A hibiscus leaf looks more like lace after being attacked by Chinese rose beetles. Photos by Dean Sensui, Star-Bulletin
The reason we aren't seeing as many spider mites in our gardens right now, says horticulturist Joshlyn Sand, is that the rains have washed them away. But given a period of dry weather, spider mites will make a comeback.
That does not mean you should reach for the strongest insecticide. "The idea should always be to prevent insects from becoming a problem in the first place. Then you won't have to worry about getting rid of them," says Sand, who works at Honolulu Botanical Gardens.
"Choose the right plant for the right environment and you will automatically reduce the occurrence of pest problems. When plants are experiencing stress, they are more susceptible to infestations," she said.
Spider mites are among the most common garden pests. You need a magnifying glass to see one of them, but not to see what they've done to your plants. "Damage from a light infestation appears as a yellow or gray stippling (a pattern of tiny dots) on the leaves. Heavy infestations turn the leaves yellow, gray or brownish, and then they fall off. Spider mites show up all over the garden, but they love basil," she said.
Sand suggested that a strong shot of water on a lightly infected plant might help, and that soap sprays like Safer's should be the next step. Chemical sprays, for a variety of reasons, should be a last resort.
These reasons include eventual resistance of the insect to specific insecticides, the replacement by a resistant bug of the one you got rid of, and the adverse effect on beneficial and predatory insects, pollinators, wildlife and more.
Aphids are responsible for leaves that curl or crinkle on newer foliage and hardening flower buds so that the blossoms are distorted. They are small sucking insects that feed on new growth, leaving what looks like sand on the plant. For that reason, hold back the fertilizer that promotes rapid, lush foliar growth.
If you are growing papayas and members of the melon family - including bitter melon, watermelon, cucumbers and pumpkins - close to each other, Sand suggests replanting the melons further away. Cucurbits (the melon family) are a reservoir for ringspot virus which aphids can carry.
An orchid plant is infested with white scale.
Ringspot virus is an immediate threat to the papaya industry. "If you have ants, you probably have aphids because the ants feed on the honeydew excreted by the aphids," Sand said. "Honeydew then creates sooty mold, the sticky black substance that is particularly bad now on ixora. Sooty mold is hard to get off. It blocks the light and interrupts the photosynthesis of the plant.
"Try high pressure water splashing every two days if the sooty mold has just appeared. Otherwise insecticidal soaps are good. You can also just prune off the infected parts."
Scale also attacks new foliage and secretes honeydew. They are found in tiny waxy green lumps along the veins and mid-ribs of leaves. Sand recommends Volck or Sun Spray oils, and you'll probably need to repeat the spraying several times.
"Don't spray Volck oil, which is petroleum based, in full sun or you may burn the plant. The early morning when the sun is low and there isn't much wind is best. Sun Spray is paraffin based, and can be used any time." These sprays are not poisons, they simply smother the insect.
Mealybugs feed on all parts of plant, and are big enough to be seen without magnification. They get into the roots of the plant where they leave cottony deposits. These yellow the leaves and stunt the growth, and are often found in "house plants," the notion which Sand describes as an oxymoron since there is no such thing as a plant that has evolved to grow best in the house.
Plants are meant to live outdoors, so house plants are constantly under stress. For bad infestations in prized house plants, Sand recommends removing the plant from the pot and planting it outside in the earth. That sometimes helps, but otherwise, bag it and throw it away.
If you have mealy bugs in a potted house plant, knock the plant out of the pot and look for the cottony infestation. Hose it off. "Repot the plant in fresh soil, wait and let it chill out, and then drench the whole pot in water to which a systemic insecticide has been added. But too often, it's a lost cause," she said.The vigor of a plant will stave off infestation. Insects invade when the plant is weak. Keep your garden properly watered and fertilized, and grow what grows best in your neighborhood.
"Don't overreact," Sand says. "Hold off on the 'Star Trek' stuff, the sprays where you need to wear a respirator and neoprene gloves. Live with a tolerable level of insects. The plant survives, the flowers grow. A few bugs are OK."