Stop powdery mildew before it explodes

Spring is in the air – and so is powdery mildew. This is the type of weather it loves.

Watch for signs of this fungal disease on roses, grapes and ornamental shrubs, particularly on new leaves. A small outbreak can explode into a big problem. The spores can go through their entire life cycle in 72 hours.

Powdery mildew hates water but loves new growth and warm weather – 68 to 77 degrees is ideal. That’s typical late-March weather in Sacramento.

It may seem counterintuitive, but water can help stop this mildew before it takes over. Watering plants in the morning – including a spray on new leaves – can thwart spores but may not be enough if an outbreak has already occurred.

Sulfur and potassium bicarbonate sprays are both effective in protecting young shoots. To make your own spray, process a few cloves of garlic – which is naturally high in sulfur – with 1 quart water in a blender or food processor, then spray leaves and shoots.

Or try this formula: Mix 1 teaspoon baking soda, 1 teaspoon liquid soap (such as Dr. Bronner’s Castile soap or Ivory Liquid) and 1 quart water in a spray container. Shake well. Make sure to spray the underside of leaves as well as the tops.

If powdery mildew has already taken hold, don’t fret too much. It disappears as soon as temperatures reach the high 80s. Infected leaves will fall off and be replaced by new foliage. Just remember to pick up and discard those fallen leaves so they can’t reinfect the plant when temperatures cool back down in fall.

Elsewhere in the garden this week:

▪ Prune and fertilize spring-flowering shrubs after they bloom.

▪ Feed camellias and citrus. This is their growing season and they can use a boost.

▪ Cut back and fertilize perennial herbs to encourage new growth.

▪ In the vegetable garden, plant seed for beets, carrots, celeriac, celery, collards, endive, fennel, jicama, kale, leaf lettuce, mustard, peas, potatoes, radish, spinach, Swiss chard and turnips.

▪ Indoors, start seed for summer and winter squash, peppers, eggplant and tomatoes. They’ll be ready to transplant in late April or May.

▪ For spring and summer flowers, plant seed for aster, cornflower, cosmos, larkspur, nasturium, nicotiana, periwinkle, portulaca, rudbeckia, salvia, snapdragon, verbena and zinnia.

This story was originally published March 16, 2017 at 8:00 AM with the headline "Stop powdery mildew before it explodes."