Volume 8, Issue 3 April 7, 2000

The Weekly Schedule Begins This Week

This will be the last issue you will receive if you havent signed up for the 2000 season. Please contact the office at 302-856-7303 if you would like to subscribe my mail or fax. If you would like an e-mail reminder please forward your address to me at wootten@udel.edu . Those who have signed up for an e-mail reminder, you should have received it this week. If you did not, please contact me.

Thank you.






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



The first asparagus beetle adults have been found on field edges. Edge treatments have provided effective control but only when applied before significant egg laying occurs and beetles move into the field. Two applications are often needed for effective control. Ambush, Pounce or Sevin will provide control.


Sweet Corn and Snap Beans.

Although conditions have not been extremely cool and wet, seed corn maggot flies remain active. Conditions favoring egg laying include situations where a green cover crop is plowed under close to planting, manure is used and/ or a field is minimum tilled. A seed treatment containing diazinon or permethrin should be used on early-planted sweet corn. In fields with a high potential for seed corn maggot (combinations of the above conditions), a soil insecticide will also be needed. On snap beans, the use of diazinon 50W as a planter box treatment has provided the best control in recent years.





Watermelon Seedling Diseases in the Greenhouse - Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; everts@udel.edu


Many abiotic problems (scorch from high temperatures, excess nutrients and chemical burn) may cause spots on the leaves of plants in the greenhouse. There are also several seedborne watermelon diseases that may show up on seedlings in the greenhouse. Gummy stem blight (GSB) is the most common, but Alternaria leaf blight and anthracnose also affect watermelons. There are several greenhouse practices that minimize infection by the pathogens of these diseases, including GSB. The greenhouse should be disinfected before planting (benches, walls, walkways, etc.). The seed source should have tested negative for the pathogen with a minimum assay number of 1,000 seeds. Use clean transplant trays (disinfect trays if they will be reused) and new soil. Destroy any volunteer seedlings and keep the area in and around the greenhouse weed free. Avoid overhead watering if at all possible, or water in the middle of the day so that the plants dry thoroughly before evening. Keep relative humidity as low as possible through proper watering and good air circulation in the greenhouse.


As the seedlings develop, inspect them carefully. Infected seedlings will have small brown lesions on the leaves and water-soaked lesions on the stem. Initial infections will occur as foci or clusters of diseased plants.


Gummy Stem Blight

(Pictures taken from Diseases and Pests of Muskmelons and Watermelons, Richard Latin, Purdue University Cooperative Extension Service)


If the seedlings have lesions or appear diseased, destroy the flats where any seedlings show symptoms. Remove adjoining flats to a separate area for observation. Monitor these seedlings daily and destroy those that develop symptoms. Do not ship any trays containing plants with symptoms of GSB. Spray with a labeled fungicide when symptoms are observed and continue until plants are shipped.


Bacterial fruit blotch (BFB) of watermelon is caused by a bacterium that may also be seedborne. Initial symptoms of BFB are water-soaked areas on the lower surface of the cotyledons. Lesions turn necrotic often with yellow halos, are frequently deliminated by veins and subsequently the seedlings collapse and die.

Bacterial Fruit Blotch on Watermelon

(Pictures taken from Bacterial Fruit Blotch of Watermelon, Don Hopkins, Bob Stall & Tom Kucharek, University of Florida; Danny Gay and Ron Gitaitis, University of Georgia; Wilton Cook and Anthony Keinath, Clemson University; Rick Latin, Purdue University)






Vegetable Disease Prevention and Control

- Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu


Sweet corn.

For early plantings especially with sugary and sugar enhanced varieties use a seed treatment for damping-off control. Apply Counter at planting to control flea beetles that carry the bacteria that cause Stewarts wilt.



Rotate 4-5 years between pea crops to reduce root rot and damping-off.



