Volume 10, Issue 8 May 17, 2002




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



As vines begin to run, be sure to sample carefully for spider mites. When sampling for mites, be sure to check the entire plant if plants are small or the crown area on larger plants for signs of stippling and the presence of mites. The threshold is 20- 30% infested crowns with 1-2 mites per leaf. If populations of mites have exploded and adult mites are the predominant life stage, Capture or Danitol should be used. If the population is a mixture of eggs, immature mites and lower levels of adult mites, Agri-Mek should be used at 8 oz/acre. A second miticide application may be needed in 3-7 days depending on the population level at treatment time. In general, dimethoate has provided very poor mite control. In recent years, Kelthane has provided good mite control and should be rotated with Capture, Danitol and Agri-Mek to avoid resistance. If populations are heavy or numerous eggs are present at the time of treatment, at least 2-4 miticide applications will be needed. Be sure to also sample melons for aphids. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Actara, Fulfill, Lannate and Thiodan are the labeled on melons and will provide melon aphid control. Dimethoate will not control melon aphids. Be sure to also scout carefully for cucumber beetle adults. Early in the day, adult beetles may be found "hiding" under the plastic. There are reports of high populations in Maryland.



Economic levels of CPB adults and small larvae can now be found in the earliest planted fields. Actara, cryolite, Spintor or Provado will provide control. To avoid the development of resistance, fields treated with Admire at planting should not receive foliar treatments of Provado or Actara. The first ECB egg masses have been detected in potatoes. Be sure to check our website (http://www.udel.edu/IPM/traps/latestblt.html) for the most recent moth catches in your area. In general, we tend to see an increase in moth populations as soon as temperatures increase after a period of cool, rainy weather. Since we have already seen the first eggs in the earliest planted fields, a corn borer spray will be needed with 3-5 days after an increase in trap catches. Potato leafhoppers have also been detected in the earliest planted fields. As a general guideline, controls should be applied if you find to one adult per sweep and/or one nymph per every 10 leaves. A pyrethroid, Actara or Provado will provide control.


Sweet Corn.

Be sure to watch the earliest planted fields for European corn borer larvae. We are starting to see our first larvae in whorl stage sweet corn that was planted under plastic. 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, the best corn control has been achieved with Ambush, Pounce, Penncap or Warrior.




Fertilization of Seedless Watermelons Through A Drip Irrigation System - Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu


Research and field experience has indicated that Seedless watermelons require about 125-140 pounds of nitrogen to grow a full crop. Seeded watermelons require more nitrogen. The following information from the Commercial Vegetable Production Recommendations provides a general fertilization program. The total amount needs to be adjusted for seedless melons.


Before mulching, adjust soil pH to around 6.5, apply enough farm grade fertilizer to supply 50 pounds of N, P205, K20, then incorporate into the soil.


After mulch and installing the drip system, apply completely soluable fertilizers to supply 25 pounds of N, P205, and K20 per fertilized-mulched acre during each application.


The first soluble fertilizer application should be applied through the drip system within 1 week after field transplanting the watermelons. The same rate should be applied 2 weeks later. The third should be made about the time of first fruit set. A fourth application needs to be applied 2 weeks before the first harvest. A fifth application can be applied right after the first harvest.




Field Crops


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



Continue to sample fields for potato leafhopper adults, especially on spring seedings and within one week of cutting for established stands. Once the damage is found, yield loss has already occurred. 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. Ambush, Baythroid, dimethoate, Mustang, Pounce or Warrior will provide effective control. We are still seeing a few cases of alfalfa weevil damaging regrowth after the first cutting. Although cutting can be used as a control option if conditions are hot and dry after cutting, this has not been the case this spring. In addition, adults as well as larvae can damage regrowth. If high populations are not treated before first cutting, enough larvae and new adults may survive to keep the second cutting from "greening up." A treatment may be needed if 30-50 percent of the new growth has been damaged and a field has not "greened up" after seven to 10 days with adequate moisture. If most of the damage is caused by adults, check the insecticide label to make sure the product is registered for adult control and that a high enough rate is applied.


Field Corn.

In addition to no-till fields planted into burned down small grain covers, you should watch for armyworms moving from small grain fields into nearby corn fields. The treatment threshold for armyworms in corn is 25% infested plants with larvae less than one-inch long. A pyrethroid will provide effective control. We are also starting to see problems showing up from soil insect problems. If you are assessing stands and they appear spotty or you seem to be "loosing" plants, be sure to check for damage from soil insects. In addition to seed corn maggot, white grubs and wireworms, we are seeing damage from rootworm larvae which appears similar to wireworm damage. In many cases, it is southern corn rootworm ( also known as the spotted cucumber beetle). This damage has been encountered in areas where vegetables are grown, especially melons. Since adult beetle populations were extremely high at the end of last season, eggs layed at the end of last summer have produced larvae that can damage corn planted into these fields this season. In addition to Southern corn rootworm, Northern and Western corn rootworm can be found throughout the state. Although we tend to think about rootworms attacking continuous corn in heavier soils, it can also attack continuous corn planted in sandy soils under irrigation. The following guidelines can help decide if a soil insect is causing stand problems:

Seed corn maggot-- Seedling skips are an indication of seed corn maggot damage. Upon digging the seed it may not be sprouted or the sprout had died.The seed will be hollowed out and you should find small white maggots in the seed or small brown pupae in the soil around the seed.

