Master Gardeners offer tips on soil moisture and zucchini mildew
Question: I know we are in a serious drought this year and I want to save water, but I don’t want my plants to die, either. How can I tell if I’m giving them enough water?
Answer: Great question and one that is on everyone’s minds right now! The answer depends on the types of soil and plants you have in your yard and the amount of sun they get each day.
Your soil type may be sand, silt, clay or loam or a combination of these types. Water moves quickly through sandy soil but moves slowly through clay soil. Clay retains a significant amount of moisture, while sandy soil dries out quickly. In general, water sandy soil quickly, for short periods. Water clay soils slowly, until the soil no longer absorbs water and the water begins to run off.
Try this experiment in your yard: Water your soil as you normally would, then after an hour, dig down 6 to 8 inches to see how far the water soaked in. If the water in your garden reaches below the root zone of your plants, you are wasting water.
Overhead sprinklers spray water into the air, where it evaporates, or onto sidewalks, driveways and tree trunks. The most efficient way to give your plants water is with drip irrigation.
After July, even though it’s still hot, the days are getting shorter and plants need less water. If you watered for 10 minutes in July, you may be able to cut back to 8 minutes in August and 6 in September.
Unlike young trees which require frequent watering to thrive, mature trees prefer less frequent but deeper watering in the summer. Native trees and shrubs are drought-tolerant. Depending on rainfall in the winter, they require either no water or water once or twice over the summer months. Native oaks should not be watered in the summer.
Check with your water supply agency for current water-use restrictions.
How to program your irrigation controller: bit.ly/3xj0Fko
Santa Rosa Water Smart: srcity.org/820/WaterSmart-Center
Watering Recommendations: bit.ly/3xjC3bD
Question: Everyone says zucchini is easy to grow, but the leaves of my zucchini are covered with a white powdery substance and the young squashes rot from the flowering end. What should I do?
Answer: It sounds like your zucchini are suffering from a combination of powdery mildew and blossom end rot. These are two very different maladies that you can treat by improving your plants’ growing conditions.
Powdery mildew is a fungal pathogen that, given the chance, will colonize an array of vegetables, such as artichokes, beans, beets, carrots, cucumbers, eggplants, lettuce, melons, peppers, radishes, squash, tomatoes and more. It thrives in our Mediterranean climate because it does not require moist conditions and favors the warm days of summer.
Powdery mildew on cucurbits (cucumbers, melons, squashes and pumpkins) first appears as pale-yellow spots on stems and leaves. The spots enlarge as a fluffy white fungal mat (mycelium) that grows and produces powdery spores. The affected leaves appear dull and start to fade, eventually becoming brown and papery. Plant death often occurs at this stage.
The best way to beat powdery mildew is to avoid the conditions that cause it. Start by controlling weeds and removing garden debris that harbors powdery mildew spores. Grow your zucchini plants in full sun, with adequate spacing between plants to allow for air circulation. Look for and plant varieties of zucchini that are resistant to powdery mildew.
We don’t recommend overhead sprinkling because it may encourage other pathogens or plant pests. Organic fungicide treatments like sulfur can be used as a preventative or to treat an infection but must be applied no later than at the first sign of the disease. Once mildew growth is extensive, it’s more difficult to control with fungicides.
Blossom end rot is a disorder of cucurbits, tomatoes, eggplants and peppers. It first appears as light-brown spots at the blossom end of immature fruit that expand to form a sunken, leathery dark lesion. Fruits with blossom end rot have a calcium deficiency. However, adding calcium, either by soil application or foliar sprays, does not help.
Blossom end rot is a physiological response to environmental stresses, such as drought, soil salinity, intense light, heat and over-fertilizing. You must address these factors to resolve the issue.
To avoid blossom end rot, take steps to decrease plant stress. In particular, avoid soil moisture fluctuations. Between waterings, do not allow the soil to completely dry out or remain saturated. If using nitrogen fertilizer, use it only in accordance with package directions.
For more information on powdery mildew and blossom end rot, visit the University of California’s Integrated Pest Management Program website at bit.ly/2RRlsw5 for information on powdery mildew and bit.ly/3pNFUL3 for blossom end rot.