White rust may be present in overwintered fields. Be looking for symptoms. Apply copper fungicides for white rust. The products with the least amount of phytotoxicity are Champ Flowable and Kocide LF at the low labeled rates. On newly seeded fields apply Ridomil Gold after seeding to control white rust and damping-off from Pythium.





Pest Control in the Greenhouse - Tracy Wootten, Extension Associate Vegetable Crops; wootten@udel.edu


We have experienced two mild winters. Consequently, rodents have been able to survive in numbers. It is important that if you have plants in the greenhouse or will be planting, to be sure to try to control mice and voles. Rodents can cause significant damage to trays, see the pictures below. Bait should be placed in the greenhouse 2-3 weeks before planting before starting plants.


Undisturbed Tray in Greenhouse After mice have eaten seed



The destruction can be severe. The white stakes are cells that the mice ate seed from; 26 cells in a 50 cell tray.


Field Crops

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



Economic levels of alfalfa weevil have been found in fields in Sussex and lower Kent County. You should look for small larvae feeding in the tips of plants producing a round, pinhole type of feeding. Once you detect tip feeding, a full field sample should be taken. You will want to avoid treating fields too early since it may result in multiple applications. Also, be sure that you do not confuse clover leaf and alfalfa weevil larvae. Cloverleaf weevils are generally larger at this time of year and have a distinct white stripe lined with red down the middle of their backs. Although cloverleaf weevils can cause damage during cool, dry springs, controls are generally not needed for cloverleaf weevils. When sampling for alfalfa weevil, randomly collect 30 stems throughout a field, placing them upside down in a bucket, and shaking the stems to dislodge larvae from the tips. Once alfalfa reaches 12-inches tall, the treatment threshold is one per stem. In 13 to 15-inch tall alfalfa, the threshold is 1.5 per stem. Baythroid, Furadan, Imidan or Warrior will provide control under a wide range of environmental conditions.

Alfalfa Weevil Clover Leaf Weevil



http://www.ent.iastate.edu/imagegal/coleoptera/curculionidae/0212.47alfalfalarva6in.html(Pictures from Iowa State Marlin E. Rice)



Field Corn.

At this time, grubs can easily be found in the top six inches of soil. As indicated in past newsletters, fields can be sampled for grubs before planting but it should be done before a field is tilled. At each site, sample one square foot of soil dug six inches deep. At least one sample, preferably two, should be taken for every 10 acres with no less than 5 samples per field. A treatment is recommended if you find 1-2 grubs per square foot in heavy soil or 0.5 1 grub per square foot in sandy soil. Counter, Force or Fortress will provide control. The highest labeled rate should be used if populations are heavy.


Black cutworm pheromone trap catches (provided by UAP Inc., Seaford, DE, see table on last page) indicate that cutworm moth activity is still low on the shore. Trap catches during the month of April can provide an indication of where black cutworm problems will occur. Although no precise thresholds are available, 9 to 15 moths per 7 day period has been associated with a moderate to high potential for cutworm outbreaks. Moth catches of 5 per night for at least 2 consecutive nights has also indicated a high potential for problems. At the present time, only 1 trap in the region has caught any moths over a 7-day period.



Aphids and cereal leaf beetle adults can be found in wheat and barley. Aphid populations are still low and are being held in check by beneficial insects. At this time cereal leaf beetle egg laying is very light; however, you can expect to see an increase in the next week to 10 days as temperatures increase. No controls should be applied for cereal leaf beetle before you find 25 eggs and/or larvae per 100 tillers AND at least 50 60% of the eggs have hatched.





