Nutrient deficiencies could be due to inadequate supply of iron, calcium, sulphur, magnesium and zinc. A. Yellow leaves on plants can indicate too much or not enough water or too much or not enough fertilizer. Pepper plants turn yellow because of nutrient deficiencies. Peppers are in the same family as tomatoes and tobacco, and may be suffering from Tobacco Mosaic Virus (TMV). Fortunately, there are plenty of fertilizers out there in the market, which can help you deal with this issue. Even though nutrients are present, plants can't take them up — even from fertilizers you add. A simple soil test identifies your soil pH and provides other important information. Aphids, whiteflies, and flea beetles are all insect pests that like peppers, and any one of them may be responsible. I also fertilized with a 3-stage fertilizer per the recommended amount. The leaves are starting to turn yellow on the LOWER part of the plant and falling off. Leaves turn yellow until pH issues are fixed. I placed a thick layer of compost down on top of the soil once they were planted. The compost consisted of 3-4 year old grass clippings. Even though the plants have relatively few problems, their leaves may turn yellow for several reasons. If your pepper plants have leaves that are turning yellow, there may be one of a few problems at work. I have Banana Peppers and Jalapenio's in my garden for the first time ever. When soil pH strays lower or higher than a plant's optimal range, some nutrients become less available to it.