Why Do My Pepper Seedlings Have Dry Brown Spots on Their Leaves?

Brown spots on pepper seedlings may be cause for alarm.

Any of the various kinds of peppers can be a rewarding crop or hobby vegetable. A gardener may easily be troubled by young pepper seedlings that develop dry brown spots. Diagnosing and addressing the cause of these spots is necessary to ensure a healthy crop. The seedlings can develop brown spots for a number of reasons. Some of these may be quite problematic while others may simply require a slight adjustment in care.

Bacterial Spot

Bacterial leaf spot, caused by the Xanthomonas campestris bacteria, is a common leaf and fruit disease of pepper. Infected seedlings have small black spots along the edges of their leaves while older plants develop small green spots on their lower leaf surfaces. These spots will enlarge, darken to a brown and generally do not merge. Heavily infected leaves will fall off and seedlings can lose all but their top leaves.

Bacterial Spot Control

Once bacterial spot is established in a seedbed or production field, it is extremely difficult to control and can spread quickly under ideal conditions. However, disease spread can be reduced by not using overhead irrigation, minimal plant handling and avoiding working or traveling through a garden or field during damp conditions. As a general rule, purchase only certified, disease-free seeds or transplants, avoid using seedbeds or fields that have had bacterial spot within two or three years and fertilize as recommended to maintain plant health. Some varieties of peppers have been developed for resistance to bacterial spot.

Alternaria Leaf Spot

Alternaria leaf spot, also known as early blight, causes brown or dark spots on the plant's oldest leaves. The spots eventually enlarge, growing up to 1/2 inch in diameter and developing a targetlike appearance. Spotted leaves will turn yellow, wilt and drop off the plant. The fungus survives in debris, soil and on the seed. Alternaria is spread by wind and splashing rain. Rotate crops, limit plant stress and use fungicide to control this fungus.

Cercospora Leaf Spot

The cercospora fungus causes the appearance of circular spots with a light gray center surrounded by a brownish margin. Spots can grow up to 1/3 inch across and develop a tan color with a yellowish halo. The fungus can survive in or on seed and in leaf debris in the soil. Cercospora is most severe during conditions of high temperature and moisture and is spread by water, wind, tools or leaf-to-leaf contact. Treat seed with hot water to disinfect it and remove any infected seedlings, along with one or two nearby plants that may be infected but may not be showing any symptoms. Space plants adequately in the field and practice crop rotation.

Inadequate Acclimation

Seedlings planted indoors and germinated under ideal conditions require a period of adjustment. Seedlings exposed to too much sudden sun may suffer some browning. Adjust the acclimation accordingly to avoid shocking the seedling. The acclimation period should take several days, with slight, incremental increases in sunlight, wind and temperature range.

References

• University of Illinois Extension: Early Blight or Alternaria Leaf Spot
• AVRDC -- The World Vegetable Center; Cercospora Leaf Spot; Ray Cerkauskas
• University of Illinois Integrated Pest Management; Bacterial Spot of Pepper and Tomato; October 1999
• Cornell University; Bacterial Spot of Pepper; Thomas A. Zitter; October 1985