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 .

Vegetables

Vegetable Insects - Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Seed Corn Maggot in Vegetables.

We are starting to find seed corn maggot flies laying eggs in recently plowed fields. Cool, wet conditions at planting, the use of manure or plowing under of green cover crops close to planting all favor maggot problems. Depending on spring weather conditions, most early planted vegetables including cole crops, peas, snap beans, melons, spinach and sweet corn are all susceptible to maggot attack. Seed treatments containing diazinon or chloropyrifos provide control of moderate populations. Diazinon 50W, still labeled as a planter box treatment for peas, corn and succulent beans, has provided good maggot control on these crops. It should be used at ½ oz per bushel of seed combined with ½ oz of graphite per bushel of seed to reduce friction between seeds. To reduce the chances of phytotoxicity, seed must also be treated with a fungicide and only treat seed that will be used immediately. A soil insecticide may also be needed if a number of conditions favoring maggots are present at planting. For many spring planted vegetables, with the exception of sweet corn, the use of a broadcast application of diazinon is the only available option. You can still use diazinon as it is currently labeled on all available material in the "pipe-line." However, diazinon is currently under FQPA review and you should be aware that the uses of this product will be changing after this use season. After the initial review, cole crops, melons, lima beans, snap beans, peas and sweet corn uses have been retained on the diazinon label. Only the seed treatment uses on peas, lima beans and snap beans will be retained. These uses will return to the re-registration process were they will look at issues like applicator exposure. Diazinon must also undergo the cumulative risk assessment with other organophosphates. Although all Agricultural uses made it through the initial review, spinach, potato, cucumber, tomato, squash and pepper labels are currently under consideration for cancellation. Since there are no other available treatments for seed corn maggot in spinach, we have informed EPA about the need for diazinon as an at-planting application on spinach. We are currently waiting for their response and will keep you aware of any new developments.

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.

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.

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.

Sweet Corn.

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 27^oF for any month. If the temperature is above 33^oF, 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.

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.

DDA Logo
Licensed and Bonded Dealers in Agricultural Products

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.

License No.	Company/Address	Letter of Credit	Bond Expiration
128-01	L & L Melon Sales Inc.		7/9/01
	P. O. Box 288, 90 U. S. Route 13
	Laurel, Delaware 19956
129-01	Wm. P. Hearne Produce Co., Inc.		12/31/01
	P.O.Box 1975
	Salisbury, Maryland 21802
130-01	Seabrook Brothers & Sons, Inc.		12/31/01
	P.O. Box 5103
	Seabrook, New Jersey 08302

Seed Corn Maggot in Vegetables.

Sweet Corn.

Crop

Submitted

Approved

Dates Effective