Vog and Your Big Island Garden

Vog-damaged rose photo from Volcanic Emissions Injury to Plant Foliage

Humans and animals aren’t the only ones feeling the effects of vog on the Big Island.

Weather is always a subject of news, comment or complaint, especially when something unusual is going on atmospherically. And since new vents have been opening up on Kīlauea Volcano, the weather has been unusual indeed, particularly for residents of Puna, Kaʻū and Kona Districts.

So what does this have to do with gardening? Well, last week, I noticed that my roses are dying. I’m not doing anything different with them—the only thing that’s different is the air.

So I went online and learned that crops on Hawai‘i Island are succumbing to the effects of tons of additional sulfur dioxide (SO2) being belched into the air each day. The leaves of eucalyptus trees in certain areas of the Big Island have also been withering. Whether it is due to the SO2 or the acid rain that occurs when precipitation passes through vog is unknown.

Although SO2 decreases as vog moves further from its source, some SO2 may still reach the “safe” northern areas of the Big Island, such as Waimea and Hawi, though amounts may be negligible.

The State of Hawai‘i website claims that “The distance from the Kīlauea Volcano is too great for SO2 to travel across the ocean in high enough concentrations to create health risks for people on islands other than Hawai‘i;” however, the islands of Maui and O‘ahu have recently reported elevated SO2 levels.

According to a study entitled Volcanic Emissions Injury to Plant Foliage, “Sensitive plants show injury at SO2 levels from .05 to .5 parts per million (ppm) for 8 hours, or about 1 to 4 ppm for 30 minutes. More resistant plants require dosages of 2 ppm SO2 for 8 hours, or about 10 ppm for 30 minutes.”

According to the study by scientists Scot Nelson and Kelvin Sewake of the Department of Plant and Environmental Protection Science at the University of Hawai‘i, vegetables showing sensitivity to SO2 are beans, soybeans, broccoli, Brussel sprouts, endive, lettuce, okra, peas, Swiss chard and turnips. More resistant crops are cabbage, celery, coffee, corn, onion, tomato, watercress and potato.

How can you tell if your plants are suffering from the effects of SO2 exposure? Generally a sudden onset of chlorosis (yellowing) of the leaves during or after extended periods of vog can be indicative of low exposure to SO2.

At higher SO2 concentrations, you would see a bleaching or browning of the tissue between leaf veins. Before you start thinking that your plants are suffering from SO2 poisoning or acid rain, determine whether there has been any problem prior to the onset of vog.

According to the Nelson-Sewake study, “The symptoms can mimic those produced by biotic stresses, such as plant pathogens causing root rot or stem blight, drought, phytotoxicity or damage from pesticides.”

You will want to try to rule out any of these common plant stressors before going through the time and expense to protect your plants from SO2 damage.

If you determine that your plants are suffering from SO2 or acid rain damage, there are things you can do. The Nelson-Sewake study says shielding plants, washing them with fresh water after acid rain and reducing the acidity of irrigation water can mitigate damage.

A spray-on baking soda (sodium bicarbonate) solution may decrease acidity levels on leaves and in the soil, and there is a possibility that treating plants with products to close leaf pores might also deter damage.

The best method of defense is to grow plants in a greenhouse, temporarily cover sensitive or valuable plants with plastic sheeting during vog episodes and, if possible, grow SO2-resistant plants.

I’ll be trying most of these “remedies” with my suddenly ailing roses and I’ll keep you posted on the outcome.

To learn more about vog and its effects, visit the USGS website. For daily air quality data reports, go online. Volcanic Emissions Injury to Plant Foliage can be viewed online or downloaded here in PDF format.
Happy gardening—and hang in there!