Volume 11, Issue 4                                                                                                    April 18, 2003


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



Imported cabbageworm and diamondback moths have been observed laying eggs in cabbage so watch for larvae, especially in the heart of the plants. Once DBM eggs hatch, young larvae will first mine between the upper and lower leaf surfaces before moving to the heart of the plants. Treatments should be applied when 5% of the plants are infested with larvae and before larvae move to the heart of the plants. Avaunt, Bt insecticides,  Proclaim, or Spintor will provide effective control of both species.  Be sure to rotate between these classes of insecticides to avoid the development of resistance.



Aphid populations have been light; however, be sure to watch for pea aphids in your earliest plantings. The recent warm weather has been favorable for aphid development. As the weather fluctuates between warm and cool temperatures, aphid populations often explode and beneficial insect activity can lag behind. On small plants, you should sample for aphids by counting 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 aphids per sweep. Dimethoate or Lannate will provide aphid control. Be sure to check the labels for application restrictions during bloom.




Sweet Corn Plantings & Weed Control Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu


Plantings for fresh market and processing sweet corn have begun.  For many years, growers have successfully utilized various herbicides that have become reliable standards: alachlor (Micro-Tech or Partner) or S-metolachlor (Dual II Magnum or other labeled formulations) for grass control, and various formulations of atrazine for broadleaf control.  Bladex was used for years, but it is now discontinued.


With the cold wet spring we are experiencing, it is possible that some plantings may not get sprayed after planting.  There are several options in this situation.  If the field can be sprayed during the “spike” stage (when the corn is just emerging and has not unfurled any leaves), then Prowl can be used to control grasses and some broadleaf weeds.  There is a danger of crop injury if the seed is planted shallow, in fact, the Prowl label specifies the seed be planted 1-1/2 inches deep, which is rarely done.


Broadleaf weed control can be obtained with post-emergence applications of the wettable powder form of atrazine, or Sandea, or Aim.  Basagran can also be used when the corn is in the three leaf stage, and 2,4-D can be used as a last resort.  Timing is critical with all of these post-emergence materials, so check the rates and other important instructions on the label.


It is also important to recognize the target weed species in the field as you select a herbicide.  Aim, for example, will not control ragweed species.  Basagran is weak on lambsquarter, unless the weeds are very small.  These details are on the labels and in the recommendation guide, Commercial Vegetable Production Recommendations, available from county extension offices in Delaware, Maryland, New Jersey, Virginia, and Pennsylvania.




Delaware Pea Planting Progress Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu


With the cold, wet spring, pea planting has been delayed and difficult.  Finding ground dry enough for planting has been a challenge.  However, as of this date, processing companies report that planting is 70% complete or higher.  Remarkable in light of the conditions!




Processing Crop Situation Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu


The USDA reports processors in the U.S. expect to contract 1.28 million acres of the five major processed vegetable crops in 2003.  Acreage increases are forecast for pickling cucumbers, green peas, and tomatoes, while snap beans and sweet corn show decreases.  In the case of sweet corn, this reflects strong cold storage and warehouse inventories.


Freezing firms expect a 2% decrease from 2002.  Green pea acreage is up 4% from 2002.  However, sweet corn and snap bean acreage are expected to be down 3% and 8% respectively, from last year.


Canneries contract intentions are up 1% from 2002.  Sweet corn acreage is up 1%, pickling cucumbers is up 20%, and green acreage is up 10% from a year ago.  Tomato acreage is up less than 1%.  Acreage for snap beans is down 13% from last season.


The increase in the pickling cucumber acreage is a reflection of some growing demand, but also a decline on reliance on off-shore product as a result of international tensions.




Field Crops

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



In general, weevil populations are still light in most fields throughout the state. The larvae we are finding at this time are a result of eggs layed last fall. Overwintered adults can lay eggs in stems any time temperatures are above 48 degrees F.  Since we have seen an increase in adult activity,  you should watch for an increase in larval activity in the next 10 days. The weevil passes through four larval stages in approximately three weeks. Larvae hatching from spring-laid eggs cause the most damage. As a general guideline, treatment should be applied if damage is visible on 50% or more of the tips. However, a more accurate way to time an application and try to avoid multiple insecticide applications would be to sample stems and determine the number of weevils per stem. A minimum of 30 stems should be collected per field, placed top first in a bucket to dislodge larvae from the tips and then count the number of weevils per stem. The following thresholds, based on the height of the alfalfa, should be used to make a treatment decision: up to 11 inches tall  - 0.7 per stem; 12 inches - 1.0 per stem; 13 - 15 inches - 1.5 per stem; 16 inches tall - 2.0 per stem and 17-18 inches tall - 2.5 per stem.


Field Corn.

