Volume 12, Issue 15                                                                     July 2, 2004



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


Lima Beans.
Be sure to watch for spider mites on seedling stage lima beans, especially in areas of the state that have not been receiving adequate rainfall. Both field interiors as well as field edges should be examined for mites. Look for the white stippling along the veins on the underside of the leaves. A treatment should be considered when you first notice the stippling and you find 10-20 mites per leaflet. Kelthane or Capture (6.4 oz/A) have provided the best control in lima beans. The earliest planted fields should be scouted for lygus bugs and stinkbugs. Treatment should be considered if you find 15 adults and/or nymphs per 50 sweeps. Lannate, Capture or Mustang can be used if both species are present. The higher labeled rates of Capture (4 oz/A) and Mustang (4.3 oz/A) will be needed if stinkbugs are the predominant insect present.

Continue to scout all melons for aphids, cucumber beetles, and spider mites. We continue to see an increase in the number of fields with spider mite and aphid infestations. If spider mite populations are high at the time of treatment, 2 sprays spaced 5 days apart will be needed. The threshold for mites is 20-30% infested crowns with 1-2 mites per leaf. Acramite (only one application per season), Capture, Danitol, Agri-Mek or Kelthane will provide control, but should be rotated to avoid the development of resistance. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Be sure to check runners carefully for aphids.  For a treatment to be effective, fields should be sprayed before you see significant leaf curling.  Be sure to watch for bees foraging in the area and avoid insecticide applications on blooming crops. 

Although corn borer catches are still generally light, we are starting to see an increase in moth catches. I
n areas where corn borer trap catches are above 2 per night and pepper fruit is ½ inch in size or larger, fields should be sprayed on a 7-10 day schedule for corn borer control.  You will also need a treatment for pepper maggot. If Orthene is used, it will also provide pepper maggot control. Otherwise, dimethoate should be added to the mix. High beet armyworm (BAW) moth catches have been reported from VA. Consultants have also found the first larvae in pepper fields. You will first notice the “shot-hole” feeding signs in the terminals. No threshold is available, so you need to watch for the first small larvae as well as their feeding signs. You will also need to use a product like Confirm, Spintor, Avaunt or Intrepid which provide good BAW control.

Continue to scout fields on a weekly basis for Colorado potato beetle (CPB) adults and larvae. The larval threshold is 4 small larvae per plant or 1.5 large larvae per plant. The threshold for each should be reduced by to ½ if all stages of larvae are present. Avaunt + PBO, Actara, cryolite, Spintor,  Provado or newly labeled Rimon will provide control of larvae. We continue to see an increase in the emergence of summer adults. Unfortunately, most of our labeled products are most effective on larvae. The higher labeled rates of Spintor and cryolite have provided some level of adult suppression this season; however, have not been adequate under high population pressure. Actara, Leverage and Provado provide adult control, but should not be used where Admire, Platinum or Gaucho were used at planting to avoid development of resistance.  We continue to find economic levels of green peach aphids in fields that did not receive Admire, Platinum or Tops MZ Gaucho at planting. A control will be needed if you find 2 aphids per leaf pre-bloom, 4 aphids per leaf post bloom and 10 aphids per leaf at 2 weeks from vine kill/harvest.  If melon aphids are found, the threshold should be reduced by ½.  If green peach aphid is the predominant species, Fulfill, Lannate, Monitor, Provado, or Vydate will provide control. If Fulfill is used, a penetrating surfactant is needed to achieve good coverage and achieve optimum control.

Snap Beans.
Continue to scout a
ll seedling stage beans for leafhopper and thrips activity. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. If both insects are present, the threshold for each should be reduced by . Dimethoate, Lannate, Asana, Capture, or Warrior will provide control of both insect pests. Once corn borer catches reach 2 per night, fresh market and processing snap beans in the bud to pin stages should be sprayed for corn borer. Acephate should be used at the bud and pin stages on processing beans. Once pins are present on fresh market snap beans and trap catches are above 2 per night, a 7-10 day schedule should be maintained for corn borer control. Lannate, Asana, Capture, Warrior or Mustang are labeled. Acephate has a 14-day wait until harvest. Since this can change quickly, be sure to check our website for the most recent trap catches and information on how to use this information to make a treatment decision in processing snap beans (http://www.udel.edu/IPM/traps/latestblt.html and http://www.udel.edu/IPM/thresh/snapbeanecbthresh.html).

