How to Deal with Black Spot Leaf Disease

Last Updated: January 31, 2023 Approved

Black spot leaf disease shows itself first with black spots appearing on the leaf, then with rings of yellow as the spots grow, until the leaf turns entirely yellow and then falls off. If left untreated, black spot spreads rapidly and weakens plants severely. As a soil-borne fungus, it's present at all times, even deep winter. Proper care can greatly reduce the instances of this disease.

Method 1

Method 1 of 3:

Treating Infected Leaves

1
Prune infected leaves immediately.^{[1]
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Research source} Ensure the overall health of your plant by removing diseased leaves entirely. To prevent the spread of disease through contact with the plant or soil, throw them away immediately with your regular trash before doing any more work in the area. Further prevent the disease from spreading by disinfecting your tool immediately after pruning each leaf. Have a solution of 1-part bleach to 4-parts water within easy reach.^{[2]
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2
Treat infected areas. Prune the infected leaves, including those that have turned yellow or are about to, since these are most likely too far gone to recover. If the infection is widespread, it’s better to prune off entire limbs rather than just removing leaves. Treat what remains, including the leaves’ bottoms as well as their tops.^{[3]
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Research source} Although there is no guaranteed cure for black spot disease,^{[4]
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Research source} try the following remedies, which can slow and prevent the disease from spreading, and use whichever shows the best results:
- Mix together a solution of 1 tbsp. baking soda, 2.5 tbsp. vegetable oil, 1 tsp. liquid soap, and 1 gallon water. Be sure to use liquid soap, not detergent. Since this may potentially burn your leaves, spray a small test area with the solution before spraying the entire plant. If burning is absent or minimal, spray the leaves once every two weeks.^{[5]
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- Combine 1-part dairy milk to 2-parts water. Spray the leaves once each week. (Sorry, vegans; non-dairy milk substitutes won’t work).^{[6]
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- Spray the leaves with neem oil once every two weeks.^{[7]
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- Use fungicides as a last resort if the disease returns for multiple growing seasons. Follow their directions regarding applications. Apply them early, before outbreaks or at the first sign of spots, since they are preventative in nature. Choose organic products if possible for both the plant’s health as well as pollinating insects.^{[8]
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3
Throw away infected leaves. Remove them from the area as soon as you prune them. Put them with your regular garbage, preferably in a tied bag. If you dump them straight into a trashcan, secure the lid firmly to prevent the wind or animals from blowing or tracking them free.
- Do not add infected leaves to compost, since the disease may survive and infect other plants when that compost is used as mulch.

Method 2

Method 2 of 3:

Preventing Future Outbreaks

1
Rake continually. Keep the base of the plant or tree clear of infected leaves that may have fallen on their own. Clear away all fallen leaves, whether they’re infected or not, since beds of dead leaves trap and retain moisture, thus creating a ripe breeding ground for the disease. Be sure to rake straight up to winter’s first snow, or even after if needed; the disease may survive the cold weather and reinfect the plant or tree when spring comes.
2
Prune the lower canopy. It’s best to prune from the bottom up. Lower leaves are more likely to be infected with black spot disease, so you’ll want to start in the lower canopy. Prune back lower branches that never completely dry and leave higher ones that receive sunlight.
- Pruning the lower canopy is also safer – you won’t need to get to those high-up branches.
3
Water your plant or tree properly. Water the soil directly. Keep the leaves dry.^{[9]
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Research source} Avoid overwatering. Allow soil to dry before watering again. Refrain from watering during rainy weather.
4
Keep the air circulating. Weed the soil to improve airflow.^{[10]
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Research source} Apply a level amount of mulch around the base of the plant or tree, leaving a ring of free space between the mulch and the trunk. Prevent weeds from growing while improving the area’s ability to dry more thoroughly.

Method 3

Method 3 of 3:

Planting with Foresight

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Purchase resistant varieties of plants. Research the type of tree or plant that you wish to include in your landscape. Find out if any particular variety has been proven to be resistant to the disease.^{[11]
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Research source} If the cost of resistant varieties is significantly higher than non-resistant ones, ask yourself which you value more: saving money now or time and labor later.
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Space new plants well apart from each other. Whenever you plant new saplings or young plants, picture the size they’ll reach once fully grown. Plant them accordingly, allowing each plenty of distance from the rest in the future. Preempt the easy spread of disease by keeping one plant from touching another once they’ve matured. Allow sunlight to reach and dry the lower leaves throughout their lifetime by eliminating the excessive shade that overcrowded canopies would otherwise provide.
- Cover the soil around newly planted areas with mulch. This will absorb water and keep the disease from splashing up into the leaves when it rains.
3
Avoid planting in overly moist areas. Since moisture facilitates black spot disease, plant in areas that dry easily after rain. Choose spots that receive direct sunlight for at least a portion of the day.^{[12]
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Research source} Keep clear of areas that are prone to standing water.
- Also adjust any lawn sprinklers so they don’t soak your leaves unnecessarily.

Expert Q&A
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Question

How long should I wait to harvest a fig tree after spraying with neem oil?

Mark Spelman
Construction Professional
Mark Spelman is a General Contractor based in Austin, Texas. With over 30 years of construction experience, Mark specializes in constructing interiors, project management, and project estimation. He has been a construction professional since 1987.

Mark Spelman

Construction Professional

Expert Answer

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Pure neem oil can be sprayed until close to harvest time. Be sure to wash all produce well if you have sprayed recently.
Question

What fungicides should I use?

Community Answer

Actinovate Lawn & Garden Fungicide and SERENADE Garden are two popular brands.
Question

How can I get rid of black spots on roses?

Community Answer

Mix together 5 litres of water, 2 tsp of BiCarb soda, a few drops of detergent and seaweed extract. This is an eco-friendly and affordable fungal spray. First, remove all the diseased leaves...then spray.