March 2021 - 25

ONIONS
The first year of a greenhouse
study on herbicides showed
Roundup, Lorox, Caparol and Tricor
provided effective control of white
campion postemergence. Chateau,
GoalTender, Tricor, Outlook, Alion
and Nortron provided effective control
preemergence. These early findings are
not yet herbicide recommendations.
Fall herbicide applications are
effective on white campion.
MSU recommendations for no-till
systems are glyphosate at 0.75 pounds
of active ingredient per acre plus
ammonium sulfate at 17 pounds per
100 gallons of spray volume in the late
fall or early spring.
Late fall in Michigan means late
October to November. Early spring
applications must be made before the
white campion is much taller than four
inches for good control.
Late fall or early spring applications
of Valor plus glyphosate or Canopy XL
plus Express plus 2,4-D ester plus crop
oil concentrate also provide good to
excellent control.
Foliar applications of 2,4-D alone
will not control white campion.
Frequent tillage in the fall and spring
will reduce the establishment of white
campion.
Stemphylium control strategies
Stemphylium leaf blight is passing
When fungicide treatments did not
start until the eight- to 12-leaf stage
or later, yields suffered similar to
the plots that were not treated with
fungicide. Treatments started at the
three to four-leaf or five- to seven-leaf
stage produced the lowest incidence
of disease, the highest percentage of
green tissue and the highest yields.
Questions on fungicide strategy
center on when to use the fungicides
that are most effective on stemphylium
leaf blight. Should they be stacked with
protectants early in the season or saved
for later season use?
MSU researchers evaluated fungicide
Stemphylium leaf blight on onion. Photo: Mary Hausback/Michigan State University
purple blotch as the biggest disease
problem for onion growers in the
eastern U.S.
When do growers start their
fungicide programs for stemphylium?
What's the best fungicide strategy?
New research from MSU may have
some answers.
" Stemphylium causes early loss
of green tissue, " said Doug Higgins,
researcher in the vegetable disease lab
in MSU's Department of Plant, Soil
and Microbial Sciences. The brown
spots of stemphylium leaf blight are
small at first, but increase in size and
extend down the leaf.
" The oldest leaves normally die
first but premature, mid-season
loss of green leaves is a symptom of
stemphylium, " Higgins said. Losing
green tissue early hurts yield. Higgins
presented the stemphylium research at
the EXPO.
In a replicated field study in muck
soil, MSU researchers evaluated
fungicide treatments started at five
timings - the three- to four-leaf stage,
five- to seven-leaf stage, eight- to 12leaf
stage, when onion bulbs were four
centimeters and when the bulbs were
7.5 centimeters. Treatments continued
at seven-day intervals.
strategies by comparing them to a
program consisting of all of the most
effective fungicides.
Protectant fungicides used early in
the season rotated with more effective
fungicides later had less green tissue
than the program of most effective
products.
However, protectants used with
more effective fungicides early in the
season, with only protectants used
later, had green tissue and yields
comparable to the program of most
effective products.
" Do we stack the heavy hitters
up front or do we use them later? "
Higgins asked. This research shows
protecting the onion leaves early pays
off at harvest. VGN
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March 2021

Table of Contents for the Digital Edition of March 2021
