Volume 10, Issue 5                                                                                                     April 26, 2002



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



We continue to find imported cabbageworm and diamondback larvae in cole crops. A treatment is recommended if you find 5% of the plants infested. The following products will provide excellent worm control: Avaunt, the Bt insecticides, Proclaim and Spintor.



Seed corn maggot flies can be found laying eggs in fields, especially where chicken manure or green manures have been recently plowed under. A seed corn maggot control should be considered in all fields planted through the end of May. A broadcast application of diazinon before planting has provided control.



We are starting to find our first pea aphids in the earliest planted pea fields.  Since early-planted fields have started to bloom, it is important to sample fields on a weekly basis until harvest. You should sample for pea aphids by taking 10 sweeps in 10 locations and counting the number of aphids per sweep. A treatment is recommended if you find 50 or more aphids per sweep. Dimethoate or Lannate will provide aphid control. Be sure to check the labels for application restrictions during bloom.



The first Colorado potato beetle egg masses and small larvae can be found in potatoes, especially near overwintering sites. The treatment threshold for Colorado potato beetle is 4 small larvae per plant or 1.5 large larvae per plant. If both small and large larvae are present, the threshold of each should be reduced by ½.  Spintor, Actara, or Provado will provide good control of adults and larvae. In fields where there is known tolerance to Admire, be sure to consider the use of cryolite in the rotation. The first European corn borer moths were caught during the last week; however, populations are low at this time. The most recent blacklight trap catches can be found at http://www.udel.edu/IPM/traps/latestblt.html. No controls should be needed for corn borer until mid-May.


Special Local Needs 24 (C) Label for Diazinon on Potatoes - Since diazinon is no longer labeled on potatoes, a request was submitted for a Special Local Needs 24(C) label. The Delaware Department of Agriculture has recently approved our 24 (C) request for the use of an at planting broadcast application of diazinon on potatoes for wireworm control. Growers interested in a copy of the label should contact Joanne Whalen or Grier Stayton at the Department of Agriculture.  



Field Crops


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


Field Corn.

Black cutworm catches continue to increase in the Dagsboro, Harrington, Little Creek and Wyoming areas. (see trap catch table on page 3 or look at our webpage at http://www.udel.edu/IPM/traps/currentbcwtrap.html )

 The first black cutworm leaf feeding activity was observed this week in 1-2 leaf stage corn. You should watch for early signs of leaf feeding which could appear as small pinholes when larvae are small. This damage often provides an indication of where you will see cut plants in the next week. No treatment will be needed until you find 10% leaf feeding or 3% cut plants on 1-2 leaf stage corn. On 3-4 leaf stage corn, the treatment threshold is 5% cut plants. A pyrethroid will provide the most cost-effective control. Since cutworms are nocturnal, applications applied later in the day or in the evening will provide the best control.


Since corn has quickly emerged and birds are starting to roost, we are starting to see bird damage in spike to 2-leaf stage corn. You can distinguish bird damage from cutworm damage by the pattern in the field: generally longer strips of damaged plants, plants pulled out of the ground, and/or plants cut high that are compressed at the base of the stems. Although birds can cut plants off at the soil surface, they tend to pull plants out of the ground. In addition, if you look closely you will see " bird prints" near the missing plants or holes where birds have pulled plants out of the ground, so do not confuse it with cutworm damage.


Small Grains.

Cereal leaf beetle can still be found in barley and wheat fields throughout the state. No treatment is needed until you find either 0.5 larvae per stem or 25 eggs and/or larvae per 100 tillers and 50% of the eggs have hatched. We have also found our first grass sawfly larvae and armyworm egg masses in barley in Kent and Sussex Counties. Now that wheat heads have started to emerge in many fields, you should begin to sample wheat and barley closely for armyworms and grass sawflies. We expect to find both larvae present in wheat by next week. True armyworm traps catches in the Harrington, Little Creek and Rising Suns areas are either approaching or have exceeded our threshold of 200 moths for the month of April. Remember,  armyworm larvae are nocturnal so look for larvae at the base of the plants during the day. The threshold is one per foot of row for barley and 2 per foot of row for wheat. Once sawfly 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 or 0.4 larvae per foot of row. If both are present, the threshold for each should be reduced by one-half. In barley, your control options for all 3 insect pests include Lannate or Parathion. In wheat, your options include Lannate, Mustang, Parathion or Warrior. Remember, Parathion can only be applied by air and has numerous set back restrictions.





Cereal Leaf Beetle Larva and Feeding



April 12 through April 19, 2002 

Trap Counts Provided by UAP Inc., Seaford, DE and University of Delaware IPM

<div align="left">Location</div>

# Moths

<div align="left">Location</div>

# Moths

Argos Corner






Little Creek






















Harrington E




Harrington N





















Soil-Applied Herbicides Need To Be Moved Into the Soil - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu


Herbicides applied to the soil surface require rainfall, irrigation, or mechanical incorporation 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.  Mechanical incorporation with a field cultivator, set no more than 3 to 4 inches deep, will physically move the herbicide into the root zone.  Field cultivator set any deeper will cause the herbicides to become too diluted.  A field cultivator will mix the soil to half the depth it is set (set to 4 inches – soil mixes to 2 inches).  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.  And 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.



