Volume 6, Issue 10                                                                                          May 29, 1998


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


Although diamondback larval activity has been light so far, be sure to watch for an increase in activity by the end of the week. Moths could be easily found laying eggs in fields at the end of last week so larvae should be found by the end of this week. Spintor or a BT will provide control. If populations have exploded, Spintor will provide the best control.


As vines begin to run on the earliest plantings, be sure to watch for increases in aphid and mite activity. Although melon aphids can be found in many fields, populations are generally low and have not reached economic levels in most fields. Treatment should be considered if 20% of the plants are infested; however, you should also see at least 5 aphids per leaf. In addition, beneficial insects can often clean up a population. Lannate is the only material labeled on melons that provides melon aphid control. Dimethoate will not control melon aphids. We have not detected any mites; however, the earliest planted fields should be sampled carefully for mites. The crown area of the plant should be checked on a weekly basis for signs of stippling and the presence of mites. Controls should be applied if 10 –15% of the crowns are infested. The only mite control options are dimethoate, Kelthane and Agri-mek. If you have not gotten control with dimethoate in the past, your first application should be with Kelthane. In field tests in 1997, Agri-Mek worked well at the 8 oz per acre rate and gave approximately 3 weeks of control.


With the increase in corn borer activity last week, we should begin to see the first larvae tunneling into plants this week. A treatment should be applied if you find 20 – 25% of the terminals infested with larvae. Since Monitor and Furadan are systemic, either insecticide will provide the best control of larvae in the stems. Potato leafhopper activity continues to increase. Economic levels of adults

(> 1 per sweep) can be found in Bt potatoes as well as fields that were not treated with Admire at planting. Furadan or a pyrethroid will provide leafhopper control.

Sweet Corn.

With the increase in corn borer moth activity last week, watch for corn borer larvae feeding in the whorls of the earliest planted fields. Fields should be treated once you find 15% of the plants infested with live larvae. Ambush, Pounce, Penncap or Warrior will provide the best control. *

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


Continue to apply a copper fungicide plus mancozeb as a foliar spray shortly after transplanting and 7-days later to reduce problems from bacterial diseases. Apply Bravo or Quadris for early blight and late blight control once fruit reach the size of a quarter, or earlier if tomatoes have been grown in the same area often.


Planting on rounded, raised beds is important if Phytophthora root and crown rot has been a problem. Apply Ridomil Gold 4E as soon after transplanting and repeat in 30 and 60 days for control. Apply a copper fungicide plus maneb as a foliar spray soon after transplanting and 7 days later for control of bacterial leaf spot.


Root rot has shown up in some fields where drainage is poor because of compaction or low lying areas. Be sure to rotate fields 3-4 years to reduce root rot pathogens. Aphanomyces and Rhizoctonia have been the principal fungi found on the infected roots. The tap root is very dark and feeder roots are absent. Plants wilt and eventually die.

Late Blight Update

DSV accumulations as of May 26, 1998 are as follows:

Location/Emergence Date

DSV's May 21

DSV's May 25


Baldwin - 4/20



10-day, low rate

Jackewicz - 4/20



10-day, low rate

Zimmerman - 4/23



10-day, low rate

Baker - 5/1



10-day, low rate

As you can see no more DSV's have accumulated since the last report. The spray schedule can be increased to 10 days. For the most current DSV's, check the Late Blight Report at the UD Extension IPM website: http://www.udel.edu/IPM   *


Vegetable Diseases - Kate Everts, Extension Plant Pathologist, University of Maryland and University of Delaware ; everts@udel.edu

MELCAST Program for fungicide scheduling for Watermelon.

We have had two field seasons of success with the MELCAST program in trials at the University of Delaware REC near Georgetown and University of Maryland LESREC in Salisbury, and on a grower's farm near Laurel, DE. Fungicide applications were reduced by two to three sprays over the season and disease control was maintained. MELCAST was developed at Purdue University. It uses weather data to schedule protectant fungicide applications for anthracnose and gummy stem blight of watermelon, so that instead of spraying on a 7-day schedule, fungicides are applied according to the weather. The model is initiated when the first spray is applied. Environmental favorability index units (EFI) are then accumulated when the weather is conducive to disease development. The EFI are based on temperature and leaf wetness readings. They reflect how favorable it is for disease development, and will range from one to ten. Sprays are advised when the accumulated values reach the threshold (30 on Delmarva). This year we have set up a network of five weather stations on Delmarva (three are located in DE, two in MD). Weather data will be collected and used to calculate EFI for MELCAST.

We will publish EFI information in the Weekly Crop Update and on the University of Delaware IPM page (http://www.udel.edu/IPM ). It will also be available by fax three times weekly. If you would like to receive the EFI information by fax, please call UD REC at 856-7303 and give your name, address, phone and fax number to Mrs. Edna Marvil. In Maryland, call UM LESREC at (410)742-8788 and give this information to Mrs. Sherry Corbin.


