By: Sandy Feather ©2007
Penn State Extension
Q. The pepper plants in my garden have been losing their leaves, starting at the bottom. They turn yellowish and fall. Most plants have lost the majority of their leaves now. I have a large garden that I have to water by hand and was wondering if they might not be getting enough water? Or maybe too much? Or could something else cause this?
A. Pepper plants lose their leaves for a variety of reasons. Plants do respond to drought conditions by dropping their older leaves - in this case, the lowest leaves on the plant - first. They turn yellow and fall prematurely. If you have not been able to provide that magical inch of water weekly during the growing season, drought stress could be a factor. This could be coupled with heat stress, given our hot, dry and sunny weather.
Overwatering can also cause leaves to yellow and drop. Gardeners can kill their plants with kindness during hot, dry weather by watering too much, too frequently. Many plants look a little wilted during the heat of the day - they curl their leaves slightly to minimize moisture loss through transpiration during very hot weather - but recover when the sun sets. Watering them even more when they appear wilted can lead to root rot. Watering deeply once or twice a week once the plants are established should be sufficient, even when it is hot and dry. Apply the water to soil as much as possible, rather then dousing the plant. This puts it at the root system where it is needed, and keeps the foliage as dry as possible to reduce the incidence of disease problems.
Since you have to hand water a large garden, I hope you use mulch to help conserve soil moisture and moderate soil temperatures during the growing season. Organic mulches such as straw or shredded leaves can do a better job of this than plastic mulch during such hot, dry weather unless you have drip irrigation installed under the plastic. Plastic or organic mulches can help keep weeds down, too. Weeds compete with desirable plants for water and nutrients, and can serve as a source of insect and disease problems. Either plastic or organic mulches can also cut down on disease problems that spread by splashing spores up from the soil during rain or irrigation.
If you apply high nitrogen fertilizers - especially during hot weather when the plants are under drought stress - you can burn them, which will also cause leaf drop. Fertilizer placed directly into the hole at planting time can have the same effect on transplants. This includes organic sources such as uncomposted manure, blood meal, and fish emulsion.
Although you do not mention any kind of spots on the leaves or fruits, peppers are susceptible to a number of diseases that can cause the leaves to yellow and drop prematurely. These include cercospora leaf spot, a fungal disease whose symptoms include round or oblong spots on the leaves and stems. These spots often have light gray centers with dark brown borders. Infected leaves turn yellow and drop when the disease is severe. The fungus is carried on infected seed and may survive over winter in the garden on infected plant material. Long periods of warm, wet weather are ideal for this disease to develop.
Control options include thoroughly cleaning out the garden at the end of the season and not saving seed from infected plants. Dispose of infected plant plants in the trash or by burning them, rather than tossing them on the compost pile. Purchase fresh seed or disease-free transplants for next season's garden, and do not plant them where infected plants were grown this year for at least two years. Avoid overhead irrigation to keep from wetting the foliage more than necessary. Spray plants with basic copper sulfate at the first sign of disease, making repeated applications as long as weather conditions favor disease development. Follow label directions regarding intervals between applications.
Bacterial spot is a bacterial disease characterized by leaf and fruit spots. It is most likely to develop during warm, wet weather. On the leaves, spots start as irregularly shaped water-soaked spots on the undersides of the leaves. They become purplish with black centers, and you may notice a yellow halo around the spot. The spots appear sunken on the upper leaf surface and raised on the lower side of the leaf. Affected leaves take on a ragged appearance, often yellowing and falling prematurely. On fruits, the spots start as water-soaked areas, that turn brown and raised. They have a corky feeling. The bacterium is usually transmitted on infected seeds and the transplants grown from those seeds.
The disease can survive over winter on infected plant debris, and is transmitted from plant to plant by splashing water, or on your hands or tools that have been used on infected plants. Remove severely infected plants from the garden, and throw them in the trash or burn them. Clean plant debris from the garden as thoroughly as possible, and practice crop rotation. Try not to plant pepper and tomato plants in the same place more than once every three or four years, since they are in the same family and susceptible to many of the same maladies. Avoid overhead irrigation to keep from wetting the foliage more than necessary, and do not work in the garden while plants are wet from rainfall. Spray plants with basic copper sulfate at the first sign of disease, making repeated applications as long as weather conditions favor disease development. Follow label directions regarding intervals between applications.
Leaf drop on peppers (and other fruit-bearing plants) can reduce the number and size, as well as the quality, of fruits because it limits photosynthesis, the process whereby plants manufacture their own carbohydrates. Reduced leaf cover also opens fruits up to sunscald, a result of their exposure to full, blazing sun.