Volume 9, Issue 5                                                                                       April 27, 2001


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



Imported cabbageworm butterflies have been laying eggs in fields for the last 10 -14 days and the first larvae have been detected. We have also observed our first diamondback (DBM) moths laying eggs in cabbage in Sussex County. Once DBM eggs hatch, young larvae will first mine between the upper and lower leaf surfaces before moving to the heart of the plants. Treatments should be applied when 5% of the plants are infested with larvae and before larvae move to the heart of the plants. Avaunt, Bt insecticides, Proclaim, or Spintor will provide effective control. Avaunt is a new insecticide from DuPont, labeled last fall. It has a novel mode of action so it can be used as an effective resistance management tool. It has provided excellent control of imported cabbageworm, cabbage looper and diamondback larvae. The use rate is 2.5 - 3.5 oz per acre for imported cabbageworm and cabbage looper and 3.5 oz/acre for diamondback. Be sure to rotate between these classes of insecticides to avoid the development of resistance.



You should begin to watch the earliest planted peas for the presence of pea aphids. As the weather fluctuates between cool and warm, aphid populations often explode and beneficial insect activity can lag behind. On small plants, you should sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. A treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. Dimethoate or Lannate will provide aphid control. Be sure to check the labels for application restrictions during bloom.



Field Crops


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



Economic levels of alfalfa weevils have been found in fields in Kent and Sussex Counties. Although a general threshold of 50% tip feeding can be used, you can more accurately determine if a treatment is needed by counting the number of larvae per stem. Sample fields by collecting 30 stems throughout a field and placing them top first in a bucket.  Shake the stems against the side of the bucket to dislodge the larvae from the stems and count the number of larvae. Treatment decisions vary with the height of the alfalfa so you will also need to determine the average stem height. A treatment is needed if you find the following numbers:


Average Alfalfa Height (inches)

Number of Weevil Larvae per Stem









17 or >



If you are at threshold and the field is in the full bud stage, early cutting is the best control option. However, if threshold numbers are present and you cannot cut within 5-7 days, a short residual insecticide should be used. Baythroid, Imidan or Warrior are your best control options. All 3 products have a 7-day wait until harvest when the alfalfa is used for hay.


Field Corn.

Black cutworm catches remain relatively low (see trap catch table on the last page or http://www.udel.edu/IPM/traps/currentbcwtrap.html). The only location were populations have increased is in the Snow Hill, MD area. Based on the lower moth catches and cooler temperatures, we should not expect to see black cutworm feeding activity until at least mid-May.



We are starting to see an increase in cereal leaf beetle egg laying activity so the first larvae should be detected next week. Controls should not be applied too early to avoid the need to re-spray fields. A treatment is needed if you find 25 or more eggs and/or larvae per 100 tillers and 50-60% of the eggs have hatched. The first grass sawfly adults have been detected laying eggs in wheat. You should begin sampling field edges for small larvae by the first week in May. A sweep net should be used to detect the first larvae, generally found along field edges. Once larvae are detected, sample 5 foot of row innerspace in 5-10 locations in a field to make a treatment decision. You will need to shake the plants to dislodge larvae that feed on the plants during the day. No treatment will be needed until you find 2 larvae per 5 foot of row innerspace.




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


Grain Markets Brace for Further Chaos
During the past two weeks the chaotic news building up throughout the world has been having a rather negative effect upon U.S. commodity prices. Just a few of the issues currently impacting the grain markets are given herein.

StarLink and other GMO issues have severely damaged grain exports, particularly for corn.

The Southern Hemisphere soybean crop reported at record levels all winter long, just keeps getting larger with each new report stemming from Brazil and Argentina.

China recently canceled a large order for U.S. soybeans. This may have been due to the current strained relations between the U.S. and China.

U.S. soybean prices across the board are now at their lowest level in 29 years.

U.S. corn production costs are now at their highest level in the history of U.S. corn production, in terms of the dollars it takes to grow corn per acre. With fuel prices continuing their upward spiral the situation is likely to get much worse before the 2001 crop is harvested.

The Japanese economy is reported to be on the verge of collapse.

The potential of a U.S. 'weather market' developing is now placed on hold until mid summer. Crop progress reports have the U.S. corn crop 20% planted, with the possibility of planting progress increasing geometrically over the next couple weeks. The National Weather Service is projecting nearly ideal weather for planting purposes in the Corn Belt for at least the next 10 days.

U.S. commodity exports are currently lagging behind last years pace.

USDA Export Sales Report
Corn: Net sales of 407,900 metric tons (MT) were off one quarter from the week earlier and one third from the 4 week average. U.S. corn exports, projected to reach 49,530 MT on the year, are currently at 29,906.1 MT cumulative total.

