Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at askthegardenguy@earthlink.net.
As we begin 2012, there have already been occasions when the concentration of sulfur dioxide in the air has reached high enough levels to cause plant damage. Consequently, a number of plants will show burn symptoms on the leaves — a yellowing of the leaves (chlorosis) and an actual necrosis, or browning of the leaves due to death of the plant cells. Some leaves will exhibit a bleaching effect where the tissue turns white.
In addition to sulfur dioxide, sulfites, ash and hydrochloric acid are also part of what we call vog, or volcano smog. Sulfur dioxide will enter the leaf through its stomata. The degree of injury will depend upon its concentration and its duration and upon the sensitivity of the specific plant. Some edibles like turnip, lettuce, sunflower, sweet pea, ginger, verbena, swiss chard and beans are very sensitive to sulfur dioxide, while other plants like asparagus, cabbage, celery, corn, onion and potato are more resistant to the damaging effects.
The problem is not necessarily more emissions coming from the volcano, but rather what the winds are doing that particular day. When the prevailing trade winds from the northeast are present, much of the sulfur dioxide is blown out to sea, causing damage in the Ka’u and Kona areas on its way out. On the other hand, when the wind condition is light or blowing from the south, known as Kona winds, the communities of East Hawaii, including Hilo will be affected.
Other factors which affect the severity of the vog include air temperature, humidity, rainfall, and of course, the amount of SO2 being emitted.
I have noticed in my garden that young kale and collard plants that were under a cover (crop cover — a woven cloth) were not affected by the vog. Those that were not covered were burned.
Hi, Nick. I hope you can suggest what to do about mealybugs! They’ve covered my poha berry plants which for a long time were doing great. I enjoy your weekly column and would appreciate any advice you can give me! — Mahalo and aloha from a faithful reader, Mariam
In general, mealybugs are under good biological control. That is, because of the presence of a number of predators and parasites, the mealybug population is kept low. There are two things that upset this balance: broad spectrum pesticide sprays and ants. The application of insecticides will not only kill the target pest but also “the good bugs.” When this happens, the pest population can be worse than better. In addition, other pest, mites in particular, will now become a menace, because their enemies have been killed.
Ants also interfere with biological control by protecting the pest from its enemies. Ant baits are often effective to control the ants, although they take time to work. By controlling the ants, the mealybug population will eventually diminish as the predators and parasite come back in. For a quicker solution, I would recommend spraying the plants with a soap and/or oil solution. See my website, www.gardenguyhawaii.com, for a University of Hawaii CTAHR soap/oil recipe. But first, try a high-pressure stream of water from a garden hose; oftentimes, this will do the trick.
And lastly, mealybugs have filaments, or hairs around their body which protect them from pesticide sprays. These hairs act to repel the spray solution. Therefore, what is needed is a “spreader/sticker” added to the spray. This product acts like soap to break down the surface tension and allow the liquid spray to spread out. Spreader/stickers are not needed when using soap and/or oil sprays, but they are needed with most other insecticidal applications.
Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at askthegardenguy@earthlink.net.