Southern corn rootworm -- A small, upward penetrating hole will be eaten between main roots at the root crown and a yellowish-white larvae with a brown tail plate may be present.

Wireworm -- Non-emerged seed will have rough holes eaten into them, or seed may be mostly consumed. Dead or dying seedlings show holes eaten into the underground stem, at or above the root crown. Before dying, the central whorl leaf will wilt. Wireworms may be found in the plant or in the soil around newly damaged plants.

White Grubs - Stunted plants are present in a somewhat circular pattern. Since grubs are not attracted to the seed, corn plants often emerge; however root and/or mesocotyl injury can stunt or kill young plants. Upon digging up damaged plants, grubs will be present and root feeding can be readily observed.


Small Grains.

Continue to sample barley and wheat for armyworm and sawflies. We have started to see head clipping from sawflies in barley and wheat. In general, this insect peaks in activity by May 20, approximately 10 days before armyworms. Once the number of clipped heads is twice the number of larvae found per 5 foot of row, then it is usually too late to treat. The treatment threshold for armyworms on wheat is 2 per foot of row and on barley the threshold is one per foot. On wheat, Warrior, Mustang, Lannate or Parathion can be used. On barley, Lannate or Parathion can be used. Remember Parathion can only be used by aerial applicators and has setback restrictions. In addition, the EPA and the manufacturer have agreed to phase out its use on all agricultural crops by 2003.



In no-till fields, seed corn maggot will remain a problem through May. Flies continue to lay eggs and maggots will be present at the time of seed germination. The hopper box treatments available with a soybean label are Kernel Guard Supreme and KickStart VP. The active ingredient in both products is permethrin. For those who have soybeans just emerging from the ground, be sure to scout for grasshoppers. The treatment threshold for grasshoppers is 1 per sweep and 30% defoliation. We are starting to find the first small grasshoppers along field edges and in fields with soybean stubble from last season. Asana, Furadan, Lorsban or Warrior will provide control, although multiple controls may be needed.




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


Small Grains.

Barley is maturing rapidly and several diseases can be seen at this time. As mentioned last week, barley rust came in on susceptible varieties such as Barsoy and Callao. Moderate levels have been seen on Wysor and Boone depending on location. Net blotch and the spot blotch form of net blotch are also present in some areas. Look for oval, chocolate brown spots on the leaves. Both diseases should not be reducing yields if they came in after the barley flowered.


Powdery mildew on wheat continues to be the dominant disease, but Septoria leaf spot caused by Septoria nodorum the cause of glume blotch is also increasing on susceptible varieties that were not sprayed with Tilt or Stratego. Warm, wet weather is needed for glume blotch to increase.

Not all white heads that are seen in the field are the result of scab or take-all. I have found a few white heads in our variety trials that if you look at the base of the plant, under the leaf sheath you can find long, lens-shaped lesions with dark brown borders. This is a fungus disease called sharp eyespot caused by Rhizoctonia cerealis. Often small areas or just a few plants can be infected and showing these symptoms. Cool, wet conditions favor infection.




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


U.S. Corn Planting A Mixed Bag

Grain market analysts are still trying to get a handle on the impact that rain, wet, and cool weather is having on the nation's 2002 corn crop. Some areas in the Eastern Corn Belt are still way behind schedule and in some cases planters have not gotten out of the machine shed. Central Illinois grain farmers have experienced 15 inches of rain in the past month. It is beginning to look like some corn acres will have to switch to soybeans, if planted at all. With 62 % of the 2002 U.S. corn crop planted, which is normal progress on average, the wet weather is likely to play a role in Dec. corn futures for at least another week.


Tighter World Corn Stocks

USDA's May 10th crop report added fuel to the corn markets ability to rally with the release of the World Supply and Demand Report indicating record low ending corn stocks for the current marketing year ending June 31, at 113.7 mmt, the lowest level in 20 years. This is well below the 124.3 mmt seen in 1995/96 when corn futures rallied to $5.00 per bushel.

Record Low Wheat Acres to Be Harvested

USDA now estimates that Great Plains farmers will harvest just 30.2 million acres of winter wheat this year, the lowest acreage in 85 years. The acreage estimated is down 4 percent from a year ago.


