PINEAPPLE - Tropical Fruits - page 356

alternate hosts. Movement from fi eld edges led to a practice of planting several
beds of pineapple in a strip parallel to the edge of the fi eld and separated from
the main fi eld by a road as a buf er. These buf ers were sprayed regularly. Ant
control using baits is more common in Hawaii.
Heart and root rot caused by P. cinammomi Rands and P. nicotianae
B. de Haan var. parasitica Dast, Waterh. and P. palmivora (Butler) Butler
does not occur uniformly and levels of infection can vary from year to year.
P. cinammomi is virulent in cooler conditions while P. nicotianae and P. palmivora
are associated with warmer and more tropical environments. Conditions
conducive to Phytophthora rots include poorly drained soils, high rainfall and
a soil pH above about 5.5. Crown plantings, especially during the wet season,
are highly susceptible to Phytophthora rots, with the loss of 30-100% not being
uncommon. The disease is controlled by pre-plant dips of planting materials
and by foliar post-plant spray using fungicides.
Butt or black rot is a universal problem of stored planting material and
of fresh fruit. The disease, caused by Chalara paradoxa (De Seynes) Sacc, is
characterized by a soft rot and blackening of the basal portion of the stem
of vegetative propagules, and similar symptoms are seen on infected fruit.
Infected propagules can completely decay if kept moist, and an infection can
quickly spread through an entire pile. In the absence of fungicide treatment,
planting material can be protected by air-curing for several days. Fruit rot is
managed by careful handling of the fruit to avoid bruising, by refrigeration
and with a fungicide dip. Infection occurs within 8-12 h following wounding.
Susceptibility varies with the cultivar, 'Red Spanish' types being more resistant
than 'Smooth Cayenne'.
Other fruit diseases - fruitlet core rot, interfruitlet corking, pink disease
and marbling disease - are universally distributed and occasionally can be
important. Brown rot or fruitlet core rot occurred in only 7% of inspected
fruit. Other postharvest pineapple diseases that begin prior to harvest may
cause sporadic economic problems.
Nematodes are a serious problem wherever pineapple is grown on the
same land over many years. Yield losses of one-third are common in the plant
crop, with total failure in the fi rst ratoon crop without nematode control.
Injury caused by nematodes feeding on the roots is compounded by the roots
non-regenerative nature. Fumigants do not completely eradicate nematodes.
Eggs and dormant larvae are harder to kill, repopulating the soil with time and
necessitating periodic post-plant application of nematicides. For maximum
ei ciency of fumigants, soil must be well prepared, with deep ploughing and
the breaking of all clods. Too much soil moisture inhibits good dispersion of
the fumigant in the soil, while fumigant escape is rapid when the soil is too
dry. Polyethylene mulch over beds helps to retain volatile fumigants in the
soil. Application of nematicides by drip irrigation is ef ective in controlling
nematodes, particularly in the ratoon crop.