‘Awa Dieback in Hawaii

brown leaf spots; or diffuse yellow blotches. Severely affected plants have rotten basal stems and stumps and black, rotten roots. Symptoms of ‘awa dieback may resemble other ‘awa diseases or conditions. The mosaic symptoms associated with ‘awa dieback resemble nutrient deficiencies (e.g., nitrogen, potassium, and iron) caused by insufficient fertilizer applications or planting in a nutrient-poor soil or medium. Stunting, yellowing, and wilting from ‘awa dieback resemble foliar disease symptoms associated with root-knot nematodes (Meloidogyne incognita) and pythium root rot caused by the fungus Pythium splendens. Wilting and collapse of plants from ‘awa dieback may resemble fertilizer burn, which leads to rotting of roots, or drought stress. ‘Awa dieback may be difficult to distinguish from leaf chlorosis or abnormality resulting from genetic anomalies or mutations. The rugosity and leaf curling associated with systemic infection of ‘awa by CMV may also be caused by feeding of nonviruliferous aphids. Blackening of entire leaf veins, which in ‘awa dieback is more often visible on both upper and lower leaf surfaces simultaneously, can be confused with damage caused by feeding of thrips (banana silvering thrips, Hercinothrips bicinctus), which causes a prominent blackening, often adjacent to veins, on the underside of ‘awa leaves. Veinal necrosis of plants with ‘awa dieback is mimicked by blackening of broken veins resulting from mechanical or wind damage. Leaf necrosis of ‘awa dieback can resemble the leaf curling and discoloration caused by mite feeding (e.g., carmine spider mite, Tetranychus cinnarbarinus). Leaf curling and discoloration of plants with ‘awa dieback may resemble the mild sunburn damage (leaf curling, mild mosaic pattern, and yellowing) developed on young plants when they are moved from partial shade in nurseries into full sun. Ringspots associated with ‘awa dieback resemble the small, ringspot-like lesions on young ‘awa leaves caused by a fungal pathogen, Colletotrichum sp., which are similar but generally smaller. ‘A word for “kava,” the name by which this plant and its products are more generally known outside Hawaii. This disease is the most important cause of kava yield reduction in the South Pacific (Davis 1999, Lebot 1997), where it is called kava dieback, and it also causes significant yield loss and plant death in Hawaii. Since the first confirmed observation of ‘awa dieback on the island of Hawaii in 1999, all common Hawaiian varieties have been found susceptible. The disease is particularly damaging to young plants and has destroyed many acres of ‘awa in some locations. Hawaiian ‘awa varieties show a wide range of disease symptoms. All Hawaiian ‘awa varieties with dieback that have been tested were positive for cucumber mosaic cucumovirus (CMV, formerly known as cucumber mosaic virus), the primary cause of the disease (Davis et al. 1996). Plants with ‘awa dieback symptoms and CMV have been confirmed on the islands of Hawaii, Molokai, Maui, and Kauai. This disease can spread rapidly from area to area through the propagation and transport of infected planting material, and within planting locations it is spread from plant to plant by viruliferous aphids, ones that have fed on virus-infected plants and retain the virus. Without proper disease management practices, dieback poses a significant threat to Hawaii’s ‘awa industry.