Volume 8, Issue 6                                                                                                                            April 28, 2000


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



Diamondback and imported cabbageworm egg laying has increased. As soon as temperatures increase, larvae will 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, Proclaim or a Bt insecticide should be used. Be sure to rotate between these 3 classes of insecticides to avoid the development of resistance to either class of chemistry.



The current cool wet weather is very conducive to seed corn maggot problems. Flies continue to lay eggs and will be present at the time of transplanting. In general, the potential for damage exists throughout the month of May so preventative treatments are needed. If a seed treatment is possible, materials containing diazinon or chlorpyrifos should be used. Broadcast applications of diazinon prior to planting have provided effective control but must be done close to planting and incorporated in 3-4 inches of soil. In addition, Admire is now labeled on cucurbits. Most of the work with Admire on cucurbits has been aimed at cucumber beetle control. At planting applications should also provide seed corn maggot protection. Admire can be applied at planting, through the drip or as a drench to transplants. Work done at Penn State University demonstrated that Admire applied one day prior to transplanting at a very low rate of 0.02 ml/plant provided cucumber beetle control for 2 weeks. They also observed leaf burning at 0.04 ml/plant at the 2-leaf stage; however, the plants grew out of this damage in 2 weeks. In addition, be sure to watch for aphids that can develop in the greenhouse prior to transplanting. A treatment should be applied if 10 to 20 percent of the plants are infested and/or if you see leaf curling. Lannate should provide control. Although listed in the Vegetable Recommendations, Provado is NOT LABELED as a foliar application on cucurbits. This label was issued by EPA last August but retracted by Bayer after the recommendation book went to print.



Pea aphids can be found in many early-planted fields and  beneficial insect activity appear to be reduced due to the cool, wet weather. Although populations have not exploded, we continue to see an increase in activity. Fields should be checked before the bud stage for aphids feeding on small plants. 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 or Lannate will provide control. Be sure to check the labels for application restrictions during bloom.



The first Colorado potato beetle adults have been detected; however, populations remain very light. No adult treatments will be needed unless you find 25 beetles per 50 plants and 20% leaf defoliation. European corn borer moth activity remains at or below one 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. Furadan, Ambush, Baythroid, Pounce or Monitor will provide corn borer control. If Colorado potato beetles are also present, Spintor applied at the 4-6 oz/acre rate has also provided corn borer control.







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



Be sure to check newly planted fields for white rust. The yellow discoloration on the upper sides of the leaves may be the first symptom that you see. Turning the leaf over reveals the white blister-like lesions of the fungus Albugo occidentalis. Spring plantings can be protected with copper. Overwintered fields continue to be seen with white rust. For fields close to harvest, harvest the crop, and wait for several days for new growth to appear. Apply Quadris to the field to protect the new growth from the disease.  Contact your county agent for a copy of the label.



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


Welcome to the 2000 Late Blight Update. This year the data for the late blight forecast will be provided by SkyBit, Inc. This is the same provider we used last season. This year we have subscribed to one site only, which is Joe Jackewicz’s farm. Although not perfect, using this site will give us usable information for the entire potato-growing region in Delaware. Delaware Cooperative Extension will maintain one Sensor weather monitoring unit at the Jackewicz location for back-up and additional weather collection.


Once again you are reminded to keep a record of when your fields reach green row (50% of the plants have emerged). Severity value accumulation begins at green row. I will use the earliest emergence date for the state, which was Dan Baldwin in Sussex, and will post several others as potatoes emerge throughout the growing area.


The SkyBit subscription is provided by the Potato Growers Association and we are grateful for their contribution. The Fax will be sent twice a week. If you know of anyone who wants to be added, please have them call 302-831-4865, email me at bobmul@udel.edu, or Fax me at 302-831-0605 and leave their fax number, name, and affiliation.


Growers will want to keep on their toes this season, because late blight was present in many seed growing areas last season including the Canadian maritimes and Maine. As always, the best control of late blight is planting disease-free seed. Protectant fungicide applications will provide protection of the crop if applied in a timely manner. Growers have the protectant fungicides such as the EDBC’s (Dithane, Manzate, Pencozeb, Polyram), chlorothalonil (Bravo, Terranil), and tin plus an EBDC. Curzate, AcrobatMZ, and Quadris, which were labeled last season, are also available.


DSV Accumulations as of April 25, 2000 are as follows:

(Remember … 18 DSV’s is the threshold to begin a spray program)


Emergence Date

DVS’s April 25


April 14


5 day, low rate

April 19


no spray

April 21


no spray






Field Crops

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


Field Corn.

As of April 25, only 40 degree days (base 50) have accumulated since peak moth catches in pheromone traps in Sussex County. If conditions remain cool and wet, we should not expect to see cutting activity until the end of May. However, corn should be checked for black cutworm feeding activity as soon as it spikes through the ground. 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.



