
3.Volume 9, Issue 1 March
23, 2001
The
Weekly Schedule Begins – April 6, 2001
Issue 1 of
Weekly Crop Update is a sample of the type of information you will receive each
week with a subscription or access via the Internet. This newsletter is designed to provide subscribers with the
latest information on disease and insect problems as they are developing, weed
control information, crop progress reports, and other timely topics related to
agronomic and vegetable crop production in Delaware. University of Delaware Extension Specialists and Agents provide
information for the newsletter. The
weekly issues will begin on April 6, 2001 and continue through the month of
September. The Weekly Crop Update can
be obtained by mail, fax or from the Internet at http://www.rec.udel.edu/TopLevel/Publicat.htm
. If you would like to receive Update
by mail or fax, the cost of subscription will remain at $30 (same as last
year). Use the enclosed form to
subscribe. If you can access the
Internet, there is no charge for the newsletter. Weekly Crop Update is mailed
each Friday. If you choose to receive
the newsletter by fax, it will be sent to subscribers on Friday evening. The newsletter is placed on the Internet by
4:30 p.m. on Fridays. We also offer to
send an e-mail reminder to those of you who wish to receive one each week. Please forward your e-mail address on the
enclosed form or at my e-mail address below.
I would like to ask those of you who plan to access the newsletter from
the Internet to notify me of any problems you may encounter during the season. Please forward any comments or concerns to
me at
302-856-7303 or at
wootten@udel.edu .
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Vegetables
Vegetable Insects - Joanne Whalen, Extension IPM
Specialist; jwhalen@udel.edu
Peaches.
EPA has granted our Section 18 for the use of Provado on stone fruit to control
aphids that vector the Plum Pox Virus. This emergency exemption (Section 18) is
effective from April 1 through Oct 15, 2001. Growers may use a maximum of 4
applications at a rate of 5-6 ounces of product per acre. No more than 24
ounces of product may be applied per acre per year. There is a zero day
pre-harvest interval.
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Weed
Control in Greenhouses – Jay Windsor, County Agricultural Agent; windsor@udel.edu
There are no residual
herbicides labeled for greenhouses at the present time. Surflan was labeled,
but is no longer registered for use in enclosed greenhouses. Roundup and or
manual removal prior to setting plants or seed in the greenhouse is
recommended.
The use of weed mats
has proven to be worth the cost of installation and will provide almost total
weed control for many years. The fabric can be used alone or covered with
gravel to provide additional drainage. Remember that transplants will root into
the gravel or even into the weed mats. Providing some sort of benching,
pallets, or framing to allow for air pruning of the roots will help with this
problem.
You have a few choices
of herbicides that can be used in the greenhouse to pick up escapes and spot
spraying even with the crop growing in
the house. Remember that when spraying
any of these herbicides, you should always turn exhaust and horizontal air flow
fans off while spraying. Leave them off for at least a half hour after spraying
to prevent any movement of spray droplets to the crop.
There are three
materials labeled for use in the greenhouse with a crop present;
1)
Reward which is a contact material and may not control perennials effectively
2)
Scythe is another contact herbicide
3)
Finale is a systemic material similar to Roundup that should be more effective
than the contact materials on some harder to control weed species.
Note:
Roundup is not labeled for use in the greenhouse when the crop is present.
Controlling any weed growth around the outside
of the greenhouse is recommended to remove cover for rodents, and host plants
for insects and diseases. You can use residual materials such as Surflan or
Princep in combination with Roundup near the base of the greenhouse. Remember again to turn off the fans if
you have a crop in the house so the spray is not drawn into the greenhouse
through the louvers. Do not use long
residual materials such as Pramitol or volatile herbicides like 2,4-D or Banvel
anywhere near a greenhouse.
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Vegetable Diseases - Bob Mulrooney, Extension Plant Pathologist, bobmul@udel.edu
Fungicide Update for Vegetables.
The following are some
recently or newly registered fungicides for 2001. Specific use information will
be found in the 2001 Commercial Vegetable
Production Recommendations E.B. 137.
Quadris 2.01F from
Syngenta in addition to tomatoes, potatoes, and cucurbits (cucumbers,
muskmelons, pumpkins & winter squash, summer squash and watermelons) it is
now labeled on spinach to control
white rust and leaf spots, sweet corn
for leaf blights, and carrots for
leaf blights. These changes did not make the new Recs book.
Nova 40WP from Rohm
&Haas is now labeled for rust control in asparagus.
Previcur
(propamocarb HCl) from Aventis has been labeled for late blight control in
white potatoes combined with another protectant such as mancozeb or
chlorothalonil.