Sweet Corn.
All fresh market silking sweet corn should be sprayed on a 5-day schedule except in the Milford area where sprays are needed on a 3 day schedule.  Since this information can change quickly, be sure to check our website for the most recent trap catches and information on how to use this information to make a treatment decision in silking sweet corn (http://www.udel.edu/IPM/traps/latestblt.html and http://www.udel.edu/IPM/thresh/silkspraythresh.html).  We are also starting to see the first fall armyworm larvae in whorl stage sweet corn. A treatment should be considered when 12-15% of the plants are infested. Since fall armyworm feed deep in the whorls, sprays should be directed into the whorls and multiple applications are often needed to achieve control.



Potato Maturity, Skinning, and Bruising: Vine Killing and Harvester Operation Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu


Moderate temperatures, especially with the relatively cool nights we have experienced, favor potato tuber bulking.  The sugars or carbohydrates formed during the day in the leaves through photosynthesis are not “burned up” as much through the respiration process.  In other words, a higher amount of carbohydrates can be accumulated in the tubers, rather than being used by the plant to keep it functioning.  While I’ve never done it, I often said our potato yields could be correlated with the average temperatures in June and early July.


Soon potato vine growth will slow and leaf senescence will increase, with the vines reaching the maximum size and then begin to decline.  Early maturing varieties will die back soon, while later maturing varieties will die back if the season is long enough, which is usually the case in Delaware.  During this period of decline, sugars and mineral nutrients in the vines become mobilized and translocated to the tubers.  Tuber growth will continue until the vines are completely dead.  At this point, 75 to 80% of the dry matter accumulated by the plant is in the tubers.  A chemical vine killer may be used to accelerate senescence. 


Vine killing not only hastens tuber maturation, often called hardening.  The outer skin, or periderm, forms from the outermost three or four cell layers of the tuber.  The collapsed walls of these cells form a barrier which prevents water loss from the tuber, protects it against pathogens, and helps limit bruising.


Tuber bruising costs potato growers across the country millions of dollars because it reduces raw product quality for processing.  In Delaware, where most of our acreage is destined for tablestock, there is not the direct linkage between the farm and the processor.  However, bruised potatoes cause great concern for fresh markets because bruised potatoes that end up in fresh pack containers present a poor image to the buyer and consumer.  Bruises can also give decay a place to start.


There are several types of Bruises.  Skinning occurs when the tubers are not completely mature.  A corky layer will form on the bruised area.  Cuts and scrapes result when potatoes strike a sharp edge or object during harvest, packing or handling.  Pressure bruise from the weight of the potatoes on themselves, especially when relative humidity is low.  Blackspot appears as a dark, semispherical spot in the tuber flesh beneath the skin 24-48 hours after impact on a hard surface.  Blackspot is a physiological disorder resulting from a serious of biochemical reactions leading to the production of a black pigment in the bruised flesh.  The injury may not be detected until the potato is peeled.  Potato varieties will differ in their susceptibility to Blackspot, but all varieties are more susceptible when soil moisture at harvest is low and the tubers are dehydrated.  Inadequate potassium may also increase the risk of Blackspot.


Allowing potatoes to reach full maturity helps reduce bruising injury.  Proper vine killing to speed maturity when an advanced harvest is desired is also important.  If the vine killing is done 10 to 14 days in advance, there will be enough time for increased skin development on the tubers.


There are three materials recommended for vine killing in Delaware:

ü      Desicate II (endothall) Apply 1.5 to 2 quarts/A 10 to 14 days before harvest.  Ammonium sulfate may be added. 

ü      Diquat 2SC at 1 pint/acre with a nonionic surfactant may be used.  It can be repeated in five days, if necessary.  Do not harvest for 7 days after treatment.

ü      Paraquat at 1-2 pints per acre with a non-ionic surfactant may be used.  Do not harvest until 3 days after treatment.  This may be the fastest kill, which could be problematic as to good hardening or “skin set.”


There are important directions and recommendations on the labels of each of these products.  Read and follow the directions carefully. 


With all of these, the proper adjustment, operation and maintenance of all parts of the harvester may be the most critical component of reducing injury.  Forward speed, chain speeds, and belt speeds should be adjusted to manufacturer’s recommendations.  Often, these adjustments need to be modified according to soil moisture conditions, crop maturity, and other field factors.