Although we can find an occasional wheat or barley field with increased levels of aphids and cereal leaf beetle, larvae can now be found.  Insect activity remains low in most fields. The first grass sawfly larvae were found in wheat at the end of last week. No armyworms have been detected. A sweep net can be used to detect small grass sawfly larvae that are first found in denser areas along field edges. Once larvae are detected, look for larvae in 5 linear foot of row in  5-10 areas of a field.  You will need to shake the plants to dislodge larvae that feed on the plants during the day. Since true armyworm larvae are generally found at the base of the plants during the day, you will also need to look at the base of plants for armyworms. The treatment threshold for sawfly is 0.4 per foot of row. The treatment threshold for armyworm is one per foot of row for barley or two per foot of row for wheat.



As you make plans to plant full season soybeans, be sure to consider controls for seed corn maggot. Although flies are attracted to no-till situations, they also like freshly plowed ground and areas high in organic matter. A seed treatment containing diazinon or permethrin should be used on all early planted soybeans.





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



Be on the lookout for Sclerotinia crown rot on young, fall-seeded alfalfa. The cool, wet weather has certainly been favorable for disease development. Young shoots will wilt and turn tan as they dry. Infected crowns will have white cottony fungal growth when relative humidity is high or it is raining. The hard black overwintering structures of the fungus called sclerotia form in the white cottony fungus and can often be seen on infected plant parts. With Sclerotinia, infection takes place in the fall and the fungus overwinters with the host and resumes growth in the spring. The key to control is to rotate away from fields that have had alfalfa or clover before and deep plow to bury the overwintering sclerotia. Spring plantings escape infection because the plants by fall are older and more resistant to infection. There are no rescue treatments for Sclerotinia crown rot. Cut as soon as flower buds form and remove the cutting. This opens the canopy and the infections dry out. By this time warmer and drier weather prevent anymore disease activity.


Wheat and Barley.

Now that heads have emerged in many parts of the state loose smut will be very easy to identify. Look for the blackened diseased heads among the healthy green heads. After a short time the black spore masses disintegrate leaving only the bare rachis. Seed kept from smut infected fields should be treated with a fungicide that controls loose smut such as Raxil, Baytan, Vitavax, or Dividend at the 120 ppm rate before planting next season.

It is important to keep scouting wheat for powdery mildew. Head emergence is the last opportunity to apply Tilt if mildew is at threshold levels.





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


Commodity Prices to Remain Erratic Through Planting Season.

The choppy erratic price action in the commodities market that we've been experiencing since the beginning of March is expected to continue for the next several weeks. Currently, the market is reacting to conflicting weather reports on almost a daily basis. Considering market fundamentals commodity traders will now wait until they get a better idea on possible planting progress, possible drought and crop conditions. Regarding the weather, the market continues to be locked into the buy the rumor (the forecast) and sell the fact (actual weather conditions) mode. This factor alone is causing most of the erratic price action.


Although the weather phenomena is currently getting all of the attention in commodity trading, a closer look at the soybean market points out a few other factors that are likely influencing soybean prices. For example, eight out of the last eleven U.S. supply and demand reports reduced the carryout estimate for soybeans. In June of last year, U.S. soybean carryout for the current marketing year was forecast at nearly600 million bushels, almost double the current April 11th estimate of 305 million bushels. In addition, world soybean stocks are now forecast to be lower, albeit slightly, than a year ago and lower than two years ago. Considering the technicals in this market, the current trend for both old crop and new crop soybean futures is up, with support for November futures at $5.62 and resistance at $5.74 per bushel. Therefore, it can be stated that even though much attention has been given to the concern over subsoil moisture in the Corn Belt there are other positive factors that are influencing this market. With current basis offerings on the shore reported at 15 under, it is now possible to achieve $5.50 or better per bushel for new crop soybeans. Even though it may be prudent to contract some beans at this price level, all things considered suggests that we keep initial new crop 2000 soybean sales to a minimum level, no more than 10 to 20% at current price levels.




Scout Your Legume and Legume/Grass  Mixtures for Nutritional Problems  -  Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu


Alfalfa, red clover, white clover, and other legumes have entered their rapid spring growth phase.  Over the next several weeks will be an ideal time to scout them for nutritional deficiency symptoms especially if you have not done a soil test recently.  This will be especially critical in legume/grass mixtures.  Grasses tend to draw heavily on soil potash reserves and will accumulate extra potash in the tissue in what is known as luxury consumption.  This rapid draw down of a nutrient essential for maximum legume production can be a critical yield limiting factor.


What visual symptoms should you look for when scouting legume fields?  For potash or potassium, the first visual symptom is usually small, white oblong spots on individual leaflets.  These spots eventually coalesce or blend together to show up as necrosis or dead tissue all around the margin of the leaflet.  The white spots are a classic potassium deficiency symptom for legumes.