Soybeans: Net sales of 132,800 MT were 84 % above the previous week, yet 26% below the 4-week average. U.S. soybean exports, projected to reach 25,940 MT on the year, are currently at 22,906.1 cumulative total.

Wheat: Net sales of 277,500 MT for the week ending April 19, 2001 were 34% below the previous week and 28% less than the 4-week average. U. S. wheat exports, projected to reach 29, 940 MT, are currently at 23,096.4 cumulative total.




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



Powdery mildew is beginning to show up on susceptible varieties. Most of the mildew in our variety plots is confined to the lower leaves on some varieties. Baytan has kept powdery mildew in check until growth stage 6-7. Powdery mildew is just beginning to be seen on Southern States 555W treated with Baytan.


Wheat spindle streak mosaic virus is a disease caused by a virus that is transmitted by a  soilborne fungus. It produces symptoms that can be confusing. The slender yellow dots and dashes that tend to be spindle shaped are seen on the leaves over most of the field. Symptoms can be worse in low spots. The chlorotic yellow spots can look like nutrient deficiencies or early powdery mildew infections that have not produced any spores. ELISA testing is the best way to confirm the presence of WSSMV. Testing can be done by sending samples to an outside lab. Contact your county agent for details. The cool weather enhances symptom development (less than 70°F). Often the symptoms disappear when warm weather arrives. Yield losses are only thought to occur if symptoms persist on the flag leaves once grain fill begins. Resistant varieties are available for WSSMV.


Two other viral diseases commonly occur in Delaware and both produce irregular patches of stunted plants in the field. Aphids transmit barley yellow dwarf virus (BYDV) and soilborne wheat mosaic virus (SBWMV) is transmitted by a soil fungus. BYDV produces yellow stunted plants early in the season. Later infected leaves can be different shades of yellow, red or purple. Yellow or reddened flag leaves on otherwise normal plants indicate late spring infections. SBWMV can look very similar to spindle streak mosaic except that soilborne wheat mosaic is often confined to the low spots in the field. Infected leaves are mottled and develop parallel dashes and streaks. It too is favored by cool temperatures. Ideal temperature for symptom expression is 60°F. No controls are possible at this time. Plant resistant varieties to control wheat spindle streak and soilborne wheat mosaic. To control barley yellow dwarf control aphids and don’t plant early.



Last season there was a marked reduction in the amount of soybean severe stunt virus (SSSV) in Sussex County. It has not disappeared but there is certainly not as much as we have seen in the past. 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:



It is still not too late to check for soybean cyst nematode. Soil test bags can be purchased at the Extension offices. If you have a fax machine and need results quickly, tests results can be sent via FAX if you provide the number on the Nematode Assay Information Sheet.




Effectiveness Is The First Consideration For Weed Control - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu


When deciding which weed control option to use, first question should not be what does it cost.  What is your approach to weed management in the field?  Your approach may be for: 1) excellent weed control because rotational crops have limited herbicide selection, 2) level of weed control that will not reduce yield, or 3) something in between.  Either way, selecting the herbicide program based on effectiveness is more critical than selecting it on cost.  An in-expensive option that does not control key weed species is going to be more costly in the end.  For assistance in selecting the most effective herbicides, refer to the 2001 Weed Management Guides for Delaware.  There is one for corn and one for soybeans available free from the county offices, on the Internet at www.rec.udel.edu (under publications) or calling 302/856-7303 and asking for Mabel Hough.




Reminder About Soil-Insecticide and Herbicide Interactions - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu


Many of the newer postemergence herbicides have restrictions for use of soil-insecticides.  The herbicides with restrictions include:  Accent, Basis, Basis Gold, Beacon, Bicep Magnum TR, Celebrity Plus, Exceed, Hornet, Lightning, NorthStar, and Python.  If you foresee using any of these herbicides, be sure to check the label for restrictions prior to planting.  The reason for these interactions is that the herbicides and organo-phosphate insecticides use the same metabolic pathways to metabolize the pesticides.  If both the insecticide and herbicide are used, the plant cannot metabolize the herbicide fast enough and the corn is injured.  The organo-phosphate insecticides commonly used in corn include Counter, Thimet, Dyfonate, and Lorsban.  These restrictions vary by herbicide, so be sure to read the label.




Acetachlor Is Not For Everyone? - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu


Acetachlor is a preemergence herbicide for corn that controls annual grasses and some broadleaf weeds.  It is in the following products: Harness, Harness Extra, Degree and Degree Extra, Topnotch, and Fultime.  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.




