Volume 7, Issue 6                                                                                                          May 7, 1999


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


Economic levels of diamondback moth larvae can be found feeding in the hearts of cabbage plants. A treatment should be applied if 5% of the plants are infested and larvae are found feeding in the heart of the plants. If larvae are only found on the outer leaves, a treatment is needed when 20% of the plants are infested. Spintor or a Bt insecticide should be used. Be sure to rotate between a Bt and Spintor to avoid the development of resistance to either class of chemistry.


As melon plants are transplanted in the field, be sure to check for melon aphid populations that may have started in the greenhouse. A treatment should be applied if 10 to 20 percent of the plants are infested and you see leaf curling. Lannate should provide control.


Although pea aphid populations have not exploded, we continue to see an increase in activity. Once fields reach the bud stage, fields should be scouted one to two times per week for aphids. The treatment thresholds are 5-10 per plant or 50 per sweep. Dimethoate, Lannate or Penncap will provide control.


The first Colorado potato beetle adults have been detected; however, populations remain light. No adult treatments will be needed unless you find 25 beetles per 50 plants and 20% leaf defoliation. Flea beetles can also been found in fields where no soil insecticide was used at planting. Economic thresholds have not been established for this insect on potatoes. However, as a general rule, no controls should be needed until you find 1- 2 beetles per sweep. European corn borer activity remains below 1 moth per night throughout the state. Once moth counts reach 10 per night, fields should be scouted for infested terminals and treatments applied when 25% of the terminals are infested. If you are unable to scout for infested terminals, the first corn borer spray should be applied 7 to 10 days after trap catches reach 10 moths per night in your area. v

Vegetable Planting Progress & Melon Planting Intentions - Ed Kee, Extension Vegetable Crops Specialist, kee@udel.edu

Despite a relatively cool spring, planting has proceeded fairly well. Peas are 98% planted. Potatoes are essentially complete. Sweet Corn plantings have gone in the ground well, but cool nights have slowed the schedule for processing sweet corn plantings. Pickle plantings began on Wednesday, May 5.

Transplanting of melons, cantaloupes, tomatoes, and other crops have begun. Seed corn maggot damage on melons has been reported already. An "unofficial, eyeball estimate" indicates that more plastic for melons, especially seedless watermelons, is out than ever before. This is generally confirmed by plastic suppliers and applicators. Whether the market will absorb this acreage at harvest remains to be seen and will be dependent on the crop in the south and other regions, weather conditions, quality, and other factors. No doubt the success in recent years with seedless watermelons, coupled with low grain prices has stimulated growers to plant this acreage. Seedless acreage was estimated in March by the Ag Statistics Service to be 900 acres in Delaware out of a total of 2200; 800 acres out of a total of 2400 on the Maryland Eastern Shore. When planting is complete, however, it seems possible that over 50% of the acreage could be devoted to seedless. Remember that one-third of the seedless acreage has to devoted to a seeded, pollinator variety. v

Vegetable Diseases - Kate Everts, Extension Vegetable Pathologist, University of Delaware and University of Maryland; everts@udel.edu

MELCAST Program for Watermelon.

We have three field seasons of experience with the MELCAST program in trials at the University of Delaware REC near Georgetown and University of Maryland LESREC in Salisbury, and on two growers’ farms near Laurel, DE. This model was developed at Purdue University. It uses weather data to schedule protectant fungicide applications for anthracnose and gummy stem blight of watermelon, so that instead of spraying on a 7-day schedule, fungicides are applied according to the weather. This year we have set up a network of eight weather stations on Delmarva (located in Sussex, Dorchester and Wicomico counties) to collect data for MELCAST. We will publish EFI information in the Weekly Crop Update and on the University of Delaware IPM web page (http://www.udel.edu/IPM/). It will also be available by fax, twice weekly. If you would like to receive the EFI information by fax, please call UD REC at 302-856-7303 and give your name, address, phone and fax number to Mrs. Edna Marvil. In Maryland, call UM LESREC at (410) 742-8788 and give this information to Mrs. Vanessa Fitzmaurice.