Should You Leave Princep Out with Later No-Till Corn Planting? - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu


In the past, it was recommended to use Princep when the cornfields were sprayed early, then switch to Bladex after mid-April.  Both products would provide residual control of crabgrass and fall panicum, however Bladex was more effective for controlling these grasses when they were emerged.  I have been asked whether it is worth to include Princep as a component of no-till spray mixes since Bladex is no longer available.  Princep will not control emerged grasses, but it will provide residual control.  But be sure to include paraquat or glyphosate to control the grasses that have already emerged, then Princep will be there to control late emerging grasses.  In fields with a history of crabgrass problems, it is a good idea to include Princep even with later plantings.





Options For Burndown In No-Till Full Season Soybeans In Light of Glyphosate-Resistant Horseweed - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu


Glyphosate-resistant horseweed (or marestail or Conyza canadensis) has been identified in DE, MD, and NJ.  The resistance is to all glyphosate products including Roundup Ultra, Touchdown IQ, and all the generic brands.  Horseweed is a winter annual weed that begins to emerge in the fall and continues into summer.


We are not discouraging growers from using Roundup Ready crops.  Rather, encouraging them to avoid repeated glyphosate applications per year, or relying solely on glyphosate for weed control year after year.  One way to avoid this is to not use glyphosate as the burndown herbicide.  Since the horseweed are resistant to glyphosate, the best herbicide option is Gramoxone (paraquat).  The occurrence of resistant horseweed has made burndown for full-season no-till soybeans more management intensive. 


Gramoxone is an alternative burndown and will improve control of other problem weeds that glyphosate is not as effective on, such as, cutleaf evening primrose, wild pansy, and henbit.  However, there are issues with 2,4-D use such as it needs to be applied at least 1 week before planting and volatility concerns with 2,4-D.


Options for controlling glyphosate-resistant horseweed with Roundup Ready soybeans.  Additional research is needed to identify consistent, effective, one-pass programs for horseweed control.


  1. Tillage


Horseweed is controlled by conventional tillage.  However, given the benefits of no-till and additional cost of conventional tillage production, the additional cost of herbicides is certainly a better option than tillage.


  1. Gramoxone programs


Over the years, the most effective program has been Gramoxone applied up to 10 to 14 days preplant followed by an additional application of Gramoxone at planting.  In some situations, one application of Gramoxone is adequate, but over half the time a second application will be needed.  Products such as Canopy, Canopy XL, or FirstRate can be tankmixed with Gramoxone and can improve control over Gramoxone alone, as well as provide residual weed control.


Another option is an application of Gramoxone plus 2,4-D at least 1 week prior to planting.  The 2,4-D will improve control over Gramoxone alone, but often is not adequate and an additional Gramoxone application is needed.  Gramoxone applications as early as possible will improve control.


Roundup (or Touchdown) plus 2,4-D or Amplify

This program is highly discouraged in areas of continuous or frequent Roundup-Ready crop production in the same field.  Since Roundup Ready soybeans are being planted, there will be at least one application of glyphosate after the soybeans have emerged.  Multiple applications of the same herbicide should not be made to the same field in the same year to minimize developing resistance.


Options for controlling horseweed after the soybeans have emerged are either FirstRate or Classic, since additional glyphosate applications will not control the resistant horseweed.   FirstRate should be applied at 0.3 oz/A and Classic at ½ to 2/3 oz/A.  Note that Classic at 2/3 oz/A may cause soybean injury.


For non-Roundup Ready soybeans, conventional herbicide programs with Canopy or Canopy XL plus a residual grass herbicide should be the best base programs to be applied with a burndown treatment.


Some of the issues for use of 2,4-D are:


Ester formulation (the more effective formulation) needs to be applied 1 week prior to planting if 1 pt or less is used or 30 days prior to plant if more than 1 pt/A is used.


Amine formulation (less volatile) needs to be applied 15 days prior to planting if 1 pt or less is used or 30 days prior to plant if more than 1 pt/A is used.


Volatility.  Should not be applied if daily temperatures are expected to be greater than 85 degrees.  With higher temperatures, it is more advantageous to spray in late afternoon or evenings.  Due to volatility concerns, applications should be made as early in the season as possible to avoid high temperatures and prior to planting and emergence of susceptible broadleaf crops.




Field Crop Diseases -  Bob Mulrooney, Extension Vegetable Pathologist, University of Delaware  bobmul@udel.edu


The Delaware Department of Agriculture granted a section 24c request to the Bayer Corp. for the use of the fungicide Stratego on wheat at any growth stage through Feekes Growth stage 10.5 (full head emergence). Previously it could only be applied up through flag leaf emergence. Stratego is a combination of propiconizole the active ingredient in Tilt plus trifloxystrobin (Flint). Testing in Maryland and Virginia has shown it to be a very good fungicide for the control of glume blotch, tan spot, rust and powdery mildew. Like Quadris it will also brighten wheat straw significantly when applied at heading. If powdery mildew is the only disease that occurs, Tilt and Stratego are comparable and Tilt will be less expensive. Yield response will depend on variety susceptibility and other agronomic factors as well as weather conditions.


