Q&A: Leaf Spots on Dracaena

What is causing leaf spots on corn plant?

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Q: I have some palm plants — maybe corn palms? — and they continuously get brown spots. I cut off the leaves with spots but the new leaves have spots too. Could spiders be causing this?
— R.S., Miss.

A: Assuming the plant you have is corn plant, or Dracaena, it sounds like the problem is leaf spot. This can appear for a number of reasons, such as poor air circulation, overwatering or high humidity. Likewise there are several potential culprits, including fungal disease, bacteria, insects and poor growing conditions.

You are already taking good steps towards resolving the problem. Removal of spotted leaves is important, so stay diligent on this practice. Also remove any fallen leaf litter within the plant's interior and on the soil surface since this decaying material can harbor diseases and pests. Take a good look at the soil. If the soil is too wet, let it dry out completely before watering again. And visa versa, if the soil is too dry, give it a good drink. Keeping plants sufficiently watered helps to keep them healthy. Instead of watering on a set schedule, water only when the soil begins to dry out.

If you notice brown spots on the tips and edges of leaves, this could be a sign of excess salts, chlorine or fluoride in the water. Avoid using tap water if possible; instead use rainwater or distilled water. If you prefer tap water, allow it to sit for at least 24 hours so that the chlorine and fluoride can evaporate. Also, if you notice an accumulation of white deposits on the outside of the pot (especially near the drainage holes), this is a sign of excess salts. Use rain water or distilled water to flush out excess salts.

It's curious that you mention spiders. Spiders don't really cause problems with plants, especially the leaf spotting you describe. Perhaps you're referring to spider mites. The symptoms of spider mite damage are most noticeable as small light-colored spots on leaves, causing them to look speckled. They are a problem particularly in dry conditions. The key indicator of a spider mite infestation is delicate webbing within the structure of the plant, including where leaves are attached to stems and the undersides of the leaves. The USDA recommends a simple treatment for this pest: Combine one tablespoon of dishwashing detergent and one cup of vegetable oil and mix. Add this mixture to one cup of water in a handheld spray bottle and shake well. Spray the entire plant, including the undersides of leaves.

Because your leaf-spot problem could be caused by several potential culprits, it's best to make sure the disease is properly identified before determining the course of treatment. Take a good sample of the damaged leaves to your local extension service office. The extension agent can identify the problem and make specific recommendations on how to treat it and whether a chemical treatment is necessary.

Good cultural practices that keep plants stress-free also help keep them healthy and disease-free. A healthy plant that receives sufficient water, sunlight and air circulation is more resistant to disease and pest problems than a stressed-out plant.

Here are some tips for maintaining healthy plants:

  1. Avoid purchasing unhealthy or disease-prone plants. Carefully inspect your plants before you bring them into your garden or home. If their health is questionable, keep them quarantined from other plants until you have been able to diagnose the problem, treat it appropriately and are sure it has recovered.
  2. Keep plants properly spaced apart. This helps to provide good air circulation around each plant.
  3. Water around the base of the plant. Avoid splashing water on the foliage.
  4. Provide adequate sunlight.
  5. If it's a houseplant, wipe leaves clean of dust.
  6. Remove any fallen leaf litter and discard. Avoid composting any plant material that could potentially harbor diseases or pests.

Unfortunately, if doing all these things doesn't work, it may be best to remove the plant altogether and start with a new one. Discard the plant in the trash. Since pests and disease can linger, it is best not to compost an infested plant.

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