Volume 8, Issue 8                                                                                                        May 12, 2000


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


With the warmer temperatures, we are starting to see an increase in asparagus beetle activity. Spot treatments along field edges will only work if the beetles have not moved into the field. A treatment is recommended if you find 5 or more beetles per plant and/or egg laying has begun. Sevin, Ambush, or Pounce will provide cost effective control.


Cucumber beetle activity has increased and adults can be found feeding on young transplants. Furadan or Admire applied at planting will provide cucumber beetle control. Admire can be used on transplants, in furrow or injected through the drip irrigation. If used through the drip irrigation, you should apply 8 oz per acre after transplanting and another 8 oz per acre once the vines begin to run. Economic levels of spider mites and aphids can be found in recently transplanted watermelon fields. A treatment should be applied for aphids if 10 to 20 percent of the plants are infested and you see leaf curling. Lannate or Thiodan are the only insecticides available for melon aphid control in cucurbits. The treatment threshold for mites is 10 15% infested plants/crowns. In addition to Agri-Mek and Kelthane, we now have Capture and Danitol (both pyrethroids) available for spider mite control in watermelons. It will be important to rotate classes of miticides to avoid the development of resistance.



During the past week, Colorado potato beetle adult feeding and egg laying has significantly increased. Both adults and larvae can be found feeding on plants. A treatment is needed if you find the following numbers per 50 plant sample: 25 adults, or 200 small larvae or 75 large larvae. If a combination of stages are present, the threshold for each stage should be reduced by 1/2. If the predominant stage is adults and defoliation exceeds 20%, Provado (3.75 oz/acre) should be used. If egg hatch has occurred, Provado or Spintor ( 4-6 oz/acre) can be used. Spintor will also provide corn borer control. European corn borer catches have increased in the Bridgeville (10 per night) and Harrington (28 per night) areas. Once moth counts reach 10 per night, fields should be scouted for infested terminals and treatments applied when 25% of the terminals are infested. If you are unable to scout for infested terminals, the first corn borer spray should be applied 7 to 10 days after trap catches reach 10 moths per night in your area. Ambush, Baythroid, Pounce, Furadan, Penncap-M, Monitor or Spintor will provide corn borer control. If you are scouting for infested terminals, generally 2 applications of the systemic materials - Furadan or Monitor - will provide the best control. If Ambush, Baythroid, Pounce, Penncap or Spintor are used and timing is based on moth catches in blacklight traps, 3-4 applications may be needed.

Sweet Corn.

Flea beetle and cutworm activity has increased above threshold levels in scattered fields throughout the state. The treatment threshold for flea beetles is 5% infested plants and the cutworm threshold is 10% leaf feeding or 3% cut plants. A pyrethroid will provide cost effective control of both insects.


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

Maxim 4FS Fungicide Seed Treatment Label Changes.

Novaritis Crop Protection announced that several new crops have been added to the marketing label and have been approved by EPA. Maxim 4FS is a fungicide that controls soil-borne and seed-borne diseases of seeds and propagating root or tuber material. It is active against diseases caused by Fusarium, Rhizoctonia, Helminthosporium, Aspergillus, and Penicillium. This is a commercial seed treatment that will come on seed purchased by the grower or you will have to request it from your seed supplier. It is not for use on farm in hopper-box, planter-box, slurry-box, or other seed treatment applications at or immediately before planting. It does not control Pythium or Phytophthora. If additional control of these two fungi is needed seed treatment with Apron will be needed if it is labeled for that crop.

The new additions to the label which will be useful for Delaware growers include: root and tuber vegetables, leafy vegetables, Brassica (cole) leafy vegetables, legume vegetables, cucurbit vegetables, and herbs and spices. Specifically this will include beet, carrot, turnip, spinach, cabbage, broccoli, Brussels sprouts, cauliflower, collards, kale, snap and lima beans, pea, soybean, cantaloupe, squash, watermelon, cucumber, pumpkin and many herbs and spices. Be sure to check the label for a complete listing of the new uses.


Late Blight Update - - Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Disease Severity Value (DSV) Accumulations as of May 10, 2000 are as follows:

(Remember 18 DSVs is the threshold to begin a spray program)

Emergence Date


May 4


April 14


10 day, low rate

April 21


10 day, low rate

April 22


no spray

April 27


no spray

No DSV accumulation since last week.

