September/October 2023 - 8

GLVPN VEG CONNECTION
Powdery mildew
P
BY JAMES JASINSKI
OHIO STATE UNIVERSITY DEPARTMENT OF EXTENSION
umpkin and squash are prominent members
of the cucurbit family, along with melon,
zucchini and cucumber. According to the 2017
Census of Agriculture,
nearly 130,000 acres
of pumpkin and
squash crops were
planted nationally,
predominantly in the
Midwestern, Mid-Atlantic
and Northeastern states.
While foliage and
fruit in this family are
susceptible to attack
from nearly the same
insects, weeds and
diseases, this article is
focused on managing
powdery mildew
(Podosphaera xanthii) on
pumpkin and squash.
Perhaps no cucurbit
disease is more
recognizable than
powdery mildew (PM),
with its characteristic
white powdered
sugar-like colonies
dotting a leaf's surface around mid-summer. This
pathogen doesn't overwinter in most northern states,
but instead infects susceptible crops with conidia
generated on cucurbit crops in southern states and
is carried northward by wind and weather fronts.
Inevitably, the question becomes: What are the
components of a good PM management program?
First, choose PM-tolerant or -resistant hybrids
whenever possible to maximize host plant resistance
against this disease. Second, scout for PM beginning
mid-summer on the upper and lower leaf surfaces
throughout the field and leaf canopy. If even a
few colonies are found, treatment should begin
immediately and continue until harvest. Third,
know the Fungicide Resistance Action Code (FRAC)
or mode of action (MOA) number (found on the label)
for each fungicide used on your farm and how to
rotate it.
8 | SEPTEMBER/OCTOBER 2023
Initial powdery mildew colonies form on the surface of a
pumpkin leaf. Photo by James Jasinski, Ohio State University
Safeguard and treat pumpkin and squash from disease
The general rule is do not use the same FRAC
numbered fungicide on sequential applications. This
means you should rotate FRAC numbers for each
spray. For example, Quintec (FRAC 13) can be rotated
with any other non-13 FRAC-coded product, such as
Procure (FRAC 3) or Luna Experience (FRAC 3 + 7).
The only exception
to this rule is the M
class products (Bravo,
Manzate, Sulfur, etc.)
can be applied back
to back as protectant
fungicides.
While a majority
of fungicides on the
market are locally or
fully systemic in some
manner, take advantage
of hollow cone or
twin flat fan nozzles
to maximize product
efficacy by delivering
droplets to both the
upper and lower leaf
surface. Other general
guidelines include
35-50 gallons per
acre with at least 60
PSI to penetrate the
deep plant canopy and
increase leaf coverage.
Plant pathologists throughout the Midwest, Mid-Atlantic
and Northeast conduct annual or biennial fungicide
efficacy trials on pumpkin and squash to determine
which compounds and spray programs to recommend.
The bottom line is state and regional vegetable
production guides list a tremendous number of
recommended fungicides to treat PM, but only a subset
can be evaluated each season. Over time, populations of
PM within a region can become insensitive to fungicides,
requiring growers to be prepared to rotate novel
products into their spray programs when significant
loss of efficacy is reported.The goal of a good PM
program is to maintain healthy foliage long enough to
maximize fruit size and quality through harvest.
Thanks to D. Higgins, C. Engfehr, M. Hausbeck,
B. Cortright, N. Lukasko, M. McGrath, C. Downing,
S. Miller, A. Taylor, J. Amrhein for information in
published Plant Disease Management Reports.
September/October 2023

Table of Contents for the Digital Edition of September/October 2023