Vegetable Crop Diseases - Bob Mulrooney,

Extension Plant Pathologist, bobmul@udel.edu



I just received a reliable report that late blight was confirmed on tomatoes in Lancaster County, PA. Tomato growers in areas that have had rainfall will want to keep up their fungicide applications. Strains or genotypes of the late blight fungus that infect tomato are usually not very pathogenic on potato, but can infect potato leaves as well. Although conditions in Kent and Sussex County have not been very favorable for infection, areas of New Castle county and nearby Maryland may be similar to conditions in Lancaster county. So be on the lookout and keep up your preventative sprays.


Lima beans.

The State Department of Agriculture recently granted a section 24(c) label for the use of Phostrol in Delaware for control of downy mildew on lima beans caused by the fungus Phytophthora phaseoli. Nufarm Americas, Inc. petitioned the state for this label, which I supported with data from field plot work in 2001 and 2003. It has been very effective for the control of downy mildew. It has been labeled at 4 pts/A in 20 gal of water by ground and 5 gallons by air. Applications should be made every 7 days when conditions are favorable for infection. This product has to be used before symptoms of disease appear. It will not be effective if the disease is already present in the field. The mode of action is presumably that the product triggers the plant’s own defense mechanisms so that it protects itself from infection. It has no pre-harvest restriction and has a 4-hour restricted entry interval (REI ). I will expand on fungicide control programs for downy mildew control in upcoming issues of WCU.



Late Blight Advisory.


Disease Severity Value (DSV) Accumulation as of June 30, 2004 is as follows:

Location: Joe Jackewicz Farm, Magnolia, DE. Greenrow: April 25, 2004






Daily DSV


Total DSV

Spray Recommendation

4/25- 5/18

















































































What is driving the spray recommendation at the present time is the need for fungicides for early blight control. Conditions are not favorable for late blight.


Application rates for protectant fungicides (Dithane, Bravo, etc.) should be at the high end of the rate with the amount of foliage present.


For specific fungicide recommendations, see pages F132-33, 2004 Delaware Commercial Vegetable Production Recommendations Book. EB 137.




Field Crops


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



Continue to sample all fields on a weekly basis for potato leafhopper (PLH) adults and nymphs. Although we have seen an increase in the number of lygus bug nymphs, controls are rarely needed for this insect. Weather conditions are favorable for PLH population increases. Remember, controls are most critical on small plants. 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.


Field Corn.

Although European corn borer (ECB) populations have been light in most non-Bt fields, especially compared to VA, be sure to check mid and later planted fields one last time if they are just starting to shoot tassels.  This will be the best time to achieve control, as long you do not see more than 1/3 of the population bored into the mid-ribs of leaves or the stalk. The treatment threshold is 50% infested plants in irrigated corn and 80% infested plants for dry land corn.

Continue to scout all seedling stage beans for leafhopper and thrips, especially drought stressed fields. Grasshopper levels continue to increase and control is best when grasshoppers are small. In addition, multiple applications are often needed for grasshoppers since they migrate in and out of fields. You can use the following thresholds as a treatment guideline: (a) Grasshoppers -- 1 per sweep and 30% defoliation, (b) Thrips -- 8 per leaflet with plant growth being held back and significant leaf cupping, and (c) Leafhoppers --- 4 per sweep in drought stressed fields and 8 per sweep in non-stressed fields.

Continue to watch for spider mites, especially in no-till fields where a heavy weed cover was present before planting.  We are starting to see an increase in fields with visible spider mite damage, especially drought stressed fields. There are also reports of economic levels in irrigated fields, especially in fields where no burn down was used at planting and weed pressure was heavy before planting. Although an edge treatment can be effective when you are trying to protect fields from mites moving in from weedy edges, this may not be effective if weed pressure is heavy throughout a field before planting. We continue to find that weeds provide an ideal habitat for overwintering mites.  It will be important to scout the entire field before deciding if an edge treatment is enough. A treatment is recommended if you find 20-30 mites per leaflet or 10% of plants with 1/3 or more leaf area damaged. At this point, the only materials available for mite control in soybeans are dimethoate and Lorsban.  If dimethoate is used, the addition of a penetrating surfactant will improve control, especially in drought stressed fields.

We are also starting to see an increase in green cloverworm populations. No controls will be needed until you find 30% defoliation pre-bloom and 15% during bloom. As a general guideline, you should also find 10-15 cloverworms per foot of row. Unfortunately, we do not have a threshold for the number per sweep.

