VegNet
Vol. 14, No. 22.
On the WEB at: http://vegnet.osu.edu
In This Issue
1. Powdery Mildew and Downy Mildew Spotted on Pumpkins in
2. Phytophthora blight
3. Pumpkin Filed Day
Powdery
Mildew and Downy Mildew Spotted on Pumpkins in
Pumpkins planted in late May and early June were showing early symptoms
of both Downy and Powdery Mildew on Tuesday, July 24th. There were no symptoms
of either disease the previous week. This field has not had any fungicides
applied prior to this date. Since it is the last week of July, powdery mildew
is arriving right about on time as in most years.
Growers should consider starting their disease control program
very soon.
Symptoms of Downy Mildew are very similar to Powdery
Mildew. Downy mildew will cause the upper sides of leaves to yellow and
brown out and produce pale gray-purple fungal masses only on the underside of
leaves.
Downy mildew of pumpkin. Symptoms on upper leaf surface (left),
and olive grey lesions underside of leaf (center) and typical symptoms in field
on (right).
Powdery Mildew will produce white fungal masses on the upper and
lower leaf surface and the stem ruining quality if left uncontrolled. Also if
downy or powdery mildew cause high defoliation, the fruit exposed to direct
sunlight on hot summer days may begin to show symptoms of sunscald. Powdery
Mildew will be more prevalent during drying weather; Downy Mildew will begin to
show up more often during cool, wet weather.
Downy Mildew Recommendations - Sally Miller
Despite generally dry weather, downy mildew has been appearing in
greater numbers of cucumbers and other cucurbit crops in
Powdery mildew pustules on upper leaf surface (left), and pustules
growing together on upper leaf surface (right).
The first signs of powdery mildew are pale yellow spots on leaves,
vines or petioles. These spots enlarge and become covered with white spores
that appear powdery. Scout your fields by looking at the older leaves first
although these symptoms can be found on younger leaves. Fields in low lying
areas where mist forms and remains for long periods during the night are
usually affected first. Make the first application when powdery mildew is
detected in the area or is detected by scouting (one lesion on the underside of
45 old leaves).
Powdery Mildew Control for Cucurbits: There
are a number of fungicides that can be used for powdery mildew management,
including sulfurs (e.g. Microthiol), chlorothalanil (e.g. Bravo), myclobutanil
(Nova) and triflumizole (Procure).
Quintec (quinoxyfen) is a very effective powdery mildew fungicide but is
labeled for melons only. Since Nova and Procure are the same type of
fungicide, only one of them should be used and alternated with products with a
different mode of action. Tank-mixing
products such as Quintec, Nova or Procure with a sulfur fungicide will provide
broad-spectrum protection, although it should be noted that sulfur can be
phytotoxic to melon under certain conditions.
Insensitivity of the powdery mildew fungus to strobilurin fungicides such
as Quadris and Pristine have been reported, so if one of these fungicides is
included in the program, particularly to manage other diseases, it must be
alternated with a fungicide with a different mode of action and tank mixed with
a contact fungicide such as sulfur or chlorothalanil.
Phytophthora
blight - Sally Miller
We have recently received samples of squash (see photo below),
cucumber and pumpkin with Phytophthora blight. Fungicide options for
management of Phytophthora blight are limited, and none of them can be expected
completely control the disease. However, if Phytophthora blight is
present in a field, fruits and vines should be protected with fungicides such
as Acrobat, Gavel, Ranman or Tanos, tank-mixed with a protectant fungicide such
as Maneb. Alternate fungicides to reduce the chance of fungicide
resistance developing. Photo by Rick Callendar.
Pumpkin Field Day, Date:
Location: Western Agricultural Research Station, 7639
S. Charleston Pike (Rt. 41),
More Info and details coming: Contact: Jim
Jasinski email: jasinski.4@osu.edu
or phone: (937/484-1526)