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



Powdery mildew has been seen and may be serious where susceptible varieties were planted and the seed was not treated with Baytan or Dividend. If early applications of Tilt at the labeled 4 oz rate are made now, the fungicide may not provide full season protection. If weather conditions are favorable later for either powdery mildew, glume blotch or tan spot a second application might be needed. With low wheat prices economics may discourage making a second application unless yield potential is very high. The labeled fungicides for wheat at this time are Tilt, Quadris, mancozeb, and Benlate. If anyone could find some Bayleton with the old label, 2 ounces would make a great economical choice as an early spray for powdery mildew. New stocks of Bayleton do not have wheat on the label. The best avenue would be to wait until flag leaf emergence to head emergence if possible and apply Tilt then, if disease pressure warrants an application. If there is no disease pressure then scout the fields and see what develops. If Tilt is applied early and glume blotch, rust or tan spot threatens late, another possibility would be using mancozeb (Dithane, Penncozeb, etc.). It will not control powdery mildew but is good against glume blotch and tan spot and excellent against rust, which is rarely a problem here in Delaware. Quadris is excellent against glume blotch, tan spot and rust. It could be used to control powdery mildew but the lowest use rate for powdery mildew is 7.7 fl. oz. and is not as good as Tilt on powdery mildew and more expensive. Planting resistant varieties and the use of seed treatments usually provide the best control of powdery mildew.


Tilt and Quadris are both excellent products, but there are some minor differences between them. The table below compares the two products. The table and the following comments were adapted from an article written by Don Hershman, Extension Plant Pathologist at the University of Kentucky.



Wheat Disease




Powdery mildew



Septoria tritici leaf blotch



Stagonospora (Septoria)

Nodorum leaf blotch



Tan Spot

Very good

Good/very good*

Glume blotch



Leaf Rust

Very Good



*Effectiveness at highest labeled Quadris use rate of 10.8 fl.oz. /A.; other diseases are adequately controlled using the 6.2 fl. oz./A rate.



Last season there was a marked reduction in the amount of soybean severe stunt virus (SSSV) in Sussex County. The drought played a big role in reducing disease incidence. However where growers have seen the disease, planting resistant varieties or planting non-host crops such as corn or sorghum will control SSSV. We are continuing to identify varieties that have resistance to SSSV. Group IV varieties with resistance from multiple year tests include Delsoy 4710, Chesapeake, Corsica, Cisne, Agripro AP4400, Stine S4900, S4790, and Pioneer brand 9492, which is also Round-up ready. Group V resistant varieties are Delsoy 5710 and Choska. Of the varieties listed Delsoy 4710, Delsoy 5710, Choska and Pioneer brand 9492 have resistance to both SSSV and the soybean cyst nematode. More information on SSSV is available in fact sheet form at the county Extension office or on the web at http://bluehen.ags.udel.edu/deces/pp/pp-45/pp-45.htm.




Reminders On Acetechlor Use Restrictions -Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu


Acetachlor is a preemergence herbicide for corn which controls annual grasses and some broadleaf weeds. It is in the following products: Harness, Harness Extra, Surpass, Topnotch, and Fultime. It has recieved a lot of advertisement in the past few monthes, but most of this advertisement does not mention the restrictions that are important in our area. The restrictions pertain to groundwater quality. The restrictions are based on depth of groundwater within one month of planting and the combination of soil type and organic matter. Do not apply acetachlor if the groundwater depth is 30 feet and you have sands with less than 3% organic matter, or loamy sands with less than 2% organic matter, or sandy loam with less than 1% organic matter.


Be Sure to Consider Last Year -Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu


In planning your weed management for a given field, consider what happened last year in that field. A number of fields throughout the state did not get a rain shower to activate the soil-applied herbicides and growers could not get a handle on the weeds. Those fields that had a large number of weeds go to seed last year, will need a more aggressive weed management program this year. So plan accordingly.


Remember, many of our hard to control weeds require a postemergence herbicide for effective control. Knowing that you are going to be spraying a postemergence herbicide allows you to adjust your soil-applied herbicide program. The result can be less money in a preemergence program knowing you will need a postemergence spray.



Should You Alter Your Burndown Program This Year? -Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu


With the warm weather we have been having weeds are further along than normal. When you start to burndown your weeds prior to no-till, be sure you check your weed stage first. Some fields have winter annuals that are getting large and starting to bolt. You may need to increase the rate of your non-selective herbicides (Roundup, Touchdown, or Gramoxone) or add a non-selective herbicide if you usually do not use one. The key here is to check the field before you start. As with everything else, there are trade-offs.


