Cucurbit downy mildew was detected in Nova Scotia for the
first time in 2021 in Annapolis, Kings, and Hants Counties. It has not yet been
found in Nova Scotia in 2022, but has been reported in New Jersey, USA on June
11th, 2022. Currently, only Clade II has been discovered in Nova
Scotia, which predominantly infects cucumbers and cantaloupes. Clade I, which
affects watermelon, pumpkin, squash, and zucchini has not yet been detected,
but monitoring should still be undertaken in these crops on the chance that it
does make an appearance.
It is important that growers remain vigilant and scout their
fields regularly for this disease, as spores may be blown into the province by
storm systems in the United States. We are not recommending protectant
fungicides at this point in time, but strongly recommend weekly scouting for
disease. Downy mildew may be identified
initially as water-soaked lesions that appear on the top side of the leaf,
which may first appear on any region of the canopy. The most ideal time to
identify these lesions are during or right after a heavy dew. The centre of the
lesion initially appears chlorotic or yellow before eventually the tissue dies,
becoming brown or necrotic (Fig 1 and 2). This disease is very fast spreading, the
lesions will continue to spread across the canopy, and quickly kill the entire
plant if left unchecked. When conditions
are humid, a “downy growth” may be observed on the underside of the initial
water-soaked lesions. These symptoms may first appear before lesions on the
upper leaf. This growth is particularly apparent in the morning, after a period
of wet weather or dew formation.
Growers must stay vigilant, scout often, and report any
positive findings they may see.
Figure 1: Chlorotic lesions associated with downy mildew
infection on cucurbits.
Figure 2: Necrotic lesions associated with downy mildew
infection on cucurbits.
If you suspect downy mildew in your field, please contact
Dustin MacLean, the Field Plant Pathologist at dustinmaclean@perennia.ca or 902
324-9623.
Posted by Dustin Maclean, Horticulturalist and Field Plant
Pathologist with Perennia