Volume 6, Issue 6                                                                                              May 1, 1998


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


The first diamondback moth larvae have been found in cabbage fields throughout the state. As temperatures increase, we should see an increase in activity by next week. Remember, as soon as larvae emerge from mining in the leaves they will move directly to the hearts of the plants. If you still have Monitor available from last year and need to use up old inventories, it can still be applied as the first application. The use rate is 1 qt/acre. The Bt insecticide will provide effective control if applied before insects move deep into the hearts of the plants and when temperatures are above 70 degrees. Although Spin-Tor has a label, there will not be any available in our area for another couple of weeks. The use rate for diamondback larvae will be 1.5 to 3 oz/acre. If low levels are present, 2 oz per acre should work well. If populations have exploded, you will need the 3 oz/A rate.


Seed corn maggot flies continue to lay eggs and will be present at the time of transplanting melons. The potential for damage will continue through May so a preventative treatment will be needed. On direct seeded melons, a seed treatment containing diazinon or chlorpyrifos should be used. Data from New York still indicates that chlorpyrifos is the best option. The only available option in transplant fields is a broadcast application of diazinon. In order for it to be effective, it must be broadcast and incorporated into the top 3-4 inches of soil before planting.


Pea aphids can be found in most fields; however, beneficial insects still are keeping most populations below threshold levels. Fields should be sampled on a weekly basis from bloom to harvest for pea aphids. When plants are small, count the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. A treatment is recommended if you find 5-10 aphids per plant or 50 or more per sweep. Dimethoate, Lannate or Penncap-M will provide control. Be sure to read the label for application restrictions during bloom.

Sweet Corn.

Even though winter conditions were mild, flea beetle populations still remain low in most fields. Fields should be scouted from spike to the 5-leaf stage for flea beetles and treatments applied if 5% of the plants are infested with beetle adults. Sevin or a pyrethroid will provide control.

Crop Pest Hotline and Trap Counts.

The Crop Pest Hotline and trap catches for corn borer and corn earworm will be updated once a week beginning May 8. This report will be updated twice a week from June through August. In state, you can access this report by dialing 1-800-345-7544. If you are out of state, dial 1-302-831-8851. You can also receive this information at our website: http://www.udel.edu/IPM   *


Post-emergence Control of Weeds in Peas - Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

To control escaped broadleaf weeds in peas, spray Basagran at 1.5 to 2 pints/acre. Do Not Add Crop Oil or any other surfactant. It is critical to spray the weeds when they are small, less than two inches, to achieve good control. This emphasizes the need to check the field early for weed escapes. Basagran will do a good job on mustards and other weeds, but is weak on lambsquarter. Lambsquarters need to be very small when Basagran is applied to get control. When scouting fields, remember that peas are very competitive and are planted at a high density. Scattered weed populations may not warrant Basagran applications, although heavy weed infestations will affect yield, trash content, and ease of harvest.

Grasses can be readily controlled with either Post (1 to 1.5 pints/acre) or Assure II (6 to 12 fluid ounces/acre). Oil concentrate can be added with this materials (1 gallon/100 gallons of spray solution). Assure II is more effective on volunteer small grains, which survive the plowing or tillage operations prior to planting the peas. Always read the label carefully for more complete directions. *


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

Section 18 Granted for Late Blight Control on Potatoes.

On April 23, 1998 the EPA granted a section 18 registration for the following unregistered fungicides for late blight control on white potatoes. Acrobat MZ, a.i. 9% dimethomorph and 60% mancozeb, manufactured by American Cyanamid Company; Curzate 60 DF, a.i. 60% cymoxanil, and/or Curzate M-8, a.i. 8% cymoxanil and 64% mancozeb, manufactured by E.I. du Pont de Nemours and Company; Manex C-8, a.i. 8% cymoxanil and 64% mancozeb, manufactured by Griffin Corporation; and Tattoo C, a.i. 30.5% propamocarb hydrochloride and 30.5% chlorothalonil, manufactured by AgrEvo USA Company may be used.

