Plant Disease of the Week No. 20b (Volcanic emission injury to plant foliage)

Hawaii's Kilauea volcano has been active for many tens of thousands of years. It is the most active volcano on Earth. The volcano has been erupting continually since 1983, emitting SO2 (sulfur dioxide), SO3 (sulfite) and HCl (hydrochloric acid) into the atmosphere. Such materials are emitted from fumaroles on the volcano even during periods of non-eruption of lava. These acid-precursor gases can affect plants directly or foster acid rain, which can also have a severe effect upon soils and vegetation, especially near or downwind from the volcano. And, volcanic ash can be deposited on plants near the volcano.

The northern and eastern slopes of Kilauea volcano have lush vegetation, whereas the summit area and a triangular area leading southwest to the Pacific Ocean are desert-like and not lushly vegetated. This is due to the normal trade winds that sweep the gases and acid rain from the summit in a southwest direction.

Since late December, 2007, SO2 emissions from Kilauea volcano at Halemaumau have been increasing. On March 12, emissions increased significantly from the new vent. In early April 2008, the Hawaii Volcanoes National Park on the Big Island was closed because the high SO2 levels were deemed a threat to human health.

Agricultural crops and plants are subject to injury by exposure to the air pollutants that emerge from Kilauea, especially at high concentrations or dosages. Farmers and gardeners in the path of the pollutants (SO2 and acid rain) have reported damage to plants caused by the southeasterly winds bringing SO2 fumes from Puu Oo and Halemaumau to downwind areas in the state.

Here we discuss the effects of the increased volcanic output upon foliar plant injury in Hawaii and what can be done to minimize it.

Disease name: air pollution injury, vog damage, sulfur dioxide injury, acid rain injury, ash fall

Pathogens: gaseous air pollution (e.g., sulfur dioxide), acid rain, ash

Type of pathogen: abiotic (non living)

Photograph: volcanic emissions from Halemaumau at Hawaii Volcanoes National Park, emerging from a new vent as of March 12, 2008 and containing high concentrations of sulfur dioxide, some other gases, and volcanic ash (Photo - www.usgs.gov).

Sulfur dioxide (SO2): sulfur dioxide must enter mesophyll tissue, through stomata, to injure leaves. If stomata are not open, due perhaps to water stress or other causes, plants may escape severe injury. Plant age may affect sensitivity to SO2 for some species. Sulfur dioxide is also produced by human activities such as burning coal and oil, smelting ore, manufacture of steel and the refining of petroleum.

Vog: ""Vog" is a term used in Hawaii to describe hazy conditions caused by gaseous emissions from Kilauea volcano. The SO2 gas in vog is greater near the sources (Halemaumau and Puu Oo vents). SO2 levels are lessened away or upwind from the vents. The haze caused by vog may be heavy in West Hawaii, but the SO2 levels are typically lower due to the geographic distance from the sources. One cannot judge the amount of SO2 in the air or its danger to humans and plants by how heavy the vog appears. Also, the SO2 levels can be high with only light vog.

SO2 concentration in the air: In unpolluted air, SO2 gas is less than 0.05 ppm (parts per million). Human health standards are set at about 0.03 ppm average daily exposure to SO2 per year,and at 0.14 ppm maximum exposure per 24 hours. Plants generally do not display symptoms of SO2 injury until these standards for human health are exceeded. Generally, the lower range of toxicity to most plants is about 0.3 to 0.5 ppm SO2.

Table 1. Sulfur dioxide air concentrations near the source at Kilauea volcano (selected dates).

Date Approximate sulfur dioxide (SO2) emission from Kilauea volcano

Normal /background            150 - 200 tonnes* per day
December 2007                   300 tonnes per day (approx. 1 ppm**, Crater Rim Drive)
February 2008                     600 - 1,000 tonnes per day
+March 12, 2008                 1,500 tonnes per day
March 13, 2008                   1,800 - 2,000 tonnes per day (approx. 40 ppm, Crater Rim Drive)
May 24, 2008                      1,540 tonnes per day

May 25, 2008 990 tonnes per day

---

* a tonne is a metric unit equivalent to 1,000 kilograms (=2,204.6 lbs.)
+ prominent new gas vent broke through the lower east wall of Halemaumau this week

** ppm = parts per million (10,000 ppm = 1%)

Source: http://hvo.wr.usgs.gov/pressreselases/pr03_14_08.html

As evident from the table, the recent SO2 output is variable but high enough to damage plants.

Sensitive versus resistant plants to SO2: Sensitive plants show injury at SO2 levels from 0.05 to 0.5 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. Plants more sensitive to SO2 include turnip and sunflower, sweet pea, verbena, and bean. More resistant crop plants include asparagus, cabbage, celery, corn, onion and potato.

Acute injury (SO2): is caused by absorption of high concentrations of SO2 during a relatively short period of time. The symptoms can appear as lesions visible on both sides of the leaves that, occurring initially between leaf veins or along leaf edges. The color of the damaged area varies from light tan to near white to orange red or brown and may depend on factors such as plant species and weather conditions.

General effects of elevated SO2 upon plants: The general effects of SO2 exposure to plants may vary and depend upon plant species and the SO2 dosage.