PCC MarchApril Final Draft

decreased the number of larvae in fruit by 72%, the
metallic mulch by 61%, and the white mulch by 52%
compared to the control.
Plastic mulches may be more effective than other
types of mulches tested for managing SWD. In our
study, we recorded the lowest adult fly populations
and larval infestation of fruit above the black plastic
mulch. A 2019 study tested black fabric weedmat as
a cultural control for SWD in blueberry in several
states and found no effect of the weedmat on SWD
infestation of blueberries 32 . It is possible that some
quality of the plastic mulch material (such as reflectivity
or lack of permeability) makes it more deterrent
to SWD than the weedmat.
In our preliminary experiment, larvae placed on the
plastic mulches died quickly. Larvae on the black
mulch died in less than one hour, and larvae on the
white and metallic mulches died in less than three
hours. We recorded high surface temperatures on
the mulches, with all mulches heating up above 87
degrees F (SWD’s threshold for development) for two
to four hours each day. On hot days, the black mulch
got above 150 degrees F.
When placed on the mulch, we observed larvae
struggling to crawl and visibly desiccating within
minutes, making it unlikely that larvae could crawl
off the mulch into the safety of the soil. We will
collect more data in summer 2021 to confirm these
promising results.
The results of our study provide evidence that black,
white and metallic plastic mulches can reduce SWD
adult and larval populations in fall-bearing raspberry
in the Upper Midwest, showing promise for
use of plastic mulches in sustainable pest management.
Combining plastic mulches with other cultural
practices including short harvest intervals (every
one to two days) and frequent field sanitation could
have an additive effect on reducing SWD populations,
potentially reducing the need for chemical
controls in conventional and organic cropping
systems.
Next Steps
Although the use of plastic mulches reduces SWD
populations in the canopy of raspberry plants, the
specific mechanisms causing this reduction are still
unknown. We are still investigating how canopy
light conditions, temperature and humidity are
influenced by the plastic mulches and whether
these factors can explain the reduction in SWD
populations we measured.
Continued on Page 22
‘Corrals’ made from plastic sandwich containers used to test mortality
of larvae on the mulch surface (photo by H. McIntosh.)
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March / April 2021 www.progressivecrop.com 21