When to Spray with MELCAST.

Do not use MELCAST if there is a disease outbreak in your field, it is a preventative program. The first fungicide spray should be applied when the vines begin to run. Once you have applied the first spray, begin to accumulate EFI (Environmental Favorability Index) values. The EFI are based on temperature and moisture readings and reflect how favorable it is for disease development. Daily EFI will vary from one to ten. In addition to weather based EFI, add two EFI if you apply overhead irrigation to the crop. The accumulated EFI units are the "spray counter". When the spray counter reaches 30, apply a fungicide spray. This is the threshold we have used in our trials on Delmarva. Begin accumulating the EFI values until you reach 30 again.

Snap and Lima beans.

Damage by Pythium root rot can be reduced with an application of Ridomil Gold 4E in a 7-inch band over the row at seeding. In fields where Pythium and Rhizoctonia are a problem apply Ridomil Gold PC in the furrow at planting.


As early transplants of muskmelon, squash or watermelon go to the field, they are at risk of developing scab. This fungal disease is favored by cool wet weather. To control, apply a chlorothalonil product (Bravo or Terranil) every 5 to 7 days.

Vegetable Diseases - Bob Mulrooney, Extension Plant Patholgist ; bobmul@udel.edu


If white rust appears, apply a copper fungicide at the lowest rate labeled for control. For fields closer to harvest, apply Aliette to avoid potential phytotoxicity with the copper fungicides. Quadris is not labeled for spinach at the present time.


To prevent bacterial diseases such as bacterial spot, speck and canker, apply streptomycin to transplants in the greenhouse every 5 days. After transplanting to the field, apply a copper fungicide plus mancozeb as a foliar spray and repeat every 7 days for one or two additional sprays. v

Field Crops

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


Alfalfa weevil populations are light to moderate and in many cases cutting will be the best control option at this time. Once alfalfa reaches 18-inches in height, the treatment threshold is 2 to 2.5 larvae per stem. If a field is in full bud, it is approaching threshold and you plan to cut in the next 3 to 5 days, cutting will be the best control options. If you are unable to cut for the next 7 – 10 days and economic levels are present, Baythroid, Warrior or Imidan will be your best control options. All 3 products have a 7-day wait until harvest for use as hay.

Field Corn.

As soon as corn emerges from the ground, be sure to check fields for black cutworm activity. The first leaf feeding has been observed in corn in Sussex county. Early feeding signs will appear as pinholes in the leaves, often before plant cutting is observed. A treatment is recommended if 10% of the plants exhibit leaf feeding or 3% of the plants are cut in 1-2 leaf stage corn. A pyrethroid will provide effective control.

Small Grains.

Although there are occasional wheat fields with increased levels of aphids and cereal leaf beetle larvae can be found, insect activity remains low in most fields. In addition, cumulative catches of true armyworm during the month of April have been low throughout the state. Reports from Virginia indicate new cereal leaf beetle egg laying activity so be sure to continue to watch for beetle activity. There have been no reports of true armyworm or grass sawfly larvae. As temperatures increase, we should begin to see the first small larvae in the next week. No treatment will be needed for armyworm until you find 1-2 larvae per foot of row or grass sawfly unless you find 2 or more larvae per 5 foot of row innerspace.