Although soybean aphid populations are still light in most areas of the Midwest, there are reports of fields being sprayed in southeastern Iowa and the first aphids have been found in PA soybean fields. Conditions favoring development is a “cool drought” so populations migrating to our area will vary based on what has happened in areas to the west and north. Since our populations are migratory from the mid-west and possibly from the north, it will be important to start sampling fields for soybean aphid. You will need to look at the entire plant when sampling for aphids. The treatment threshold is 250 per plant up to growth stage R-3 with 80% of the plants at that level. You should also pay attention to predator populations that can help control aphid populations.  Numerous products are now labeled for soybean aphid including Asana, Baythroid (suppression only), Mustang MAX, Warrior, and Lorsban. Dimethoate has not provided adequate control and Furadan 4F only has a 2ee label for the Midwestern states.



Mites on Soybeans WarningDerby Walker, Sussex County Extension Ag Agent, derby@udel.edu


Warning: Growers should be checking soybean fields for mite damage.  There have been several calls this week on soybeans that have died and/or are declining.  After examining the field, drought stress and mites are the culprits.  Be sure to check areas of the field that you know will be the first area of the field to be affected by drought.  Mites are attracted to stressed plants, and therefore will show up in these areas first.  Many times we see mites starting on field edges and moving into the field.  One area investigated was located in the middle of the field.  Damage did not start along the field edge. Some plants were dead. Mites starting in the middle of the field is not typical activity.  At first glance you may suspect nematode damage or some other problem.  Be sure to investigate these areas further.  For spider mite controls, refer to Joanne’s article above.


Two spotted spider mite



Spider mite damage on soybeans


(Photos taken from the University of Delaware Integrated Pest Management Website)




Field Crop Diseases - Bob Mulrooney,

Extension Plant Pathologist, bobmul@udel.edu


Soybean cyst nematode damage shows up as stunting of the soybean plants in irregularly shaped areas of the field. Anytime after about 32-34 days the white or yellow females can be seen on the roots of infected plants. Carefully dig up suspected plants with a shovel or trowel and examine the roots.  They are smaller than the nitrogen fixing nodules and can be difficult to see especially if the soil is dry. Traditionally we see severe stunting of young plants when we have high SCN populations in the soil and conditions are dry early in the growing season. Abundant rainfall that we had last season can mask increasing soil populations of SCN resulting in stunting early in the season. Take a soil sample with a few root systems of the plants and submit for testing at your County Extension Office. Be sure to sample soil from around the roots. Usually sampling between the plants in the row works best.


Numerous SCN cysts and N fixing nodule (large tan in picture) for comparison.



Magnified view of lemon-shaped SCN cyst.




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


General Comments.

The June Grain Stocks and Acreage reports came in close to trader expectations, although there is some concern as to whether the impact of diverse weather, in some parts of the Corn Belt, are truly reflected in USDA's planted and harvested acreage estimates. Nevertheless, the reported acres will go into the July 12th Supply and Demand revisions. Farmer certification for '04 planted acres of corn and soybeans in the U.S. will not be completed until mid-July.


The two primary driving forces impacting commodity prices the next month will be weather in the Corn Belt and the short supply situation in old crop soybeans. As a reminder, the highs recorded for July '04 soybean futures occurred in mid-March and again in early April with July old crop futures hitting slightly over $10.50 per bushel.


Export sales reported for the week were larger than anticipated for corn and soybeans. They were also reported to be at the high end of trader expectations for wheat.


Corn Analysis.

U.S. corn planted acreage totaled 80.97 million acres, up from the March planting intentions of 79 million and the year ago final of 78.74 million acres. For corn, USDA projects that 90.6% of this acreage will be harvested as compared to 90.3% last year. There is some chance that the harvested acreage estimate could be revised downward at a later date. Corn for grain stocks on hand were reported at 2.97 billion bushels, about the same as a year ago. It has been suggested that what is not accounted for in these estimates is the variability in the stages of development in the corn crop in portions of the Corn Belt.


Soybean Analysis.

Soybean planted acreage, pegged at 74.81 million acres, is down from the

75.41 million acres reported in the March intentions and up from '03 acres of 73.4 million. Soybean stocks were reported at 410 million bushels, slightly above the average trade guess of 395 million bushels. Last year's U.S. soybean stock level at this point in time was 602 million bushels.


