Volume 6, Issue 11                                                                                          June 5, 1998


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


If you are growing cabbage varieties that are susceptible to thrips, be sure to watch for an increase in feeding activity. A treatment should be applied when 20% of the plants are infested. Dimethoate, Metasystox-R or Warrior have provided the best control.


Corn borer larvae can now be found in the terminals of potato plants as well as tunneling in the stems of the earliest planted fields. Furadan (1 pt per acre) or Monitor (1 qt/acre) will provide the best control once larvae are in the stems. Leafhoppers and Colorado potato beetles have also reached economic levels in fields not treated with Admire at planting. Provado will provide control of leafhoppers and Colorado potato beetles. Agri-Mek can also be used to control Colorado potato beetles; however, it should be applied when larvae are small. 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 for each.

Snap Beans.

Continue to monitor fresh market and processing snap beans for leafhopper and thrips activity. A treatment is needed if you find 5-6 thrips per leaflet and/or 5 leafhoppers per sweep. If both insects are present, the threshold of each should be reduced by the level for each insect. Lannate should be used in fresh market snap beans and Lannate or Orthene in processing snap beans.

Sweet Corn.

European corn borer whorl infestations have increased to 30 to 60% infested plants in many fresh market and processing sweet corn fields. The treatment threshold is 15% infested whorls or tassels. If you plan to wait and treat just as tassels are emerging, timing of sprays will be important. Since we can find a range in the size of larvae, the majority of the larvae may not have pupated before tassel emergence and will have a chance to make it into developing ears. Ambush, Baythroid , Pounce, Penncap or Warrior have provided the most consistent corn borer control. If bees are foraging in the area, Penncap should not be used. Fresh market sweet corn that was planted under plastic and is now silking should be treated on a 5-6 day schedule for corn earworm control. *


Post-emergence Weed Control in Snap & Lima Beans - Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

As plantings are reaching the early trifoliate stages, take a good look and scout your snap and lima bean fields for broadleaf weeds and grasses. Poast will control annual grasses in both crops. Assure II is labeled for use in snap beans only, and is effective on perennial grasses as well as annual grasses. Basagran will control many broadleaf weeds, but works much better if sprayed when the weeds are small. Check the label for instructions on crop oil and surfactants. *


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

Late Blight Update

DSV accumulations as of June 1 , 1998 are as follows:

Location/Emergence Date

DSV's May 28

DSV's June 1


Baldwin - 4/20



7-day, low rate

Jackewicz - 4/20



10-day, low rate

Zimmerman - 4/23



10-day, low rate

Baker - 5/1



10-day, low rate

Conditions continue to be unfavorable for late blight development. If we continue to get severe weather that can tear leaves either by wind or hail, protectant fungicides can prevent damaged leaves from getting infected by early blight or other secondary fungal pathogens. Early blight is not a disease that we often worry about except on susceptible varieties like Belrus or possibly Conestoga, but can infect mechanically damaged leaves. The protectant that you have been using for late blight control, will control early blight as well. 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

Section 18 Approval for Maryland

The U.S. E.P.A. has recently approved Maryland Department of Agriculture’s request for a specific exemption under Section 18 of FIFRA. This exemption is for use of Tattoo C on Tomatoes for control of late blight. Use Tattoo C at a maximum rate of 2.3 pints product per acre when early blight (caused by Phytophthora infestans) is present. Alternate Tattoo C with other fungicides for resistance management. A 7 day pre-harvest interval should be observed.


MELCAST for Scheduling Fungicide Sprays on Watermelon

MELCAST is a weather-based fungicide application for watermelon. Weather data (EFI values) will be available three times a week by fax or on the University of Delaware IPM page (http://www.udel.edu/IPM). 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.

To use MELCAST to time watermelon fungicide sprays, apply the first fungicide spray by the time the vines touch in the row. After the first spray, accumulate daily EFI from the nearest weather station (accumulated EFI are called the "spray counter"). Add two points for every overhead irrigation. Watermelon fields should be sprayed with a fungicide when the spray counter reaches 30 EFI. Once a spray is applied, begin accumulating EFI again. *


MELCAST Program EFI Values

Phil Shields, University of Maryland, ps136@umail.umd.edu

Below are the EFI values from weather stations located on the Eastern Shore May 26- June 3.

