Volume 11, Issue 10 May 31, 2003



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



Continue to scout all melons for aphids, cucumber beetles, and spider mites. Economic levels of melon aphids can be found in many fields and cucumber beetle populations are starting to increase. The treatment threshold for aphids is 20% of the plants infested with at least 5 aphids per leaf. Actara. Fulfill, Lannate and Thiodan are labeled on melons and will provide melon aphid control.



Continue to sample for aphids. Since harvest is delayed compared to the 2002 season, a treatment will be needed if you find 5-10 aphids per plant or 50 or more aphids per sweep. Dimethoate or Lannate will provide aphid control.



Continue to sample peppers for thrips and corn borers. Watch for corn borer egg masses as well as check local moth catches in your area. A treatment with a pyrethroid may be needed if corn borer moth catches exceed 10 moths per night, especially if corn planting is delayed in your area or you are using rye strips as windbreaks. In general, 2 applications will be needed to achieve effective control.



Sample fields for Colorado potato beetle adults and larvae. The treatment threshold for adults is 25 beetles per 50 plants and 10 % defoliation. Once larvae are detected, the threshold is 4 small larvae per plant or 1.5 large larvae per plant. If multiple life stages are present, reduce these thresholds by one-half. Actara, cryolite, Spintor or Provado will provide control. Corn borer catches have increased. A corn borer spray will be needed 3-5 days after an increase in trap catches or when we reach 700-degree days (base 50). Currently we have only accumulated 432 degree-days. Be sure to check our website (http://www.udel.edu/IPM/traps/latestblt.html) for the most recent moth catches in your area. Ambush, Baythroid, Furadan, Penncap, Pounce or Spintor will provide control. If you are scouting for infested terminals, the first treatment should be applied when 20-25% of the terminals are infested. Furadan or Monitor will provide the best control if you are waiting until you see infested terminals. Potato leafhoppers populations remain light. Controls should be applied if you find to one adult per sweep and/or one nymph per every 10 leaves. Dimethoate, a pyrethroid, Actara or Provado will provide control.


Snap Beans.

All fields should be scouted for leafhopper and thrips activity, especially seedling stage beans. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. If both insects are present, the threshold for each should be reduced by 1/3. Dimethoate, Lannate, Asana, Capture, or Warrior will provide control of both insect pests.


Sweet Corn.

Flea beetles and cutworms are still active in seedling stage sweet corn. The treatment threshold for flea beetles is 5% infested plants. The cutworm threshold is 3% cut plants or 10% leaf feeding. Continue to sample any corn in the whorl to pre-tassel stages for European corn borer larvae. A treatment should be applied if 15% of the plants are infested. The best timing for a treatment is just as the tassels are emerging from the whorls. In recent years, Baythroid, Mustang, Penncap or Warrior have provided effective control. If corn was planted under plastic, the first silk sprays will be needed as soon as ear shanks are visible. Treatment will be needed on a 5-6 day schedule in Kent and Sussex Counties.




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

The U.S. Environmental Protection Agency (EPA) has approved a new fungicide from Syngenta Crop Protection for the control of foliar and soil-borne diseases in potatoes and vegetables. According to the company, potato and vegetable growers can now enjoy the performance of Quadris fungicide in a dry formulation called Amistar. This fungicide has received EPA approval for control of foliar and soil-borne diseases and will have limited introductory quantities available in the 2003 season.


Amistar provides growers with the same active ingredient as Quadris. Applied either by ground or air, the product controls diseases from all four classes of fungi including early blight, late blight, powdery mildew and black dot in potatoes and powdery mildew, downy mildew, septoria leaf spot and anthracnose in vegetables, according to the company.

The EPA has designated Amistar a reduced risk pesticide, according to the company. In addition, the product has a re-entry interval of four hours. As with all fungicides, resistance management is key to protecting its efficacy.

From Spudman.




Field Crops


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


Grasshoppers in Field Crops.

We are starting to see the first grasshopper nymphs in no-till fields and along field edges. Although very few soybean fields have been planted, be sure to watch fields carefully at emergence for grasshopper activity. As a general guideline, non-crop areas should be treated if you find 20 or more grasshoppers per square yard. In corn and sorghum, a treatment is justified if you find 5-8 grasshoppers per square yard. In soybeans, the threshold is one per sweep and 30 percent defoliation. In all 3 crops, dimethoate, Lorsban, Asana and Warrior will provide control, but multiple applications may be needed. Furadan is also labeled on corn and soybeans and has provided good grasshopper control.



