Registration
of Procure in NY Provides Growers with Valuable Tool to Manage Cucurbit Powdery
Mildew: June 2006
Procure
is a valuable addition to the fungicide arsenal for combating powdery mildew in
cucurbit crops because it is a DMI fungicide that can be applied at a high
dose. It was registered in NY for this use in early 2006. DMI (demethylation
inhibiting) fungicides (FRAC Group 3) are highly effective and they are mobile
in leaves which enables them to suppress powdery mildew on the lower surface of
leaves, where this disease develops best, resulting in excellent control. DMIs have continued to be important for
managing powdery mildew although resistance has developed in the pathogen. This is because resistance to DMIs is quantitative
and the current level of resistance in the pathogen is not sufficient to allow
it to tolerate high DMI dose. Thus
Procure is highly effective despite resistance. With quantitative resistance, pathogen strains
exhibit a range in fungicide sensitivity depending on the number of genetic
changes they possess that affect the fungicide’s ability to function. The first DMI registered for cucurbit powdery mildew, Bayleton, became
completely ineffective due to resistance about 15 years ago. Nova, the second DMI registered for this use,
has continued to provide excellent control when applied at high label rates in
fungicide efficacy experiments, but poor control has been reported with low
label rates. DMIs are expected to continue to be important for managing
cucurbit powdery mildew if resistance is managed.
Procure
is labeled for use at up to twice the dose of Nova, the only other DMI
registered for cucurbit powdery mildew. Procure 50WS at the highest label rate of 8 oz/A provides 4 oz/A of its
active ingredient (triflumizole), whereas Nova 40W at 5 oz/A provides 2 oz/A of
its active ingredient (myclobutanil). Although Procure was not more effective than Nova where compared
recently in university fungicide efficacy experiments, including Cornell, and
the highest label rate of Procure is not needed to effectively suppress powdery
mildew, high rates are generally recommended for managing quantitative
resistance. High rates will control any
pathogen strains present that are able to tolerate low doses. When these moderately resistant strains are
able to survive there is potential for development of strains with higher
levels of resistance. It is not possible
to predict the genetic potential of the cucurbit powdery mildew fungus to
continue developing DMI resistance, therefore high rates are needed. Hopefully this pathogen is not capable of
developing a sufficiently high level of DMI resistance that it will eventually
be able to tolerate full label rates of Nova or Procure resulting in control
failure as occurred with Bayleton. It is
important to realize that resistance needs to be managed before fungicide
efficacy is affected, thus the recommendation to use high rates now. Since managing further development of DMI
resistance in the cucurbit powdery mildew pathogen is critical for successful disease
control, Procure applied at a high label rate (6-8 oz/A) is thought to be a
better choice than Nova at its highest label rate of 5 oz/A. Cost is similar: about $17.63-$23.50/A for
Procure versus about $21.53/A for Nova. When
compared in 2005 at Cornell in Riverhead, excellent control of powdery mildew was
obtained on the lower leaf surface with both DMIs: 93% with Procure at 6 oz/A and
82% with Nova at 5 oz/A (these numbers are not statistically different). To determine their efficacy in this experiment
these products were applied alone on a 7-day interval, a use pattern that
should never be used in a commercial field.
Note that the new 480SC formulation of
Procure will soon replace the original 50WS formulation. It is labeled for use at 4-8 fl oz/A, the
same rate of active ingredient as the 50WS, with a season maximum of 40 fl oz/A.
In
addition to applying Procure at a high label rate, other resistance management
strategies need to be implemented for optimum resistance management and to
ensure effective control of powdery mildew. These strategies include selecting varieties with genetic resistance,
applying Procure tank-mixed with a protectant (contact) fungicide, and applying
Procure alternately with other mobile fungicides in different fungicide classes
(FRAC groups). Procure should not be
alternated with Nova. There are two
other mobile fungicides to use in alternation with Procure in NY: Quintec and
Pristine. These also are at-risk for
resistance development and thus are also recommended used in alternation. Quintec (FRAC Group 13) was granted an
emergency exemption (Section 18) by EPA to NYS
DEC again for 2006 for powdery mildew in non-edible peel cucurbits. Users must have a
copy of this label when they use this product. Quintec labels can be obtained from local distributors and the extension
office as well as at http://pmep.cce.cornell.edu/regulation/sec18/2006/index.html. Pristine (Group 7 and 11) is recommended over other Group 11 (QoI, aka strobilurin) fungicides (e.g. Amistar, Flint,
Cabrio) because this is the only product in this fungicide group that has an
additional active ingredient in another chemical class, boscalid (Group 7). Cucurbit powdery mildew is the only vegetable
disease that Procure and Quintec are labeled for. Pristine is labeled for other diseases in cucurbits
as well as other crops, but it was not as effective for powdery mildew. Alternating among these 3 mobile fungicides, with
each tank-mixed with a protectant, is expected to provide effective control of
powdery mildew plus provide some control of some additional diseases.
Please Note: The specific directions on fungicide labels
must be adhered to -- they supersede these recommendations, if there is a
conflict. Any reference to commercial
products, trade or brand names is for information only; no endorsement is
intended.
