Pepper plants can suffer from any number of nutrient deficiencies that cause issues. Two common deficiencies will express themselves in yellowing leaves. The first is a Magnesium deficiency. This affects the oldest leaves first and causes yellowing in intravenous sections of the leaves.
This can sometimes happen from an excess of potassium, or particularly hot and dry weather. Correct magnesium deficiency by mixing an Epsom salt solution and feeding it to your pepper plant. Also, reduce any applications of potassium.
Yellowing accompanied by slow growth, low fruit set, and brittle leaves is a sign of phosphorus deficiency. This is correctable but should be noted as a possible larger soil-related problem. Phosphorus comes from organic matter in the soil: plant material, manure, compost.
A phosphorus deficiency points to a soil with low quantities of organic matter which will cause further problems if left alone. Apply rich, living compost as a mulch and water through it.
The three most common pepper pests all can have a yellowing effect on plant leaves.
- Flea Beetles
- White Fly
If the yellowing appears in tiny dot patterns it could be from insects. Turn the leaves over and examine them. Aphids and white flies will be clustered on the undersides of the leaves. Flea beetles are fairly easy to spot and look exactly as they sound. These pests won’t kill pepper plants right away, but they will weaken them until they die or contract a disease.
Combat pest problems a few ways. For an immediate remedy spray the plants with neem oil over the course of a week or two until they appear to recover. In the long run, encourage predatory insects and birds into the garden by planting friendly plants and creating habitat for them.
A disease is the worst possible cause of leaf yellowing because it is almost impossible to correct. Leaf spot, wilt, and blight can all cause yellowing of the leaves and the only thing to do is pull the affected plants.
It’s better to take preventative measures when it comes to disease. Avoid soluble fertilizers that can swell plants and make them weak and vulnerable to disease. Use organic composts and worm castings instead. Keep pepper plants from being exposed to extreme temperatures and moisture extremes which can also render them susceptible.