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 70F). 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 60F. 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.


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




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


Farm Bill Done Today?

House and Senate farm bill conferees are expected to reach a farm bill agreement either today or by the end of the week. Farm bill provisions that are relevant to the 2002 crop will be reported as soon as they become available.


Are Agricultural Futures Broken?

The answer to that question was pondered by experts in the grain trade this week. The consensus appears to be that although not broken, the commodity markets are working differently now than they did just a few years ago. The reason being the globalization of the grain trade and how that impacts commodity prices. The U.S. domestic market used to be the dominant player in e.g., the soybean market, or the wheat market. In the case of soybeans, we now have the Southern Hemisphere as a dominant production area and exporter of soybeans. For wheat, the Ukraine, India, and Pakistan are now all wheat exporters. The bottom line effect of the transition taking place in the U.S. commodities and world markets is the diminished use of futures for hedging purposes. In other words, the opportunity to hedge or forward contract a commodity are currently fewer and farther between than they have been in the past.


Marketing Strategy

The announcement of Farm Bill details may help to shed some light on individual marketing plans for the 2002 crop year.  Loan rates should remain the same as last year since 2002 loan rates were set in the previous Farm Bill.  No new sales are being recommended at this point in time.




Sulfur Deficiencies Potential - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu


After two years of excellent crops in many areas of the state, there is an increased risk on sandy, low organic matter soils for early season sulfur (S) deficiency on corn and soybeans.  High yields and at or above normal rainfall has removed much of the available S from the top 12 inches of very sandy, low organic matter soils.  This is especially true for irrigated corn and bean production fields on sandy soils since high yields and downward leaching of S with excess irrigation water is probably the normal situation.  Sulfur deficiency in the topsoil can lead to reduced stands, especially in corn.  If you observe or scout the fields early enough you’ll notice yellowing of the newly emerging leaves and overall stunting of the plant.  For those with fields in areas of Maryland that have deep sands, I’ve seen it affecting entire fields or at least large areas of some fields in the past.  Watch for it first on the sandy knolls where there is little organic matter in the soil.  Symptoms will be more severe in fields that receive only nitrate as the nitrogen source since S is needed for the nitrate reductase enzyme system that reduces nitrate-nitrogen into compounds (amines) that the plant can use to make amino acids and then proteins and enzymes.


Although we seldom notice it in soybeans, S deficiency can have an adverse effect on Bradyrhizobia nodule formation and can significantly reduce the effectiveness of the nitrogen fixing system of legumes such as soybeans.  Again, symptoms besides slow nodulation include general yellowing of the plant and stunting of the plant.


What can be done about S deficiency?  Often, we seldom see actual yield responses to S fertilization.  This is because many of our soils, even the sandiest of soils, have clay lenses about 16 to 22 inches deep in the soil.  These clay lenses capture and hold much of the S that leaches out of the top soil.  Studies here at the University have shown that 300 to 500 lb S/acre can actually be present in sandy soils that a surface (0 to 8 inch) soil sample indicates is deficient in S.  So what growers need to do is to support the crop until it can establish a root system that can reach the deep S supplying layers.  To do this, you can add a small amount of ammonium sulfate or other S fertilizer source in with starter fertilizers or early season broadcast fertilizers or herbicide applications.  Generally, it takes only a small amount of S to feed the seedling corn or soybean plant until the root system develops enough.  Crops use about 20 to 40 or more pounds of S per acre per year so 5 to 10 lbs S/A at planting should be enough to support crop growth until the roots reach the deeper soil layers and the S reserves.




Christmas Tree Diseases -  Bob Mulrooney, Extension Vegetable Pathologist, University of Delaware  bobmul@udel.edu



Christmas Tree Growers.



Rhabdocline needlecast has been identified in Kent and New Castle counties on Douglas fir. Christmas tree growers with Douglas fir need to check their plantings now. This is the only needlecast or needle spotting disease that we see on Douglas fir. Heavy infections and subsequent needle loss can make trees unfit for sale for several years. Look for reddish brown needles on last year's growth. The undersides of the needles will have long pustules that will split to spread the spores of the fungus to the new growth. Protect the new growth with applications of chlorothalonil (Bravo, Daconil).


Rhabdocline is a fungus disease caused by the fungus Rhabdocline pseudotsugae and R. weirii. Infection occurs from late April through early June. Wet needles and cool temperatures (53-59°F is ideal) favor infection.



1. Plan plant placement and weed control to insure good air circulation to reduce humidity and period of needle wetness.


2. Three or four applications of chlorothalonil:


1st as first buds break,

2nd one week later,

3rd three weeks after first buds break,

4th if spring is prolonged by cool   weather,6 weeks after first bud break.






                   Weather Summary

Week of April 19 to April 24, 2002



0.05 inches: April 21

0.21 inches: April 22


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


Air Temperature:

Highs Ranged from 84°F on April 19 to 56°F on April 23.

Lows Ranged from 64°F on April 19 to 34°F on April 24.


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 University and the United States Department of Agriculture cooperating, John C. Nye, 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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