Root
Knot Nematodes.
Remember that spring sampling for root knot is
not very predictive (not very accurate) of what the overwintering population
might be. Population levels tend to be lower and thus more easily missed when
random samples are taken. In winter, a higher proportion of the population is
in the egg form which may not show up in the lab technique that is used to
extract the nemtodes from the soil. Zero counts and low counts are hard to
interpret at this time of the year. High counts at this time of year indicate
high levels in the field and are reliably used for decision making. Fall
sampling is best for root knot.
Winter Temperature Index for Predicting
Stewart’s Wilt in Sweet Corn 1994-2001.
Corn flea beetles are the overwintering host and
vector of Erwinia stewartii, the
bacterium that causes Stewart’s wilt.
Winter survival of the flea beetles can be predicted using a winter
temperature index which is calculated by adding the average temperature for
Dec., Jan., and Feb. Flea beetles do not survive well when the average
temperature is below 27oF for any month. If the temperature is above
33oF, flea beetles may be present in early plantings of sweet corn.
The occurrence of Stewart’s wilt on early-planted sweet corn usually
corresponds with the ability of flea beetles to overwinter. The following table
shows that overwintering is very likely again in Delaware and the prediction
would be for a severe Stewart’s wilt season.
Fortunately for Delaware growers, resistant varieties of sweet corn have been available for most processing sweet corn. A dependable level of resistance in fresh market sweet corn has been more elusive. Despite years of favorable flea beetle overwintering, we continue to have few losses from Stewart’s wilt. Why? Growers have planted resistant varieties and have effectively used the insecticides that have been available. Growers need to continue to plant the most resistant varieties available and scout sweet corn for flea beetles and treating with insecticides when thresholds are exceeded. The use of seed treatments to control flea beetles is another avenue that is being carefully examined and research is currently underway to see if it will be of value to Delaware growers.
Winter Temperature Index For Predicting
Stewart’s Wilt in Delaware Sweet Corn, 1993-2001
Average monthly temperatures in oF
at Georgetown, DE REC. 1994-2001.
2000-01 1999-00 1998-99
1997-98 1996-97 1995-96
1994-95
December 31.2 40.3 41.3 39.3
42.0 33.5 43.0
January 33.8 33.9 39.5
42.6 35.0 33.5
39.0
February 38.8 39.7 38.7 40.6
41.5 34.7 33.8
INDEX 103.8 113.9
119.5 122.5 118.5 101.7 115.8
Average monthly temperatures in oF
at Newark, DE Experiment Sta.
1994-2001.
2000-01 1999-00 1998-99
1997-98 1996-97 1995-96
1994-95
December 31.1 39.1 41.0 38.4 40.9
32.1 41.8
January 31.5 32.6
34.8 40.9
33.2 30.9 37.6
February 38.4 37.8
38.0 40.6
40.3 34.7 31.7
INDEX 101.0
109.5 113.8
119.9 114.2 97.7 111.1
Severity Index:
< 90, usually absent; 90-100, intermediate; >100, usually severe.
________________________________________________________________________
Prediction for 2001 Newark:
Severe; Georgetown: Severe
Note: These are lowest values since the 1995-96 growing season.
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Section 18 Requests for
Vegetable Herbicides for 2001 – Ed Kee,
Extension Vegetable Crops Specialist; kee@udel.edu
Applications for Section 18 Emergency Exemptions
have been made for the herbicides listed below with the EPA, in cooperation
with our Delaware Department of Agriculture.
We will notify you of their status as soon as we receive the decision on
each of these materials:
|
Herbicide |
Crop
|
Submitted
|
Approved
|
Dates Effective
|
|
Dual
Magnum |
Spinach |
4 |
4 |
9/00
– 5/1/01 |
|
Sprout-Nip |
Spinach |
4 |
4 |
3/1/01-12/31/01 |
|
Command |
Watermelon |
4 |
|
|
|
Sinbar |
Watermelon |
4 |
|
|
|
Reflex |
Snap
Beans |
4 |
|
|
Please check with your Extension Office,
Ag-Chemical Dealer, and/or the label for details on all these materials before
using.
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The
Delaware Department of Agriculture grants licenses to Dealers of Agricultural
Products. The Dealers include Delaware brokers, as well as, out-of-state
brokers licensed as dealers of agricultural products in the State of
Delaware. The Department of Agriculture makes no warranty concerning the use
of this list. For more information,
contact Cliff Hudson, DDA, 302-739-4811.
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