December 2020 - 33

MELON
pathogens, " he said. Other currently
available fumigants have " some efficacy "
but are not replacements. Non-fumigant
nematicides that are registered for
use in watermelon are Nimitz (a.i.
fluensulfone), Vydate (oxamyl), Velum
Prime (fluopyram) and Movento
(spirotetramat).
Cultural practices
Several cultural control practices may
also help reduce pathogens.
Although labor-intensive, removing
residual plant roots from the soil
has been shown to reduce nematode
populations by 90%. Soil can also be
" solarized " or heated by covering it with
clear plastic to trap sun rays and kill
off nematodes with temperatures above
100˚ F, but Hajihassani points out this
also kills off beneficial microbes.
Some cover crops are known to
be effective for root-knot control.
Hajihassani's lab found that Mucuna
pruriens (velvet bean), Aeschynomene
americana (joint vetch), Tagetes spp.
(marigold), Crotalaria juncea (sunn
hemp) and some cultivars of sorghumsudangrass
(Sorghum bicolor × S.
arundinaceum) have been successfully
used in the South as cover crops for
root-knot control.
Grafting rootstocks
While breeders have looked for
natural resistance to root-knot
nematodes, finding a watermelon
variety strong enough to bring to the
commercial market has been difficult.
" As far as I know, there are no
commercial resistant varieties on the
market, " Hajihassani said. " Most of
the resistance that has been found in
the past has been in multiple lines or
accessions of watermelon that cannot be
used as commercial varieties because of
lacking horticultural and/or agronomy
traits such as flavor, color and crop
productivity (yield). And transferring
that resistance from those watermelon
lines to commercial varieties is not
possible - at least, at the time we're
talking it hasn't successfully been done. "
While their fruit may be
unmarketable, disease-resistant
cucurbits are still of use as rootstock
into which melon vines may be
grafted. For instance, Hajihassani said,
the hybrid squash and bottle gourd
rootstocks have shown resistance
to fusarium wilt, but not root-knot
nematode. In contrast, citron melon,
called Carolina Strongback, has
resistance to both pathogens.
" These grafted plants are still not
common; the growers are not usually
using them, because of their high
price, " he said. " In fact, these are costly
compared to using the pesticides
(nematicides and fungicides) and nongrafted
watermelons. To me, the use a
rootstock that has resistance to both
pathogens seems ideal. ... If you're
suppressing two pathogens with only
growing one resistant rootstock, that
would be beneficial, not only in terms
of the economic value but in terms of
reducing the environmental concerns
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VGN | DECEMBER 2020 | 33
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Stokes Seeds Trial Evaluation
Researching the best for our customers since 1881.
OUTLAW
57 day, upright bushy plant with
concentrated sets of glossy,
5.2 in/13 cm dark green straight
pods. Resistance to BCMV.
CRAVE
78 day, bicolor Glacial type.
Great husk package, large ear
and excellent eating quality
that everyone will crave.
Strong disease package. Widely
adapted.
associated with the use of chemicals. "
While some researchers have looked
at robotic systems for reducing the
cost of grafting, for now, grafting
remains costly in terms of labor.
" The growers need something that
can not only be justified economically,
but also helpful for them, " Hajihassani
said. " Finding a solution like
improving grafting technology to
effectively control these pathogens
will be a 'must win' for growers. " In
the meantime, Georgia growers can
still beat fusarium wilt and root-knot
nematodes with current options, but
there are no cheap-and-easy shortcuts
to doing that. VGN
Plant pathologist Deborah Fravel observes growth of the plant-pathogenic strain of fusarium
oxysporum that causes fusarium wilt. Photo: Keith Weller/ USDA ARS
EARLY GIANT
SIRIUS
95 day, Early maturing tall
25-30 lb fruit with an excellent
deep orange color.
74 days, Personal sized fruit
with medium thick rind.
Good plant vigor with maturity
approx. 2-3 days earlier than
similar varieties.
NEW

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December 2020

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