Soil-Applied Herbicides Need Water - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu


Herbicides applied to the soil surface require rainfall or irrigation to move them into the soil where the plants will absorb them.  The amount of water needed to “activate” these herbicides depends on the water solubility of the herbicide and moisture content of the soil.  Most soil-applied herbicides require 0.5 to 0.75 inches to be moved in the soil if the soil is “dry” (less water if the soil is moist).  Princep requires 0.75 to 1.0 inches of water to become “activated”.  If you have irrigation and your corn herbicides have been applied but you have not received at least 0.5 inches of water, you should consider applying that amount with your system.  This is one situation where spending a little money now could save money later.  For instance, if your residual grass herbicide is not moved into the soil and grass control is poor, you are looking at a postemergence application of Basis Gold or Accent-containing pre-mix.  Control of crabgrass with postemergence herbicides is only fair.  Spending the money to irrigate and activate the herbicides could save a high herbicide bill later.




Shop TalkJames Adkins, Extension BioResources Engineer; adkins@udel.edu.


Tractor Ballasting.

In the spring rush to get all of the tillage completed and crops planted, we often overlook the importance of proper tractor set up.  It’s no fun to change tire pressures and weights, but if you want a tractor that’s going to perform better, cover more acres per hour and use less fuel, that’s what you need to do.  There is definitely a payback.


Just like you set up a planter, calibrate a sprayer or adjust a combine you need to set the tractor to maximize productivity and efficiency. When it comes to weight and tire pressures, less may be better.  In many cases, tractors are over ballasted and poorly balanced resulting in inefficient performance and unnecessary compaction.


Most tractor manufacturers recommend 100-110 lbs of total tractor weight per PTO horsepower for average loads in the optimal 5-6 mph range.  For heavier loads at lower speeds, 130 lbs per PTO horsepower may be necessary.  This means that a 145 PTO horsepower tractor should weigh 15,950 lbs. for average loads and 18,850 lbs. for maximum loads at low speeds.


145 PTO hp  x  110 lbs/hp  =  15,950 lbs of total tractor weight.


Note that this weight includes any liquid ballast, cast weights or saddle tanks plus the dry weight of the tractor.  Additionally, whenever weight is added, (including the mounting of three point hitch implements), tire inflation pressure must be adjusted to compensate for the increased axle loads and to prevent tire failure.


These recommendations are based on the average ballast required to maintain optimal wheel slippage (5%-12%) for maximum drivetrain and tractive efficiency.  Weight balance is also an important factor in maintaining proper slip and preventing power hop and road lope.  Look for more information on wheel slip, weight balancing, tire pressures, and tire selection in the upcoming issues.





Strawberry Twilight Meeting

Thursday, May 17, 2001

Wye Research & Education Center

Queenstown, Maryland

6:00 p.m. –until



Topics to be covered:

v     Strawberry Varieties and Breeding

v     Frost Protection and Environmental Modification

v     Composted Ammendments and Red Stele Control

v     E-Weather and Strawberry Canopy Forecast

v     And other items


Featured Speakers:

v     Dr. Craig Chandler, Strawberry Breeder, University of Florida

v    Dr. Joe Russo, ZedX, Inc.

v     Dr. Harry Swartz, University of Maryland

v    Dr. Brent Black, Dr. Pat Millner and Mark Davis, USDA Small Fruit Team

v     Bob Rouse and Mike Newell, University of Maryland Wye Research & Education Center


Please join us!


For more information, call 410-827-8056 ext. 115


Pre-registration is not necessary.



                              Weather Summary

Week of April 19 to April 25


0.11 inches: April 24

0.04 inches: April 25

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

Air Temperature:

Highs Ranged from 85°F on April 23 to 56° F on April 25.

Lows Ranged from 62°F on April 22 & 23 to 28°F on April 19.

Soil Temperature:

62°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

Black Cutworm Pheromone Trap Counts - April 16 - 22, 2001 

Provided by UAP Northeast and Syngenta



# Moths 


# Moths

Bridgeville, DE


Lincoln, DE


Bucktown, MD


Little Creek, DE


Cheswold, DE


Magnolia, DE


Cordova, MD


Mardela, MD


Crumpton. MD


Marydel, DE


Delmar, MD


Middletown, DE


Denton, MD


Milford, DE


Dover/Wyoming, DE


Millsboro, DE


East New Market, MD


Milton, DE


Easton, MD


New Church, VA


Eldorado, MD


Newark, MD


Ellendale, DE


Pocomoke, MD


Farmington, DE


Preston, MD


Federalsburg, MD


Princess Anne, MD


Felton, DE


Queen Anne, MD


Frederica, DE


Rhodesdale, MD


Georgetown/Redden DE


Salisbury, MD


Goldsboro, MD


Seaford, DE


Greensboro, MD


Selbyville, DE


Greenwood, DE


Smyrna, DE


Harbeson, DE


Snowhill, MD


Hebron, MD


Sudlersville, MD


Hickory Hill, DE


Trappe, MD


Hurlock, MD


Vernon, DE


Kenton, DE


Vienna, MD


Laurel, DE


Westover, MD


Leipsic, DE


Willards, MD



Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University 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.  It 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.

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