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 accumulation to 0 and start over. 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. *

Field Crops

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

Field Corn.

As the earliest planted fields reach 18-inches in height, begin checking fields for the presence of European corn borer larvae, especially fields where Bt varieties were not planted. Low levels of corn borers and southern corn stalk borers have been detected in the earliest planted non-Bt fields. Since we rarely treat for the southern corn stalk borer, 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. 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. Ambush, Pounce, Penncap-M or Warrior will provide the best control. If bees are foraging in the area, Penncap should not be used.


Bean leaf beetles continue to be the main pest feeding on seedling beans. Damage appears as small circular holes in the leaves. In comparison, Mexican bean beetle feeding will appear as a lacey pattern on the leaves. No controls are needed unless you find at least 2 bean leaf beetles per plant and they are reducing the stand by 25 percent. A pyrethroid or Sevin will provide control. Grasshopper nymphs can also be found in no-till fields and along field edges. As you begin to plant soybeans after barley harvest, these fields should be checked carefully for grasshopper activity. Early control of nymphs will provide the best control. Once grasshoppers are found in a field, a treatment is needed if you find one grasshopper per sweep and 30% defoliation. Asana, Sevin or Warrior have provided the most consistent control. *


Injury With Preemergence Herbicides - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

I have seen a fair amount of chloroacetamide (Dual, Harness, Frontier, etc.) injury this year, even with products which generally have good crop safety. The heavy rains a few weeks ago followed by cool and cloudy weather for 3-4 days really pushed the herbicide down and did not let the corn metabolize the herbicide like it should. Areas with overlaps and compaction layers tend to be worse. I have seen this with Bicep in my plots and with Surpass, Bicep, and Frontier on commercial fields.

The safener in Bicep, Surpass, Harness Extra makes it a lot "safer" but with the conditions we had a few weeks ago, the safeners were not enough for some fields.

There are limited options with severe damage. Most times the corn plants grow out of the injury, with lower leaves torn and shredded. If the plants leafed out underground, then it is unlikely the plant will survive. If stand loss occurred, you will need to evaluate stands and determine how severe it was. In all likelihood, its more damage than you want but it’s not severe enough to do anything about it. *


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

U.S. Corn Update

The market's focus on the weather from a longer-term standpoint is beginning to be pulled in opposite directions. The El Nino weather phenomenon continues to be a concern, however, the current weather pattern completely contradicts the 1983 El Nino event. With cool temperatures in place in the corn belt for the time being, the record yields set in 1992 and 1994 become a bit more of interest as both of those years saw below normal temperatures during the summer. Rains during the July-August period will be of critical importance to determining the eventual direction of 1998 corn prices. One Chicago Board of Trade market analysts indicated this week that farmers should be encouraged not to let $2.55 to $2.60 December corn go by.

U.S. Wheat Update

Market analysts suggest that 1998 U.S. wheat production may prove to be above the preliminary USDA estimate of 2.356 billion bushels for all wheat. This would only add to the possibility of increasing stocks again for 1998/99. Overall, the possibility of increasing wheat stocks does not indicate much in the way of price strength potential in the long run. Providing good yields similar to last year for winter wheat and spring wheat performs average or better, than the possibility of Chicago July Wheat trading down to the $2.75 level prior to expiration can not be discounted.

U.S. Soybean Update

Weather is expected to determine overall price direction. The impact the weather is having currently on prices is neutral, at best, to bearish. Soybeans are currently running on the oversold side, as traders wait to get a clearer idea about the weather through next week.

Without a major weather problem, a very burdensome new crop supply situation is indicated, compounded by record South American stocks and lackluster Asian demand growth (if any). Economic problems in Russia could spillover into E. Europe which would further erode demand prospects.

With average to above average yields, U.S. ending stocks are building to over 500 million bushels or better. Barring a major crop problem November beans are expected to decline to $5.25 per bushel or lower by harvest. *


Barley Harvest Underway - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

With the unusual weather this spring, small grains are maturing as much as two weeks earlier than expected. This offers both opportunities and challenges. The opportunity is the chance to plant double-cropped soybeans or grain sorghum much earlier than expected which can mean a larger than expected yield potential if growing conditions for the rest of the summer are good. For example, double-cropped soybeans grown under irrigation can yield in the range of 50 to 60 bu/A planted this early in the season. Also, sorghum yield potential can be greatly improved and may be close to full-season yield potential when planted this early.