Curzate DF in combination with a protectant fungicide may be applied by ground or air at a maximum rate of 3 1/3 oz product (0.12 lb. cymoxanil) a maximum of 7 times per season. A 14 day PHI will be observed. Curzate M-8/Manex C-8 may be applied by ground or air at a maximum rate of 1.5 pounds product (0.12 lb. cymoxanil) a maximum of 7 times per season. A 14 day PHI will be observed. If the maximum applications of Curzate M-8/Manex C-8 are made per season, a maximum of 6.7 lb. mancozeb will be used.

Acrobat MZ may be applied by ground or air at a rate of 2.25 pounds product (0.2 lb. dimethomorph) a maximum of 5 times per season. A 14 day PHI will be observed. If the maximum applications of Acrobat MZ are made per season, a maximum of 6.75 lb. mancozeb will be used.

Tattoo C may be applied by ground or air at a maximum rate of 2.3 pints product (0.9 lb. propamocarb) per acre. A maximum of 11.5 pints product (4.5 lb. propamocarb) may be applied per acre per season. A 14 day PHI will be observed. If the maximum applications of Tattoo C are made per season, a maximum of 4.5 lb. chlorothalonil will be used.

We have not needed these products in Delaware the past several years because late blight has not occurred, but it is good to know that these tools are available should we need them.

Late Blight Monitoring Stations.

Four Sensor Instruments Field Monitors (automated weather monitoring stations) will collect weather data for late blight monitoring. The locations are as follows:

County Location
New Castle County Baker Farms, Ed Baker
Kent County

Rt. 9 area near Leipsic:

Magnolia area:


Broad Acres, Dan and Fred Zimmerman

Joe Jackewicz, Jr.

Sussex County Sayre Baldwin, Inc., Bridgeville area, Dan Baldwin

These machines will be monitored this season as a result of grower and industry funding of this program. I would like to thank those growers and companies that contributed. Weather data from these units will used in a computerized model (WISDOM) that predicts the occurrence of late blight.

The computer model uses the weather data and determines the occurrence of severity values that accumulate over time. The accumulation of 18 disease severity units (DSVs) indicates that weather conditions for infection by the late blight fungus is likely to occur if the fungus is present.

For each potato field you should record:

I. Planting date.

II. Emergence date

(This is the first day when at least 50% of the plants have emerged. You should be able to see a green row at this time. The computation of severity values for predicting late blight begins at emergence.)

Request For FAX Numbers

Once again we will be FAXing you as much information as we can on late blight and other pest control problems. We need your FAX numbers! If you received a FAX last season and your FAX number has not changed you do not need to contact me. If you have a FAX machine and would like me to contact you by FAX please take a minute and call me at 302-831-4865 and give me your FAX number. You can leave a voice mail message any time of day or night and request the FAX.

The Potato FAX Reports will also be 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

Maryland specific exemption (Section 18) has been approved for the use of Acrobat MZ, Curzate 60 DF, Curzate M-8, Manex C-8, and Tattoo C to control late blight on potatoes. All these materials have a 14 day PHI. This section 18 exemption became necessary because there are new aggressive strains of Phytophthora infestans that are resistant to Ridomil. Protectant fungicides should be applied early in the season, according to a late blight forecasting model. *


Field Crops

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

Small Grains.

Cereal leaf beetle populations remain at low to moderate levels in many fields. Beneficials still appear to be keeping aphids in check in most wheat fields. The highest levels of aphids can still be found in barley fields; however, most populations are confined to the lower part of the plant. At this time, decisions should be based on the number of aphids found in the grain heads of barley. The treatment threshold is 20 to 25 per head. Although aphids feeding in the grain heads can affect test weight, no controls will be needed after grain reaches the early dough stage. The first small armyworms and grass sawflies have been found in wheat in Sussex County. Although moth catches remain low, you can expect to see pockets of activity. As temperatures increase, be sure to check fields for true armyworms and grass sawflies. Since grass sawflies will quickly clip grain heads, the treatment threshold is 0.4 per foot of row. The armyworm threshold is one to two larvae per foot of row. Remember, armyworms can cause greater damage in barley so be sure to use the lower threshold. Also, if both insects are found in a field then the threshold of each insect should be reduced by one-third. Warrior, Lannate, or Parathion will control both worm pests. Remember, only Lannate and Parathion are labeled on barley. Also, Parathion can only be applied by air and has set back restrictions.