Potatoes that have emerged after April 22 have not reached the 18 DSV threshold. Fields that reached green row on April 21 and before should continue to be sprayed. We probably accumulated 1-2 severity values from the storm last night, but that would not change the spray recommendation.

If growers do not feel comfortable with the "no spray" recommendation and the plants are getting larger, the first application of fungicide should be applied when the plants are 6-8 inches tall or touching down the row. The lowest recommended rate is suggested.


Lima Bean Weed Control Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

Lima bean planting will soon begin and continue to mid-July. The standard herbicide treatment has been a premergence tank mix Dual Magnum at 1 pint/acre and Pursuit at 2 to 3 ounces per acre. This could also be applied as a preplant incorporated treatment, but the residual carry-over is longer when incorporated. Control is essentially the same as preemergence treatments.

Growers who follow lima beans the next year with vegetables may need to avoid the use of Pursuit. In that case, growers can apply a preplant incorporated treatment of Dual Magnum at 1 pint and Treflan at 1 pint. While some broadleaf weeds may escape this treatment, cultivation and possible use of Basagran as a post-emergence treatment will provide good weed control.


"Excellence in Lima Beans" - Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

The Delaware Extension Service is conducting a field survey program in lima bean fields this summer. The purpose is to try to identify and then correlate production practices that are associated with improved yields. We hope to survey as many as forty fields. Many growers have already indicated a willingness to participate, but if you haven't been contacted and are interested, please call your County Agricultural Agent, or myself.


Field Crops

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

Field Corn.

Continue to watch for cutworm activity. As of May 10th, 200 degree days (base 50) have accumulated since peak moth activity. If the weather remains warm, we should begin to see cutting activity from black cutworm by the end of the current week. The first armyworms have been detected in no-till corn. Watch for true armyworm feeding in no-till corn fields planted into small grain covers or where volunteer grain was present at burndown. A pyrethroid tanked mixed with pre-emergence herbicides will provide control. If a pyrethroid was not used pre-emergence, fields should be scouted and treatments applied if 25% of the plants are infested before larvae are one-inch in length.


We can now find aphids, cereal leaf beetle, true armyworm and grass sawfly in fields throughout the state. Be sure to check fields for all 4 insects at this time. We have experienced significant increases in true armyworm moth activity during the last week, especially in the Harrington and Little Creek areas. Based on moth catches in the Milford, Harrington and Little Creek areas, we may see significant armyworm populations in those areas. In other areas of the state, you can expect to see hotspots of economic levels. Remember, barley can be quickly damaged by armyworm populations. The treatment threshold for armyworms in barley is one per foot of row. The true armyworm threshold in wheat is two per foot of row. Once fields reach the soft dough stage, no treatments will be needed for cereal leaf beetle or aphids.


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


A few rust pustules were seen this week on wheat. Look for small slightly raised spots or pustules as we like to call them on the upper surface of the leaves. Usually leaf rust occurs here very sporadically and usually too late to cause damage.

With most wheat headed out, continue to scout for foliage diseases until soft-dough stage. The heat this week slowed powdery mildew development, but the return to cooler weather may favor some more activity. Someone asked me what are black flecks that can be seen in the old, tan powdery mildew spots. They are the sexual fruiting bodies of the fungus called cleistothecia. These contain the oversummering and overwintering spores and provide the genetic variability that we see with this fungus. We always need new varieties of wheat with resistance to powdery mildew because the fungus continues to change either slowly or quickly.

If it stays dry during the flowering period for wheat, scab will not be a problem, but if it is wet and warm (77-86F) scab can be troublesome especially in no-till wheat into corn stubble.



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

Export Sales Favorable to Grains and Soybeans

Weekly U.S. export sales data showed a recovery in corn from last week's poor performance. New sales totaled 748,300 metric tons which placed corn exports over the top end of pre-report trade guestimates.

Wheat estimates were reported just ahead of the low end of pre-report guestimates at 328,000 mt. Soybean exports were at the top end of trade guestimates at 297,100 mt. Favorable news from the weekly export report and trader expectations that the weather is likely to turn back to hot and dry in the midwest is providing support for prices. Commodity prices for the week are very similar to last week's levels, with only wheat showing a very slight gain from last week.Commodity price volatility has been picking up in recent weeks and they are expected to remain volatile for the next three month's. La Nina is reported to be live and well. USDA releases the next crop report on Friday, May 12th.