As you make plans to plant full season no-till soybeans, be sure to consider controls for seed corn maggot. Flies continue to lay eggs and are attracted to no-till situations. A seed treatment containing diazinon should be used. The newer seed treatments containing permethrin should also provide control. v

Field Crop Diseases - Bob Mulrooney, Extension Plant Patholgist ; bobmul@udel.edu


Powdery mildew is increasing in severity on susceptible varieties at the present time. For the most part, the mildew is not advancing on the flag and the leaf below the flag leaf. I am also seeing brown leaf tips in some areas. This is some environmental factor, either frost or possibly wind desiccation. Some yellowing is occurring that looks like barley yellow dwarf mosaic virus, we need to confirm this. Purpling of the flag leaf often is a good symptom of barley yellow dwarf as well as the yellowing of the upper two leaves. Several samples were received today that looked like wheat soilborne mosaic and wheat spindle streak mosaic virus. Wheat soilborne usually occurs in patches and causes small yellow streaks and blotches on the leaves. Wheat spindle streak mosaic virus can look similar but the spots tend to be more slender and it occurs usually over the whole field. The only way to confirm these is by serological testing. What can really be confusing are the wheat varieties that produce a small flecking in the leaves that is a varietal characteristic that has nothing to do with an infectious disease, but resemble virus infections. Nothing can be done for virus diseases at this time. I have not seen any Septoria leaf spot or tan spot yet.


Soybean growers were encouraged to soil sample for the soybean cyst nematode in the first issue of Crop Update. This is just a reminder to soil test before planting susceptible soybeans in areas where it occurs. Nematode sample bags are available from the county Extension offices. It makes sense and can save you money. v

Grain Marketing Highlights - Carl German, Extension Crops Marketing Specialist ; clgerman@udel.edu

Corn Planting Progress Hits 21 %
USDA's weekly Crop Progress report placed corn planting at 21 % compared to the five-year average of 34 %. Three big key states for corn production; Illinois, Iowa, and Indiana are running well behind their normal pace. On a recent trek from St. Louis, Mo. to Litchfield, Ill. one field of corn was observed to be emerged. A whopping total of three tractors were spotted in the field on Sunday.

Marketing Strategies
Corn is expected to rally this week, maybe 10 cents per bushel, based upon the National Weather Service call for more rain in the corn belt. For those needing to advance new crop corn sales this will present an opportunity to get some sales done, bringing initial sales up to at least 1/3 of intended production. For those with their initial sales previously completed, depending upon basis offerings it may be wise to consider sales of another 5 to 10 % of intended production. Next week's highlights will consider USDA's May crop report. v

Residual Herbicides with Roundup-Ready Soybeans - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Use of a soil-applied herbicide is not recommended if there are no weeds present at planting and the Roundup Ultra application is between the first to third trifoliate stage of the soybeans. If you are not able to get the application out in that time frame, then a residual is recommended. When spraying prior to the first trifoliate, tankmixing a residual herbicide like FirstRate, Pursuit, or Classic with Roundup Ultra will reduce the possibility of a second application (although none of these residual herbicides are particularly effective for broad-spectrum grass control). If you anticipate needing to spray after the third trifoliate stage (about 4 weeks), using a residual at planting is recommended. A full-rate of the residual herbicide is not needed if you plan on spraying Roundup Ultra after the fourth week. The residual herbicide will control the very susceptible weeds and slow the growth of less susceptible species. Perennial weeds should be sprayed as late as possible. v


When: Tuesday, May 18, 1999

5:30 PM – till(?)

Where: University of Delaware Research and Demonstration Area; -mile east of Armstrong Corner, on Marl Pit Rd. (Rd. 429).

What: Come join your fellow farmers and Extension staff for an interactive and hands-on experience as we:

Wheat and Barley


Nutrient Management

Discuss and demonstrate the use of the Pre-sidedress Nitrogen Test (PSNT).


Discuss timely questions/issues.

We’ll wrap the session up with a dessert treat and more chance to continue discussion.

Important: DDA will award (2) private applicator re-certification credits in the Agricultural Plant category. Certified Crop Advisor credit(s) will also be applied for.

Whether or not you can join us on the 18th, stop by at your convenience throughout the season. Handouts and maps will be available in the plastic information box mounted behind the UD sign. This meeting is free, and everyone interested in attending is welcome. For more information or special consideration in accessing this meeting, please contact our office in advance at (302) 831-COOP (2667).