Although black cutworm moths have been found in many traps, they still have not reached peak levels. These moths will be attracted to weed covers and larvae will be most active in later planted corn. Although we can see leaf feeding early, we generally do not see cut plant damage until we reach 300 DD from peak catches. Also, early cutting often occurs from variegated cutworm which we can find while sampling for grubs. Although Herculex Bt corn can provide good cutworm control; fields should still be scouted for leaf feeding and cut plant damage. A treatment should be considered in 1-2 leaf stage corn if you find 3 % cut plants or 10% leaf feeding.  Pyrethroids and Lorsban provide cost-effective control. For the most recent pheromone trap catches, see the trap catch table on the last page of the newsletter, or check our website at http://www.udel.edu/IPM/traps/currentbcwtrap.html.


As far as grubs and wireworms, it appears that the winter temperature and the recent rainy weather have not affected populations. Since wireworms remain in the soil for 3-5 years as larvae, we are finding economic levels in the same areas that experienced wireworm  damage in 2002. We can also find threshold levels of grubs when sampling in full season and double crop soybean stubble. If you plan to use a seed applied treatment (i.e. Gaucho or Cruiser) and no soil insecticide,  you will want to also use a hopper box treatment of diazinon/lindane or permethrin for wireworm and seed corn maggot control, especially in areas where the potential for insect pressure is high.


Small Grains.

We can now find cereal leaf beetle adults, eggs and small larvae in barley and wheat in Sussex Counties. If you are growing high management wheat, a treatment should be considered if you find 25 eggs and/or larvae per 100 tillers and at least 50% of the eggs have hatched. If fields are scouted on a routine basis, a threshold of 0.5 larvae per stem  (flag leaf and next 2 stem leaves) and 10% defoliation can also be used. Lannate, Mustang or Warrior will provide effective control. Lannate is labeled on both crops. Mustang and Warrior are only labeled on wheat.  Sevin will also provide control; however, it can only be applied to wheat and we have seen aphid outbreaks after Sevin use. Furadan will also provide control, but it can not be applied after heads emerge from the boot. We have just started to catch true armyworm moths in light traps. Trap catches totaling 200 or more moths for the month of April generally indicate a potential for outbreaks.



Cereal rust mite populations remain low compared to last season; however, conditions during the next couple of weeks will determine if we see population explosions. If timothy appears curled and has a "rusted" appearance, but it is not drought stressed you should suspect rust mites. The only available control option is Sevin XLR. Apply 3 pts per acre with ground equipment only with adequate water for complete coverage (20 or more gallons by ground).  One application should provide enough suppression to prevent economic yield and quality losses. Apply at approximately 3-4 weeks after green-up in fields with a previous history of rust mites and/or when 25% of the plant tillers exhibit curled tips of the new leaf blades. 


2003 Black Cutworm Pheromone Trap Counts



Found on page 8.





Choosing Corn Populations with Irrigation Water Limitations - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu ; Derby Walker, Jr., Sussex County Extension Ag Agent; derby@udel.edu


When we think of irrigation, we usually think about having plenty of water to grow corn at high seeding rates.  Many of the new corn hybrids available are designed for seeding at rates of 32,000, 34,000 or even higher populations.  The hybrids are able to produce superior yields at these very high plant populations.


However, not every field has the potential to irrigate such high populations.  Sometimes, it is the soil type that limits water infiltration rates to the point that if enough water were applied to keep a 30,000 plus population going, severe ponding would be evident in many areas of the field.  On other fields, the available aquifer can’t supply water at a rate adequate for an ultra high seeding rate.  In other fields, the available equipment may not be able to keep up with crop water demand in years like the 2002 growing season.


Review your corn production for 2002.  Did you have fields that didn’t make 175 bu/A under the center pivot system during the 2002 growing season?  Last year, we noted a number of irrigated fields that produced irrigated yields of about 125 bushels per acre.  If you did, these are the fields that really need attention in the future. Do you know why the fields underperformed last year when the drought was so severe?  Was it because your water supply was inadequate?  Did you begin irrigating too late to be able to keep up with the drought?  Would irrigating more often have helped or is that possible with your system?


Once you have a grasp of what the problem is, you can begin to formulate a plan to solve it.  If the problem is one of timing or frequency of application, or amount of water per application and your system can adjust to the changes, then maintain your current seeding rates and work on making management changes to boost yield potential.


If the problem is one of inadequate water output from your well, or is due to too slow or uneven infiltration rates, then you should consider reducing your seeding rate down to 24,000 to 26,000 seed per acre and select a corn hybrid that has the flex ear trait.  By making critical changes in hybrid selection and dropping the seeding rate, you will find that you can boost your long term yield average and profitability in these problem fields.




Consider Lowering Populations of Dryland Corn on Sandy Soils - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu; Derby Walker, Jr., Sussex County Extension Ag Agent; derby@udel.edu


On sandy soils, rarely has population or actual fertilizer rate limited corn yields.  In 7 out of 10 years, water is the key yield limiting factor because of drought damage before pollination/silking causing asynchrony between pollen release and silk emergence or after pollination during seed set and grain fill.


