Pesticide use is governed by state and federal regulations. The person applying the pesticide must read the pesticide's label to learn about application rates, limitations, and use precautions. The label also specifies the insects that the insecticide is effective against. Insecticides currently registered for coffee in Hawaii are Volck® Supreme Oil, Safer's® Insecticidal Soap Concentrate, and Clean Crop® Superior 70 Oil.
Green scale, Coccus viridis, sucks sap from the coffee plant and excretes a sweet substance referred to as honeydew that covers the leaves and supports growth of a black sooty mold that reduces photosynthesis. Scale requires constant attention when the trees are young and growing, particularly in dry areas or dry seasons. Unless scale is controlled, coffee trees will become stunted and sometimes die. Control green scale by spraying either an oil or soap emulsion according to label directions. CTAHR has submitted data for registration of a new insecticide, Admire® (imidacloprid), which should be very effective against scale if its use is approved.
Figure 37. Adult green scales on coffee leaf.
Figure 38. Black sooty mold is powdery yet sticky, this is the most obvious symptom of major scale infestation.
Sooty Mold on Tree
Figure 39. Young tree with black sooty mold on leaves heavily infested with ants tending scale. This tree will not survive if scale is not controlled.
Ants "herd" and protect the scale insects and therefore are chiefly to blame for the spread and increase of green scale. If ants are prevented from getting to a coffee tree, the green scale frequently disappears, controlled by its natural predators. Eliminating the ants is not easy, because no pesticides for ants are approved for use in coffee orchards. Ant-control baits such as Logic® are for use only in young, nonbearing coffee orchards or in uncropped areas around the orchard. Amdro® is very effective against ants, but it is not registered for use in coffee crops and may be used only in uncropped areas around the orchard.
The adult scale is oval, bright pale green, and legless, with short, curved black markings on the back. They are found on coffee leaves, stems, and cherries but most commonly on the underside of leaves, along the veins. Sometimes as many as 500 can be found on one leaf. When infestation is severe, leaves and fruits drop, growth is stunted, and young plants can even be killed.
Green scale attacks more than 70 plant species, including guava, mango, plumeria, and gardenia. Females reproduce without males. Eggs hatch within minutes after being laid. Scale has three growth stages (instars). The first, called a crawler, has two long tail-like structures; it wanders over the plant before settling to feed. The second and third instars are slightly larger. The life span from egg to adult is two months in Hawaii.
The scale and black sooty mold problem in Hawaii was first observed in 1905. Green scale was accidentally introduced to Hawaii on lemon seedlings imported from Fiji and caused the "coffee blights" that occurred in Kona during the early 20th century.
The first and most successful biological control agent against the scale is the white halo fungus (Verticillium lecanii) introduced from Florida around 1910. It destroys millions of scales in Kona during the more humid periods of the year. It also attacks other scales, aphids, and occasionally beetles, flies, and mites. When no insect host is available, it lives in the soil on dead plant material. It invades and destroys scales within two days. After 10 days, it grows out of the scale to produce the characteristic white halo around the scale that can be seen before the scale disappears.
Figure 40. Dead green scale infected with the white halo fungus, note ring around the scale.
The white halo fungus requires high humidity to germinate and rain to spread its spores. Even at 96 percent relative humidity, germination falls by two-thirds, hence the lack of fungus activity during dry weather. Temperatures above 77°F reduce effectiveness, and at 85oF germination and growth stop. It is likely that this fungus will control scale in other locations that have cool, wet conditions.
Five introduced ladybird beetle (ladybug) species feed on the green scale. The most common is Azya orbigera. The adult has a black back, except for two circular spots and short hairs. The legs and abdomen are orange-brown. The young resemble large mealybugs.
Seven wasps parasitize the green scale, but they are not effective in hot, dry, windy areas.
Growers can spray an organic insecticide such as Safer's® Insecticidal Soap to kill green scale. If trees are grown as individuals, not in hedgerows, and no other plants touch the leaves, then an ant barrier can be used on the trunk. A band of woven polyester fiber about 3 inches wide is wrapped tightly around the trunk about 12-18 inches above the ground. A smooth plastic strip is wrapped around this, and sticky material such as Tanglefoot® is applied to coat the plastic strip.
Figure 41. Gauze, wrapped in plastic with sticky "tanglefoot" is barrier to ants.
Provided blowing dirt and debris are kept off the barrier, ants become trapped in the sticky material as they attempt to cross. Thus other natural enemies of the scale can attack without the ants attacking them. The sticky material is toxic to coffee bark, which is why it is put on the plastic. The gauze beneath the plastic is to wick away water that might injure the bark; it also serves as a barrier to ants going beneath the sticky strip. It is essential that the sticky trap block the only route for ants to get into the tree, because they will find and cross the smallest blade of grass that touches the tree and circumvents the barrier (Reimer, 1991).