Wheat Analysis.

All wheat acreage, reported at 59.87 million acres was up slightly from March at 59.46 million acres, and down from the 61.7 million acres a year ago. Wheat stocks, pegged at 546 million bushels are up from June '03 of 491 million bushels and slightly above pre-report trade guesses. 


Market Strategy.

Considering the drenching that new crop corn, soybean, and wheat prices have taken this week, the short supply situation for old crop soybeans coupled with the need to ration supply, and the fact that we are now entering the most critical period for '04 corn and soybean crop development farmers are advised to hold sales positions at current levels.



Manganese Deficiency is Showing Up in Soybeans - Sean Scanlon, Cooperative Extension Intern and Richard W. Taylor,Extension Agronomist, rtaylor@udel.edu


In touring the state, it is quite evident that manganese (Mn) deficiency (or in some cases possibly Mn toxicity) of soybeans is rather widespread this growing season.  Usually, the symptoms appear in localized areas of a field rather than as a general problem throughout the field (See Photo 1).


Photo 1.  The front part of this field showed moderate to severe manganese deficiency but the back half (different soil type) was still green and growing.  (Photo by R. Taylor)


In a number of locations, this problem is a reoccurring one in that Mn deficiency symptoms appear each year that soybeans are grown.  This can be due to slightly high soil pH from liming activities, low native Mn soil levels, or differences in soil type within a field.  In locations where the problem reoccurs, it’s not likely necessary to confirm deficiency with a tissue or soil analysis if the symptoms are similar to those in Photo 2.  If, however, you have not noticed symptoms in a particular field or area of a field, then you should test the soil for pH to be certain the problem relates to Mn deficiency and not a toxicity related to low pH.  This year a number of fields are showing severe to moderate problems associated with low soil pH so it will be important to accurately diagnose the problem before applying Mn as a foliar spray (see article on causes of low pH in next week’s issue of Weekly Crop Update).


Photo 2.  Manganese deficiency is characterized by leaves with green veins and yellow to white tissue between the veins and with symptoms appearing on the youngest growth.  (Photo by R. Taylor)


Symptoms of Mn deficiency include:

  • Pale green to yellow or white color between green veins.
  • Mottled effect from leaf yellowing with veins remaining dark green to olive green.
  • Stunting.
  • Leaf symptoms appear on youngest leaves since Mn is not mobile in the plant.
  • In severe cases, the most recently expanded trifoliate leaf will be very pale yellow to white.
  • Yield impacts can be severe if foliar Mn or another source of Mn is not provided.


Treatment options include:

  • Foliar application of 1 to 2 pounds of actual Mn per acre as either managenese sulfate (such as techmangam) or EDTA or chelated Mn.


  • Foliar application as above, but included with Roundup Ultra on Roundup Ready soybean varieties.  Tests have shown EDTA Mn to be safe when mixed with Roundup sprays, but other Mn products can reduce weed control if not handled properly.  Always add ammonium sulfate at a rate of 1 to 2 percent by weight or 8.5 to 17 pounds per 100 gallons before either adding the Roundup Ultra or techmangam.  This will prevent the Mn products from binding to Roundup and reducing its performance.


  • If the problem shows up year after year, it may be worth using a broadcast soil application of some form of Mn (the more expensive chelated forms will not offer an advantage in this form of application so go for the less expensive form).


  • If using wide rows and starter fertilizer with either this crop or another crop that shows Mn deficiency, Mn can be applied in a fertilizer band at a rate of 8 to 10 lbs of actual Mn per acre to help prevent problems or an acid form of starter can be used to acidify a band of soil to help make Mn available to the crop.




Best Wishes to You and Your Family for a Safe and Happy July 4th Holiday!





                     Weather Summary


Week of June 25 to July 1, 2004


0.13 inches: June 26

0.11 inches: July 1


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


Air Temperature:

Highs Ranged from 87°F on July 1 to 79°F on June 28.

Lows Ranged from 65°F on June 25 to 57°F on June 27 & 30.


Soil Temperature:

78°F average.

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


Web Address for the U of D Research & Education Center:  http://www.rec.udel.edu



Compiled and Edited By:

Tracy Wootten

Sussex County Extension Agent – Horticulture

University of Delaware





Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating.  Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Delaware Cooperative Extension, University of Delaware. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age or national origin.

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