Volume 6, Issue 13                                                                                             June 19, 1998


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


Be sure to watch melons, pickling cucumbers and fresh market cucumbers for explosions in melon aphid populations. With the anticipated warmer weather, you can expect to see explosions in populations. The treatment threshold is 20% infested plants with at least 5 aphids per plant (small plants) or runner (larger plants). Lannate will provide melon aphid control but coverage is important, especially if leaves have begun to curl.


In fields where Admire was used at planting, we can now find all stages of Colorado potato beetles. The predominant stages are small and large larvae. If economic levels are being found and Admire was used at planting, Kryocide/cryolite (8 –10 lb per acre) or Agri-Mek (8 oz/acre) should be used. Unfortunately, we still do not have an aerial label for Agri-Mek. Potato leafhopper adults can still be found in many fields. A pyrethroid will provide effective control.

Snap Beans.

Leafhoppers continue to be found in seedling stage snap beans. A treatment should be applied pre-bloom if you can find 5 or more per sweep and the plants are stressed. Processing snap beans that are in the bud to bloom stage should receive an Orthene treatment for corn borer control. If corn borer catches are in the 2 to 5 per night range, a second treatment of Orthene will be needed on processing beans at the pin stage. Once corn borer trap catches reach 2 to 5 per night in your area, fresh market snap beans should be sprayed at the pin stage with Lannate. If corn borer catches remain above 5 per night, sprays should be applied on a 7-day schedule until harvest.

Sweet Corn.

Corn borers, corn earworms and low levels of fall armyworms can all be found in whorl stage sweet corn. The treatment threshold is 15% infested plants. If the predominant species are corn borer and corn earworm, Ambush, Baythroid, Pounce, or Warrior should be used at tassel emergence and again in 3-4 days. Corn earworm catches have recently increased so most fresh market silking sweet corn should be sprayed on a 3 to 4 day schedule except in northern Kent and New Castle Counties where sprays should be applied on a 5-6 day schedule. Be sure to check the Crop Pest Hotline on Tuesday and Friday for the most recent BLT catches (1-800-345-7544 – in-state; 1-302– 831– 8851 – out of state; www.udel.edu/IPM). *


Drift in Watermelons - Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

A few weeks ago, 2,4-D drifted from a field adjacent to a field with seedless watermelons and cantaloupes on plastic and drip irrigation. The crinkling, twisting, and cupping of the leaves, as well as general distortion of the stems was easy to find on many, but not all of the young watermelon transplants. This "drift" was probably not directly from the sprayer, but from volatization of the 2,4-D, even though it was the amine form.

The question at the time was how much permanent damage was done and would flowering and fruit set be affected. That is impossible to answer, because it cannot be determined how much 2,4-D was actually absorbed by the plants. However, like many of these situations, the watermelons have grown out of the damage. The concentration of 2,4-D was enough to cause the symptoms, but not enough to translocate through the plant and cause any long-term injury. The new growth is vigorous and healthy.

Perhaps a few days of maturity delay was caused, but that is hard to measure and document because so many variables come into the picture. In addition, 2,4-D at very low doses has been shown to stimulate root growth and other physiological functions on potatoes and some other crops, so the compound is not automatically an agent of death. However, these advantages are hard to achieve in a commercial setting and are not relied on or recommended. It is just evidence that plants can survive small doses of the material.

Certainly, drift or volatization situations like this are to be avoided, but often the dosage is well-below sub-lethal levels, causing symptoms and no lasting damage. Patience, common sense, and keen observation of the plant’s progress are necessary to evaluating the situation and resolving the issues related to these occurances. In many cases, a fair resolution of the problem becomes easily apparent. *


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

Sweet Corn & Field Corn.

In New Castle County sweet corn and field corn are showing symptoms of Stewart’s wilt. This flea beetle transmitted bacterial disease is favored by mild winters that favor survival of the beetles. In an experimental sweet corn trial susceptible plants are dying. Leaves of infected plants have linear, pale green to yellow streaks with irregular or wavy margins that parallel the veins and may extend the length of the leaf. Field corn seedlings rarely die, but leaf symptoms usually don’t show up this early. Most field corn hybrids have some resistance. Sweet corn varies in its resistance and resistant hybrids should be selected or susceptible ones sprayed with insecticide to prevent transmission of the bacteria.


The Delaware Department of Agriculture has issued a special local needs 24c registration label change for Quadris fungicide (Zeneca Ag Products) on tomatoes. The 24c registration allows for a one (1) day preharvest interval. The federal label has a 7-day pre-harvest interval and residue data from Zeneca supports the 1 day PHI. This will make the fungicide more useful for fresh market tomato growers. All other label directions are to be followed . This is an excellent new product for use on tomatoes. For more information on tomato disease control see the 1998 Commercial Vegetable Recommendations E.B. 137.