As you make plans to plant full season soybeans, be sure to use a seed treatment containing diazinon (e.g. Agrox-DL, Kernal Guard) on your no-till soybeans. Seed corn maggot flies can still be found laying eggs, especially in fields with high amounts of organic matter. *


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

Small Grains.

Barley diseases that can be seen at the present time include scald, net blotch, rust, and loose smut. For most situations the price of barley and the advanced stage of crop growth would not warrant treatment at this time.

Wheat appears to have fewer diseases at the present time. Powdery mildew continues to be the most common disease. Once wheat reaches the flowering stage fungicide applications for mildew control are generally not recommended. Septoria leaf and glume blotch has not been seen to date. For Septoria, scouting should continue at weekly intervals. Randomly select 10 locations within a wheat field. At each location, examine and record the number of indicator leaves out of 10 main tillers with one or more leaf and glume blotch lesions. If 25% of the 100 indicator leaves in the field have one or more lesions, then a fungicide application is needed. For wheat in the swollen spike stage to the beginning of flowering the indicator leaf is the Flag minus 2 (F-2); from flowering complete to top of spike to watery ripe stage the indicator leaf is the F-1 leaf (leaf below the flag leaf). Check 1998 Pest Management Recommendations for Field Crops for more information. *


Canada Thistle and Horsenettle Control in Roundup Ready Soybeans - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

Research in 1997 identified the most effective control of Canada thistle and horsenettle in soybeans was with a Roundup Ready program. Roundup Ready was compared with a wide variety of herbicides for control of these two species, and Roundup Ready was the best approach. One application of Roundup Ultra at 1 qt/A, applied to 6 to 8 inch Canada thistle or horsenettle was much better than any other treatments. The one quart rate looked as good as the 1.5 qt/A rate. However, by waiting for Canada thistle or horsenettle to get to the 6 to 8 inch size the annual weeds could be hurting yield (about 4 to 6 weeks after planting). I would suggest a reduced rate of a soil-applied herbicide at planting to reduce the weed population followed by Roundup at the correct weed stage. This is one instance that a soil-applied herbicide has a place with Roundup Ready soybeans.

For programs without Roundup Ready soybeans, Basagran at 1 qt/A will burn off the top of Canada thistle, but expect regrowth. With horsenettle, wait as late as possible, then till the ground to help deplete the root reserves as much as possible and to break up the root systems. None of the postemergence herbicides are very effective. Including Blazer or Cobra will slow weed growth, but do not expect to see significant control. *


Does Your Weed Management Program Consider Resistance Management - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

Herbicide resistant weeds are a reality on Delmarva. We have confirmed triazine resistant pigweed and lambsquarters and Scepter resistant pigweed. Reliance on a triazine or ALS-inhibiting herbicide for weed control is setting yourself up for resistance. If using a triazine herbicide (atrazine, simazine, or Bladex) be sure to tank mix with another herbicide that will have some activity on the weeds in your field or plan on using a postemergence spray to clean up escapes. The ALS-inhibiting herbicides (Accent, Beacon, Permit, Exceed, Basis, Basis Gold, etc) should be tank mixed to prevent development of resistance. In corn, combining 4 oz of Banvel or Clarity is a very cost effective approach. In soybeans, using tillage (conventional tillage or cultivation), narrow rows and/or a sequential herbicide application with herbicides with differing mode of actions are needed. Resistance management requires a long-term approach. *


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

Wheat Futures Hit New Contract Lows.

July wheat futures declined to new contract lows this past week, with the other wheat future contracts either finishing on or near session lows. The decline in wheat prices is attributed to large supplies, both domestic and in the world. Technical action is driving this market. Fundamentally, there is not enough friendly news to attract buying interest. Even though downside risk in the wheat market looks fairly played out on a daily chart, a look at the weekly and monthly charts shows further downside potential.

USDA’s Response.

In light of the recent down trending wheat market, USDA has announced this week that ways to increase U.S. exports and export financing are being considered. USDA is currently studying many of the mechanisms that have been used in the past to foster export sales, particularly for wheat. Some 30 different programs are being considered. One of those mentioned is a long-dormant program referred to as direct export credits (GSM-5). Using this program, idle since the early 1980’s, or some combination of programs to boost wheat prices is being considered as a result of a recent inquiry made by the National Wheat Growers Association.

