PCC MarchApril Final Draft

Continued from Page 19
insect pests including aphids, whiteflies,
Asian citrus psyllid and Mexican bean
beetles 27-30 .
Plastic Mulches for SWD
Based on the extensive body of literature
reporting that plastic mulches can
modify the crop microclimate, control
some insect pests and provide other
horticultural benefits, we tested the impact
of three colors of plastic mulches
on SWD adult and larval populations.
Our study was conducted in 2019 and
2020 on a small fruit and vegetable
farm in South Central Wisconsin in
fall-bearing raspberries.
In this study, we tested black and whiteon-black
biodegradable plastic mulches
(Organix Solutions AG film), metallic
polyethylene mulch (Imaflex SHINE N’
RIPE) and a grower-standard control
where grass filled in the space between
the alleyway and the raspberry plants.
We assessed the three mulches’ impact
on SWD adult and larval populations
in fall-bearing raspberry.
We laid the mulches by hand when the
raspberry canes were just emerging
from the soil in late April. We laid two
mulch strips (25 feet long by 2.3 feet
wide) along each side of the row, leaving
a six-inch gap between the strips
for the canes to grow. The edges of the
mulches were secured with biodegradable
sod stakes. All four treatments
were randomly distributed in each of
four rows of fall-bearing raspberries
(cultivars “Polana” and “Caroline”),
totaling 16 plots.
Starting when the first flies were detected
in June, we measured the adult SWD
populations passively using clear sticky
cards placed in the fruiting zone, which
were replaced weekly to estimate fly
populations by week.
Larval infestation of fruit was
evaluated by counting the number
of larvae using the salt float method
31 . The evaluations were done two
to four times per month starting in
August.
Adult and larval populations were
measured throughout the season
until adult populations reached zero,
usually in mid-October.
We also did a preliminary experiment
to test whether plastic mulches
could kill larvae that fell onto the
mulch surface. We put lab-reared
larvae into ‘corrals’ made from
plastic sandwich containers and
recorded their mortality and movement
over three hours.
Population Reductions
In both years of our study, we found
significantly lower SWD populations
above all three plastic mulches
compared to the control plots. Over
the two-year period, the black and
metallic mulches reduced the adult
population of SWD by 51% and the
white mulch reduced flies by 42%
compared to the control.
Experimental plots of plastic mulches in fall-bearing raspberries in Wisconsin (photo by H.
McIntosh.)
Interestingly, the plastic mulches
only reduced female fly populations
and did not impact the number
of male flies caught on the sticky
cards. With fewer female flies in the
canopy above the plastic mulches,
it was unsurprising that we also
found fewer larvae infesting the
fruit in the mulched plots. Over the
two-year study, the black mulch
20 Progressive Crop Consultant March / April 2021