The recent wet weather has been very favorable for late blight development. If a fungicide has not been applied recently an application should be made and another 5 days later. Late blight was reported and confirmed from one field near the MD/VA border last weekend. Little or no fungicide had been applied prior to the detection, but as of this writing it has been contained and the plant pathologist that visited the field indicated that the infection originated from the seed pieces. There is no reason to believe that if potato growers have been spraying weekly or according to the WISDOM recommendations that their potatoes are at risk from late blight. It is always a good practice to be checking fields regularly and maintaining the recommended spray interval to protect the crop.

Early dying is showing up at the present time. Plants begin to turn pale, droop and collapse early. Cutting through the stem of infected stems reveal brown streaking in the water conducting vessels. This discoloration is due to an infection by the soilborne fungus Verticillium. Early dying is much worse when the lesion nematode populations in the root are also high. Longer rotations and/or fumigation will provide some control. Planting Verticillium resistant cultivars also aids control.

Late Blight Update

DSV accumulations as of June 15, 1998 are as follows:

Location/Emergence Date

DSV's June 11

DSV's June 15


Baldwin - 4/20



5-day, mid rate

Jackewicz - 4/20



5-day, mid rate

Zimmerman - 4/23



5-day, mid rate

Baker - 5/1



5-day, mid rate

Rainfall accumulations for the same sites are as follows from 6/11-6/15: Baldwin 1.15 in., Jackewicz 1.34 in., Zimmerman 1.68 in., Baker 3.16 in. The Late Blight Report is also posted electronically 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 ; Phil Shields, University of Maryland, ps136@umail.umd.edu

MELCAST for Fungicide Application on Watermelons.

Do not use MELCAST if there is a disease outbreak in your field, it is a preventative program. Below are the EFI values from weather stations located on the Eastern Shore June 10 - 17. Any questions please call Phil Shields at (410) 742-8788 or e-mail: ps136@umail.umd.edu

EFI Values



















Wootten Farms, Galestown,MD









Mark Collins, Laurel, DE









U of D, REC Georgetown, DE









Vincent Farms Laurel, DE









Watermelon Fields should be sprayed with a fungicide when 30 EFI values have been accumulated by the weather station nearest your fields. Add 2 points for every overhead irrigation. After a fungicide spray, reset your counter to 0 and start over. If a spray has NOT been applied in 14 days, apply a fungicide and reset the counter to zero. The first and last day above can be partial days so use the larger EFI value of this report and other reports for any specific day. *

Fungicide Use for Control of Diseases… A Reminder.

Read pesticide labels carefully and abide by all restrictions (re-entry intervals for workers, and pre-harvest intervals). Do not use products on crops for which they are not yet labeled. There are more reasons for this than can be discussed in this space. However, keep in mind that fungicides often have a specific use pattern to avoid buildup of resistance in the pathogen population or to reduce crop injury. Information on use patterns will only be available when the label is approved.

There are also many legal reasons for avoiding unlabeled material. If residue is detected on a vegetable, an entire farm may be unable to sell produce. A public pesticide scare may decrease demand for a commodity and cause prices to plummet. The bottom line is that the label is a legal document, and should be strictly followed.

Control of Gummy Stem Blight.

Chlorothalonil and mancozeb fungicides are the currently registered products available for control of the three major diseases of watermelon (gummy stem blight, alternaria and anthracnose). These products are very effective when used as protectants. Even when outbreaks of gummy stem blight (GSB) have occurred, chlorothalonil does a good job of reducing yield losses. Benzimidizole fungicides such as Benlate and Topsin M have been recommended to enhance GSB control mid-season. However, since 1996 we have documented a high level of resistance to Benlate in the pathogen population that causes GSB. This means that the pathogen is less sensitive to the fungicide than in the past. Until we have new products registered, chlorothalonil and mancozeb remain the best choices available. *

Field Crops

What Is In Those Soybean Herbicide Pre-mixes? - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

The following is a summary of the products in commonly used pre-mixes for postemergence soybean herbicides. This is meant as a reference point to compare the amount of various products based on the use rate that is appropriate for you.

