Management of bacterial diseases through flowering to harvest

Pink disease has been controlled with insecticides, which are thought to control insect vectors. Where pink disease occurs sporadically, insecticide applications have not been economic. In the Philippines, where pink-disease epidemics are seasonally predictable, pink disease has been controlled with applications of disulphoton. Disulphoton at 0.83 kg a.i. ha-1 per application starting at the red-bud stage and with three additional applications at 5-day intervals (throughout flowering), has resulted in the highest level of control (Kontaxis, 1978).

Applications of ethephon to inhibit flower opening and reduce nectar flow have resulted in partial but significant control of fruit collapse (Lim and Lowings, 1979a) and pink disease (K.G. Rohrbach, unpublished results). Forcing plantings, so that flowering does not coincide with fruiting in adjacent plantings, which may have fruit collapse, can reduce disease development. Applications of Bordeaux mixture have resulted in variable control (Lim, 1985). Any treatment that reduces bacterial heart rot may reduce primary inoculum levels for flowering plants. Sanitation is an important factor in initial low incidences of fruit collapse. Infected plants and fruit should be destroyed or removed from the field, as they may provide a source for secondary inoculum.

Currently, no known controls of marbling exist. When epidemics occur, infected fruit can be detected and excluded prior to going through the cannery by external appearance and a test to measure fruit firmness, such as sticking a knife into the fruit. If incidences are extremely high, all fruit must be discarded. In contrast to pink disease, infected fruit tissues that are not discarded before processing can be discarded before packing problems if imported into the southern USA, particularly Florida, because it has been observed to feed on maize, cacao, Heliconia and several other bromeliads (Rohrbach, 1983).

The adult stage of the bud moth deposits its eggs on the inflorescence prior to anthe-sis. The larva infests the fleshy parts of the bracts and feeds inside the developing inflorescence. Buds and open flowers are entered directly, with larvae penetrating developing fruit and digging out holes of varying depths. This results in malformed fruit, which is unmarketable (Py et al., 1987). In response to the actions of the larvae, the pineapple fruit forms an amber-coloured gum (gummosis), which exudes and hardens on contact with the air (Fig. 9.24). This resembles the resin exuded by pine trees (sometimes called 'resinous' by Brazilians). When secondary infections are due to F. moniliforme var. subglutinans, the exudate is more fluid and glassy, characteristic of fusar-iosis disease. The pathogen can penetrate the

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