Vog can leave plants scorched, bleached


Recently, have you noticed a number of scorched plants? Leaves with brown (necrotic) spots, as well as brown margins or even the entire leaf? Then perhaps those plants suffered from the latest period of vog that the east side of the Big Island has experienced. Different plants have varying degrees of susceptibility to the vog. Consequently, a number of plants will not be affected at all, whileothers will exhibit a slight burn to outright death of the plant.

Plants adversely affected by the elevated levels of sulfur dioxide may show symptoms of foliar necrosis due to death of the plant cells (the burnt look), reduced chlorophyll content, decreased plant growth, entire death of the plant and a greater susceptibility to disease.

Some leaves may exhibit a bleaching effect as the tissue turns white.

What you can do: adequately rinse leaves with water after exposure, grow plants under cover such as greenhouses, or temporarily cover valuable plants with fabric or plastic.

Plants that have been documented to be susceptible to vog include:

— Ornamentals: African lily, Oriental lily, cypress, Dutch iris, eucalyptus, ginger, hydrangea, heavenly bamboo, pine, podocarpus, rose and tuberose.

— Native plants: koa, naio, pilo, uki, akala.

— Vegetables: broccoli, cauliflower, Chinese cabbage, daikon, lettuce, Swiss chard, tomato and watercress.

Some of the more resistant plants are asparagus, celery, coffee, corn, and ohia.

For more details on the vog and its effects on plants, read “Volcanic Emissions Injury to Plant Foliage,” by Scot Nelson and Kelvin Sewake, University of Hawaii Department of Plant and Environmental Protection Sciences. The publication can be found on the CTAHR website: http://www.ctahr.hawaii.edu/Site/Info.aspx.

Can you suggest a good fertilizer for my potted anthurium plants? The plants are very healthy; leaves are beautiful … green, large and healthy, but the flowers which are supposed to be tiny pink are in bad shape … very small, no color and do not seem to bloom properly. They also dry up before maturity. I used an all-around fertilizer — 16-16-16 — but it does not seem to work. Thanks for your help! — N.H.

Triple 16 fertilizers are recommended for anthuriums, in addition to a 10-20-20. In Florida, Osmocote 14-14-14 and 19-6-12 are also used. Sometimes a color breakdown in the spathe can be caused by calcium deficiency, in which case lime or calcium nitrate should be applied.

Yet since the plants look healthy and the leaves are large and green, nutrition may not be the problem.

With the blooms in “bad shape” here are three situations that affect the flowers.

1. Light: Mature plants may produce many leaves, but few flowers can be corrected by increasing the intensity of the light.

2. Nematodes: These are microscopic worms that infest plant roots. Stunting and poor growth are usually the first signs of burrowing nematode infestations. Plants will also produce fewer and smaller flowers and appear nutritionally deficient. Rootsand lower stems often rot. Using nematode-free plants, sterile potting media along with growing the plants on raised benches are essential.

3. Thrips. These are common pests of anthuriums. Damage appears as unsightly scarring and/or white streaks on the front and back of the spathe as well as deformed spathes. In severe cases, spathes fail to open while plant growth is reduced.

When treating for thrips, it is best to remove infested flowers and foliage before spraying to allow for good spray penetration and coverage.

Caution should be used when applying insecticides on anthuriums because phytotoxicity (burning the plant) may occur under hot, dry conditions. Generally, the population of anthurium thrips increases during the summer and decreases during the winter, therefore spraying is required more often from May through August.

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.

 

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