Downy
mildew (DM) was diagnosed on cucumber Monday, August 29th, 2022, in
Annapolis County, Nova Scotia by both visual inspection and spore
identification using microscopy. The strain of DM that affects cucumber also
affects cantaloupe. At this time, cucurbit crops other than cucumber and
cantaloupe are not at risk.
Figure
1: Downy mildew infected cucumbers
Growers should now add DM-targeted fungicides to cucumber and cantaloupe spray
programs. Rotate between FRAC groups of targeted materials and combine targeted
materials with broad-spectrum, preventative materials to prevent resistance
development.
Where
possible, tank mix Zampro (maximum 3 applications per year, 1 day PHI) or
Orondis Ultra (maximum 4 applications per year, 0 day PHI) with chlorothalonil
(maximum 2 applications per year, 2 day PHI) or mancozeb (maximum 3
applications per year, 14 day PHI). Never make back-to-back applications of the
same product or products from the same chemical family. Follow a 5 to 7-day
application interval, and rotation of the three products can be repeated as
necessary.
Downy
mildew can often be confused with angular leaf spot, bacterial leaf spot and
Alternaria leaf spot. Downy mildew can be identified by dark sporangia growing
on the underside of the leaf.
If you would like confirmation that downy mildew is present in your crop you can contact Dustin MacLean, Perennia Field Plant Pathologist at dustinmaclean@perennia.ca or call 1 902 324-9623
Figure 2: Sporangia developing on underside of cucumber leaf.
Table 1. Downy mildew multi-site,
broad spectrum fungicides
|
Common name (FRAC group) |
Trade Names |
Rate per hectare (Rate per Acre) |
PHI (days) |
Re-entry interval |
Max applications |
|
mancozeb
(M03) |
Dithane
Rainsheild, Penncozeb 75DF Raincoat Manzate Pro-Stick |
3.25
kg (1.3 kg) |
14 |
12
hours |
3* |
|
chlorothalonil
(M05) |
Bravo
ZN Echo |
4.8
L (1.9 L) |
2 |
12
hours |
2 |
|
Common name (FRAC group) |
Trade Name |
Rate per hectare (Rate per Acre) |
PHI (days) |
Re-entry interval |
Max applications |
|
amectotradin (45) + dimethomorph (40)* |
Zampro |
0.8-1 L |
1 |
1 day for hand harvesting, pruning or thinning , 12
hours for other activities |
3 |
|
oxathiapiprolin (49) + mandipropamid (40)* |
Orondis Ultra |
0.4-0.6 L |
0 |
12 hours |
4 |
