VegNet Vol. 14,
No. 18.
July 2, 2007
Ohio State University Extension Vegetable Crops
On the WEB at: http://vegnet.osu.edu
In This Issue
1. Survey of Stewart’s wilt on sweet corn in Illinois in 2007
2. Crop Reports
Survey
of Stewart’s wilt on sweet corn in Illinois in 2007 by Jerald Pataky, Univ. of Illinois
Each year since 1999 the University
of Illinois sweet corn pathology program in cooperation with UI
Variety Testing Program has assessed the incidence of plants infected with
Stewart’s wilt for sweet corn hybrids with different levels of resistance or
susceptibility. Trials are planted at
nine locations (Table 1) in the southern two-thirds of Illinois. Incidence (%) of infected
plants is measured from three replicate plots of about 150 plants of each
hybrid (about 450 plants per hybrid per location). The 2007 survey was completed June 4. The results illustrate the effects of winter
temperature and host resistance on the occurrence of Stewart’s wilt (Table 1).
At the three northernmost locations,
Dwight, Monmouth and Goodfield, incidence of
Stewart’s wilt was 1% or less for hybrids that have resistant (Bonus, Ambrosia,
and XT 182A) or moderate reactions (Shimmer, Bodacious, XT 273A, Honey Select,
and Double Gem), and 2% or less for moderately susceptible to susceptible
hybrids (Snow White, Coho, Jubilee, and Supersweet
Jubilee). At these locations, the
average temperature for December, January and February was less than 26 F which
probably resulted in relatively small overwintering
populations of the corn flea beetle, the insect that vectors the Stewart’s wilt
bacterium, Pantoea stewartii.
At three central Illinois locations where the average winter temperature ranged from
28.7 to 29.9 F, Stewart’s wilt incidence was below 2% for resistant hybrids
except at New Berlin where 2.7% and 3.7% of Bonus and Ambrosia plants were
infected, respectively. For hybrids with
moderate Stewart’s wilt reactions, incidence ranged from 0 to 5.7% and was
above 2% in 7 of 15 comparisons. For
hybrids with susceptible reactions, incidence ranged from 0.4 to 19.3% and was
above 2% for 11 of 12 comparisons and above 5% for 6 of 12 comparisons..
At three southern Illinois locations where the average winter temperature was above
freezing, incidence of Stewart’s wilt infected plants was below 2% for
resistant hybrids except for Ambrosia planted at St. Peter. For hybrids with moderate Stewart’s wilt
reactions, incidence ranged from 0.4 to 4.7% and was above 2% for 5 of 15
comparisons. For hybrids with
susceptible reactions, incidence ranged from 1 to 17.2% and was above 2% for 10
of 12 comparisons and above 5% for 8 of 12 comparisons.
Previously, we’ve calculated that
seed treatment insecticides (e.g., Poncho, Cruiser, Gaucho) are economical (the
$ value of control is greater than the cost of the seed treatment) if the
incidence of Stewart’s wilt in the absence of seed treatment control is above 1
to 2% on sweet corn hybrids grown for fresh market and above 5% on hybrids
grown for processing. Using this
guideline, Stewart’s wilt control from seed treatment insecticides usually would
not have been economically beneficial in 2007 for hybrids grown in the three
northern locations or for the resistant hybrids grown in the central or
southern Illinois locations. In central
and southern Illinois, Stewart’s wilt control from seed treatment insecticides
would have been economically beneficial most of the time in 2007 on susceptible
hybrids and more than half of the time on hybrids with moderate Stewart’s wilt
reactions.
Reactions of sweet corn hybrids to
Stewart’s wilt and other prevalent diseases are available at the University
of Illinois sweet corn pathology website (www.sweetcorn.uiuc.edu).
TABLE 1. Survey
of Stewart’s wilt on sweet corn in Illinois in 2007.
Crop
Reports by Ron Becker and Brad Bergefurd
Wayne County Report, From: 6/29/07
Diseases - The downy mildew infestation on the farm where it was
initially found this year by scouts from the Wayne County Integrated Pest
Management program has increased significantly over the past week. Three
other farms in the West Salem area
were also found to have downy mildew on cucumbers. Powdery mildew was
found in a field of cucumbers on June 25th. Anthracnose and angular leaf spot
are also being found in several fields of vine crops. Early blight is
being found in about half of the area tomato fields. Bacterial spot
has been found in pepper varieties that do not have genetic resistance.
Copper has been keeping it under control for the last several weeks.
Bacterial speck is being found in several area tomato fields.
Insects - Flea beetles were heavy in many cole
crop fields this week, especially in brussel
sprouts. Cabbage worms had been controlled in most fields, but eggs were
still present. Colorado potato
beetles increased significantly this week with many potato fields needing to be
treated. Potato leafhoppers and flea beetles also had to be sprayed for
in several fields. European corn borer is being found at threshold
levels in sweet corn that is starting to tassle.