Continue to sample fields for potato leafhopper adults and nymphs. Since it has been 3 weeks since the first potato leafhopper adults were detected, we are starting to see our first nymphs. Although all stages can cause damage, nymphs can quickly cause plant damage. The treatment thresholds are 20 per 100 sweeps on alfalfa 3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100 per 100 sweeps in 7-11 inch tall alfalfa. Baythroid, dimethoate, Mustang or Warrior will provide effective control.


 Field Corn.

Continue to sample no-till fields for cutworms and true armyworm. The treatment threshold for armyworms in corn is 25% infested plants with larvae less than one-inch long. A pyrethroid will provide effective control, but only if worms are less than one-inch long.


We can also find flea beetles feeding on seedling stage field corn. In general, this insect does not cause economic losses in field corn. Although it can vector Stewart's bacterial wilt, most field corn hybrids are resistant to Stewart's wilt. However, if plants are stressed and numbers are high, they can stunt plant growth. A treatment may be needed if 50% of the plants are infested with 5-6 beetles per plant.


Slug activity continues to increase in many no-till fields. The following is information from Galen Dively, University of Maryland on his slug research in field corn:


" I conducted a field study several years ago to measure the corn plant's ability to withstand slug damage. The work was done in a no-till field with closed seed slots and an average of ten slugs per plant at emergence. At the 2-3 leaf stage, individual plants were rated for damage and then flagged for later assessments of seedling mortality and plant growth at 1, 2, and 4 weeks after the initial rating. No controls were applied, so the slug population present at plant emergence was allowed to develop and feed on seedlings after the damage ratings were made. The rating categories included: 1= seedling completely severed at ground level; 2= all leaves consumed except one remaining intact (greater than 75% defoliated); 3= all leaves showing moderate damage, but entire plant intact (25 to 50% defoliated); 4= only one leaf showing damage (less than 25% defoliated); 5= no damage. Approx. 100 plants were rated in each category and the following data were obtained:




Avg. % Seedling Mortality

Avg. No. of leaves

At 1 wk

At 2 wks.

At 4 wks.






















The study showed that a considerable amount of slug injury could be tolerated before plant density and growth is severely affected. Although regrowth delayed the production of leaves, 32% of the severed plants and 83% of the plants that were more than 75% defoliated recovered after 2 weeks from the initial onset of injury. All plants in categories 3 (25 to 50% defoliated) and 4 recovered completely and were not significantly different from undamaged plants with respect to the number of leaves and plant height later in the season. Although individual plant yields were not determined, there were no observable differences in plant or ear size at harvest between damaged and undamaged plants; thus, any yield loss from slug damage is probably directly related to stand reduction.


Based on this study, populations of five or more slugs around each plant prior to the 3-leaf stage may be economic, especially if injury is heavy, plant growth is slow, and cool, wet conditions prevail. If the weather turns hot and dry, 10 or more slugs per plant may be tolerated if the seedlings reach the 3-leaf stage. Generally, if a heavily infested field reaches the 3-leaf stage without severe seedling mortality, the crop has survived the critical period and should outgrow further slug injury, regardless of the population pressure. "


Small Grains.

Fields should be scouted for cereal leaf beetle through the hard dough stage and for aphids through the soft dough stage. The cereal leaf beetle treatment threshold is 0.5 larvae per stem. The treatment threshold for aphids is 20--25 per head with low beneficial activity (less than 1 per 50 aphids). Sawfly and armyworm populations remain low. In both wheat and barley, the treatment threshold for sawflies is 2 per 5 foot of row innerspace or 0.4 per foot of row. The armyworm threshold is one per foot of row in barley and two per foot of row in wheat. If multiple pests are present in barley, your control options 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.



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


Net blotch and the spot blotch form of net blotch are present in many parts of the state. The spot blotch form produces an oval dark brown spot with or without a yellow halo. Typical net blotch with net-like symptoms is present as well which has not been common here. I see mostly the spot blotch symptoms more often. This can vary due to change in varieties and the type of resistance present in those varieties. See the attached photos for symptoms. We have no data on the benefit of controlling net blotch in barley, but it would be difficult to justify from an economic point of view.



