PCC March 2019

Continued from Page 16
Research and Extension Center (IREC)
in Tulelake, California are investigating
insecticides and insecticide application
methods to find alternatives to
chlorpyrifos. This research effort has
received admirable support from the
California Garlic and Onion Research
Advisory Board with the hopes of
pro-actively finding alternatives before
chlorpyrifos restrictions. Insecticide
applications at planting can be made
in-furrow, broadcast, or as a seed
treatment. IREC research has shown
the efficacy of different application
methods is dependent on insecticide
choice. For example, spinosad was
only effective when applied as a
seed treatment (Regard) as spinosad
(Entrust) applied in-furrow at planting
had similar onion stands compared to
the untreated control.
Insecticide Alternatives to
Chlorpyrifos
Seed treatment with spinosad (FarMore
OI100 and FI500) or clothianidin
(Sepresto) provided similar or better
suppression of maggot compared to
chlorpyrifos at the maximum labeled
rate in-furrow. This trend was true
multiple years in multiple studies
conducted at IREC. Outside the
research world, multiple Tulelake onion
growers had success using spinosad or
clothianidin seed treatments instead
of chlorpyrifos in 2017 and 2018.
Applying chlorpyrifos in combination
with spinosad and clothianidin seed
treatment did not increase onion
stands compared to using either
seed treatment alone. Cyromazine
(Trigard) seed treatment is another
alternative. Trigard provided similar
maggot suppression compared to
FarMore FI500 and Sepresto in 2018,
and it is seed treatment used in other
parts of the United States for maggot
control. Bifenthrin was the only tested
insecticide applied in-furrow that
provided similar efficacy compared to
chlorpyrifos. Unfortunately, bifenthrin
is not currently labeled for use in
California onions.
Other Considerations
Fungicides used in combination
with insecticide seed treatment may
influence onion stands. In 2018,
Sepresto (insecticide) + FarMore F300
(fungicide) + pro-gro (fungicide)
resulted in the highest onion stands in a
field with a combination of maggots and
smut. In fields without smut, thiram
and FarMore F300 fungicide package
gave good early season disease control
in IREC studies.
Yellow sticky traps placed along field
edges can offer growers an early
warning for potential maggot problems
(see picture). Seed corn maggot and
onion maggot flies are readily captured
on sticky traps and the traps (changed
once a week) provide growers an
indication of the number of flies during
onion establishment. Tillage of green
plants, plant residues, and manures
attract thousands of egg-laying female
flies and crop damage is often severe
when crops are planted within the first
Early season onion stand differences
caused by maggot feeding.
Seed corn maggot larvae feeding on
onion seedling.
few weeks of tillage. Cool, wet weather
and delayed plant emergence are other
factors that promote crop damage from
seed corn maggot. First generation
maggots are most problematic as their
feeding kills seedling plants, but later
generation maggots can feed on plants
and bulbs in the summer. Damage from
later generation onion maggot is rarely
economically important in California
except for fields with diseased, decaying
onion bulbs making mid-season and
late season disease control important to
prevent late season maggot problems.
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at article@jcsmarketinginc.com
Hand-harvesting onions to determine
yield differences.
Late season onion maggot feeding on an
onion bulb.
18 Progressive Crop Consultant March/April 2019