Additional Weed Control Options in Sweet Corn (?). - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

A couple of products have been labeled for sweet corn over the last year, but their usefulness may be quite limited due to crop safety concerns. Last year Accent received a label for use on processing sweet corn (Bonus, Excalibur, GG-43, GG-55, More, Reward, Viking and Zenith only varieties labeled). Accent can not be used on sweet corn that was treated with Counter due to crop injury. We tested Accent on Bonus and observed some yellowing and stunting, but yield was not reduced. My caution when using Accent on sweet corn, even labeled varieties, is to expect some injury. The label recommends the addition of nitrogen, but this is liable to further increase injury.

Prowl has received a federal label for postemergence application on sweet corn. The rate of Prowl ranges from 1.8 to 3.6 pints for most of the soils in our region. Applications can be made up to 20-24 inch corn (or 8 visible leaf collars). Prowl will not control emerged weeds, thus it will only provide residual control from time of application.

Sempra, from Monsanto, which has the same active ingredient as Permit has been labeled for postemergence treatments. Timing is from spike through crop layby. Use rate is 2/3 of an ounce. According to the label "the user assumes responsibility for use"; meaning you are assuming the responsibility for crop injury. Also, it is not recommended to spray sweet corn previously treated with an organophosphate insecticide such as Counter. We have not had this herbicide on any of our sweet corn trials yet, so I have no prior experience to share.


When Is Too Late to Spray Burndowns? - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

I have been asked a couple of times this year about no-till fields that were planted but the corn emerged before the burndown herbicides could be applied. Use of Roundup or Touchdown will be very touchy. We have tried it and killed some of the plants in the spike stage. We also tried it with sweet corn and killed the majority of the plants. My recommendation is do not try it.

Gramoxone on corn plants just spiking will cause brown and dead tissue on the margin of the leaf, but does not kill the plants. Expect to see some leaf burn. Once the plant gets beyond the spike stage, look for other methods.

Better crop safety would be to apply your postemergence herbicides at this time. Most of the postemergence herbicides can be sprayed very early postemergence. These other options offer better crop safety than Gramoxone. Be sure to match the correct herbicide to the weeds you have present and be sure to consider residual weed control. The soil-applied premixes (Bicep, Harness Xtra, Fultime etc.) can be sprayed early postemergence, but I have had limited success with these herbicides to provide adequate burndown control.


Banvel Precautions - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

With the warm weather we have been having, spraying postemergence herbicides in early planted corn may require additional consideration because of the temperature. It is not recommended to spray Banvel when the temperature is expected to be 85 degrees or hotter; or spray late in the day when temperatures drop below 85. A number of pre-mixes have Banvel included, so the temperature consideration applies to them as well. Pre-packaged mixtures containing Banvel include: Distinct, Celebrity Plus, Marksman, and NorthStar.

Be Sure to Scout Fields - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

This weather has been nothing short of amazing. Therefore it is difficult to predict what is going on in some fields. I have seen nightshade with 6 leaves in some fields. Nightshade is usually a weed that emerges late. So be sure to look at those fields that need postemergence spraying and be sure the weeds present are the ones you are expecting.


Japanese Knotweed Control - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Japanese knotweed, also called Japanese fleece flower or Mexican bamboo, is becoming more wide spread. This is a perennial plant found along ditches and the edge of woods and occasionally in production fields. It is a very aggressive plant and difficult to control. In a greenhouse study, Roundup at 1.5 qts or Pursuit were not effective on it; and we did not include any other soybean herbicides. Of the corn herbicides, Banvel (8 oz/A), Basis Gold, or Marksman were the best at about 65% control. Permit, Exceed, Accent, or Stinger were not effective on it. In non-crop areas, Arsenal was the best product (almost 90% control). For non-crop areas be sure to read and follow the Arsenal label; Arsenal can limit revegetation of an area.