Silking sweet corn is on a 5-7 day schedule for corn
borer control. Potato leafhoppers are being found in green beans with
several fields needing to be sprayed. Cucumber beetles are being found at
threshold levels in several fields. They are also starting to cause
damage to ripening fruit. Thrips are
being found in onion fields at threshold levels
(10-15 thrips per plant). We are also
finding botrytis in several onion fields. Tomatoes and peppers have low
levels of aphids in them. Timber rot is being found both in the
field and in high tunnels. Eggplant has had flea beetle, potato
leafhopper and potato beetle damage at threshold levels.
Southern Ohio VegNet
report for 6/29/07
Bacterial canker has been positively diagnosed
by Nancy Taylor at the OSU Plant and Pest Diagnostic Clinic using a serological
test in fresh market tomato plants from a Bainbridge Ohio field,
about 2 acres in size, which had not been treated with any fungicides.
Bacterial canker is a very serious disease of tomatoes and has caused severe
economic losses and reduced quality in processing tomato over the past 20 years
in Ohio and has been showing up more in
fresh market tomato in recent years with severe crop loss experienced. For more information on bacterial canker of tomato visit http://ohioline.osu.edu/hyg-fact/3000/3120.html
, http://www.oardc.ohio-state.edu/tomato/kabelkaposter.pdf
. Most important, if the disease is diagnosed in your fields control
irrigation to minimize the time foliage is wet and avoid working among wet
plants such as with harvesting, scouting, tieing or
suckering in an attempt to reduce the spread of disease within the field. Also
do not take equipment or harvest containers from an infected field to a non
infected field for this could also spread the disease between fields. Following
a fungicide program will help with this and other bacterial and fungal diseases
in tomato. Visit http://ohioline.osu.edu/b672/pdf/Tomatoes.pdf
for suggested fungicide programs for commercial tomato plantings.
Irrigation continues to be on the mind of growers, like it has the past 10
weeks. Drip, overhead, center pivot and big gun irrigation systems have been
running almost 24/7 last weekend and early this week on vegetable, fruit and
also in corn and soybean fields where available. I have received reports from
some county Agricultural
Educators that some growers have been putting on too much water with drip
irrigation systems which has led to leaf curling and rolling in tomato fields.
If using drip or any irrigation system it is important to monitor irrigation
amounts being applied and not to exceed about an inch of water per week from
rainfall and irrigation combined. For more information on use and monitoring of
irrigation systems visit http://ohioline.osu.edu/aex-fact/0370.html
, http://ohioline.osu.edu/b672/pdf/Irrigation.pdf
or http://agalternatives.aers.psu.edu/crops/Irrigation/DripIrrigation.pdf
.Most growing areas did receive some rainfall the past 4 days, 6/29, 6/28 ,
6/27 and 6/26 from evening showers and thunderstorms with some areas
receiving less that 1/2 inch to some areas receiving over 3 inches for the
period. The cool temperatures associated with these storm fronts have been
welcomed to relieve crop stress due to the recent high heat in the mid to high
90's and continued drought conditions.
Harvest of high tunnel tomatoes is in full swing with very high quality,
yield and market demand. Growers who did not get shade cloth applied to tunnels
are reporting yellow shoulder disorder and sunburn on tomato fruit due to the
high temperatures, in the low 100's, in these non covered tunnels.
Indeterminate tomato varieties being harvested in tunnels have been topped in
preparation for harvest of field tomatoes in the next 10 days to 2 weeks. Some
growers will be replanting their tunnels in 2 to 4 weeks for a fall high tunnel
tomato crop harvest with harvest usually lasting into November and early December
weather dependent. Some growers have reported misshapen fruit due to poor
pollination. It is important to pollinate high tunnel tomato crops to increase
fruit quality and yield. For more information on pollination of greenhouse
tomato visit http://edis.ifas.ufl.edu/pdffiles/CV/CV26600.pdf
. Walking up and down the rows with a simple leaf blower or mist blower
without water in it, directed at the flower clusters to vibrate them and loosen
the pollen is sufficient for pollination. Pollination should be done at least
every other day but daily does not hurt.
Sweet corn harvest is in full swing for Ohio
River growers with some smaller ear size in some plantings due to the
lack of rainfall and drought conditions. Harvest of summer squash, fresh market
cucumbers, fresh market pickles, cabbage, broccoli, snap peas, snap beans,
sweet onions and high tunnel tomatoes continues. Harvest of black raspberries,
blueberries and summer red raspberries is also in full swing. Harvest of
machine harvested processing pickles will begin today (6/29) and tomorrow
(6/30), weather dependant, and will continue through the 4th of July weekend.
Planting of sweet corn, melons, tomatoes, peppers, pumpkins, winter squash,
summer squash, cucumbers, radish, turnips, green beans, snap peas and red beets
continues.
Planting of sweet corn, green beans, cucumbers, pickles, summer squash,
pumpkins, winter squash, radish, turnip, red beets, melons, watermelons, field
tomatoes, bell and hot peppers continues. Bird damage and reduced plant stands
in recently planted pumpkin fields has been reported where the seed has not
germinated for three weeks due to the drought conditions and dry top soil
allowing for the birds to find the seed. Some mouse and rodent damage to seed
in no till pumpkin plantings has been reported.
Hand hoeing and cultivation continues for weed control since many pre emergent
herbicides were not successful since there has been no rainfall this spring to
activate the herbicides.