Reminder Timing for Small Grain Herbicides -Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu


The following are the timing limitations for small grain herbicides. The timing restrictions are based on crop safety.


2,4-D - up to jointing stage (pre-jointing)

Bavel - up to jointing stage (pre-jointing)

Buctril - up to boot stage

Harmony Extra - up to flag stage (pre-flag leaf)





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


USDA Releases 2000 Planting Intentions; and March Grain Stocks Report
Commodity markets reacted mostly neutral to the release of the March 31st USDA Planting Intentions and Grain Stocks reports. U.S. farmers intend to plant 75 million acres of soybeans, 77.9 million acres of corn, with spring wheat planting intentions bringing the 2000 cropping season total wheat acres to 61.7 million acres. Although acreage estimates for all three crops are slightly above seeded acres for 1999, commodity markets remained in check with the March 1 grain stocks report reflecting smaller numbers as compared to March 1,1999 grain stocks. March 1 U.S. grain stock estimates were placed at 1.397 billion bushels for soybeans, 5.606 billion bushels for corn, and 1.412 billion bushels for wheat. The grain stocks estimates were 61 million bushels, 90 million bushels, and 33 million bushels, respectively, less than the levels reported for March 1, 1999.

Marketing Strategy
With corn planting getting well underway in the corn belt, commodity traders are keeping a close watch on weather systems moving across the U.S. December corn remains in the middle of the recent trading range of $2.50 to $2.64. May soybeans have currently established a trading range of $5.40 to $5.54. May wheat futures currently have support established at the March low of $2.48 with resistance at $2.60. Any reports of precipitation amounts being less than needed in the corn belt are likely to move these markets toward their resistance levels.





Weather Summary


March 23 to April 5


0.30 inches : March 25, 2000

0.53 inches : March 27, 2000

0.40 inches : March 28, 2000

Readings taken for the previous 24 hours at 8 a.m.

Air Temperature:

Highs Ranged from 72 F on March 25 to 57 F on March 31.

Lows Ranged from 57 F on April 3 to 34 F on April 1.

Soil Temperature:

55F average for the week.

(Soil temperature taken at a 2 inch depth)


Black Cutworm Pheromone Trap Counts

March 30 through April 2, 2000

Trap Counts Provided by UAP Inc., Seaford, DE



# Moths per 7 Days


# Moths per 7 Days

Bridgeville, DE


Leipsic, DE


Cheswold, DE


Lincoln, DE


Cordova, MD


Little Creek, DE


Crumpton. MD


Magnolia, DE


Delmar, MD


Mardela, MD


Denton, MD


Marydel, DE


Dover/Wyoming, DE


Middletown, DE


East New Market, MD


Milford, DE


Easton, MD


Millsboro, DE


Eldorado, MD


Milton, DE


Ellendale, DE


Newark, MD


Farmington, DE


Pocomoke, MD


Federalsburg, MD


Preston, MD


Felton, DE


Princess Anne, MD


Frederica, DE


Queen Anne, MD




Rhodesdale, MD


Goldsboro, MD


Salisbury, MD


Greensboro, MD


Seaford, DE


Greenwood, DE


Selbyville, DE


Harbeson, DE


Smyrna, DE




Snowhill, MD


Hebron, MD


Sudlersville, MD


Hickory Hill, DE


Trappe, MD


Hurlock, MD


Vernon, MD


Kenton, DE


Vienna, MD


Laurel, DE


Westover, MD




Willards, MD



(1) Moth catches of 9 to 15 moths per 7-day period have been associated

with a moderate to high potential for cutworm outbreaks.

(2.) Moth catches of 5 per night for at least 2 consecutive nights have

also indicated a high potential for problems.

(3.) You can expect to see cutting activity around 300 degree-days, base of 50 degree F from peak moth activity.





Compiled & 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.