Volume 6, Issue 9                                                                                           May 22, 1998


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


Cucumber beetles can be found in fields throughout the state, especially if Furadan was not used at planting. Cucumbers and muskmelons are the most susceptible to bacterial wilt so be sure to check fields soon after emergence or transplanting for beetles. Sevin or a pyrethroid will provide control.


With the recent warm weather, we are starting to see an increase in corn borer moth activity. In areas where corn borers are approaching 10 moths per night, we are finding low levels of corn borer egg masses. We should not begin to see infested terminals until the last week in May. The first Colorado potato beetle egg masses and low levels of small larvae can now be found in the earliest planted fields. The treatment threshold is 4 small larvae per plant. Agri-mek, cryolite or Provado will all provide control. Potato leafhopper adults can now be found in fields that were not treated with Admire. As a general guideline, controls should be applied if you find one adult per sweep and/or 1 nymph per every 10 leaves. A pyrethroid or Provado will provide control.

Snap Beans.

Begin to check your earliest planted fields for thrips and leafhoppers. At this time, populations are very light; however, they could explode quickly if the weather remains hot and dry. The treatment thresholds are 5-6 per leaflet or 5 leafhoppers per sweep. If both insects are present, the best control option would be Lannate in fresh market beans and Lannate or Orthene in processing beans.

Sweet Corn.

Small true armyworms and corn borer larvae can be found in the earliest planted fields. The treatment threshold for both insects is 15% infested plants. The best control options for corn borer control are Ambush, Pounce, Penncap or Warrior. If true armyworm is the main pest, a pyrethroid will provide the best control.  *


Update on Transplants -Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

Last week we reported transplants that were wilted down, flopped over, and suggested that depending on the length of their exposure to the cold temperatures, they may come back. However, the 40 degree temperatures did mortal damage to many of the plants. The duration of exposure to these low temperatures for several nights caused this damage, especially after several days of no sunshine, low temperatures, and resultant cool soils. The worst damage occurred on fields that were planted on May 5, 6, or 7, just prior to the bad weather. It is also notable that the damage occurred on plants grown in 72 trays, which has become a standard practice. However, transplants from 54 size trays, with a large root system, survived much better.

Dr. Frank Schales, Retired University of Maryland Vegetable Crops Specialist, demonstrated the value of larger cell sizes for cantaloupes and watermelons back in the 1970s. Larger root systems offer two major advantages: (1) better survivability, especially under stress conditions, and (2), get off to a quicker start to mature earlier for the early market. We estimate that probably 80% of our transplants are grown in "72s" to utilize greenhouse space efficiently. However, it may make sense to use larger cell sizes for the earliest plantings.  *

Pea Harvest/Lima Bean Plantings/No-Till Soybeans After Peas - Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

Pea Harvest is beginning on Delmarva this week, with all companies beginning by May 28 or so. Over 90% of the acreage is harvested with the pod stripper type combines, which do a more aggressive job of pulling leaves and other vegetative matter off the plants than the old pull-type combines. It usually also distributes threshed out trash material across the field more efficiently. Because of this, allowing pea vines to decay for several days before tillage is no longer as critical. Large concentrations of decaying vines can release a cyanide type gas that has been shown to kill young seedlings of the succeeding crop.

We still recommend waiting at least a day after harvest, and then plowing for lima beans. This allows the initial decay to begin and any damaging "gas" to disseminate. Moldboard plowing is more effective in burying certain disease organisms, especially Rhizoctonia root and stem rot. In talking with veteran (now retired fieldmen), they report only a few instances of "gas damage" even with the old pull type viners in over forty years of experience for each.

Some growers plant soybeans after peas, and if the trash from the peas is evenly distributed, and the interval between pea harvest and planting is two days of sunny weather, we have seen successful no-till planting of soybeans. The herbicide program consists of a burn down herbicide coupled with a residual herbicide program. No-till soybeans after peas can save significant time during this busy period.  *


Vegetable Diseases - Kate Everts, Extension Plant Pathologist, University of Maryland and University of Delaware ; everts@udel.edu


Several trays of watermelon transplants have been brought in for diagnosis that are heavily infested with gummy stem blight. Gummy stem blight will appear initially in small clusters of plants in the greenhouse. These plants will have dark brown lesions on the cotyledons and true leaves. There will be a watersoaked lesion where the cotyledons attach to the seedling stem. Gummy stem blight can be seedborne or may overwinter in greenhouses that are not adequately sanitized. The cloudy, rainy weather last week provided ideal conditions for disease spread.

