Marigold Leaf Problems: Treating Marigolds With Yellow Leaves

Many orange marigold flowers growing on a plant
(Image credit: Kateryna Pavliuk)

Marigold blossoms are a bright, sunny yellow, but the foliage below the flowers is supposed to be green. If your marigold leaves are turning yellow, you’ve got marigold leaf problems. To learn what might be causing your yellowing marigold leaves, read on.

Marigold Leaf Problems

Yellow leaves on marigolds can be attributed to many things.

Powdery Mildew – The most familiar symptom of a powdery mildew infection is powder. Powdery white blotches form on the leaves and stems of a plant. This may not seem relevant to your marigolds with yellow leaves. However, when leaves are severely infected, they can twist or turn yellow due to this infection.

What to do when you have powdery mildew as one of your marigold leaf problems? As soon as you spot that powder, wash it off thoroughly with the hose. You may prevent further infection by thinning your plants so that air can pass between them.

Aster Yellows – When you have marigolds with yellow leaves, your plants may be infected with a disease called aster yellows. Aster yellows is caused by a very small organism known as a phytoplasma. When this phytoplasma gets into the leaves of plants, they are discolored to yellow or red. This may be what is causing your yellowing marigold leaves.

The phytoplasmas are transferred from plant to plant by leafhoppers. These insect pests ingest plant sap through their sucking mouth parts. As they do so, they also get some of the phytoplasmas. The insects transfer them to any plant they subsequently eat from. You cannot cure marigolds with aster yellows. Your best bet is to dig them up and destroy them and try again.

Leaf Burn – When you see that your marigold leaves are turning yellow, ask yourself whether you’ve given the plants any micronutrient solutions lately. If so, your plants may have leaf burn, the result of excess boron, manganese, or other nutrients.

You’ll know your plants have leaf burn if the yellow leaves on marigolds are actually a yellowing of the tips and margins of the leaves. Prevent this issue by measuring micronutrient solutions with care before applying.

Pest Attacks - When you notice yellowing or browning of the leaves, this could also be attributed to insect pests. Although marigolds are not bothered by too many insects, and may even deter most of them, the plants can, on occasion, find themselves victim to pests like mealybugs. Oftentimes, treatment with neem oil can help with this.

Teo Spengler

Teo Spengler has been gardening for 30 years. She is a docent at the San Francisco Botanical Garden. Her passion is trees, 250 of which she has planted on her land in France.