Market Strategy.

Besides the export credit programs, there may be some other reasons to believe that wheat prices will eventually rebound. One of those reasons is the "cool-wet-weather" theory. The basic premise behind this theory is that 1998 U.S. wheat yields may be reduced due to the prevailing cool, wet conditions. Wheat and other small grains tend to yield better when general weather conditions are on the dry side. If we believe the theory may hold true for 1998 production and we note that U.S. wheat plantings are down 6% from last year, and at the lowest level in ten years, then we might expect wheat prices to show some promise, thereby, eventually rebounding off of current lows.

Considering current price levels, further wheat sales are not recommended at this time. An individual’s ability to hold out for higher wheat prices may depend upon storage availability.

For those without adequate storage, cash sales can be replaced with the purchase of call options.

For assistance in considering the use of call options in your wheat marketing strategy call Carl German at 302-831-1317. *


Corn Stand Variability-What are some of the Causes? Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

In seasons similar to this one, corn emergence is often variable even when everything works as it should. As soon as feasible after corn nears full emergence which occurs between 125 to 160 growing degree days after planting, corn fields should be scouted for planting problems in case replanting is required. The former superintendent at Purdue University’s Agronomy farm said "The sins of planting will haunt you all season!" Use your first planted fields to be sure everything mechanical is working properly.

What kind of variability is there? This is generally variability among plant spacing within the row. Very crowded plants here and there along the row is typically an indication of a planter malfunction. Large gaps between plants can be caused by either planter malfunction or poor germination or survival of the seedlings. Sometimes there are mixtures of crowded plants and large gaps between plants.

What are the common causes of variability? Seed germination is rarely 100 percent so even when seed is evenly placed in the row you will often see some larger than desired spacings but these are often of little consequence unless the germination percentage is much lower than normal. Irregular patterns of missing or dead plants can indicate damage from insects, slugs, diseases, or hail. Variability also can be caused by planter malfunction including worn out planter parts, incorrect planter settings and adjustments, operator error, and excessive planting speed. Speed can be dangerous and often is a temptation when we get behind in planting. As the speed of planting increases the capability of the metering unit to singulate individual kernels diminishes, any rocks or hard pans and just the speed can cause the row units to bounce and interfere with the flow of the seed to the furrow, seed to soil contact can become irregular, and planting depth can become variable. Although yield losses do not always occur, Purdue’s agronomist, Dr. Bob Nielsen, found that for every 1 mph increase in speed yield losses can approach 2 to 5 bu/A. To put speed in perspective, Dr. Nielsen says that at 5 mph you are traveling 7.33 feet per second and at a target seeding rate of 26,600 seeds per acre the metering rate is 11.2 seeds per second!

Variable establishment is not only spacing oriented but also time oriented. We often notice that not all seedlings emerge on the same day and, if emergence is delayed by much, the delayed emergers cannot compete with the older, more established plants and will ultimately contribute little to yield. How much does delayed emergence contribute to yield loss. In a study reported in the journal, Crop Science, Nafziger, Carter, and Graham stated that a 10-day delay resulted in an eight percent loss and a 21-day delay resulted in a 10 to 20 percent loss. How do you estimate the amount of delay? As a rule of thumb, delays of 10 or more days translate to growth stage differences of 2 leaves or more. Count leaves by the number of leaf collars (the whitish area where the leaf blade connects to the leaf sheath at the stem) emerged from out of the whorl of leaves.

What causes delayed emergence? Soil moisture differences; soil type and tilth variations; uneven seeding depths; poor distribution of crop residues or failure of row cleaners to move residues off the row; tillage traffic patterns; variable soil temperatures (often involving one of the above factors); and uneven seed to soil contact due to rough, cloddy seedbeds, excessive amounts of crop residues, or poor adjustment of either the furrow openers or furrow closers.

