We may be tired of our recent hot, humid weather but annoying garden pests are thriving in these conditions. The bug and weed populations are having a heyday outdoors while we try to stay dry and cool inside. Lots of gardening challenges increase during the summer in Kona, unless you anticipate them and employ some preventive measures or can control pest outbreaks as soon as they occur.
We may be tired of our recent hot, humid weather but annoying garden pests are thriving in these conditions. The bug and weed populations are having a heyday outdoors while we try to stay dry and cool inside. Lots of gardening challenges increase during the summer in Kona, unless you anticipate them and employ some preventive measures or can control pest outbreaks as soon as they occur.
First, the weeds. A weed is a plant in the wrong place. Some are attractive, some are medicinal and many cover bare ground. Before you remove them, have something else in place or ready to go in. You don’t want to leave bare ground subject to erosion during our rainy season. If you identify the plant and discover its merits, you may decide to leave it in place. When undesirable weedy plants get ahead of you, try the least toxic methods first. Of course, the no-tox way is meditative weeding. Good for your mind and body, bad for the weeds. Get them out by the roots.
Check online at gardensalive.com or groworganic.com for descriptions of several low-tox organic herbicides. Horticultural vinegar, herb oil concentrates and weed flamers will kill the tops of weeds. Glyphosate products, including Roundup, will kill weeds systemically but these chemical formulas are also harmful to beneficial soil microbes and fungi and are definitely not organic. Before the weeds get going, you can use organic weed suppressants that contain corn gluten or you can place weed cloth in areas prone to getting weedy. Applying mulch to an area once weeds are removed will slow their return.
Bugs love warm weather and long summer days of sucking and chewing. Before waging war on insects, it is best to first identify the enemy. Sucking insects often hide on the underside of leaves along the veins to suck juices from your plants. In large infestations, you may see them on the top of leaves or on the stem. Insects including aphids, mites, thrips and whiteflies can all be killed by contacting them with a combination of soap and oil. Safer horticultural soap and neem oil are an ideal combination to use. Follow directions on the containers or check online. If ants are present, they are probably “farming” the sap-sucking insects in order to harvest the “honeydew” they excrete. Outdoor ant stakes or sticky barriers wrapped around the stem or trunk of larger plants can help control ants and leave the sucking insects more vulnerable to your attack.
If you have evidence of chewing on the leaves of your plants, you may have caterpillars or beetles at work. Many insects, including moths and butterflies lay their eggs on plants that they know their young will like. Their eggs hatch into hungry caterpillars, that can cause serious damage to your plants in a short time. Products containing the organic bacteria bacillus thuringiensis are an organic way to deal with caterpillars. Apply it as soon as you suspect their presence. Once they have eaten the product, they will die in a day or two.
Another prevalent leaf eater in our midst is the Chinese rose beetle. Their damage looks like shot holes and can give the plant’s leaves a lacy appearance. Chinese rose beetles feed just after sunset, which is a good time to go into the garden with gloves, a flashlight and a jar with alcohol in the bottom to collect them. Neem oil and neem fertilizers will discourage them. Some systemic insecticides list them on their label. If they are listed, you can use the product but for edible plants be sure the product is organic and approved for use on edibles.
Wet weather also encourages slugs and snails to increase in number and munch the night away on your greens. Beer is probably the least toxic way to attract and kill mollusks. A tuna can with some cheap beer will bring them to feed where they will die from drowning or drunkenness. Organic slug and snail baits are also available and very effective.
Diseases also thrive in our summer moist heat. Next week will focus on preventing, diagnosing and treating some of our more common plant disease issues. If you have plant problems that you cannot identify or do not know how to treat, you can get help by contacting the University of Hawaii Master Gardener Helpline from 9 a.m. to noon Thursdays at 322-4892 or sending photos to it at konamg@ctahr.hawaii.edu.
Tropical gardening helpline
Melanie asks: Will olive trees fruit in Hawaii? Would they make a good commercial crop here?
Answer: Olea europaea, which is the European olive, is native to southeastern Europe and grows and produces well in the Mediterranean Basin as well as western Asia, northern Africa, Iran and southern California.
Olive production begins three to 10 years after planting but is very limited or nonexistent without a winter chill. They produce best in Mediterranean coastal areas with calcareous, limestone soils that are hot and dry in summer and have winter nighttime temperatures that consistently fall below 45 degrees in order to trigger the dormancy required for flower development.
In Hawaii, commercial olive production would probably only be possible at elevations between 2,000 and 4,000 feet where the summer and winter temperatures come close to the Mediterranean conditions. Challenges to successful olive production in Hawaii might include dealing with unforeseen pests and diseases as well as having adequate labor for hand harvesting. Though olives can be preserved on a small scale, presses for making olive oil are very expensive.
Another important down side to growing olives in Hawaii is that they can become invasive and they have in several areas around the state. Mature trees can produce from 50 to more than 1,000 of seeded fruit annually. Many birds and mammals eat the fruit and disperse the seeds. Moving water, earth-moving equipment, car tires, garden refuse dumping and humans can also contribute to olive seed dispersal.
The seeds germinate quickly and can form dense canopies that shade out understory plants posing a serious threat to plant diversity in our native forests. “Hawaii’s Most Invasive Horticultural Plants” at gchonolulu.org/FlowerShow2012/HORTICULTURAL%20PLANTS%20Invasive.PDF lists several olive species. Species including the wild olive (Olea oleaster) as well as the autumn and Russian olive have already taken over large areas of native forest on Maui.
Getting rid of olive trees can be difficult. They have a sturdy and extensive root system making them hard to remove. They also send out new shoots quickly if they are stumped. Once established the trees are very long lived. The oil rich trees also increase the fire hazard in areas where they are growing. In addition to these issues, olive trees have allergens in their pollen and leaves that can cause severe reactions in some people.
Considering the problems that growing olive trees present here, it is probably best not to plant them in Hawaii.
Email plant questions to konamg@ctahr.hawaii.edu for answers by certified master gardeners. Some questions will be chosen for inclusion in this column.
Diana Duff is a local organic farmer, plant adviser and consultant.
Gardening events
Thursday: Kona Coffee Farmers Association’s Annual Fundraiser Dinner from 5 to 9 p.m. at Daylight Mind Coffee Co. in Kailua-Kona. The $95 cost supports the KCFA in its work. For more information, the menu and to reserve a seat, visit konacoffeefarmers.org/events.
Farmers markets
Wednesday: Hooulu Farmers Market, 9 a.m. to 2 p.m. at the Sheraton Kona Resort & Spa at Keauhou Bay
Wednesday: Sunset Farmers Market, 2 p.m. to sunset at the north makai corner of the Kmart parking lot
Saturday: Keauhou Farmers Market, 8 a.m. to noon at Keauhou Shopping Center
Sunday: South Kona Green Market, 9 a.m. to 2 p.m. at Amy B. H. Greenwell Ethnobotanical Garden in Captain Cook
Monday to Saturday: U-Pick greens and produce, 10 a.m. to 4 p.m. Tropical Edibles Nursery in Captain Cook
Plant advice lines
Anytime: konamg@ctahr.hawaii.edu
Thursday: 9 a.m. to noon at UH Cooperative Extension Service in Kainaliu, 322-4892.
Monday, Tuesday and Friday: 9 a.m. to noon at UH CES at Komohana in Hilo, 981-5199 or himga@hawaii.edu.