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Wildfire brings more ozone problems

Blotchy green citrus leaves
These citrus leaves show ozone damage. (Photo
courtesy UC IPM)

Hot, smoky conditions
create high pollutant levels

Plants may be able to cope with wildfire smoke better than people. But ozone is another matter.

After prolonged exposure to two weeks of wildfire smoke, foliage on many plants in the greater Sacramento area are showing signs of ozone damage. It starts out as stippling – little dots all over large leaves. Or parts of leaves may look like they were sun-bleached white or silver.

In my Sacramento garden, I noticed it in particular on a large dahlia plant. Besides funky foliage, its vivid red petals also were bleached white at the tips. That bleaching was accompanied by a build-up of soot on its leaves.

Ozone is what happens when wildfire ash and other pollutants get “cooked” by triple-digit heat. It makes our eyes water and throats hurt. And there’s a lot of it right now.

According to Sacramento region air quality monitors, our air quality is rated “very unhealthy” for the next several days with particle levels remaining high, especially in El Dorado and Placer counties. Through at least Thursday, Sacramento is forecast to rate 250 on the Air Quality Index. (“Good” is below 50.)

While ozone high up in the atmosphere is a good thing, ground-level ozone can be dangerous. In our case, it’s created by a combination of wildfire ash and other pollutants (usually nitrogen oxides and volatile organic compounds), intensified by bright sunlight and triple-digit heat.

Ground-level ozone can prevent a plant's leaves from properly doing their job. Ozone enters the leaf's stomata and burns the leaf's tissue.

Signs of ozone damage include dark stippling and bleaching of foliage. Plants lose their vigor and stop blooming or yielding fruit. Ozone damage weakens the plant and makes it much more susceptible to pests and disease.

Worried about the long-term effects of too much ozone, researchers and the National Park Service surveyed plants in national parks across the country and found hundreds of species with ozone sensitivity from ash and asters to sycamores and yarrow. Maple, cherry, polar and plum trees are all on the ozone-sensitive list. Find it here:

Meanwhile, keep plants hydrated. Wash ash and soot from leaves.  Lower temperatures later this week may bring some ozone relief, too.


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Dig In: Garden checklist for week of Feb. 5

Make the most of sunny days and get winter tasks done:

* This is the last chance to spray fruit trees before they bloom. Treat peach and nectarine trees with copper-based fungicide. Spray apricot trees at bud swell to prevent brown rot. Apply horticultural oil to control scale, mites and aphids on fruit trees soon after a rain. But remember: Oils need at least 24 hours to dry to be effective. Don’t spray during foggy weather or when rain is forecast.

* Feed spring-blooming shrubs and fall-planted perennials with slow-release fertilizer. Feed mature trees and shrubs after spring growth starts.

* Finish pruning roses and deciduous trees.

* Remove aphids from blooming bulbs with a strong spray of water or insecticidal soap.

* Fertilize strawberries and asparagus.

* Transplant or direct-seed several flowers, including snapdragon, candytuft, lilies, astilbe, larkspur, Shasta and painted daisies, stocks, bleeding heart and coral bells.

* In the vegetable garden, plant Jerusalem artichoke tubers, and strawberry and rhubarb roots.

* Transplant cabbage and its close cousins – broccoli, kale and Brussels sprouts – as well as lettuce (both loose leaf and head).

* Plant artichokes, asparagus and horseradish from root divisions.

* Plant potatoes from tubers and onions from sets (small bulbs). The onions will sprout quickly and can be used as green onions in March.

* From seed, plant beets, chard, lettuce, mustard, peas, radishes and turnips.

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