When to Spray with MELCAST.

Do not use MELCAST if there is a disease outbreak in your field, it is a preventative program.

  1. The first fungicide spray should be applied by the time the vines begin to run.
  2. Once you have applied the first spray, accumulate daily EFI units.
  3. In addition to weather based EFI, add two EFI if you apply overhead irrigation to the crop.
  4. The accumulated EFI units are the "spray counter". When the spray counter reaches 30, apply a spray of chlorothalonil.
  5. Reset the spray counter to zero. Again, accumulate the EFI units until the spray counter reaches 30.
  6. If a spray has not been applied for 14 days, apply a fungicide and reset the spray counter to zero, continue accumulating EFI.


Below are the EFI values from weather stations located on the Eastern Shore May 20-26.

Any questions please call Phil Shields at (410) 742-8788 or e-mail: ps136@umail.umd.edu

EFI Values










Salisbury, MD








Wootten Farms

Galestown, MD








Mark Collins

Laurel, DE








U of D, REC

Georgetown, DE







Vincent Farms

Laurel, DE









Field Crops

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

Small Grains.

Sawfly head clipping has increased significantly in fields that did not receive an insecticide treatment for cereal leaf beetles. The decision to treat for sawflies should be made this week. Once the number of heads clipped is twice as great as the larval count, it is generally too late to treat. Armyworm activity has increased in barley. Larvae can be found feeding on the leaves as well as clipping heads. Controls should be applied if you can find one larva per foot of row. Since Warrior is not labeled on barley, Parathion (by air only), Lannate or Penncap should be used. Penncap should only be used if the larvae are small and should be avoided if bees are foraging in the area.


Seed corn maggot flies are still actively laying eggs; therefore, all full season no-till soybeans planted this week should still be treated with a seed treatment containing diazinon. As early-planted soybeans emerge, be sure to watch for bean leaf beetle and Mexican bean beetles. Control will not be needed until you find 40% defoliation and/or they are feeding on the cotyledons and the stand count is being reduced by 25%. A pyrethroid or Sevin will provide control of both insects. *


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


Scab and glume blotch continue to be seen. Wheat heads that are bleached out can be that way for several reasons. Check to see if the head can be easily pulled from the stem. If it pulls out easily, it was clipped by a corn borer in the stem. Usually the pattern in the field will be scattered, if corn borer is present. If the head does not pull out easily the problem may be the soilborne fungus take-all. Take-all infections will produce heads that are bleached but also have very poor root development. Scrape away the leaf sheath at the base of the plant and look for the diagnostic black streaking or darkening from take-all infections. When take-all levels are low scattered plants may be infected, but heavier infections will produce irregular patches of stunted plants with bleached heads. *


Pinnacle Has A Postemergence Label for Corn - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

Pinnacle herbicide from DuPont now has a supplemental label for early postemergence use on field corn in the Northeast and Mid-Atlantic states. Application timing is 2 to 6 leaf corn at 1/4 oz/A. Do not apply to field corn taller than 8 inches or 3 collars, whichever is more restrictive. There is a restriction with OP insecticides, refer to the label. *


Control of Perennial Weed Seedlings - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

Soil-applied herbicides do not control established perennial weeds emerging from roots or rhizomes. However, soil-applied herbicides can control those plants that emerge from seeds. In fact, what you are doing is controlling the weeds as if they are annuals. Perennial plants emerging from seeds can produce perennial root structures very rapidly, as little as three weeks after emergence. A study funded by the Delaware Soybean Board was designed to determine if soil-applied herbicides can control perennials emerging from seeds. The following is a list of weeds and herbicides that provided the greatest level of control:

Weed Herbicide with Greatest Level of Control
Hemp dogbane Authority, Command, Sencor/Lexone, and Canopy
Common milkweed Sencor/Lexone and Canopy
Canada thistle Command, Lorox, Sencor/Lexone, Python, Scepter, and Canopy
Common pokeweed Command, Authority, Sencor/Lexone, Python, and Canopy
Horsenettle Sencor/Lexone and Canopy

Where you are concerned about seeds being deposited into a field or part of the field previously not infested, there are some herbicide options for controlling the seedlings before they become established.  *


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

Grains Make New Lows

Corn Update

Prices closed on May 26 sharply lower with a 10 month low in December futures and a contract low for July. Near ideal weather pressured prices. Asian economic concerns added to the bearish mood, raising questions about demand. Asian economic concerns were fueled by new lows in the Japanese yen and declines in the Korean stock market.

Weekly export inspections were on the high side of expectations but were overwhelmed by the weather impact, with corn exports now running 22.3% behind last year's pace. As of May 24th, 93% of the U.S. corn crop is in the ground, compared to the average of 79%. Emergence is well ahead of last year.

