March 2022 - 20

Cranberry weed impact studied by researchers
By Lorry Erickson
FGN Correspondent
Precision weed management offers
cranberry growers the potential to
increase yields and reduce input costs
by using decision-making tools to
decide when herbicide applications are
warranted, said Jed Colquhoun, professor
and integrated pest management director
in the Department of Horticulture at the
University of Wisconsin-Madison.
Speaking at the 2022 Wisconsin
State Cranberry Growers Association
annual winter meeting, Colquhoun
shared research from studies he and his
colleagues in Massachusetts and New
Jersey are conducting to develop weed
thresholds for some of the major weed
species impacting cranberry yields.
Colquhoun and his collaborators are
creating a methodology to document
weed impacts on both cranberry yield
and quality. The long-term goal is to
establish what he called a " weed impact
library " with specific weed thresholds
that growers can use in making weed
management decisions.
" Some weeds simply may be
aesthetically unpleasant but may have
very little impact on berry yield or quality.
Other weeds may have adverse impacts
beyond yield, such serving as host plants
for insect pests that affect berry quality.
Cranberry operation worker Brian Allen spot spraying weeds. Photos: Lorry Erickson
With that in mind a decision support
system can help us prioritize which weeds
we go after on a marsh, " Colquhoun said.
In most crops, it is rare for a single
weed species to dominate a cropping
system. Cranberries are an exception
however, oftentimes having only a few
weed species growing in cranberry beds.
" I would say in the two dozen or so
horticultural crops that I work in that
cranberries have the situation most
commonly where there are patches of
single weed species versus the crop, "
Colquhoun said.
One example is bristly dewberry, a
low-growing perennial shrub commonly
found on Wisconsin cranberry marshes.
If present dewberry tends to form dense
colonies in the corners of cranberry beds.
Data collected over the past two
seasons showed that 20% dewberry
groundcover caused a loss in cranberry
yields of 4,143 pounds (41.43 barrels) per
acre. The shading of vines by dewberry
also resulted in an 18% loss in fruit color.
Besides dewberry, the weeds that
Colquhoun and his counterparts in
Massachusetts and New Jersey are
focused on at present include slenderleaved
goldenrod, seedling maple trees,
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March 2022

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