Carl P. Davis

Extension Agent, Agriculture, cpdavis@udel.edu

Pesticide BriefsSusan Whitney, Extension Pesticide Educator; swhitney@udel.edu

If you have questions concerning pesticide applicator training, certification and recertification, visit the University of Delaware Pesticide Website at http://www.udel.edu/pesticide   v

Upcoming Meetings…

Strawberry Twilight Meeting

University of Maryland, Wye Research and Education Center, Cheston Lane, Queenstown, MD

Thursday, May 13, 1999

6:00 p.m.

What you will see:

Annual Plasticulture: 7 named varieties, 3 N.J. selections, 22 breeding lines from MD and USDA

June Matted Row: 12 named varieties and 11 N.J, breeding lines

Lime Sulfur Renovation Trial

Who will be with us:

Dr. Joseph Fiola, Rutgers; Dr. Stan Hokanson, USDA; Curt Massey, Special Strawberry Researcher; Dr. Harry Swartz and other University of Maryland Specialists

For more information, call 410-827-8056.


Small Grain Twilight Tour

University of Maryland, Wye Research and Education Center, Cheston Lane, Queenstown, MD

May 20, 1999

6:30 p.m.

For More Information, contact Ted Haas at


                    Weather Summary

Week of April 29 to May 5

0.08 inches: May 3, 1999
0.01 inches: May 4, 1999
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 74F on May 5 to 56 F on May 3.
Lows Ranged from 52F on May 4 to 36F on April 29.
Soil Temperature:
63 F average for the week.
(Soil temperature taken at a 2 inch depth, under sod)

Web Address for the U of D Research & Education Center:


Compiled and Edited By:

Tracy Wootten

Extension Associate - Vegetable Crops

Cooperative Extension Education in Agriculture and home Economics, University of Delaware, Delaware State College and the United States Department of Agriculture cooperating, John C. Nye, Dean and Director. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, sex, disability, age or national origin.

Black Cutworm – Pheromone Trap Catches – 1999 Season

Data Provided by Terra Inc., Bridgeville, DE

Trapping Period : April 25 – May 1, 1999

NOTE: Moth catches ranging from 7 to 15 moths per 7 day period have been associated with a moderate to high potential for cutworm outbreaks. Once moth catches in an area reach this level, the first larvae are generally seen within 300 degree days (using a temperature base of 50 degrees F). Since April 4, 97 degrees days have accumulated at the Research and Education Center located in Georgetown, DE.




# Moths/7Days

American Corner, MD


Lewistown, MD


Argos Corner, DE


Magnolia, DE


Atlanta, DE


Mardela Springs, MD


Bayard, DE


Marydel, MD


Berlin, MD


Milford, DE #1


Bethel, DE


Millsboro, DE


Bridgetown, MD


Milton, DE


Bucktown, MD


Newark, MD #1


Burrisville. MD


Newark, MD #2


Cambridge, MD


New Church, VA


Clarksville, MD


Oak Orchard, DE


Dagsboro, DE #1


Pocomoke, MD #1


Dagsboro, DE #2


Pocomoke, MD #2


Delmar, DE


Preston, MD


Denton, MD


Public Landing, MD


Easton, MD


Redden, DE


Eldorado, MD


Reids Grove, MD


Ellendale, DE


Reliance, MD


Farmington, DE


Rhodesdale, MD


Federalsburg, MD


Ridgely, MD


Georgetown, DE


Seaford, DE #1


Goldsboro, MD


Seaford, DE #2


Greenwood, DE


Selbyville, DE #1


Hurlock, MD #1


Selbyville, DE #2


Hurlock, MD #2


Snow Hill, MD #1


Laurel, DE # 1


Snow Hill, MD #2


Laurel, DE # 2


Snow Hill, MD #3


Laurel, DE # 3


Trappe, MD


Leipsic, DE


Vernon, DE


Lewes, DE


Wyoming, DE


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