What are the challenges? Many of us are still trying to finish up full-season soybeans and sorghum, in some locations soil conditions are very dry although recent showers may have added enough moisture to germinate double-crop beans or milo, some barley fields have lodged, and we will have to manage the barley residues carefully to ensure good soil to seed contact for rapid germination and uniform emergence.

With barley harvest underway, keep an eye on your wheat fields as wheat also appears to be maturing early especially where dry soil conditions forced the crop to begin maturing early.*


Hay and Pasture Fertilization - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

Many hay fields have been cut for the first time and pastures have been through several grazing cycles. For legume-based fields, it’s time to think of phosphorus, potash and boron applications to improve the crop’s stress tolerance for the upcoming hot, summer weather. Base the amount of fertilizer you apply on your most recent soil test. If you have not taken one in the past two years, consider taking a new one so you can accurately assess the nutrient status of your fields. For alfalfa fields with a medium soil test level (a 50 on our index value system), apply about 60 lbs P2O5 per acre plus 150 lbs K2O per acre plus about 2 lbs boron per acre (every year). The fertilizer can be applied either as one application after the first or second harvest or split between now and the last harvest in August. If the phosphorus index falls below about 40 on the index value, topdressing with P may not be effective in correcting the problem. You may want to consider taking the field out of alfalfa production for a summer so you can apply and work into the soil enough P to reestablish adequate soil test P levels.

For grass-legume mixture fields with a medium soil test, apply about 50 lbs P2O5 per acre plus 105 lbs K2O per acre plus about 0.5 to 1 lb boron per acre. The fertilizer can be applied either as one application after the first or second harvest or split between now and the last harvest in August. If the fields have from 25 to 50 percent legume, add about 25 lbs nitrogen per acre after each hay harvest or each grazing cycle. If there is less than 25 percent legume in the mix, then apply up to 50 lbs nitrogen per acre per cutting or grazing cycle.

For all your fields, keep watch on the soil pH so it stays in the optimum range. When needed, surface applications of lime are effective but do not wait too long as frequent smaller applications will be more efficient at maintaining productivity than one heavy application . Also keep in mind with boron applications, that although boron is required for maximum productivity of pastures and hay fields, even slight over-applications of boron can be toxic to the crop. Be very certain the application rates are within agronomic guidelines. *


Sussex County Reminders - Derby Walker, Sussex County Agricultural Agent, derby@udel.edu

Yellow Corn.

Local fields have spots of stunted and yellow corn. You may feel the need to rush out and apply fertilizer. However, warm night time temperatures and some more moisture will correct most of the problem. The roots have not reached the fertilizer at the 6-12 inch depth.. We did our own little test plot on yellow, stunted corn here at the REC farm, and found that it did not matter what kind of fertilizer we applied or did not apply. All the corn looks better after we caught a few showers at the beginning of the week.

Sorghum Too Thick?

Why not cultivate and make 7 or 15 inch rows into 15 or 30 inch rows? Sorghum is drought tolerant when it is not planted too thick and is over fertilized with nitrogen.

Buggy Whipped Corn.

Buggy whipped corn that is laying flat on the ground can be found in fields. This injury is caused by the grass herbicides commonly used on corn. Injury is visible where rates are double due to overlap on the ends and short rows. This problem is especially noticeable on very sandy soils. Most (but not all) corn will recover with time and good growing conditions.

Herbicide Drift.

Just a reminder to be aware of wind direction and speed when spraying. Choose herbicides carefully, with adjacent fields in mind as you consider your options. Materials like 2,4-D and Banvel are always potential problems. Our no-till mixes can drift and cause severe crop damage. Protect your investment with a little planning, especially near vegetable crops. *


Tuesday, June 9, 1998

6:00 p.m.

Raspberry Walkabout

University of Maryland

Wye Research & Education Center

Cheston Lane

Queenstowne, Maryland

For Information or directions, call 410-827-8056

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 U of D Research & Education Center at 302-856-7303.

Weather Summary

Week of May 29 to June 4

0.22 inches: June 1
0.35 inches: June 3
0.02 inches: June 4
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 94 F on May 31 to 80 F on June 3 & 4.
Lows Ranged from 68 F on May 29 to 55 F on June 4.
Soil Temperature:
74.5 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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