Corn Replanting - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu

Much of the early-planted corn appears to have come through the cold wet weather in very good condition but there have been a few problem fields observed. Now is the time to take the time to visit each field and evaluate the stands. Replanting corn late is very often not economical but a quick decision at this time has more of a chance to pay dividends in replanting. Fact sheets are available from your local county agricultural Extension office that cover how to evaluate stands and how to calculate whether replanting is economical.

In evaluating your corn stands, you will need to estimate the population that was achieved in the initial planting. If new plants are emerging and they are more than about two leaf stages behind the majority of the plants already emerged, these new plants will contribute very little to yield and should not be counted in your population estimates. The two-leaf stage difference generally means about a ten-day delay in emergence and translates to about an 8 percent yield loss. Under some conditions such as early-planted no-till followed by cold and wet conditions, the delay can be as much as 21-days and this can reduce yields by 10 to 20 percent.

When evaluating corn stands, dont just count plants and look at population. Also important is plant spacing. Ideally, the plants should be equidistant from each other within the row but this is not often what happens especially if the planter units have begun to wear. Research at Purdue University has shown that for every inch increase in the standard deviation of plant spacings (a mathematical estimate of how variable the spacing is), yield decreases by about 2.5 bu/A. Most ideal field situations have a standard deviation of about 2 but in the Purdue study 84 percent of the fields had standard deviations of plant spacings of 4 or greater and 24 percent had standard deviations of 6 or greater. Thats a 15 bu/A or greater yield loss at the beginning of the growing season.

With that much yield loss at stake, why take the chance. Scout your fields, evaluate your corn stand, and use our fact sheets to determine if replanting is an option.


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

Ive observed a number of hay fields that were harvested during the spate of favorable weather during the past week. Many fields just received rainfall that will increase the soils available water supply to a level that will support excellent regrowth. Therefore, harvested hay fields and grass pastures already grazed should be fertilized with enough nitrogen to ensure rapid, vigorous regrowth and replace that removed as hay or grazed material. If legumes are present in amounts greater than 25 percent, fertilized with reduced rates of nitrogen and add about one pound boron per acre. Both grass and grass-legume mixtures also should receive potash (potassium) fertilizer either now or after the next cutting or grazing cycle. Potassium helps forages tolerate the heat, moisture, and pests stresses they experience during the upcoming summer weather.


                  Weather Summary

Week of May 4 to May 11


0.12 inches: May 10, 2000

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

Air Temperature:

Highs Ranged from 93F on May 7 to 75 F on May 4.

Lows Ranged from 70F on May 9 to 47 F on May 4.

Soil Temperature:

79F average for the week.

(Soil temperature taken at a 2 inch depth, under sod)

Web Address for the U of D Research & Education Center:


Note: These are the final counts for the 2000 season

Black Cutworm Pheromone Trap Catches 2000 Season

Trap Counts Provided by UAP Inc., Seaford, DE

May 1-7, 2000


# Moths per 7 Days


# Moths per 7 Days

Bridgeville, DE


Leipsic, DE


Cheswold, DE


Lincoln, DE


Cordova, MD


Little Creek, DE


Crumpton. MD


Magnolia, DE


Delmar, MD


Mardela, MD


Denton, MD


Marydel, DE


Dover/Wyoming, DE


Middletown, DE


East New Market, MD


Milford, DE


Easton, MD


Millsboro, DE


Eldorado, MD


Milton, DE


Ellendale, DE


Newark, MD


Farmington, DE


Pocomoke, MD


Federalsburg, MD


Preston, MD


Felton, DE


Princess Anne, MD


Frederica, DE


Queen Anne, MD




Rhodesdale, MD


Goldsboro, MD


Salisbury, MD


Greensboro, MD


Seaford, DE


Greenwood, DE


Selbyville, DE


Harbeson, DE


Smyrna, DE




Snowhill, MD


Hebron, MD


Sudlersville, MD


Hickory Hill, DE


Trappe, MD


Hurlock, MD


Vernon, MD


Kenton, DE


Vienna, MD


Laurel, DE


Westover, MD



Willards, MD


Moth catches of 9-15 moths per 7-day period have been associated with a moderate to high potential for cutworm outbreaks.

Moth catches of 5 per night for at least 2 consecutive nights have also indicated a high potential for problems

You can expect to see cutting activity approx.300 degree-days (base 50) from peak moth activity (9-15 per week or 5 per night for at least 2 consecutive nights)

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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