Because of the weather last week and the presence of infected transplants, there may be a high level of inoculum being introduced into fields, very early. Normally our recommendation is to begin sprays when the vines begin to run. However, growers should examine transplanted watermelons carefully and treat with chlorothalonil if symptoms are observed. In addition, do not transplant watermelons that have symptoms of gummy stem blight.  *


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


Recently some growers have noticed some leafspotting that was black and was mostly found on the margins of the lower leaves. It caused some concern because of its resemblance to late blight. After the sun came out, many of these spots turned brown and papery thin.. Fortunately this was not late blight, but a physiological leaf spot that we have seen in the past during periods of rapid plant growth. It is good to be looking for possible disease problems, but this leafspot is not pathogenic.

Late Blight Update

DSV accumulations as of May 18, 1998 are as follows:

Location/Emergence Date

DSV's May 14

DSV's May 18


Baldwin - 4/20



10-day, low rate

Jackewicz - 4/20



7-day, low rate

Zimmerman - 4/23



10-day, low rate

Baker - 5/1



10-day, low rate

What a difference a week makes! The present weather pattern has not been favorable for late blight. But, this is the time to be on the lookout for infections that could have occurred when conditions were very favorable. Disease pressure has lightened for the time being. Keep up the preventative sprays at the appropriate spray interval. The Late Blight Report is also posted electronically at the UD Extension IPM website: http://www.udel.edu/IPM *

Field Crops

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


Be sure to watch fields carefully within one week of harvest for potato leafhopper adults. Leafhopper adults can now be found laying eggs in fields and populations can explode quickly if the weather remains hot and dry. Spring planted fields are also very susceptible to damage so be sure to begin sampling those fields on a weekly basis. When alfalfa is 3-inches or less in height, the treatment threshold is 20 per 100 sweeps. In four to six-inch tall alfalfa, the treatment threshold is 50 per 100 sweeps. Ambush, Baythroid, Dimethoate, Pounce or Warrior will provide effective control.

Small Grains.

Armyworms continue to be found sporadically in barley and wheat fields. We should be at the peak in sawfly activity and head-clipping damage should be over in the next 7 –10 day period. Armyworm larvae still vary in size from to one-inch long. Since armyworms prefer to feed on the vegetation in the lower part of the canopy, no sprays should be needed in wheat until you begin to see head clipping or if larvae begin to move up the plants feeding extensively on the foliage. Remember that armyworms will clip heads faster in barley so fields approaching threshold levels of one per foot of row should be watched closely for damage.

Field Corn.

Be sure to watch fields closely for cutworm and true armyworm activity. In spike to 3-leaf stage corn, a treatment will be needed if you find 10% leaf feeding or 3% cut plants. As plants reach the 4-5 leaf stage, no sprays will be needed unless you find 5% cut plants and larvae can be found. True armyworm larvae can be found in fields that were planted into a burned down small grain cover and/or where a small grain cover was not completely plowed under before planting. The treatment threshold is 20 – 25% infested plants. A pyrethroid will provide control of both insect pests.  *


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

Small Grains.

Barley is beginning to dry down and leaf rust has exploded during the past week on susceptible barley varieties. Wheat diseases continue to develop. Last week I mentioned seeing both Septoria leafspots and this week I have seen tan spot rapidly progressing on the leaves in the upper canopy. It is rapidly overgrowing the Septoria lesions. Tan spot begins as small tan-brown flecks that expand into irregular to lens shaped lesions, with yellow halos. Many spots have grown together and have blighted whole leaves. This fungus does not produce the characteristic dark brown pycnidia (fungal fruiting structures) of the Septoria diseases and does not infect the heads.

Glume blotch and scab are beginning to appear on the heads of wheat. Glume blotch produces purple discolored areas that turn brown and often will have the diagnostic fruiting structures imbedded in the infected tissue. Scab symptoms include white heads or parts of the head that are bleached white to tan and may or may not have grain. If grain is present it is often shriveled and moldy. During periods of wet, humid weather the bleached areas often have pink to orange coloration from the production of spore masses of the fungus. The fungus infects the head during flowering and if the weather is wet during flowering infection can occur. Wheat no-tilled into corn stubble is the most at risk because the fungus that causes scab, Fusarium, also causes stalk rot of corn. To minimize the risk of scab, plant wheat varieties with different flowering dates to prevent all of your crop from being vulnerable to scab should weather conditions during flowering be favorable for scab infection. Fungicides and resistant varieties are not available for scab control. Tan spot and glume blotch can be controlled with Tilt or other labeled fungicide. Varieties differ in their resistance to glume blotch and tan spot, so plant resistant varieties.  *


