QUESTION: The foliage on our cucumbers does not look healthy. It almost looks as though someone sprinkled white flour all over the leaves. Should we spray them with something?

ANSWER: Based on the symptoms you have described, your cucumber foliage is most likely infected with powdery mildew, which is a very common fungus disease.

Our warm August temperatures, along with dew formation, provide nearly ideal conditions for the development of this disease. Powdery mildew first appears as white, powdery spots that may form on both surfaces of leaves, on shoots, and sometimes on flowers and fruit. These spots gradually spread over a large area of the leaves and stems.

Leaves infected with powdery mildew may gradually turn completely yellow, die, and fall off, which may expose the fruit to sunburn. On some plants, powdery mildew may cause the leaves to twist, buckle or otherwise distort. Powdery mildew does not usually grow on the vegetable fruits.

Most powdery mildew fungi grow as thin layers of mycelium (fungal tissue) on the surface of the affected plant part. Spores, which are the primary means of dispersal, make up the bulk of the white, powdery growth visible on the plant’s surface and are produced in chains that can be seen with a hand lens.

In addition to cucumbers, a variety of vegetables are affected by powdery mildews, including artichoke, beans, beets, carrot, eggplant, lettuce, peas, peppers, pumpkins, squash, tomatoes and turnips. Powdery mildews generally do not require moist conditions to establish and grow, and normally do well under warm conditions.

The best method of control is prevention. Planting resistant varieties when available, or avoiding the most susceptible varieties, planting in the full sun, and following good cultural practices will help control powdery mildew in many cases. There are a number of fungicides which are effective in controlling powdery mildew, but they must be applied no later than the first sign of disease.

Sulfur products have been used to manage powdery mildew for centuries, but are only effective when applied before disease symptoms appear. The best sulfur products to use for powdery mildew control in gardens are wettable sulfurs that are specially formulated with surfactants similar to those in dishwashing detergent. Although fungicide applications are not effective on infected leaves, they will prevent newly emerging leaves from becoming infected.

QUESTION: Some of our tomatoes are malformed at the blossom end. What causes this? Is there anything we can do to prevent it in the future?

ANSWER: Blossom-end rot or catfacing, are two common disorders of tomato fruits that commonly show up this time of year. They are often mistaken for an infectious disease and can affect a high percentage of the fruit. Blossom-end rot is a disorder of not only tomatoes, but eggplants and peppers as well. It is a physiological condition caused by a lack of calcium in the fruit of the plant. Calcium is needed for normal cell growth. As the fruit rapidly develops, the tissues break down if sufficient calcium is not available.

This results in characteristic black leathery sunken areas on the blossom-end of the fruit. Secondary pathogens can invade the damaged tissue. These opportunistic rots and molds often destroy the entire fruit.

To help reduce the occurrence of blossom-end rot maintain soil even soil moisture; avoid fluctuations between extremely wet and extremely dry. Have the soil tested and apply lime in low pH soils to maintain the pH near 6.5. Avoid over fertilization which encourages rapid growth.

Catfacing refers to a pattern of large scars on the bottom of the fruit. The most common cause of catfacing is exposure of the plants to cold temperatures (below 50F) for two days or nights during fruit initiation. The scars show up much later during the growing season so growers do not always connect the damage to cold weather earlier in the year.

Nothing can be done to cure the cold-induced catfacing, but fruits ripening later on should be free of the condition. Herbicide and wind or storm damage can also cause catfacing.

EDITOR’S NOTE: For answers to local gardening questions, contact Master Gardener Rachel Gana at 642-8723 or e-mail her at: baiter1@pacifier.com.