Weather developments remain the key to this summer's pricing decisions. For the moment weather patterns have moderated weather concerns. However, this year's El Nino continues to parallel 1983's which may threaten a late summer drought.

Wheat Update

Wheat prices were sharply lower making new contract lows. Recent rains have been viewed as beneficial for 1998 crop yields. Export inspections for the week ending May 21 were 20.4 million bushel compared with 11 million last week and 7.0 million last year.

New crop U.S. production may prove to be above the preliminary USDA estimate of 2.356 billion bushel for all wheat, which would only add to the possibility of increasing stocks for 1998/99. The overall July wheat expected trading range is $2.75 to $3.50 per bushel, with the upper range only visited if a weather scare develops during June.

Soybean Update

Prices were sharply lower across the soybean complex. Weather was the predominant bearish factor, with the forecast being nearly ideal for crop development. Planting progress is nearing 65%, well ahead of the 42% five year average.

Export inspections were bearish, further eroding support. Sharp declines in cash palm oil prices over the last two weeks, led by reduced demand, have eroded support for soybeans.

Economic problems in Asia, Russia, and China have all fueled concerns about demand for beans slackening.

Sideways to lower price trends are expected for the near term. Without a weather problem developing, upside is likely to be limited.


Market analysts agree that selling potential summer rallies becomes the order of the day for advancing any 1998 crop sales. It now becomes imperative to keep a close watch on the weather situation. *


Sorghum Planting Weather - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

With the onset of hot, humid weather, soil temperature is or will shortly be ideal for planting grain sorghum. Sorghum germinates best when soil temperature reaches 75 F. or greater although seed with a fungicide seed treatment germinates adequately at even 65 F. Whenever soil is wet and cold, use fungicide treated seed to ensure good emergence.

In the past few seasons in research sponsored by the Maryland Grain Producers Utilization Board, I have noticed that there is a big difference in how sorghum varieties germinate in dry soil conditions. If your fields are beginning to become critical for moisture for germination, check your seed size. For those varieties and seed lots that have fewer seed per pound (9,000 to 12,000 seed per pound), plant these only if adequate moisture is available. For smaller seed (15,000 to 19,000 and smaller), this seed can be planted in dry soil and often will be able to germinate and emerge. The smaller sorghum seeds will germinate in soil that you would not consider planting to soybeans. When conditions get too dry for soybean planting and you plan to plant some sorghum acreage, switch over to sorghum, especially the smaller seed lots.

In general, the best row spacing for sorghum is when it is drilled on 6 to 8 inch rows. However, many older drills are not able to meter the seed uniformily within the row. In these cases, you will find that skipping every other row by taping over the opening will help you get a more uniform within row spacing of seed and plants. Uniformity within row is critical for sorghum to maintain its drought tolerance. Plant population does not have a very large influence on yield because sorghum like soybeans can compensate for low population. On fields that often experience severe drought conditions and when planting with equipment that does not space seed evenly, use the lower end of the suggested seeding rate. For sandy soils, plant 0.5 to 1 seed per foot of row drilled, 1 to 3 seeds per foot of row on 15-inch rows, and 3 to 5 seeds per foot of row on 30-inch rows. For sandy loams and loams and the better loamy sands, plant 1 to 3 seeds per foot of row drilled, 2 to 4 seeds per foot of row on 15-inch rows, and 4 to 6 seeds per foot of row on 30-inch rows.

On most soils unless the soil test indicates low or very low phosphorus or potassium levels, the only additional fertilizer sorghum will need is nitrogen. In research sponsored by the Maryland Grain Producers Utilization Board, I have found that 2 tons of broiler cleanout litter provides enough nitrogen for sorghum to yield up to 140 bu/A. Based on this work and previous research on the effect of crop rotations on nitrogen requirement for grain sorghum, I suggest using 25 to 50 lbs nitrogen per acre when sorghum is planted following soybeans or a legume cover crop and 50 to 75 lbs nitrogen per acre when sorghum is planted following corn or sorghum. *

Upcoming Events…

June 23-24, 1998

Quarterly Pesticide Applicator Training & Testing

Location: Dover, DE

For More Information, contact the Delaware Department of Agriculture at 1-800-282-8685.

July 21, 1998

Annual New Castle County Agronomic Crops

Field Day

Location: Middletown, DE

For More Information, contact the New Castle County Extension Office at 302-831-2506.

August 12, 1998

University of Delaware Farm & Home Field Day

Location: Research & Education Center in Georgetown, Delaware

Time: 8:30 a.m. - 1:00 p.m.

For More Information, contact the University of Delaware Research & Education Center at 302-856-7303.

                        Weather Summary

Week of May 23 to May 29

0.01 inches: May 23
0.07 inches: May 28
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 84 F on May 26 to 72 F on May 23.
Lows Ranged from 64 F on May 27 to 48 F on May 25.
Soil Temperature:
71 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 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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