Berry interesting take aways from the Nova Scotia Horticultural Congress 2025
The 2025 Nova Scotia Horticultural Congress featured a
review of the best management techniques for Spotted-Wing Drosophila (SWD). Dr.
Cesar Rodriguez-Saona, Professor and extension specialist at Rutgers University,
shared the latest advancements in Integrated Pest Management (IPM) strategies,
focusing on biological control, insecticide application, adjuvants, and
repellents.
SWD, an invasive pest from Asia, was first detected in California in 2008 and has since spread across North America. Unlike common fruit flies, female SWD possess serrated ovipositors, allowing them to lay eggs in fresh, ripening fruit. Their rapid reproductive cycle and broad host range (including strawberries, raspberries, cherries, and blueberries) make them a major threat to fruit growers. Wild plant species in wooded areas can also serve as SWD hosts, increasing their persistence in agricultural landscapes.
Efforts to introduce natural predators against SWD have
seen mixed results. Researchers have explored several parasitoid wasps,
including Pachycrepoideus vindemiae and Trichopria drosophilae, with limited
success. These species have a broad host range but show low parasitism rates
(0-10%). More promising candidates, such as Ganaspis kimorum and Leptopilina
japonica, are being introduced in North America, with release trials in New
Jersey showing potential for SWD suppression. In 2022, 5,000 adult wasps were
released in five sites, followed by 10,000 additional releases in 2023 and
2024. While parasitism rates remain variable, these efforts mark a significant
step in biological control integration.
Chemical control remains an essential tool for managing
SWD, with extensive testing conducted across multiple U.S. states. A 2020
efficacy ranking included results from 10 states and 19 crop combinations,
identifying the most effective insecticides. Dr. Cesar Rodriguez-Saona included
an excellent slide in his presentation, ranking the effectiveness and grouping
the insecticides tested into their IRAC group.
The take away from this for Nova Scotia growers was that all the
products registered for SWD in Canada had a rating of good to excellent. However,
repeated applications pose risks such as insecticide resistance, residue
accumulation, and outbreaks of secondary pests. Dr. Cesar Rodriguez-Saona indicated
that there was a resistance issue with Entrust in California where organic
growers may have overused this product. This will mean that Success will also
be ineffective in the affected area.
Growers were cautioned to maintain a good rotation involving multiple
IRAC groups in order to maintain effectiveness of all currently registered
products. Organic growers in California were looking at including Pyganic in
their spray rotation in order to slow the spread of resistance to Entrust. Pyganic has an efficacy rating of fair when
tested in the US. In Canada, Pyganic is
not registered on SWD despite being registered on highbush blueberry for other
pests. To
maximize efficacy, researchers recommend applying any insecticides at dawn and
dusk when SWD activity is highest.
An emerging approach in SWD control is the use of
adjuvants like Combi-Protec (a product similar to molasses), a feeding
stimulant that enhances insecticide effectiveness. Field trials in highbush and
lowbush blueberries, as well as raspberries in states like Oregon, New Jersey,
Maine, and New York, demonstrated its potential. Cage field trials involving
100 released SWD flies per treatment showed reduced egg-laying and adult survival
when Combi-Protec was mixed with some insecticides (Imidan, Delegate) while
other insecticides did not show a great improvement in control when it was
added (Up-cyde, Malathion).
Beyond killing SWD, researchers are investigating ways to
repel them. Previous studies identified compounds such as 1-Octen-3-ol,
Geosmin, and 2-Pentylfuran as potential repellents. New research has focused on
volatile organic compounds (VOCs) released from diseased fruit. Botrytis
cinerea (grey mold) and Colletotrichum fioriniae (anthracnose fruit rot) were
found to emit odors that naturally repel SWD. Experimental trials using Ethyl
Butyrate, Ethyl Crotonate, and 2-Pentylfuran in controlled environments showed
significant reductions in SWD oviposition. A multiple-choice assay demonstrated
that certain volatiles consistently deterred SWD from laying eggs, marking an
exciting avenue for non-lethal pest management.
Dr. Rodriguez-Saona emphasized that a single control
method is insufficient. Instead, an integrated approach combining cultural,
chemical, behavioral, and biological strategies is essential. Farmers are
encouraged to:
-Monitor SWD populations using effective baits and
attractants before infestations occur.
-Time insecticide applications during peak SWD activity.
-Incorporate adjuvants to enhance control efficacy.
-Remove alternative host plants from surrounding wooded
areas to reduce SWD reservoirs and prune to increase spray penetration and
reduce favorable (humid, calm air) environment within the field.
-Dispose of infected fruit approprately so that the crop is not reinfected
I would like to thank Dr. Cesar Rodriguez-Saona for taking
a great deal of time out of his busy schedule to travel to Nova Scotia to
present at the Horticultural Congress. I’m hoping he returned home safely
between the storms.