Gardening: Tomato Leaves Turning White

Powdery Mildew

• Powdery mildew presents first as bright yellow spots on lower leaves of the plants. As the disease progresses, leaves turn fuzzy and white, then wither and die. The powdery fungus attacks leaves, stems, shoots, flowers and fruit. The mildew grows from spores of Erysiphe lycopersici fungus and can defoliate entire plants.

Treatments

• Treat powdery mildew on tomatoes as you would treat any fungal infection. Prune away dead or infected foliage; this foliage will die eventually, and extensive pruning minimizes spreading. Apply fungicide for powdery mildew, per manufacturer directions, to protect the remaining foliage and any other plants in the area. You can use organic alternatives as well, including sulfur sprays, neem oil, jojoba oil or horticultural oil.

Prevention

• Prevention is the best treatment for future powdery mildew outbreaks. Plant disease-resistant tomato cultivars in sites with full sun and good air circulation. Give each tomato plant 24 to 36 inches of space and stake them to encourage air and sun exposure. Powdery mildew spores grow best in moderate temperatures, shade and moisture. Manipulate the growing site to restrict the fungus's growing opportunity.

Other Growing Tips

• Healthy plants survive in the face of diseases such as powdery mildew, with loss of some foliage but ongoing growth and eventual fruit production. Supplement the fungicide and correct placement with standard care such as soil, water and exposure. Plant tomatoes with organic compost soil amendments for soil quality and health, and use 10-10-10 or 12-12-12 fertilizer as directed for nutrition. Water tomatoes with 2 inches of water every week and minimize splashing soil with 2 inches of organic mulch. Powdery mildew spreads through the air but may overwinter in the soil.