Management of pests and diseases on seed material

Pest- and disease-free seed materials are critical to preventing the establishment of insects and pathogens in newly planted pineapple fields. The presence of mealybugs, scales and mites, as well as Fusarium-infected seed materials, must be monitored at the seed source before transport for planting, in order to implement effective controls. The pineapple red mite (D. floridanus) will only become a problem on stored seed under dry conditions. Mealybugs, scales and the red mite can be controlled by dipping seed in an approved insecticide, such as diazinon (Petty and Webster, 1979). Red mites can also be controlled by orientating seed material in its normal vertical position, so that the leaf axils collect natural rainfall or dew, or by methyl bromide fumigation of the seed material (Osburn, 1945). The blister mite (P. sakimurae) can be controlled by dipping seed materials in an approved miticide, such as endosulphan.

Pineapple Pests

Fusarium-infected seed has been hot-water-treated at 54°C for 90 min with benomyl at 50 g 100 l_1, but growth was retarded and up to 50% of the plants were killed (Maffia, 1980). Resistance to F. subglutinans occurs in Ananas and Pseudoananas (Laville, 1980). Resistant cultivars are being developed (Cabral et al, 1997).

Butt rot is controlled by harvesting seed material during dry weather and curing it on the mother plants, where there is good air circulation and exposure to inoculum-infested soil is minimized (Fig. 9.12). Where mechanization has permitted immediate planting of freshly removed seed material, thus eliminating the time required for

Fig. 9.12. Curing (drying) 'seed material' (crowns) on the mother plants and storage until collected for planting.
Fig. 9.13. Pineapple dipping equipment for treating seed materials with fungicides for butt-rot control or insecticides to control scale or mealybugs.

Some pineapple insects and disease organisms may become quarantine issues if seed materials are transported between countries or production areas where pest organisms are present and areas where they are not established. With the increasing importance of low-acid, fresh-fruit cultivars for niche fresh-fruit markets, the potential for international movement of seed materials presents some significant quarantine issues, when specific pests and diseases are not established in the importing country. Potential quarantine insects and diseases because of limited distribution are the pineapple bud moth, Thecla basilides (Geyer), from Central America and the pineapple stem borers from South America and the Caribbean (Castnia icarus (Cramer), Metamasius ritchiei (Marshall) and Paradiophorus crenatus (Billberg)), Erwinia chrysanthemi (Burkholder et al.), causing bacterial heart rot, and F. subgluti-nans from South America, causing stem and fruit rot. Seed materials originating in areas where these pests and diseases are reported to occur should be excluded from areas where they are not established or should be quarantined before planting in production areas (Rohrbach, 1983).

curing, seed must be dipped in an approved fungicide, such as benomyl or triadimefone within 12 h of removal from the fruit or, in the case of slips, from the plant (Fig. 9.13; Rohrbach and Schmitt, 1994).

Cultivars vary in susceptibility to butt rot with the 'Red Spanish' types being more resistant than 'Smooth Cayenne' (Smoot et al., 1971). Hybrid cultivars have also shown a wide range of susceptibility (K.G. Rohrbach, unpublished results).

The strong association of a complex of at least two closteroviruses with pineapple mealybug wilt indicates that virus-free seed may be important for wilt control (Sether and Hu, 1998; Melzer et al., 2001). Elimination of the virus from pineapple plants has been attempted with heat treatments (Ullman et al, 1991, 1993). Tissue-culture techniques have eliminated virus infection (Sether et al., 2001). Genetic engineering for virus resistance is also being attempted (Rohrbach et al., 2000).

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