FALL TOPICS
As the summer growing season
turns into fall, many growers are
completing harvest of their fall crops
and beginning preparations for win
ter. I know that the growing season
must be coming to a close since I’ve
begun making preparations for the
winter grower meetings.
This month I’ll cover a few topics
related to the season and provide an
update on plum pox.
Blotchy Ripening
In Tomatoes
I have a planting of tomatoes at
the research farm that I am still har
vesting and I have noticed a large
amount of irregular ripening in the
fruit. .
Symptoms include poor color de
velopment on large areas of the fruit
or irregular coloring on smaller
areas. This disorder appeared back
when we had the first wave of cold
weather earlier this month.
Tomatoes are known to ripen
poorly if the temperature falls below
60 degrees. I’m sure many growers
are observing the same conditions in
their late tomatoes. This disorder is
known as blotchy ripening or gray
wall.
As I mentioned, the first symp
toms of this disorder are blotchy,
brownish-gray areas on ripening
fruit. These areas never color proper
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ly and may remain grayish or turn
yellow. The rest of the fruit colors
normally, resulting in an unmarket
able fruit. If you cut an affected fruit
open, there may be some browning
in the vascular tissue just inside the
skin.
What causes this disorder? While
we do not fully understand what
causes gray wall, we do know that
certain conditions seem to increase
its development. High nitrogen, low
potassium, high soil moisture, high
humidity, rapid plant growth, tem
perature fluctuations, low light lev
els, low temperatures, and soil com
paction are all related to the
occurrence of this disorder. In addi
tion, there may be some involvement
of certain bacteria or fungi as well as
tobacco mosaic virus.
Of this list the only factors that we
can control at this point in the sea
son are the levels of nitrogen and po
tassium as well as soil compaction. If
you have a history of problems with
this disorder, be sure to know the nu
tritional status of your plants prior
to the occurrence of cool weather
next fall. You should also assess your
fields for compacted soils and correct
any problem areas you find.
In addition, there seems to be vari
etal differences in the occurrence of
this disorder. When planting your
late tomato crop next season, try to
include a few plants of other variet-
ies to see if there is a different vari
ety that may be better suited for fall
production on your farm.
I have received this question in the
office in the past and thought I
would mention it here.
Basically the answer depends on
your harvest plans. If you are grow
ing pumpkins, you can stop spraying
about one to two weeks before you
plan to harvest. If you will be letting
the fruit lay in the field longer, it
should still be protected from black
rot and the handles still need to be
protected from powdery mildew as
long as they are green. If you do
pick-your-own, be sure to observe
the necessary PHI.
As for other crops, you are still
also mainly interested in protecting
the fruit. If you have done a good job
of spraying up to this point, then you
should, have enough foliage to finish
maturing the crop. What disease are
you most concerned with? If it only
affects foliage then you can probably
stop spraying, especially if you ex
pect to complete harvest within two
weeks. However, diseases that affect
fruit can destroy the remainder of
your crop and you should seriously
consider another fungicide applica
tion if the crop has a reasonable
chance of maturing.
Greg Krawczyk, tree fruit ento
mologist at the Biglerville fruit lab,
notes that the fruit from your or
chards at harvest time represent a
cumulative record of insect and dis
ease activity for the season. This re
cord can provide valuable insight
into how well an integrated pest
management program is working
and what changes in the program
need to be made in the following
year.
A sample of fruit from each or-
“The Sign v
In Engineered
When Should I
Stop Spraying?
Know Your Fruit
Problem Pests
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chard block should be inspected, in
sect and disease damage identified,
and a written record made. The writ
ten record should be referred to next
year when making decisions about
insect and disease control.
Plum Pox Update
As you know, the Pennsylvania
Department of Agriculture (PDA)
has been conducting an extensive
survey of Pennsylvania stone fruit
orchards this season to determine
how far the plum pox virus (PPV)
may have spread. Within the known
infected areas, a door-to-door survey
is being conducted to identify back
yard stone fruit trees that may re
quire testing. In addition, weed spe
cies are being tested in the
quarantine area for the presence of
PPV. Quarantine areas include Lati
more, Huntington, Dickinson, and
South Middletown townships in
Adams County and portions of Me
nallen and Tyrone townships in
Cumberland County.
Sampling of Lancaster county or
chards was completed this summer
and, as of this date, I have heard of
no positive results in our county.
Sampling in the county will probably
be conducted next season and for
several additional seasons until au
thorities are reasonably certain that
the virus has not spread beyond the
known quarantined areas.
So far this year, 38,434 field sam
ples have been processed by the PDA
lab, of which 398 have tested posi
tive. This number has remained the
same since July. The positive sam
ples were detected early on from 39
blocks belonging to nine different
growers in Adams and Cumberland
counties. In addition, about 294
homeowner and fruit tree nursery
samples were processed by the PDA
Virology Laboratory in Harrisburg.
All of these samples were negative.
The Fruit Research and Extension
Center in Biglerville has been sam
pling backyard home orchards and
weed species within the quarantine
area, but so far all are negative.
There have been no new develop
ments in terms of controlling this
disease. The only way to control the
virus at this time is to eliminate the
infected trees by burning and to keep
the aphids that spread the disease
under control by chemical applica
tions.
New information from France in
dicates that aphids (under laboratory
conditions) can spread PPV from in
fected fruit to healthy trees. Growers
and fruit handlers are being urged
not to dispose of imported stone fruit
that could expose infected fruit to
aphids. Burning or burying fruit im
ported from PPV areas (Europe,
Chile) will keep the virus spreading
into new areas.
Early this year, three nectarine
trees tested positive for PPV in Can
ada. This outbreak of PPV in Cana
da did not originate from these three
Fantasia trees that were imported
from Pennsylvania in 1997.
There is evidence that PPV was in
Canada as early as 1992. It is possi
ble that the Fantasia trees may have
been infected in Canada.
The original source of PPV in
Canada is still not known. Current
ly, stone fruit trees with the plum
pox virus have been located in all
major peach and nectarine produc
tion areas of the Niagara peninsula.
In addition, positive trees have been
identified in southwestern Ontario.
There are now more than 300 pos
itive samples involving many grow
ers. To date, a total of 120 acres of
stone fruits have been removed in
Canada.
The Canadian government and
scientists are working hard to contin
ue the surveying and identification
of infected trees in order to de
termine the extent of the disease.
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