The rains that finally arrived in late March were very welcome, but their timing was bad. Late rains and cooler than normal temperatures during blossom and planting season actually shorten our growing season at a critical time. We need to get our vegetable gardens planted quickly before the first hot spell (usually in late April or early May) hinders flower set. We also should be monitoring for diseases such as fire blight and downy mildew, which proliferate in warm, humid spring weather.
Here are a few problems you might see in your garden in the next two to three weeks during this late planting time.
▪ Tomatoes: Tomatoes flowers will not set when nighttime temperatures are below 55 degrees or daytime temperatures are above 90 degrees. Hormone flower set sprays are only effective when temperatures are cool. Tapping the stakes or shaking the plants sometimes helps with flower set.
If you’re transplanting tomatoes this week, look for indeterminate varieties that mature later in the season. Those varieties will be able to set flowers again after the worst heat in July and August for a September/October harvest.
Many tomato problems such as blossom end rot and cracking are caused by inconsistent watering. Deep irrigate tomatoes when the top 1 or 2 inches of soil has dried.
▪ Eggplants, peppers: Eggplants and peppers will set flowers in temperatures up to 100 degrees but require a long growing season. Pollination will be reduced in the summer heat when pollinators are less active. You might see misshapen fruit with no seeds inside due to poor or incomplete pollination (also a problem for cucumbers and squash).
▪ Downy mildew: Downy mildew, as opposed to powdery mildew, is not a common problem here in the hot, arid Central Valley. After spring rains though, when humidity is high and temperatures are cooler than normal (as during the third week of March), the fungus causes yellow or brown spots on upper leaf surfaces and fuzzy growth on the lower surfaces. Grapes are especially vulnerable to downy mildew.
Remove affected leaves, clean up all debris and spray with a fungicide labeled as treating for downy mildew every seven to 10 days until high temperatures reduce the fungal infection. Neem oil is an effective remedy, but the plants must be thoroughly coated with the oil and neem oil is somewhat toxic to beneficial insects.
▪ Fire blight: Fire blight is a bacterial disease that affect members of the pome or apple/rose plant family that includes roses, pears and ornamental pear trees, hawthorn, and pyracantha. When combined day and night temperatures exceed 120 degrees (such as 75 degrees during the day and 45 degrees at night), the bacteria multiply and are carried into flowers by insects.
Treatment includes spraying fixed copper at bloom time but it’s too late for preventative spraying now. Monitor susceptible plants and trees for wilted, blackened flowers and twig tips that look as though they’ve been scorched by fire. Cut back affected twigs and branches at least 12 inches below the affected tissue in summer after the disease stops spreading. Disinfect pruning tools with rubbing alcohol or a 10 percent bleach solution after each cut.
Next spring, spray a fixed copper solution just before bud break on previously infected plants.
Elinor Teague: firstname.lastname@example.org