Watermelon
growers have a new fungicide to use in their ongoing battle against
gummy stem blight. BASF Ag Products recently released the fungicide
“Pristine” for control of gummy stem blight, anthracnose,
powdery mildew, downy mildew, Alternaria blight, Cercospora leaf
spot in watermelon, cantaloupe and other cucurbit vegetables. Pristine
is a mixture of two fungicides: pyraclosrobin (Cabrio) and boscalid
(Endura).
Pristine shows great
promise of being a very strong weapon for growers in areas where
gummy stem blight and other foliar diseases are a problem. University
of Georgia fungicide screening trials at Attapulgus, Cordele and
Tifton showed Pristine to be highly effective in controlling gummy
stem blight and downy mildew in 2003.
In Cordele, GA trials,
seven different fungicides were applied in a four block spray program
following four applications of chlorothalonil. All applications
were made on a seven day schedule. Pristine gave the highest level
of disease control in the test. While Pristine’s ratings were
not statistically different than season-long chlorothalonil applications,
the plots were visibly stronger. Gummy stem blight was the major
disease present with downy mildew appearing late in the season.
In Attapulgus, GA trials,
only gummy stem blight was present. The top rated treatment was
again Pristine. In this test Pristine provided control that was
statistically superior to chlorothalonil.
The Tifton trials yielded
similar results. This was a fall trial with extremely heavy pressure
from gummy stem blight and respectable downy mildew pressure. Pristine
used alone and Pristine alternated with chlorothalonil both provided
control superior to chlorothalonil alone.
The broad spectrum of
control achieved by the mixture of the two fungicides offers growers
in the East protection against several major diseases in one package.
Since the loss of Quadris due to resistance buildup in Georgia,
growers have been depending upon chlorothalonil-based disease prevention
programs. While these programs have provided good control of gummy
stem blight and anthracnose, additional sprays have had to be made
for powdery mildew and on occasion for downy mildew late in the
season. The Georgia scientists are optimistic that Pristine will
give control of all four of these diseases in one shot, decreasing
trips across the field, the amount of pesticides applied into the
environment and hopefully increasing the profits of watermelon producers.
The Achilles heal of
Pristine could very well be the development of resistance to the
fungicide. While there is currently no evidence of disease resistance
to Pristine, all of the newer site specific fungicides have a greater
danger of resistance than our older multiple site fungicides. Remember
the lessons of Quadris? The development of gummy stem resistance
to Quadris in Georgia was swift and painful on our pocketbooks.
Therefore, using this
new tool must be in accordance with resistance management strategies.
Some basic principles of resistance management to follow are: 1)
fungicides should be rotated so that no two with the same mode of
action are applied back to back, 2) do not exceed the maximum number
of applications or the maximum rates per season, 3) use as a preventative
rather than as a curative. Pristine is not labeled for, and should
not be used in, the greenhouse. Many plant pathologists feel that
repeated greenhouse use is the perfect environment for resistance
to develop. The Pristine label outlines these precautions and disease
resistant strategies. Every farmer should carefully read and religiously
follow BASF’s recommended resistance management program.
