A32-Lancaster Fanning, Saturday, March 16,1996
Potato Growers
(Continued from Pago A 1)
and germinates well,” said Kirk.
The amount of lesions per leaf are
high.
In 1995, outbreaks of late blight
were controlled, despite humid
weather in Michigan, according to
Kirk. One reason is that even
though rains came, they were
short-lived and evaporated quick
ly, and the pathogen couldn’t get
started on the plants. ‘‘There was
no duration of leaf wetness, lucky
for us,” noted Kirk.
Michigan growers took heed
and listened to the reports prepared
by the university. Most used vari
ous tools, including Blitecast, to
plan their fungicide programs.
Spraying began before the appear
ance of the fungus on the actual
plant.
Fungicide programs that spread
material uniformly and get the
underside of the leaf are effective.
The fungus attacks the leaves of
the potato, creating a brown lesion.
Tomatoes and hairy nightshade
plants are also at risk. Gradually,
the disease moves to the tubers,
eventually causing them simply to
rot and die.
The pathogen can overwinter in
Dr. Willie Kirk spoke about the challenges Michigan
growers faced In the past two years with late blight
outbreaks.
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the tuber. Kirk showed evidence
that even in cull piles at freezing
temperatures, deep in the piles the
fungus survives. “Culled piles are
dangerous,” said Kirk.
Researchers know the fungus
can survive freezing temperatures,
but for how long? The temperature
range at which the fungus survives
is wide, from below freezing to
temperatures at 85 degrees. “The
temperature range is absolutely
frightening,” said Kirk. More
work is needed on the temperature
‘Survivability of the pathogen,
according to the researcher.
Kirk offered tips to ensure con
trol of the disease. Growers should
select cultivars that are resistant to
blight The seedstock used should
be pathogen-free. Crop rotation
helps, but it is important the grow
er inspects the stands regularly,
after planting, and use forecasting
tools such as Blitecast and
Envirocaster.
According to the researcher,
timing and correct application of
fungicides is critical. Kirk
reviewed the Michigan spray prog
ram and the effectiveness of vari
ous fungicide applications. In the
trials, fungicide was applied at a
@
water nte of SO gal lona per acre at
100 psi in a seven-day preventive
program.
* ‘We have a saying in Scottland,
‘lf it*s raining, it’s a blight per
iod.’” said Kiik.
Equipment and storage areas
must be sanidzed. Also, domestic
gardens that neighbor a potato
field can harbor the pathogen.
“We can’t wait before bringing
in the artillery,” said Kirk. We
must work to remove the stigma
associated with having a late blight
problem in the field, because if a
grower has it. neighbors need to
know. ‘ ‘Nothing is more important
than knowing a neighbor has late
blight,” he said.
Air Assist
. Potato growers can “provide
good fungicide coverage even with
lower volume applications if you
use the right size droplet and right
techniques" said Dr. Richard Der
ksen, Cornell assistant professor of
engineering and pest management,
to those at the institute.
Any sprayer can put fungicide
on the top of the leaves. But by
switching to a flat-fan sprayer and
using air assist technnology,
canopy coverage can extend to the
bottom of the leaves while using
less water volume.
The water droplet size is
decreased and more uniform
spread of active ingredient occurs.
Even better application of fungi
cide is achieved with the use of
electrostatic sprayers, which elec
trically “charge” the water dro
plets, which fasten readily to the
plant surface.
While there is no “silver bul
let” of application technology,
growers have a choice and that
choice can determine how to
improve pest management
The key to improved fungicide
application may be the use of the
air-assist spraying techology.
which provides a “superior”
means of obtaining good applica
tion results over conventional,
hollow-cone, drop sprayers.
Derksen reviewed the results of
various treatments that compared
various nozzle types and spray
methods to control Colorado pota
to beetle. The results indicated that
as long as some material made it to
the leaf, control of the beetle was
Potato growers can “provide good fungicide coverage
even with lower volume applications If you use the right size
droplet and right techniques” said Dr. Richard Derfcsen,
Cornell assistant professor of engineering and pest man
agement, to those at the Institute.
sufficient and wasn’t different
from differing spray technologies.
With control of fungus, the elec
trostatic sprayers provided more
droplets per square inch and were
more efficient, “even using 1/7 the
spray volume of conventional
sprayer,” according to Derksen.
Results of the trials provide “no
easy answers,” said the pesticide
engineer.
In 1995, these trials looked at a
combination of nozzle and spray
ing technologies. The results
showed that applicators can reduce
the amount of water used to get the
same coverage more efficiently by
using flat fans, which provided
“more uniform coverage and
higher coverage • than flood”
techniques.
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One study compared the elec
trostatic spraying system (ESS)
with drop spraying. The ESS trial
covered one acre at 4.S gallons per
acre at 30 psi in 8-inch spacing.
The drop spraying was done at 20
gallons per acre at 60 psi at 43-inch
spacing. Results point to a 16 per
cent coverage efficiency using
ESS over 7 percent with the drop
sprayer. Using air assist, coverage
improves to 36 percent, according
to Derksen.
A Wisconsin grower found that,
in early blight management, best
coverage came with an air-assist
rig applying water at 21.3 gallons
per acre.
Overall, the frequency and tim
ing of application is most impor
tant to control insects and fungus.
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