Powdery mildew does not seem to be as bad as one would guess from all the wet weather. The cool temperatures (below 59F) may be helping, but if temperatures rise, more could be seen, but most wheat is past flowering and the impact this late would be minimal.


The developing disease of concern now appears to be speckled leaf blotch caused by Septoria tritici. This disease is widespread in many varieties in our variety trial plots in Middletown. It is staying on the lower leaves and research indicates that it is not as aggressive as Septoria nodorum which causes Septoria leafspot and glume blotch. It is the only Sepotria present in the plots, but in most years both can be found. This cool, wet weather pattern favors the speckled leaf blotch and not glume blotch, which needs warmer temperatures in the high 70s and 80s and wet weather to cause a problem.


Wheat in the Middletown plots is just flowering and just a few varieties have not begun to flower which would be the last opportunity for an application of Tilt, Stratego, Quadris or Headline. Symptoms of speckled leaf blotch can vary so identification is difficult unless you look at the spores. Speckled leaf blotch can produce narrow spots with parallel sides or a more oval spot with or without a yellow halo. Both produce fruiting bodies (pycnidia) in the spots. Those of speckled leaf blotch are dark and very numerous when the spots are old. Those of Septoria nodorum are light brown in color and not as numerous. The attached photos should help identify the disease.


Please note that tan spot has not been identified in either DE or MD so far.


1.      Typical net blotch symptoms on barley


2.      Closeup of net blotch.





3.      Speckled leaf blotch on wheat caused by Septoria tritici



4.      Different symptoms of speckled leaf blotch.


Wheat Flowering with Anthers emerged. Labels prohibit fungicides applied at this stage and later. Feekes 10.5.1.



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


Commodity Markets React to Weather Conditions and Fund Activity

New crop corn and soybean prices have slacked off slightly this week, both commodities reacting to expected improvements in the '03 crop planting progress. Yesterday afternoon's (May 26th) report confirmed trader expectations, although the '03 crop is a long way from being made.


For the 18 states included in the weekly crop progress report, U.S. soybean plantings are now 50% complete, representing a 25% jump over last week. This planting rate was expected by the trade and is 12% below the historical average. Soybeans are considered 17% emerged as of yesterday, compared to 33% on average and 14% last year. The 18 states included in this survey accounted for 95% of the 2001 soybean crop.


U.S. corn plantings are now considered 88% complete, ahead of last year's pace of 82% and the average of 91%. The trade was expecting corn plantings to be 90% complete. U.S. corn is now considered to be 64% emerged, 21% more than last week. This compares to last year's emergence of 51% and the average of 71%. The 18 states in the survey produced 92% of the 2002 corn crop.


Winter wheat conditions improved slightly from last week with a 1% increase in the excellent, a 1% increase in the good, no change in the fair, a 1% decline in the poor, and a 1% decline in the very poor categories. Winter wheat is now rated 55% good to excellent, compared to a 33% rating last year.


Spring wheat is now considered 90% planted, a 12% increase over last week and in line with last year's pace of 86% and the average of 88%. Emergence is reported at 71%, compared to 49% last year and 67% on average. The six states represented in this survey produced 99% of the spring wheat crop in 2002.


Weekly Exports

Exports were reported just below expectations for U.S. corn, and just above expectations for soybeans and wheat, at 23.4 million bushels, 10.7 million bushels, and 12.6 million bushels respectively. The weekly exports report and the weekly crop condition ratings were delayed one day this week due to the Memorial Day holiday.


Marketing Strategy

New crop Nov '03 soybeans are currently trading at $5.61 per bushel and a strong case is being made by at least one private grain analyst that soybeans may have reached their price peak for the season. Among the other speculative reasons given, the two that appear most convincing are the decline in the demand for U.S. soybeans in the Asian market, and the likelihood that Brazil will now double crop recently harvested soybeans with soybeans rather than corn, as is the usual practice. This is likely because of the world price of soybeans. To what degree this may happen remains to be seen. Breaking news about SARS this week and BSE in Canada is likely to reduce Asian demand further and soybean demand in general.


