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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:
https://irma.nps.gov/NPSpecies/Reports/Systemwide/Ozone-sensitive%20Species%20by%20Park

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 Sept. 25

This week's warm break will revive summer crops such as peppers and tomatoes that may still be trying to produce fruit. Pumpkins and winter squash will add weight rapidly.

Be on the lookout for powdery mildew and other fungal diseases that may be enjoying this combination of warm air and moist soil.

* Late September is ideal for sowing a new lawn or re-seeding bare spots.

* Compost annuals and vegetable crops that have finished producing.

* Cultivate and add compost to the soil to replenish its nutrients for fall and winter vegetables and flowers.

* Plant for fall now. The warm soil will get cool-season veggies and flowers off to a fast start.

* Plant onions, lettuce, peas, radishes, turnips, beets, carrots, bok choy, spinach and potatoes directly into the vegetable beds.

* Transplant lettuce, cabbage, broccoli, kale, Brussels sprouts and cauliflower.

* Sow seeds of California poppies, clarkia and African daisies.

* Transplant cool-weather annuals such as pansies, violas, fairy primroses, calendulas, stocks and snapdragons.

* Divide and replant bulbs, rhizomes and perennials.

* Dig up and divide daylilies as they complete their bloom cycle.

* Divide and transplant peonies that have become overcrowded. Replant with "eyes" about an inch below the soil surface.

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