to direct sunlight remains in the young plant for one or two years. Since seedlings germinated and grown under glass do not exhibit this sensitivity, lethality is presumably caused by UV radiation. In the field, pawpaw seeds normally germinate from mid-July to mid-August, and grow very little the first year (5-10 cm). Experiments have shown that long daylengths typical of early summer are most conducive to growth (Allard, 1955). In the greenhouse, seed planted February 1 germinated April 1 (roughly) and grew 25-50 cm the first year, whereas seed planted 6 weeks earlier germinated during the short days of February, grew about 10 cm, and then set a terminal bud (Peterson, unpublished).
Despite the versatility and facility with which a variety of grafting and budding techniques may be used on the pawpaw (Davis, 1974; Thomson, 1974; Hickman, 1980), grafting as a method of multiplying pawpaw cultivars has a major drawback: rootsuckers inevitably sprout some distance from the main trunk, reproducing the rootstock genotype, not the cultivar. Methods which would circumvent this problem, namely asexual propagation by tissue culture or vegetative cuttings, have not been discovered. Root cuttings have given variable results that depend on the clone (Thomson, 1974) and the time of year the cuttings are taken (Glaser, 1961). Hardwood cuttings fail almost 100 percent of the time (Thomson, 1974). Tissue culture methods are being investigated but results have not yet been reported (Hickman, 1987).
Although the pawpaw is frequently extolled for being free of pests, that is not entirely true. The most horticulturally important predator is the larval stage of a small Tortricid moth, Talponia plummeriana Busck (Heinrich, 1926; MacKay, 1959), christened by Swartz "the pawpaw peduncle borer." This pest, about 2-5 mm long, burrows in the soft tissues of the receptacle beneath the ovaries, causing the flower to wither, blacken, and drop, and can be the cause of a large loss of flowers in some years (Allard, 1955).
Another pest of potential economic consequence is the larva of Eurytides marcellus Cramer (syn. Papillio marcellus), the Zebra Swallowtail butterfly. These larvae are exclusive feeders of young Asimina foliage. Damman (1986) studied the Florida species of Asimina and found that all were preyed upon by E. marcellus, but that the woolly-leafed pawpaw, A. incana (Bartr.) Exell, resisted attack better because of a heavy leaf pubescence, and that under normal circumstances E. marcellus larvae were heavily parasitized and were aggressively cannibalistic. Damage caused by E. marcellus in the collection at Wye, Maryland, U.S.A., has been generally light; small, newly transplanted pawpaws can be defoliated, however. Micro-organisms do not appear to be of economic consequence. Late in the growing season a leaf spot condition is common that can be caused by a variety of fungi, principally Mycocentrospora asiminae (Ellis et Kellerm.) Deighton, Rhopaloconidium asiminae, (Ellis et Morg.) Petr. and Phyllosticta asiminae Ellis et Kellerm. (Farr et al., 1989); occasionally the skin of
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