March 2023 - 10

GLVPN VEG CONNECTION
A
B
Figure 1: At the MSU Entomology Research Farm, six plastic mulches were tested. A) The plastic mulches were
cut into rectangles and secured to the ground. B) Three potted onions were placed on top of the mulch and were
monitored for onion thrips populations weekly for six weeks. Photos: Michigan State University
Onion thrips management with plastic mulches
BY NATALIE CONSTANCIO AND
ZSOFIA SZENDREI
DEPARTMENT OF ENTOMOLOGY,
MICHIGAN STATE UNIVERSITY
P
lastic mulches are used
in agriculture fields for a
variety of reasons, including
increased weed control and soil
moisture retention when compared
to bare soil. However, selecting the
correct color of mulch is important.
For example, in cooler climates, a
standard black plastic mulch can
help raise the soil temperature in
the spring, prolonging the growing
season and increasing plant growth.
In a warmer climate, white plastic
mulches will retain soil moisture but
will not raise the soil temperature as
much as black plastic mulch.
In addition to benefiting plant
growth directly, plastic mulches
can also be used for insect pest
management.
When using plastic mulches for
insect pest management, their
efficacy is often dependent on the
interaction between the color of the
mulch and the insect. In tomatoes,
red mulches (compared to bare soil),
increase the presence of whiteflies
while reducing thrips and aphids.
Also in tomatoes, black plastic and
10 | MARCH 2023
white plastic mulches increase
attractiveness to thrips.
In pepper production, reflective
plastic mulches reduce western
flower thrips populations by 60%.
In zucchini, aphid populations were
lowest on reflective mulches. For
cucumbers, there were significantly
more striped cucumber beetles on
black plastic mulches compared
to reflective mulches. Despite the
variable outcomes of using plastic
mulches for insect management,
across most cropping systems,
reflective plastic mulches tend to
reduce insect populations.
For onion thrips management,
reflective silver and red plastic
mulches have been reported more
effective in reducing their numbers.
Interestingly, white plastic mulches
and black plastic mulches have
been reported to increase thrips
populations compared to bare ground.
However, none of these mulches
have been tested in onion cropping
systems, where onion thrips are the
main insect pest. This led us to ask
two questions:
1. Can plastic mulches be used to
reduce onion thrips populations?
2. Do different types of reflective
mulches produce different
results?
We set up a field trial at Michigan
State University's Entomology Farm
to test the effectiveness of six plastic
mulches: black, white and red
(made by Ken-Bar), and three
reflective mulches:
1. The black plastic (1.0 mil)
was marketed to increase
soil temperatures, retain soil
moisture, and suppress
weed growth.
2. The white mulch (1.25 mil)
claimed to reduce soil
temperature while increasing the
amount of light reflected onto the
plant leaves.
3. The red mulch (1.0 mil) was
designed specifically for tomato
production to increase yield.
4. The metallic reflective mulch
(1.25 mil, Ken-Bar) was
marketed to reduce disease
spread, which onion thrips are
often associated with.
5. The silver plastic mulch
(thickness not specified, from
Dubois Agrinovation) was
designed to eliminate weeds and
keep plant roots cool.
6. The last reflective mulch tested
was a " diamond " mulch (6 mil,
from Viagrow), which was gray
and had a dimpled texture to
increase light reflection.

March 2023

Table of Contents for the Digital Edition of March 2023