As stated previously, the weather can have a significant impact on commodity prices and the impact on this year's corn and soybean production is uncertain. However, it seems prudent at this time to be thinking about advancing new crop soybean sales to the 30% level.


New crop corn and wheat sales should be placed on hold this week. For those needing to advance new crop wheat sales it is important to note the premium being offered for Dec '03 vs. July '03 futures.









Delayed Soil-Applied Herbicide Application - Mark VanGessel, Extension Weed Specialist, mjv@udel.edu


If corn has been planted but 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 often not provide enough residual control of many late emerging weeds.



Maximum Corn Height


12 inches


30 inches or 8 leaf


not labeled for emerged corn

Dual II Magnum

5 inches


5 inches


5 inches


12 inches


5 inches


do not apply to emerged corn


2 inches


30 or 8 collar, whichever is more restrictive

Topnotch / Harness / Degree

11 inches




not labeled for emerged corn


no later than 2 collars

Bicep II Magnum * / Cinch ATZ*

5 inches

Bicep Lite II Magnum *

5 inches

Bullet *

5 inches

Field Master *

not labeled for emerged corn

Fultime * / Keystone*

11 inches

Guardsman Max*

12 inches

Harness Xtra * / Degree Xtra *

11 inches


2 inches

Lumax *

5 inches





Excess Rainfall Can Cause Loss of Soil-Applied Herbicides - Mark VanGessel, Extension Weed Specialist, mjv@udel.edu


The excess rainfall we have been getting can cause some of the herbicides to dissipate and lose their effectiveness sooner than we see in drier years. Its a double-edged sword, you need rainfall (or irrigation) to activate the soil-applied herbicides, but then too much will cause them to not work as long as needed. How much rain is too much? It will depend on the herbicides you used. Those herbicides that are highly water soluble are more likely to be lost than those with less solubility. The other way to think about it, is those herbicides that need more rain to activate them are more likely to last longer in a wet year.


NOTE: ++++ does lose activity 4 times faster than +; it is used to demonstrate herbicides with more +s are more likely to lose activity with excess rainfall.





Solubility (ppm)

Likelihood of Losing Activity










Dual II Magnum






Harness / Degree



Lasso (Micro-Tech, Partner)


















Bicep II Magnum

Dual II Magnum, Atrazine

Bicep Lite II Magnum

Dual II Magnum, Atrazine

Field Master

Harness, Atrazine, Roundup

Fultime / Keystone

Topnotch, Atrazine

Guardsman Max

Outlook, Atrazine

Harness Xtra / Degree Xtra

Harness (or Degree), Atrazine


Dual II Magnum, Callisto, Atrazine



Fields will need to be scouted more intensively to be sure that weeds emerging prior to layby are treated. If the field is clean, (no emerged weeds) at layby it should be fine. But if weeds start to emerge prior to layby they may need to be treated. Often times you can not tell if weeds have started to emerge unless you walk the field.






Agronomic Crops Twilight Session


When: Tuesday, June 3, 2003

Where: UD Cooperative Extension Research and Demonstration Area

(3/4-mile east of Armstrong Corner, on Marl Pit Rd. Rd 429)

Time: 6:00 PM


Join your fellow producers and the UD Extension team for an interactive and hands-on experience as we discuss demonstration trials and address in-season production issues in

small grains, corn, and soybeans. We will focus on:

  • Small grain variety comparisons,
  • Corn fertility and nutrient management,
  • Insect, weed, and disease management.


We will apply for both DE Pesticide and Nutrient Management re-certification credit.


This meeting is free and everyone interested in attending is welcome. To register, for more information or special consideration in accessing this meeting, please call our office in advance, at (302) 831-2667.


See you there!

Carl P. Davis, Extension Agent, Agriculture




Weather Summary



Weeks of May 23 to May 29, 2003


0.30 inches: May 23

0.01 inches: May 24

0.01 inches: May 25

0.61 inches: May 26

0.03 inches: May 27

0.35 inches: May 28

0.04 inches: May 29


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

Air Temperature:

Highs Ranged from 72F on May 29 to 56F on May 23

Lows Ranged from 56F on May 26 to 49F on May 27

Soil Temperature:

62F 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, Robin Morgan, 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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