant and cause leaves to drop. Black spot thrives in warm and damp environments.  

Inspect Plants Regularly: It’s important to keep an eye on your plants to detect any problems. It will be easier to control black spot if you catch it early before it has time to spread. You’ll also want to inspect any plants before you bring them home. You don’t want to purchase a plant that has signs of black spot.

Set Your Plants Up for Success: Keeping your plants healthy means giving them the nutrients they need. You’ll want to make sure your plants are set up to receive enough sunlight and water. Every plant has different needs, so researching ahead of time will ensure you are prepared.

Water Plants Carefully: Black spot needs moisture to spread and reproduce. How you water your plants can increase or decrease the chance of black spot occurring. To avoid water accumulating on leaves and minimize splashing, it’s best to water plants at their base.

Create Space Between Your Plants: Spacing out your plants can help to prevent black spot and other fungal diseases from taking over your garden. Good air circulation will minimize moisture build-up, which is important to preventing black spot. The space will also make it more difficult for the disease to spread.

Remove Infected Leaves: If your plant starts to develop black spot, you can remove the infected leaves. Pruning these leaves will help to prevent the disease from spreading. Place the clippings in a sealed bag and dispose of the bag in your trash can. Make sure to clean your gardening tools to avoid infecting healthy plants.  

If your plants are dealing with black spot, you will need to treat them with a fungicide that is labeled for the disease. Maggie’s Farm offers two products that can help to prevent and control black spot.

Plant-Based Insecticide Sprays

Our 3-in-1 Garden Spray and our Vegetable Garden Insect & Disease Control spray are labeled to prevent and control black spot. Our 3-in-1 Garden Spray is formulated using plant oils as the active ingredients. It can be used on indoor and outdoor plants such as roses, flowers, shrubs, and edible or ornamental plants. Our Vegetable Garden Insect & Disease Control spray is formulated using pyrethrins and sulfur. It can be used on houseplants and in home gardens and home greenhouses. It is labeled for use on roses, flowers, vegetables, and ornamental trees and shrubs.

Application Tips

When applying our garden products, it’s best to avoid spraying in the heat of the day. Applications should be done early in the morning or in the evening. For best results, apply as a protective spray early in the season before diseases are noticed. It’s important to spray all parts of the plant. Our 3-in-1 Garden Spray should be applied so that the solution runs off the tips of the leaves. You can apply every 7–10 days or after rain. The spray may be used up to the day of harvest. When using our Vegetable Garden Insect & Disease Control spray, don’t wet plants to the point of runoff or drip. It’s best to avoid using the product if temperatures are expected to be over 90° F. You can reapply every 7–10 days. This product may be used up until the day before harvest.

We recommend test treating a small inconspicuous area of the plant first before applying to the entire plant

Fungal diseases like black spot can hinder your plant’s health, which is why it’s important to take steps to protect your plants. Implementing preventative techniques and using the right products can help to keep black spot from attacking your plants.