What Causes Spinach Leaf Spots?
Leaf spots on spinach are likely the result of a fungal disease or a pest, such as a leaf miner or a flea beetle. The spinach leaf miner (Pegomya hyoscyami) larvae tunnel into leaves creating mines, hence the name. These mines are at first long and narrow but eventually become an irregular blotched area. The larvae look like a whitish maggot and are shaped like a carrot. There are a few species of flea beetle that may result in spinach with leaf spots. In the case of flea beetles, adults feed on the leaves creating small, irregular holes called shot holes. The small beetles may be colored black, bronze, blue, brown, or metallic gray and may even be striped. Both pests can be found throughout the growing season. To control them, keep the area weed free, remove and destroy any infected leaves, and use a floating row cover or the like. Leaf miner infestations may need to be treated with an organic insecticide, spinosad, in the spring. Traps can be set for flea beetles in the spring.
Fungal Leaf Spots on Spinach
White rust is a fungal disease that first appears on the underside of spinach leaves and then on the top side. The disease appears as small, white blisters that, as the disease progresses, grow until they consume the entire leaf. White rust is fostered by cool, moist conditions. Cercospora also causes spots on spinach leaves and may also affect other leafy plants such as Swiss chard. The first signs of infections are small, white spots on the surface of the leaf. These tiny, white spots have a dark halo around them and turn gray as the disease progresses and the fungus matures. This disease is most common when the weather has been rainy with high humidity. Downy mildew is yet another fungal disease that causes leaf spots on spinach. In this case, the spots are gray/brown fuzzy areas on the underside of the leaf with yellow blotching on the upper side. Anthracnose, another common spinach disease, is characterized by small, tan lesions on leaves. These tan lesions are necrotic or dead areas of the leaf. All of these fungal diseases may be treated with a fungicide according to the manufacturer’s instructions. Read the labels carefully, as some fungicides may be phytotoxic when applied at high temps. Remove and destroy any diseased leaves. Keep the area around the plants free from weeds that may harbor pathogens and insects.