Pre-Mix Products
Conclude B&G (co-pack) B at 1.5 pt

G at 1.5 pt

1.5 pt Storm 4S

1.5 pt Poast Plus 1.5E

Stellar 3.1E at 5 fl oz 6 fl oz Cobra 2E plus 4 fl oz Resource 0.86E
Storm 4S at 1.5 pt 1 pt Basagran 4S plus 1 pt Blazer 2S
Synchrony STS 42DF at 0.5 oz 0.64 oz Classic 25DF plus 0.20 oz Pinnacle 25DF
Tornado 1.75E at 1 qt 0.75 pt Fusilade DX 2E plus 1.0 pt Reflex 2S


Timing of Roundup Ultra in Soybean in Conventional Tillage Soybeans - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

The time to apply Roundup on RR soybeans is based on weed size and weed density. The application needs to be timed to avoid impact of weeds on yield and effectiveness of control. A conservative estimate for application timing is 21 to 28 days after planting. This is based on obtaining at least 90% weed control and no impact on yield. Do not base the application on the calendar, but use the 21 days after planting as a guideline for when to scout your field for a weed management decision. With a residual herbicide included in the tank mixture, applying prior to the 21 days after planting also provided 90% control and no yield reduction. This is work done on conventional tillage soybeans planted in narrow rows. At the present time it's the best estimate for no-till full-season beans as well. *

Canada Thistle Control in Wheat - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

The time to control Canada thistle in wheat is prior to harvest. Roundup is the product of choice because it is the most effective and allows greatest flexibility in crop rotation. Waiting until after harvest will result in less control due to less leaf area and severely injured plants. The label specifies an application of 1.0 quart/A after the wheat is in the hard dough stage (30% moisture). Wait 7 days prior to cutting the wheat. *


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


Continue to watch for potato leafhopper adults and nymphs, especially in spring planted fields. Once you see yellowing you have already experienced a yield loss. In addition to adults, watch carefully for nymphs that do not fly and can be found moving "sideways " on the leaves. It is this stage that can quickly cause damage. Remember that a sweep net is needed to get an accurate sample of both stages. Early cutting can be used as a control option if the field is 60% or more in bud and it has been 35-40 days since your last cutting. If economic populations were found before cutting, be sure to re-sample the field with in one week of cutting. On alfalfa 3-inches tall or less, the treatment threshold is 20 leafhoppers per 100 sweeps.

Field Corn.

Continue checking fields for the presence of European corn borer larvae, especially in fields where Bt varieties were not planted. Corn borers, corn earworms and southern corn stalk borers continue to be found in non-Bt fields. Since we rarely treat for the southern corn stalk borer or corn earworm, be sure to pull out the whorls of 10-20 plants per field to determine which insect is causing the damage. Southern corn stalk borer larvae will appear spotted compared to the cream colored body of the corn borer. Small corn earworm may also appear spotted but will always have microspines (small hairs that look like beard-stubble) along the entire length of the body. In irrigated corn, a corn borer treatment should be considered if 50% of the whorls are infested with live larvae. In non-irrigated corn, the treatment threshold is 75 -80 % infested plants. If more than one-third of the larvae have begun to bore into the midribs of leaves or into the stalk, controls will no longer be cost effective. Ambush, Pounce, Penncap-M or Warrior will provide the best control. If bees are foraging in the area, Penncap should not be used.


Before the recent rains, economic levels of thrips and leafhoppers could be found on seedling soybeans. Fields with economic populations before the rain should be re-checked to determine if these insects are still active. A treatment will be needed if you find 8 thrips per leaflet or 8 leafhoppers per sweep. If both insect pests are present, the threshold of each insect should be reduced by one-third. A pyrethroid or dimethoate will provide effective control of both insects. *


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

Field Corn. See the Vegetable Crop Disease section. *


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

Grain and Soycomplex Markets Posed for Catch-up Sales

U.S. Corn Update

Corn futures ended trading on June 17th with impressive gains. Flooding problems in key growing areas of the midwest along with forecasts for potentially damaging hot weather moving into the region next week, kept prices improving. Technically inspired buying served as a catalyst for the upward move, with prices pushing toward double digit gains. One CBT market analyst believes that prices simply got too cheap, based upon the fact that we are extremely early in the growing season. The fact remains that we are in for a potentially very large crop, maybe even record breaking. However, this crop has a long way to go before it is made and commodity traders and analysts are now accounting for the uncertainty in eventual crop size with a technical correction in the market.

U.S. Soybean Update

Good growing conditions and an outlook for a record crop sent prices in a nosedive to new contract lows during the first half of last week. Spillover strength from soyoil and a light short covering rally tempered the weak trend by mid week. By June 17th soybean futures finished solidly higher as bullish enthusiasm propelled prices in day session trade. Speculative short covering, a rebound in Asian financial markets and spillover from corn and soymeal kept prices pushing higher for most of the day. Weather related uncertainties provided additional strength, with price advances trimmed later in the session by active farmer selling.

