Diseases and Nematodes

The major coffee-growing regions throughout the world have serious diseases such as coffee rust (Hemileia vastatrix) and coffee berry disease (Colletotrichum coffeanum) that require costly control measures, but these diseases are not present in Hawaii. They are described at the end of this section (see also Trujillo et al. 1995).

State regulations require a permit to import green coffee for roasting, and afterward the coffee bags or other containers must be destroyed. Our quarantine and Hawaii's isolated location have prevented the introduction of most diseases and pests of coffee. People traveling from coffee areas anywhere in the world to Hawaii need to take precautions if they have been at a coffee farm or mill. Washing your clothes and hair before arriving in Hawaii is recommended.

Coffee nematode decline caused by the Kona coffee root-knot nemtaode

Coffee nematode decline caused by the Kona coffee root-knot nematode A serious disease of coffee has occurred in the Kona region in recent years, characterized by the occurrence of individual or clustered, poorly growing or stunted coffee trees. Initially, it was referred to as "transplanting decline," "replant problem," "nutritional stress," and "Kona wilt." CTAHR plant pathologists have determined that it is caused by a new species of root-knot nematode, named Meloidogyne konaensis. Nematode entry and feeding within roots disrupts plant growth processes and causes growth decline, so infection by them is considered a plant disease (see Schmitt 1996, Serracin et al. 1999). Root-knot nematodes are the most harmful of the extremely small, parasitic roundworms known as nematodes, although the burrowing nematode, which is also found in Kona, is also a pest of coffee.

Root-knot nematodes have been a misunderstood problem on coffee in Kona for many years. Coffee trees have died at CTAHR's Kona Research Station and on some commercial farms. At the station, in the infested area, CTAHR researchers assessed four rootstocks and two cultivars of coffee for performance in the presence of root-knot nematodes. It was determined in 1991 that the nematode on the station was a new species. Subsequent surveys revealed that at least four commercial plantings in the Kona area were infested with this new species. The nematode was described and named in 1994.

Experimental evidence proved that the Kona coffee root-knot nematode is damaging to the 'Guatemalan' variety. It was calculated that the damage threshold is about 1.5 nematode eggs per 250 cm3 (approximately 1 cup) soil. At the level of 150 eggs, 20-40 percent of the roots were galled and up to 44 percent of the roots were rotted.

Nematode Damage
Figure 46. Note corky areas on coffee root caused by nematodes.

Tolerant rootstocks are a promising means of nematode control. In a field infested with the Kona coffee root-knot nematode at the Kona Research Station, most rootstocks tested (including C. arabica 'Purpuree', C. congensis, C. dewevrei, and C. kaffe) suppressed populations of the nematode better than the susceptible 'Guatemalan' cultivar. C. dewevrei was especially effective in reducing the nematode population. The grafted trees grew vigorously and the rootstock had no detectable effect on cupping quality. In a subsequent experiment in which yields were collected, the grafted treatment yielded about 10 times more than seedling 'Guatemalan' in the nematode-infested orchard.

Dewerei Leaf
Figure 47. Coffee dewevrei leaf is much large than a arabica leaf.

Dewevrei Rootstock
Figure 48. C. dewevrei rootstock of a Kona typica (left) compared to same aged but heavily nematode-damaged Kona typica roots (right).

Limited amounts of C. dewevrei seeds are available to growers or nurseries for growing mother trees to produce seeds for rootstocks, although buying grafted plants is recommended. The grafting procedure is fairly simple but tedious because the plants are grafted at a very young age. The rootstock seeds are planted 2-3 weeks before the scion seeds. The best time to graft is after the rootstock seedlings and scion seedlings have germinated and before or just after the cotyledon leaves emerge from the parchment coat. A C. dewevrei seedling is cut in half with a razor blade, and the stem is split less than 1/4 inch (5 mm) to make a cleft to receive the scion. A 'Guatemalan' seedling is the scion, which becomes the top of the new grafted plant. It is cut in half, and the razor blade is used to make two angled cuts to form a wedge at the bottom of the stem. This wedge is then gently pushed into the cleft in the top of the C. dewevrei seedling, so they fit together. The two parts of the new plant are held in place with vegetable grafting clips (see Sources, p. 2) for a few weeks until the graft union has formed. After grafting, the seedling flat should be covered with clear plastic to prevent drying and kept out of direct sun. Once the grafted plants begin to grow, they can be planted in plastic or paper sleeves like any other seedling to grow until they are ready for transplanting into the field.