What are the important considerations for the day you seed? First, be aware of the soil temperature especially when planting early and/or using no-till in fields with heavy surface trash. Remember rapid and uniform corn germination and emergence depends on having soil temperatures no lower than 50 F. Adjust your planter according to seed size and remember to re-adjust as necessary when you switch hybrids or seed lots. Choose an appropriate seeding depth for the field conditions, soil type, and weather outlook and once in a field take time to verify the actual depth of seeding. In no-till, adjust the depth and tension of the coulters for each field. Be sure they are either cutting through the trash or your row cleaners are working properly. Trash trapped inside the furrow will often lead to germination and emergence problems. Adjust the tension of the furrow closing wheels according to the conditions of the soil for each field but do not let them apply excessive pressure or you will restrict emergence. Do not exceed the planting speed recommended by the manufacturer and try to stick to the optimum range of speed. Be certain to lubricate all chains and bearings. This is best done at the end of the planting day when they are warm and helps spread the lubricant evenly.

Finally, yield losses potentially begin even before you get in a field. Begin you goal of top yielding corn by preparing your equipment, making adjustments appropriate for field conditions, and managing all the factors listed above so you will optimize plant distribution within the row and obtain even, rapid germination and emergence. *


Weather Summary

Week of April 24 to April 30

0.11 inches: April 27
0.02 inches: April 28
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 77 F on April 27 to 59 F on April 24.
Lows Ranged from 54 F on April 26 to 35 F on April 28.
Soil Temperature:
58 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:



Small Grains Troubleshooting For Producers

Improving Diagnostic Skills-Correcting Small Grains Production Problems

May 21, 1998

3:00 p.m. - 5:00 p.m.

University of Delaware Research & Education Center, Georgetown, Delaware

Weeds Insects Nematodes Fertility Variety Yield Potential

University of Delaware extension personnel will provide hands-on training to improve your troubleshooting skills in small grains. Participants will be involved with problem solving scenarios in a field setting and will be expected to help recommend corrective and preventative solutions.

Pesticide recertification credits will be earned.

Small Grains Troubleshooting For Producers is open to everyone. Prior registration is required. Participation is limited to the first 60 applicants. Minimum sign-up required is 15 applicants. Registration fee is $15.00 per person. Registration deadline is May 15. Checks confirm reservations.

Registration starts at 2:30 p.m. in the grove. Training starts at 3:00 p.m. Program will be finished by 5:30 p.m. with dinner provided. Hand lens and sweep nets will be available for use if needed.







PHONE:___________________ FAX:_______________________

Include check for $15 made payable to University of Delaware. Return by May 15.

Mail to: Attn. Mabel Hough, Research & Education Center, R.D 6, Box 48, Georgetown, Delaware 19947



Compiled & 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.

Black Cutworm – Pheromone Trap Catches – 1998 Season

Data Provided by Terra Inc., Bridgeville, DE

Data also available at www.udel.edu/IPM

Trapping Period : April 17 - April 24, 1998




# Moths/7Days

American Corner, MD


Lewistown, MD


Argos Corner, DE


Magnolia, DE


Atlanta, DE


Mardela Springs, MD


Berlin, MD


Marydel, MD


Bethel, DE


Milford, DE #1


Bridgetown, MD


Milford, DE #2


Bucktown, MD


Millsboro, DE


Burrsville. MD


Milton, DE


Cambridge, MD


Newark, MD #1


Clarksville, MD


Newark, MD #2


Dagsboro, DE #1


New Church, VA


Dagsboro, DE #2


Oak Orchard, DE


Delmar, DE


Pocomoke, MD #1


Denton, MD


Pocomoke, MD #2


Easton, MD


Preston, MD


Eldorado, MD


Public Landing, MD


Ellendale, DE


Queen Anne, MD


Farmington, DE


Redden, DE


Federalsburg, MD


Reeds Grove, MD


Frankford, DE


Reliance, MD


Georgetown, DE


Rhodesdale, MD


Goldsboro, MD


Ridgely, MD


Greenwood, DE


Seaford, DE #1


Harmony, MD


Seaford, DE #2


Hurlock, MD #1


Selbyville, DE #1


Hurlock, MD #2


Selbyville, DE #2


Laurel, DE # 1


Snow Hill, MD #1


Laurel, DE # 2


Snow Hill, MD #2


Laurel, DE # 3


Snow Hill, MD #3


Leipsic, DE


Trappe, MD


Lewes, DE


Vernon, DE


    Wyoming, DE


Hit Counter