If you grow dryland corn on sandy soils, you can save a few dollars and improve your long-term yield average by matching the plant population to the soil type.  It may mean missing the very top yield in the 1 out of 10 or 1 out of 20 years where rainfall is abundant, but with the frequency of yield limiting drought years you will do so much better in the long run.


In most years other than the very worse droughts, no-till systems will produce higher yields because of moisture conservation.  We would suggest that if you plan to plant corn on the sandier soils in southern Delaware, you should consider seeding at 17,000 to 18,000 seed per acre in hopes of getting a population of around 16,000 plants per acre.  Also, if you take population counts and you only have about 14,000 plants per acre dryland in a sandy field, do not plow this under to replant thinking the population is too low.  In a majority of years, these low populations may help you produce harvestable yields when the traditional 22,000 to 24,000 stands fair so poorly as to be unharvestable.  Many of the new hybrids are able to flex enough to make very good yields if adequate rainfall comes your way, but be sure to select the hybrids that have the best flexing ability and have been shown to have the most stress tolerance.


Another aspect to not overlook is your nitrogen (N) management program.  Timely rains have more effect on yield potential than putting on additional units of N.  In good corn years when adequate or timely rains occur, it is not uncommon to grow as much as 150 or 160 bu/A with only 125 pounds or less of N/A.  Be sure to maximize the efficiency of the N you apply by using a starter to carry the crop until it is about 12 to 18 inches tall when the remainder can be dribbled on at a time when the crop can make maximum use of it.




Alfalfa Inoculation Failure and a Remedy - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu; Derby Walker, Jr., Sussex County Extension Ag Agent; derby@udel.edu


Purchasing lime-coated, preinoculated alfalfa seed does not always ensure successful inoculation by the specialized bacteria that help supply the alfalfa crop with upwards of 350 lbs of nitrogen (N) per acre per year.  As seen in Photo 1 compared with Photo 2, a difference of only a month in planting date can have significant consequences when all the seed has been stored where hot summer temperatures may have injured the Rhizobia bacteria.  The darker stripes in the field follow traffic patterns that allowed some seed to germinate faster.  The rapidly growing alfalfa seedlings were able to extract the last of the available N from the soil before last fall’s rains leached it away.


Photo 1.  Mid-September alfalfa planting where preinoculated seed failed to properly nodulate and most plants were only 1 to 2 inches tall by mid-April (Photo by R. Taylor).



Photo 2.  Mid-August planting of same alfalfa cultivar where preinoculated seed successfully nodulated and plants were 6 to 9 inches tall by mid-April (Photo by R. Taylor).


For alfalfa to be grown successfully, it must be adequately inoculated as seen in Photo 3.  When sliced open, the center of a nodule will turn pink to red.  The pink color indicates that the nodule is actively fixing N.  In the case of the plants in Photo 1, a few single, small, scattered nodules could be found on an occasional plant, but when sliced open the nodules remained white indicating that they were non-functional.


Photo 3.  Nodulation mass on young alfalfa root (Photo by R. Taylor).


If your field looks like the one in Photo 1, is there anything that you can do about it or must you plow it under and lose a whole production year?  Luckily, the answer is yes you can do something about it.  There are three methods that can be used and have been tested in research trials at North Carolina State University (from publication Ag Series #226 June 1984 by J. T. Green, Jr., J. P. Mueller, and D. S. Chamblee and entitled “Inoculation of forage Legumes”).


The first method for spring rescue of a fall alfalfa seeding is to mix about 1.5 pounds of a peat-based inoculant (1 × 108 Rhizobia per gram) or 0.25 pounds of a sterile inoculant (2 × 109 Rhizobia per gram) with enough water to make a paste and then use the paste to make a fine slurry in 20 gallons of water and apply the slurry as a broadcast spray at a rate of 20 gallons per acre.  The inoculant application should be applied late in the day either just before rain is expected or just after a rain.  If irrigation is available, immediately after the broadcast spray apply about a half inch of irrigation water to help move the inoculant into the soil where the bacteria can come into contact with alfalfa roots and begin nodule formation.  Avoid applying when temperatures are above 85˚ F or in direct sunlight.  This method works best if used in late March or April following a fall seeding that has failed to nodulate.


The above research report indicated that additional screening before spraying is advantageous.  I would suggest mixing each unit of paste in one gallon of water and pouring this into the filled spray tank through several layers of cheese cloth or other screening material.  What is caught on the cheese cloth can be mixed in more water until a lump-free slurry is formed and then add this through more cloth into the tank.  Be sure to clean the spray tank and lines thoroughly to prevent injury to the Rhizobia from previously used toxic chemicals.  Also, use vigorous agitation and large spray tips without screens to reduce the potential for clogged nozzles and to keep the Rhizobia in suspension.  Do not mix inoculants with either fertilizers (especially nitrogen and potassium) or other chemicals.