If the plants show a general chlorotic or yellow cast to the leaves and are generally shorter than normal, the crop is suffering from a sulfur deficiency present or the crop has failed to nodulate.  Nodulation failure is really a nitrogen deficiency since the Bradyrhizobia bacteria are not present to fix atmospheric nitrogen in a form usable by the crop.  To decide which it might be, dig up legume plants in several locations and check the roots to see if nodules are present.  If nodules are present on the roots, cut several nodules open and see if they are active.  If active, they should show a reddish or pinkish color on the cut surface of the nodule.


Boron is another deficiency that might be present.  Boron deficiency symptoms range from an orangish yellow to a reddish yellow color on the upper terminals.  The internodes are often quite short giving the plant an odd stunted appearance.


If you see visual symptoms and can’t pin them down to a particular nutrient deficiency, use either a soil test or a tissue test to confirm a diagnosis of the problem.



Compaction Potential on Wet Ground  -  Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu


Driving around the state as well as on the way home, I’ve noticed several tractors stuck in the fields where someone was trying to get some type of tillage completed so they could get in to plant.  Even though the season is moving along rapidly, the weather has been making field work a very iffy proposition.  We’re all anxious to get crops in the ground but keep in mind that compaction results when ground is worked too wet.  Compaction can be a significant yield-reducing factor and often is an invisible enemy.


Another worry for those of us who may have planted corn already is that the cold wet weather has delayed emergence.  When corn sits in the ground for much more than three weeks, the risk of seeing stand problems increases dramatically.  In those fields that have been planted for a long time, be sure to scout them frequently to spot potential problems as soon as possible.  If replanting is necessary, it is best to do it as soon as possible.  When you’re scouting these early-planted fields, dig some kernels up to examine them for possible seed and seedling rot diseases.  Also, note how far apart the first and last plants to emerge are.  If plants are emerging as much as ten days after the first plant emerges, yield loss can be as great as 8 percent.  If there is as much as a 21-day delay between the first and the last plant to emerge, yield losses of 10 to 20 percent can occur.







Delayed Soil Applied Herbicide ApplicationMark VanGessel, Extension Weed Specialist; mjv@udel.edu


If early-planted corn has not been sprayed yet, there is still time.  The following is a table for applying residual herbicides to emerged corn with maximum height of corn at time of application.  An * indicates these products contain atrazine.  An early postemergence application (weeds less than 1 inch tall) of atrazine will control most weeds.  Use of a non-ionic surfactant or crop oil concentrate with atrazine (or its pre-mixed products) will increase weed control, but also increases the likelihood of corn leaf burn.  Another option for emerged weeds is to include a low rate of a postemergence herbicide.  Postemergence herbicides alone at this time will not provide enough residual control of late emerging weeds.



Corn Height




no later than 4th visible leaf


do not apply to emerged corn




no later than 2-leaf stage



Axiom *

not labeled for emerged corn


no later than 2 collars

Bicep II *


Bicep II Magnum *


Bicep Lite II Magnum *


Bicep II Magnum TR *


Broadstrike SF + Dual


Bullet *


FieldMaster *

not labeled for emerged corn

Fultime *


Guardsman / LeadOff *


Harness Xtra *





Reminder About Soil-Insecticide and Herbicide InteractionsMark 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, Python, Scorpion III.  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.





Pesticide Container Recycling in Delaware:

                                             May 25
                                             June 22
                                             July 20
                                             August 24
                                             September 21
                                             October 26

 Sussex Conservation District Maintenance yard, Shortly Road, Georgetown. 

 Collections from 9:30 a.m.-1:30 p.m. 

 The service is FREE, but  containers must be properly RINSED clean. 


For more info, call DDA  1-800-282-8685 or 302-739-4811.





                    Weather Summary






Week of April 20 to April 26


0.44 inches: April 21, 2000

0.54 inches: April 25, 2000

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

Air Temperature:

Highs Ranged from 71°F on April 21 to 53° F on April 26.

Lows Ranged from 48°F on April 22 to 38° F on April 20.

Soil Temperature:

56°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:



Black Cutworm – Pheromone Trap Catches – 2000 Season

Trap Counts Provided by UAP Inc., Seaford, DE

April 17- 22, 2000



# 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



NOTE: As of April 25, 40 (base 50) degrees days have accumulated since peak moth flights in Sussex County, DE.

·        Moth catches of 9-15 moths per 7-day period have been associated with a moderate to high potential for cutworm outbreaks.

·        Moth catches of 5 per night for at least 2 consecutive nights have also indicated a high potential for problems

·        You can expect to see cutting activity approx.300 degree-days (base 50) from peak moth activity (9-15 per week or 5 per night for at least 2 consecutive nights)

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.

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