Question: I live in Michigan and we have a large grapevine with tons of grapes. However, the grapes are starting to rot before ripening. What's wrong?
Answer: It sounds like your grapes have black rot fungal disease. Black rot starts as small, yellow lesions on the leaves. As the fruit develops, the disease infects the grapes, too, causing sunken brown spots. Eventually, the grapes shrivel and rot. During periods of warm, humid weather, the disease can spread quickly to infect whole clusters.
To control the disease, prune vines heavily in winter so the plants have good air circulation. The disease spreads on wet leaves and fruits so avoid overhead watering. Pick off and destroy any infected grapes as they develop and clean up all old grapes and leaves in fall. In the future, plant grape varieties less susceptible to black rot disease, such as 'Mars' and 'Cascade'. For this year's crop, try spraying Bacillus subtilis or copper to minimize spread of the disease.
Question: I'm living in California and need to know how often to water tomato plants. Right now we are having a heat wave and I'm not sure how much water they need.
Answer: The rule of thumb is that vegetables need an inch of water a week for optimal production. In reality, the amount of water plants need varies dramatically depending on the weather and the size of the plant. For full-grown tomatoes, growing in hot dry conditions, the soil should be consistently moist down to 6 to 8 inches deep. You may need to water deeply every few days if nature doesn't provide rain. Don't let the soil dry out. Repeated cycles of soaking and drying can cause problems, including curled leaves, and blossom end rot and cracking on fruits.
Since California is in the middle of a drought, I'd suggest mulching with straw to conserve soil moisture, using drip irrigation or watering cones to concentrate the water at the roots, and shading the plants from the hot afternoon sun during heat waves.