New Farm Bill Now in Place

The 2002 Farm Bill will involve may changes. Farmers need to get ready to update their base acres and yields, and information will be forthcoming from FSA regarding that process. Delaware loan rates have not been set at this point in time. New crop loan rates are to be in effect on the first day of the marketing year for each crop. Farmers can learn more of the preliminary details concerning the Farm Bill at <www.usda.gov/farmbill>. The national target prices have been published. They are: Wheat $3.86, Corn $2.60, Soybeans $5.80, Sorghum $2.54, and Barley $2.21 per bushel (Cash Price Received + LDP (if any) + Direct Payment + Counter Cyclical Rate (if any) = Target Price).


Marketing Strategy

Tight corn stocks, record low wheat acres to be harvested, new target prices, and wet weather in the ECB are more than enough from a fundamental perspective to sit tight on advancing new crop sales. Unless I am missing something, the 2002 target prices now become the new minimum price levels for commodities. In other words, the target price now becomes the new 'free' put, the minimum price that the farmer can receive. The higher target prices now gives more lead way to farmers in advancing new crop sales.



First Harvest Hay Yield Potential Appears Low - Richard W. Taylor, Extension Agronomist, rtaylor@udel.edu


Many hay producers in the state are noticing that growth of cool-season grasses is unusually variable this spring. As the grasses are beginning to head out at this time, it has become easy to see the patchy, up and down nature of the grass growth. This is especially true in orchardgrass dominated hay fields. Its been reported that winter grain mite, aphids, and white grubs have caused damage to many orchardgrass fields across the region. Greenbug aphids have been reported in some fields and this aphid can transmit barley yellow dwarf virus although we have not confirmed the presence of this virus in orchardgrass.


In inspecting some fields this week, we believe we were seeing evidence of the hard freeze we had a number of weeks ago, and that killed a number of tillers on winter wheat across the state. In this case, we observed either whole tillers dying with the collapse of the internode between the first and second or second and third node above the plant crown. The growing point on the tiller was obviously dead and new tillers were beginning growth from the crown region. Another symptom we observed was the bleaching of a portion of the leaf that was undergoing cell division and maturation during the hours of cold weather. On either side of the band, the leaf looked perfectly normal for orchardgrass.


Were hopeful that orchardgrass and the other cool-season grasses that were damaged by frost, dry winter weather, and insect problems will recover some of its vigor for the second hay cut. Be sure to check your soil test results to ensure that you have adequate nutrition in the soil for rapid, vigorous recovery of the crop. Phosphorus is especially important if white grubs were feeding on the roots last winter and have weakened the root system. Our recommendations call for 50 pounds of N/A if the clover content of the hay field is low.


Below are two pictures of the damage we observed in orchardgrass fields.






Watch For Manganese Deficiency on Corn- Richard W. Taylor, Extension Agronomist, rtaylor@udel.edu


During the next several weeks, manganese (Mn) deficiency symptoms often begin to appear on corn that is being grown on soils low in available Mn, has low organic matter content, and having pH values in the mid-6 range or higher. Although native Mn soil levels are important, we generally see more frequent Mn deficiency problems on fields as the soil pH approaches or goes above 7.0.


Yield reductions can be avoided to a large degree by early diagnosis and treatment with foliar application of Mn. Ignoring or not catching the problem till later in the season can not only reduce yield potential, but make a foliar application more difficult and possibly more expensive.


Manganese deficiency symptoms began as interveinal chlorosis with the veins a dark green but in between the veins a light green or yellowish color. Symptoms progressed rapidly from the slight interveinal chlorotic cast to areas of bleached white to slightly yellow around the leaf margins (edges) about mid way up the leaf blade. The oldest leaves appear to be the most affected. Some necrosis or dead spots can appear along the margins of the leaf blade and at leaf tips.


Crop health can decline so rapidly that you may not have time to wait for the results of a tissue analysis to confirm that Mn is the responsible nutrient. If your soil test shows soil test Mn to be marginal and the soil pH is higher than optimum for your soil, it could be well worth applying a foliar application of 1 to 2 lb Mn/A applied without waiting for a tissue test. Whole plant samples would allow you to make a more definitive diagnosis if your scouting program helps you spot such problems in the early stages.



Comparison of Various Glyphosate Formulations - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu


There are numerous products containing glyphosate in the marketplace, but there is no consistency in how the companies report what is contained in the jug. Glyphosate is an acid, but it is formulated as a salt for packaging and handling. Roundup uses the isopropylamine salt, whereas Touchdown is formulated as a diammonium salt. Some companies report their product as acid equivalent (glyphosate acid) or some report it as active ingredient (glyphosate plus the salt), and others report both. In order to compare performance of different formulations, it is critical to know how the products were formulated. Since the salt does not contribute to weed control and different salts have different weights, the acid equivalent is a more accurate method of expressing, and comparing, concentrations. 




