March 2021 - 24

ONIONS
Thrips, white campion, stemphylium leaf blight eyed
By Dean Peterson
VGN Correspondent
Onion thrips are a major pest in
onions and can vector some plant
diseases, but organic onions raise an
interesting question. Do organic and
conventional onion fields differ in
the percentage of plants with foliar
disease?
Research taking place at Michigan
State University (MSU) indicates
that, yes, there is a difference and
organic fields have fewer onion
plants with disease symptoms than
conventional fields.
That's a message from Natalie
Constancio, MSU graduate student.
Constancio's research on onion
thrips with Zsofia Szendrei, associate
professor in MSU's entomology
department, was displayed at the
recent Great Lakes Fruit, Vegetable and
Farm Market EXPO, which was held
virtually.
The EXPO session was one of several
focused on sharing results of MSU
onion research projects.
In visits to onion fields around
Michigan, researchers observed about
80% of the plants in conventional fields
had foliar disease symptoms, whereas
Thrips damage on onion. Photo: University of Massachusetts Amherst
only 30% of the plants in organic fields
showed symptoms. The numbers of
onion thrips per plant was similar
between organic and conventional fields.
" We're not sure why we found fewer
symptomatic plants in organic fields
compared to conventional fields, "
Constancio said. Trying to find an
answer to that question is one of the
future goals of the research.
Researchers also evaluated organic
pesticides on how well they control
thrips. Neem oil plus surfactant, Entrust
plus surfactant, neem oil plus Kocide,
Entrust plus Kocide and Kocide alone
were compared to a control.
In preliminary comparisons, all of
the organic pesticides managed onion
thrips slightly better than the control
and performed similarly to each other.
The research is continuing. Other
goals are to do more testing of organic
pesticides and explore other organic
options for managing thrips and foliar
disease in onions.
White campion control
White campion is becoming a
problem weed in onions, but new
research at MSU may provide more
answers on its control.
White campion can grow as a winter
or summer annual, biennial or shortlived
perennial. It reproduces primarily
by seed. Seedlings emerge in mid to
late spring and again in late summer.
Research in its first year at MSU is
focusing on germination studies and
preemergence and postemergence
herbicide evaluations. That's from
Sushila Chaudhari, assistant professor
in MSU's Department of Horticulture.
Chaudhari spoke on onion weed
control at the Great Lakes EXPO.
Seed germination is being studied
for ideas on improving control.
Preliminary results show germination
rates do change. About one-fourth of
the weed seeds planted immediately
after being harvested germinated.
About two-thirds of the seeds
planted one month after harvesting
germinated. The seed for the study was
collected from an onion field.
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March 2021

Table of Contents for the Digital Edition of March 2021