Scion Seedling
Figure 49. Scion seedling cut off even before cotyledons emerge from the parchment this is called the 'matchstick' or 'soldier' stage, ready for grafting. Note orange grafting clips.

Dewevrei Roostock
Figure 50. Cutting off the top of C. dewevrei rootstock just before grafting.

Grafted Seedlings
Figure 51. Flat of newly grafted 'Kona typica' on C. dewevrei, note that grafting can be done before the cotyledons emerge from the parchment.

Commercially available nematicides do not significantly help recovery of nematode-infected or declining coffee trees, they are expensive, and they are not registered for use on coffee in Hawaii. Nemacur®, a nematicide, was evaluated by CTAHR nematologists. It was applied bimonthly at 0.5 pounds a.i./acre for two years on trees damaged by the Kona coffee root-knot nematode. The nematicide treatments gave little or no improvement in yield. Other nematicides based on organic products such as fungi or plant products (e.g., sesame) are becoming available. These products have not been tested on coffee and probably require a lengthy period of use before good nematode control is realized, if at all.

CTAHR's Agricultural Diagnostic Service Center assays soil for nematodes and identifies them, for a fee. If nematodes are present, consider the full range of management options. These options include the use of grafted plants on rootstock of Coffea dewevrei, which is tolerant of nematodes; weed control; nutrition and water management; organic soil amendments; growing coffee under shade; etc. (see Serracin et al. 1999).

Cercospora leaf spot (brown eyespot),
Cercospora coffeicola

Cercospora fungus is found in coffee-growing areas worldwide. It is common in Hawaii but not economically important. Good growing conditions, sufficient air circulation, adequate fertilization, and irrigation if necessary to prevent drought will normally prevent the problem. Copper fungicides registered in Hawaii are necessary only in a serious outbreak. Symptoms appear as small chlorotic spots that expand to 3/16-5/8 inch in diameter on leaves. The outer portion of the leafspot becomes brown; the center becomes gray-white. The spot's eye-like appearance distinguishes it from other leafspot diseases. Spots can occur on the cherries, appearing as sunburn, a black, dried, elliptical scar on the skin. These make the cherry difficult to pulp and may reduce the green bean quality. The disease is favored by high humidity, rain, warm temperature, and drought stress after flowering. Exposed, unshaded trees and nursery seedlings are most susceptible.

Cercospora Symptom
Figure 52. First symptom of infection of Cercospora coffeicola, coffee berry blotch.

Cercospora Later Symptoms
Figure 53. Later symptoms of Cercospora coffeicola, coffee berry blotch.

Diseases not found in Hawaii that could be accidentally introduced

Coffee leaf rust, Hemileia vastatrix

This fungus is the most widespread, serious coffee disease everywhere except Hawaii and Australia. Symptoms are yellow-orange lesions under the leaves; the lesions may grow together. Tiny spores (seeds) produced by the lesions give a dusty appearance to leaves. Spores are spread by wind, rain, coffee bags, and clothing and hair of people in the area. Control is by quarantine, copper fungicides, and resistant varieties. Hawaii already has a quarantine. Kocide® (copper hydroxide) is already registered in Hawaii to control coffee rust. Resistant varieties have been imported by CTAHR and the Hawaii Agriculture Research Center. If this disease should reach Hawaii, prompt destruction of infected plants may stop it from spreading. If you suspect that you have observed this disease, it is important to report the symptoms to the Hawaii Department of Agriculture or your CTAHR Cooperative Extension Service agent immediately.

Coffee berry disease,
Colletotrichum coffeanum

The aggressive strain of this fungus is found only in Africa. Other less dangerous strains are widespread. The initial symptom is brown, sunken lesions on green cherries. Spore-producing bodies appear as very small black dots in the lesions. The lesions grow, covering the green cherry and causing it to shrivel and blacken, destroying the bean. The dried, shriveled cherries may drop or hang on the tree. These are not the dried cherries that occur with overbearing dieback. Flowers can also be infected.

The ability of the fungus to remain dormant for a long time in healthy plants and shriveled cherries makes detection and destruction of all infested plants impossible. Quarantine remains the best control. Hawaii does not allow the import of any green bean or coffee plant parts from African-grown coffee for roasting or production. If you suspect this disease, which is not known to be in Hawaii, it is important to report the symptoms to the Hawaii Department of Agriculture or your CTAHR Cooperative Extension Service agent immediately.