Black twig borer
The black twig borer (coffee twig borer) (Xylosandrus compactus) is not usually a serious pest, although infestations on individual farms can be severe. The tiny, brownish-black, cylindrical beetle was first found in Hawaii in 1961. It is a type of ambrosia beetle, and it attacks both the lateral and vertical branches. Besides coffee, it infests over 110 hosts including avocado, cacao, mango, macadamia, hibiscus, tea, orchids, anthuriums, and other ornamental and forest trees and shrubs.
Black Twig Borer
Figure 42. Adult and eggs in chamber inside lateral.
Figure 43. Leaves have dried but remain on the blacken lateral for some time.
Figure 44. Wilting of leaves at end of a single lateral is first sign of Black twig borer infestation.
Figure 45. Entrance hole of Black Twig borer in lateral is size of pencil lead.
Typical symptoms of black twig borer are wilting and death of leaves and wood beyond the beetle's entry hole. The wilted leaves frequently stay on the tree but turn dry, and the bark beyond the affected area turns black. The circular entry hole, less than 1/16 inch in diameter, is usually between the last healthy leaf and the first wilted leaf on the dying lateral. Although a single beetle hole may kill a twig, often several burrows are required before the lateral is killed. On the thicker verticals, even heavy infestations do not always kill the branch.
Pregnant females bore into the twig to make a tunnel for eggs and to grow food for the larvae. The female carries a fungus, Fusarium solani, which she cultivates within the tunnel to feed her larvae. This fungus produces a toxin that kills the twig and leaves beyond the entrance hole. This beetle generally attacks trees weakened by drought, girdling, heavy pruning, standing water, or lack of fertilizer. Some coffee cultivars are more susceptible than others.
The best control is maintaining healthy trees. Infested laterals should be pruned behind the last entrance hole as soon as wilting is observed, because new adults will emerge in a few weeks. Pruned laterals should immediately (the same day, if possible) be chipped, burned, or buried to kill the beetles and young. Simply cutting off the wilted lateral and leaving it in the orchard will not kill the adult or young-they will leave the lateral and move to another tree. No insecticide registered for coffee is effective against this pest (Jones and Johnson 1996).
Minor insect pests
The Mediterranean fruit fly, or medfly (Ceratitis capitata), is not a serious pest of coffee. As late as 1913, medfly caused serious damage to coffee in Kona, but a parasitic wasp was introduced to attack the medfly's larvae. Cherry loss to medfly is not a problem today, although coffee is a preferred host of the insect. Many cherries will have medfly larvae or maggots in them, but the few maggots in the cherry do not negatively affect tree productivity or the taste of the bean. Medfly eggs are not laid until the cherry has attained its maximum size and its seeds, the beans inside the parchment, are already mature; thus only the pulp is affected.
A new species of crab spider, Gasteracantha sp., with webs that are a nuisance and a bite that is slightly painful, was discovered in Hilo in 1986. It spread to Kona and became a nuisance in coffee orchards by 1988. CTAHR and Hawaii Department of Agriculture entomologists found that populations of this pest fluctuate drastically. Solutions of a household soap such as WiskR sprayed on the spider helped control it; however, Wisk is not labeled for this use. Crushing the spider's green-to-yellow, quarter-sized egg masses also helps. A parasitic wasp reduces the population.
The Fuller rose beetle (Pantomorus cervinus) is not a serious coffee pest in Hawaii. The beetle first reached Maui in 1894 and spread to all islands to inhabit elevations from sea level to 5000 ft. Its hosts are avocado, coffee, citrus, koa, rose, corn, sugarcane, gardenia, and hilograss. The beetle feeds at night by eating large pieces from around the edges of leaves. The damage is different from that of the Chinese rose beetle, Adoretus sinicus, which eats small holes within the leaf margin. Sometimes adults attack young shoots and flower buds. The larvae live in the soil and eat small roots. The adults, all females, cannot fly, and they live in crevices and under dead leaves on the ground during the day. They lay pale yellow eggs covered with a spongy white material in bark crevices. When the eggs hatch, the larvae drop to the ground and bury themselves. The life cycle from egg to adult takes less than a year.
The West Indian flatid (Melormenis antillarum) is also not a serious coffee pest. First found in Hilo in 1967, it is now found throughout the state, although it is more commonly seen on coffee in dry areas. The adult is powdery gray and has square wings with one large dark spot on each wing. It feeds on a wide range of hosts, including castor bean, hibiscus, eggplant, mulberry, and tangerine.