Trade name

Acid equivalent

Active ingredient

Formulation (salt) of the glyphosate acid

Rates for 0.75 lb acid equivalent

Roundup Original



isopropylamine salt

32 oz

Roundup Ultra



isopropylamine salt

32 oz

Roundup Ultra Max



isopropylamine salt

26 oz

Touchdown IQ



diammonium salt

32 oz

Glyphomax Plus



isopropylamine salt

32 oz




isopropylamine salt

32 oz

*based on calculated value.




Rainfastness and Height Restrictions for Corn Herbicicdes - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu


Rainfastness is number of hours needed between time of application and rainfall or irrigation to ensure sufficient absorption in the plant.


Broadcast applications refer to an over the top application and directed refers to use of special spray equipment to direct the spray and avoiding the spray coming in contact with the whorl of the corn. When corn height and collar number are given, base decision on whichever feature is first attained.


an - means no information on label







interval (hr)

Maximum corn size



broadcast: 6 collars or 24 in.

directed: 10 collars or 36 in.



broadcast: up to 8 collars

directed: when necessary



12 inches tall





more than pt/A:

broadcast: 5 lvs or 8 in.

directed: 36 inches tall

pt/A or less: 36 inches tall



broadcast: min- 4 inches tall

max- 20 in. tall or 6 collar

directed: pre-tassel



30 inches tall or 8 collars

2,4-D Amine


broadcast: 8 inches tall

directed: pre-tassel

2,4-D Ester


broadcast: 8 inches tall

directed: pre-tassel



directed only: 12 inches tall do not apply 3 weeks before tasseling

Harmony GT


1 - 4 collars or 12 inches tall



broadcast: 24 inches tall or 7 collars

directed: 20 to 36 inches tall



broadcast: 16 inches tall or 5 collars

directed: 16 to 36 inches tall



broadcast: 48 inches tall

directed: when necessary



broadcast: 2- to 10-lf collars

directed: when necessary; when corn leaves interfere w/ spray

Roundup Ultra

and UltraMax


up to 30 inches or 8 collars



24 inches tall



up to 8 collars






2 collars or 6 inches tall

Basis Gold


5 collars or 12 inches tall

Celebrity Plus


broadcast: 4 to 24 inches tall



6 oz rate: 4 to 10 inches tall

4 oz rate: up to 24 in. tall



broadcast: min- 4 in. tall

max- 20 in. tall or 6 collar

directed: 20 to 30 inches tall

Field Master


Do not apply to emerged corn

Hornet WDG


broadcast: 20 inches tall or 6 collars

directed: 20 to 36 inches tall



12 inches tall

Liberty ATZ


12 inches tall



broadcast: 12 inches tall

directed: 20 inches tall



broadcast: 5-lf stage or 8 inches tall



broadcast: min- 4 inches tall

max- 20 in. tall or 6 collar

directed: 20 to 30 inches tall

Ready Master ATZ


emergence until 12 inches tall



broadcast: 8 inches tall

directed: 12 inches tall

or if rate >2 pts



broadcast: 20 inches tall or 6 collars (min. 4 in. tall)

directed: 20 to 24 inches tall (before tassel emerg.)



less than 12 inches or 6 collars





Delaware Wheat Crop Profile Online For Your Review Susan Whitney, Extension Specialist, Pesticides, Urban Entomology, swhitney@udel.edu


The Delaware Wheat Crop Profile has been posted at:



Wheat growers are encouraged to review this crop profile and send suggestions for revision to Susan Whitney (swhitney@udel.edu) . EPA will use this document when making pesticide registration decisions under the Food Quality Protection Act. If you wish a hard copy, please contact Whitney (831-8886).





Pesticide Briefs Online (5/10/02) Susan Whitney, Extension Specialist, Pesticides, Urban Entomology, swhitney@udel.edu


Go to:






























Household Hazardous Waste Collection (includes small businesses)
June 1, 2002 Southern Solid Waste Management Center
Rt 20 (Jones Crossroads), Georgetown DE
8 am to 3 pm
Call Delaware Solid Waste Authority at

1-800-404-7080 for details



Ag Fact


In 2001, total food expenditures by Americans was $855 billion split 52.29% for food at-home and 47.71% for food away-from-home.





Weather Summary

Week of May 10 to May 16, 2002


May 13: 0.32 inches


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

Air Temperature:

Highs Ranged from 84F on May 13 to 64F on May 14.

Lows Ranged from 63F on May 13 to 48F on May 15.

Soil Temperature:

70F 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, Dean and 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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