July 2023 - 22

PLANT & SOIL HEALTH
What's good for
the gooseberry ...
Organic growers have options for Anthracnose leaf spot
BY CHRIS MCGUIRE & LESLIE HOLLAND
A
s the popularity of alternative
healthful and flavorful fruits
has increased, growers are
increasingly raising gooseberries for
local markets.
These berries are used by smallscale
processors in preserves and
baked desserts and the fresh fruit
are popular with some consumers.
Growers can select varieties and
manage harvest timing to suit
different markets. Tart, underripe
berries are well suited for many
processing uses, while riper, sweeter
and highly flavored fruit are best for
fresh eating. In the Upper Midwest,
prices typically range from $6-$8
per-pint for fresh berries sold at retail
and $4-$4.50 per-pound for berries
sold wholesale to processors.
Gooseberries grow quickly and
begin to bear as early as their second
year. Varieties vary widely in yield,
growth habit and susceptibility to
various pests. With little published
information available, growers must
often identify the best varieties for
their farm through trial and error.
In the upper Midwest, many
growers have struggled to control
Anthracnose leaf spot. This
troublesome fungal disease infects
leaves beginning in late spring,
causing dark purple spots on
the leaves, followed by massive
defoliation as early as late June.
Over several years, defoliation
presumably reduces plant health and
22 | JULY 2023
yield. Without access to synthetic
fungicides, organic growers can be
particularly hard-pressed to manage
Anthracnose leaf spot.
Research at Two Onion
Farm
Organic fruit growers Chris
and Julie McGuire of Two Onion
Farm, Belmont, Wisconsin, were
determined to find a better way
to control Anthracnose leaf spot.
With advice and help from Leslie
Holland, fruit crop pathologist
at the University of WisconsinMadison,
and with funding from
a USDA-Sustainable Agriculture
Research and Education (SARE)
grant, the McGuires have trialed
different organic methods for
controlling Anthracnose over two
growing seasons.
The McGuires grew four
gooseberry varieties to look for
differences in susceptibility to
Anthracnose. They also compared
untrellised bush plants to tall
narrow plants grown with the
cordon trellis system, thinking that
the trellised plants might suffer
less disease because their sparse,
narrow canopies would dry more
quickly after dew and rain.
They used three organic sprays:
Cueva (copper soap) tank-mixed
with Double Nickel 55 (bacillus
amyloliquefaciens strain D747),
Carb-O-Nator (potassium
bicarbonate), and Regalia (extract
of reynoutria sachalinensis), all
compared to an unsprayed control
treatment. Overall, it was a complex
experiment, with 32 combinations of
variety, trellising method and spray
treatments, each replicated six
times in a quarter-acre field.
Are trellises justified?
Measurements of disease severity
and defoliation showed clear patterns.
" During the statistical analysis,
it was gratifying to see such
clear results emerge and remain
consistent over two growing
seasons, " Holland said.
Of the varieties trialed, Hinnomaki
Red was most resistant to
Anthracnose, and Tixia was most
susceptible. But Chris McGuire
notes that growers will need to
consider other factors besides
disease resistance.
" In our experience, Hinnomaki
Red is a very small, compact and
difficult-to-harvest plant with
modest yield, " he said. " Captivator,
by contrast, is more susceptible to
Anthracnose, but yields abundantly
on large, easy-to-pick plants.
There are also differences between
varieties in flavor and processing
characteristics. "
In the trial, trellising reduced
disease by a small but significant
amount. Chris McGuire points out
that although trellising reduces
disease, it may not be justified
because of its high cost.
July 2023

Table of Contents for the Digital Edition of July 2023