Keep a close watch on the current rally to advance and catch-up on both old crop and new crop sales *


The Future of Crop Yields: What's the Limit for Corn? Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

I would like to share with you some remarks on an article that I read about modern agriculture’s challenge to keep up the pace of food production so the world’s increasing population can be fed. For corn, the article stated that, on the one hand, corn yields have been going up 2 bushel per acre per year since 1940 and, on the other, average U.S. corn yields have not risen much above the 120 bu/A level. Although a chart of corn yield averages since 1940 in Delaware shows much variation due to weather, there is a strong upward trend close to a 2-bu/A/year level.

Can corn yields continue to rise? Dr. Thomas Sinclair, USDA agronomist with the South Atlantic Area Crop Genetics and Environmental Research Unit in Gainesville, Fla., has scoured harvest data for what’s possible. He looked for what he called the "Mount Everest" of cereal yields. For corn, the yield winner was over 300 bu/A at a site in Grand Junction, Colo. He and another researcher also studied what factors appear to limit yields in deep, rich soils in the U.S. Corn Belt. For 1965 to 1988, they found that most of the variation in yields in Champaign County, Ill., could be traced to the availability of water. They also found that many growers had reached a point at which the cost of boosting crop yields with more fertilizer (nitrogen, in particular) outweighs the value of the harvestable bonus.

In my opinion, we have not yet reached the yield limit on corn. With new improvements in plant breeding techniques using biotechnology, plant breeding gains of 1 to 2 bu/A/year should continue. Additionally, we have not seen what the impact of charting the corn’s entire DNA genome (the road map in each corn cell that tells it how to build a corn plant) will be. If corn’s architecture can be changed as scientists are doing in rice, further yield gains may be possible by diverting more of the plant’s dry matter to the grain out of the stalk and leaves. Another potential area for gain comes from the use of variable rate technology and the global positioning and geographic information systems (the VRT and GPS/GIS you read about). Although we do not know whether absolute and economic gains can be obtained with these technologies, many agronomists are optimistic. *

Upcoming Events…

June 22, 23, 25, 26, 1998

Poultry Educational Seminar

"Drinking Water Quality and Nipple Operation/Maintenance"

See following page for further information

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 Cooperative Extension Office at 302-831-2506

August 12, 1998

U of D Farm & Home Field Day

Location: Research & Education Center, Georgetown, DE

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

For More Information, contact the REC at 302-856-7303

Weather Summary

Week of June 12 to June 19

0.72 inches: June 12
0.10 inches: June 13
0.43 inches: June 14
0.56 inches: June 16
0.77 inches: June 17
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 88 F on June 17 & 18 to 77 F on June 12.
Lows Ranged from 65 F on June 16 to 61 F on June 12-15.
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:




"Drinking Water Quality and Nipple Operation/Maintenance"

The Cooperative Extension Services of the Universities of Delaware and Maryland cordially invite all poultry growers to attend the next quarterly educational seminar.

This seminar series will provide information on:

* How to get your poultry house water tested, what to have it tested for, how to interpret the results, what components in drinking water affect poultry performance, and what are some of the cost-effective alternatives to correct water quality problems.

* How to operate and maintain the various types of nipple drinker systems used on Delmarva will be discussed by equipment company representatives. This discussion will include: unique operating features of the various systems, common problems and maintenance issues, optimum operation for summer and winter, and the effect of poor water quality on drinker (and fogger) equipment.

* At each seminar location, an experienced poultry grower having outstanding drinker management will share their program and thoughts on why they feel they have been successful.

To accommodate poultry growers’ work schedule during warm weather, we will have morning meetings (9:00 AM to 11:00 AM). Refreshments and pastries will be provided.

Dates                       Locations:                                  Contact For Registration &                                                                                      Directions

                    Monday, June 22     Kent Co. Extension Office,       Susan Truehart

                                                                                                       Dover, DE (302-697-4000)

                    Tuesday, June 23     Unity Washington                      Betsy Gallagher

                                                    Methodist Church                      Hurlock, MD (410-228-8800)

Thursday, June 25   Gumboro Fellowship Church     Jeanie Johnson

                                                                                                      Gumboro, DE(302-856-7303)

Friday, June 26         Snow Hill Library                      Turp Garrett

                                                                                                      Snow Hill,MD(410-632-1972)


To protect your investment and the Delmarva poultry industry, poultry growers are requested to:

1. After your last poultry house visit, shower and change your clothing and footwear before attending this seminar.

2. Travel to the seminar in a vehicle that is not used in your daily poultry operation.

3. After returning from this meeting, change your clothing and footwear and use a different vehicle to reenter your poultry operation.

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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