Method two works best if problems in fall or spring seeded alfalfa are detected early and the application can be made within four to six weeks of seeding.  For fall applications, apply it in October at the latest as research shows that applications in mid- to late-November or December are unsatisfactory probably due to low temperatures.  For this method, mix 1.5 pounds of the non-sterile, black peat inoculant with 50 to 100 pounds of sand, cottonseed meal, wheat middlings, or limestone.  Uniformly broadcast this mixture over one acre.  If not applied between rain showers or immediately watered in with irrigation, there is an advantage in using a grain drill or other method to place the inoculant into the soil rather than on the surface.  Because of the higher numbers (20X) of Rhizobia per gram in some sterile inoculants, the rate can be reduced (I’m suggesting using it at 0.25 lb/A rate.)


A third method involved the use of a granular form of inoculant at about 3 pounds per acre, but the availability of this form for small seeded legumes on a commercial basis is unknown.  I did not locate any in my recent web searches.


A final note is one of thanks to two company reps who helped me gather information and locate inoculant.  Mr. Jim Davis (Marion, SC) with BeckerUnderwood and Mr. Roger Young (Logan, Ohio) with Nitragin Company were extremely helpful and I extend my thanks to them.




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


Soybean Stocks Historically Tight

Ending Stocks for the 2002/03 marketing year for U.S. soybeans now pegged at 145 million bushels yield a projected stocks/use ratio of 5.2 %. The ratio is noted as the lowest in the last 27 years. Evidence of the current tight supply can be found in soybean futures prices, with the nearby old crop May '03 futures price currently bidding at $6.09 per bushel and the new crop Nov '03 futures price bidding at $5.33 per bushel. The old crop Southern Delaware soybean basis is currently being offered at even to 5 under, which is 0 to 5 cents better than the historical average. The new crop Southern Delaware soybean basis is currently being bid at 15 to 20 under the Nov '03 contract, which is about average compared to historical records. The question remains as to whether we will see any improvement in either the basis levels being offered or the futures price being bid as we enter the summer months. The current new crop price level offering at $5.18 per bushel is just 7 cents/bushel above the 2003 Delaware soybean loan rate. With just 21 weeks remaining in the current marketing year, we are already within less than 11 million bushels of USDA's new export projection of 995 million bushels. The Southern Hemisphere crop is now online for a nearly 51 million metric ton crop.


Corn Stocks Are Adequate

Ending stocks of U.S. corn project a different picture for the U.S. overall, with some modification locally. The local modification stems from the extremely short crop that was produced on the Eastern Shore last fall. Ending stocks for U.S. corn, now projected at 1.009 billion bushels were viewed with some disappointment in the wake of a lower than expected March ending stocks estimate. Record Chinese corn exports have slashed U.S. corn exports with South American corn production exceeding earlier expectations, equating larger export competition from both Argentina and Brazil. Current marketing year exports for corn, now projected at 1.675 billion bushels are 325 million less than the earlier season projection. At the current rate, corn exports are running at their lowest level in five years.


Locally, the old crop corn basis being offered in Southern Delaware is at 40 to 60 over the May '03 future, currently bidding at $2.39 per bushel, equating an old crop corn spot price of $2.79 to $2.99 per bushel. This basis level is historically better than the average corn basis offered at this time of year by nearly 12 to 32 cents per bushel. New crop basis offerings at 15 over Dec '03 futures are about mid-range to the historical average.


Marketing Strategy

Timely rains are needed in the heart of the corn belt this season in order to keep row crops progressing in an orderly fashion. New crop corn prices at the current levels have been achievable a large percentage of the time since December. With the 2003 Delaware loan rate at $2.21 per bushel and the possibility that a 'weather market' could play a major role in pricing opportunities yet to come, new crop corn sales are likely better left at the 10 to 30 % of intended production level at the present time.






2003 Black Cutworm Pheromone Trap Counts


Trapping date: April 8-14, 2003






















Georgetown (UD REC)
































Little Creek






(1)     Moth catches of 9 to 15 moths per 7-day period =mod. to high potential for outbreaks.

(2)  You can expect to see cutting activity around 300 degree-days, base of 50 degree F from peak moth activity




                       Weather Summary



Weeks of April 10 to April 16, 2003


0.25 inches: April 10

0.73 inches: April 11

0.35 inches: April 12


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

Air Temperature:

Highs Ranged from 83°F on April 16 to 43°F on April 10.

Lows Ranged from 59°F on April 16 to 35°F on April 14.

Soil Temperature:

53°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:




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, 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.

FastCounter by bCentral

FastCounter by bCentral