118 – II.2. SQUASHES, PUMPKINS, ZUCCHINIS, GOURDS (CURCURBITA SPECIES)
cultivars of both ssp. pepo and ssp. ovifera are grown. Elsewhere in the world, ssp. pepo
is the more economically important subspecies.
Management issues
Amongst the Cucurbita, C. pepo can present a weed problem in certain agricultural
settings; these problems are associated with free-living members of the species in
North America. C. pepo var. ozarkana is considered a weed in the states of Arkansas,
Louisiana and Mississippi in the United States in soybean and cotton fields (Boyette,
Templeton and Oliver, 1984; Oliver, Harrison and McClelland, 1983). While a perennial
problem in Arkansas, reports from Louisiana and Mississippi are based on “outbreaks”
that are evidently linked to sporadic flooding events and associated fruit dispersal into
cultivated fields. Whereas in wild habitats (i.e. those not directly influenced by human
activity), individual plants or small groups of plants are widely dispersed along flood
plain corridors, in weedy habitats (i.e. disturbed habitats created by human activities),
populations can be very dense and cover agricultural fields. Neither Cucurbita pepo
var. texana nor var. ozarkana are found on the United States Department of Agriculture’s
Federal Noxious Weeds List (USDA, 2011b).
Morphological and isozymic evidence suggests that some free-living C. pepo
populations in Illinois (Decker and Wilson, 1987; Wilson, 1990), Kentucky (Cowan and
Smith, 1993; Decker-Walters et al., 1993) and possibly elsewhere (Asch and Asch, 1992)
may have evolved purely as escapes of ornamental gourds, which may or may not have
experienced subsequent introgression with other nearby cultivated, weedy or wild
material of C. pepo. Such wild-habitat populations in northeastern Mexico, Texas and
many parts of the Mississippi Valley in the United States have long histories of
occupation in their general areas, however, and have been accepted as indigenous
(e.g. Smith, Cowan and Hoffman, 1992).
Unlike the wild C. pepo which wards off predation by producing small, hard-shelled,
tough-pericarped, bitter-fleshed gourds, the edible cultivars under human selection have
yielded characteristics that hinder the cultivars’ ability to persist in the wild, e.g. large,
fleshy, non-bitter fruit. The edible cultivars consequently do not survive as long-lived
escaped populations in wild or weedy habitats. C. moschata, C. maxima and C. ficifolia
are known to grow outside of cultivation in the United States. The species have been
collected from various habitats outside of cultivation: oak-pine woods, agricultural fields,
brush and trash heaps, roadsides, ditch banks, vacant lots and disturbed sites. In addition
to the US localities, C. moschata has been reported as naturalised in the West Indies,
Central America (Belize) and South America (Galapagos, Guyana, French Guiana,
Surinam). In most cases, these plants are most accurately described as “waifs” as they
apparently do not maintain themselves in persistent populations (Nesom, 2011).
The edible cultivars can occur as volunteers in fields and thus present certain
management considerations. Because of their rapid germination and large canopy, certain
of the Cucurbita are used in weed control strategies, e.g. C. argyrosperma in traditional
growth systems in smaller agricultural holdings (Anaya et al., 1987; Anaya, Ortega and
Nava Rodriguez, 1992). Rapid vine growth and large leaves make the Cucurbita
relatively weed tolerant and these characteristics can be used to reduce weed pressure as
seen in traditional native agriculture (Anaya et al., 1987; Anaya, Ortega and Nava
Rodriguez, 1992; Radovich, 2011).