Early Postemergence Options for Corn - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

Some of the earliest planted corn needs to be scouted for decisions on weed management. Delaying a decision often means less options or a more expensive option later. Be careful about use of 2,4-D or Banvel (or premixes with either of these herbicides) if the afternoon temperatures get above 80 to 85, because of increased volatility. Basis is relatively new and it can be used if the corn is 2 collars (4 leaves) or less. It is excellent for lambsquarters. Basis Gold is also labeled for postemergence and it contains Accent for grass control. The rate of Accent is quite low so be sure you use it on small grass weeds, before the are 3 to 4 inches tall. Basis Gold is not as effective on lambsquarters as Basis.

I have seen more yellow nutsedge this year than I have in the past. Permit has the best postemergence activity on yellow nutsedge.

When considering the postemergence herbicide, remember that organophosphate insecticides can interact with the ALS-inhibiting herbicides (i.e. Basis, Basis Gold, Accent, Beacon, Permit, etc) and can cause corn stunting and injury. If you use an organophosphate insecticide at planting, review the herbicide and insecticide labels for options. *


Should You Use a Soil-applied Herbicide with Roundup Ready Soybeans - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

I have had good control in Roundup Ready soybeans without a soil-applied herbicide. I have not been able to show a yield advantage when using a soil-applied herbicide followed by Roundup over using Roundup alone. Roundup at 1.5 to 2 pts/A often will not provide 100% weed control, yet the weeds that are not killed are often not competitive enough to impact yield. If maximum weed control is your goal, consider tank-mixing another product with Roundup for morningglory or ragweed control. However, tankmixing can reduce the control of other species (primarily fall panicum) so choose a tankmix partner based on the weeds in the field. Using a soil-applied program with Roundup Ready soybeans will provide a longer window for Roundup application without impacting yield. However, if you are able to apply Roundup in a timely fashion, we have not been able to show any yield loss. If you need to use a soil-applied herbicide with Roundup Ready soybeans, consider using only a grass herbicide and/or use lower rates because you are going to be spraying postemergence. Use of a soil-applied herbicide has a place with perennial weed control, because the Roundup should be applied later than you would apply Roundup with annual weeds.  *


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

Planting Progress Pressures Markets

Solid planting progress for corn and soybeans in the Midwest has weighed heavily on commodity futures this past week. Monday's Crop Progress Report pegged the U.S. corn crop at 78% planted, up from 60% the previous week and ahead of the 63% five year average. U.S. planting progress on soybean acres was placed at 38%, far above the 23% five year average. One long time commodity trader was noted as saying "We're still trying to keep a weather premium in the market. If we have no weather event, beans will fall 50 cents or even $1.00 per bushel". It isn't uncommon to hear price forecasts, assuming normal weather conditions, in the vicinity of $2.35 per bushel for new crop corn and $5.75 per bushel for new crop soybeans (dropping $1.00 per bushel from current levels will place beans in the $5.25 per bushel vicinity).

Market Strategy

Marketing opportunities are getting more limited. This phenomena typically happens when price levels begin to trek into the lower one-third of the price range. Those who have previously sold at least 30% of their new crop corn and soybeans need only sit tight for the time being. For those who still haven't sold any of the 1998 crop, most market analysts agree that you need to take sales to the one-third level. On any given day, the question to answer for each individual decision will be just how to get that done. Technical assistance in making those decisions is available from my office.

Part of our current dilemma stems from the Freedom to Farm Act. It was written under the assumption that export demand would continue to increase in Asia. That simply has not and is not happening. The point is that even in the event that we get some further 'pricing windows' for the 1998 crop this summer, prices are not likely to improve significantly unless we see a severe weather market develop.  *


Soybean Planting Tips - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

Soybean planting is now underway and it will pay to pay close attention to several helpful hints:

Upcoming Events…

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.


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 University of Delaware Research & Education Center at 302-856-7303. *

Weather Summary

Week of April 24 to April 30

Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 90 F on May 20 to 82 F on May 15.
Lows Ranged from 64 F on May 20 to 41 F on May 15.
Soil Temperature:
72 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:


Note to growers accessing marketing and weather information via satellite: If you are having trouble accessing this information, you may need to reset your equipment due to the satellite drifting problems we are currently experiencing. Contact the company for instructions on changing the settings.  *

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.

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