Weekly Crop Update

University of Delaware Cooperative Extension

Volume 5, Issue 15

July 10, 1997

 Field Crops:

Field Crop Insects -

Joanne Whalen, Extension IPM Specialist.




As a result of the dry weather, grasshopper activity has increased in soybeans, sorghum and field corn. In many cases, damage is no longer confined to field edges and grasshoppers can be found in the whorls of corn and sorghum plants. The threshold in corn and sorghum is 5-8 per square yard. The soybean threshold is one per sweep and 30% defoliation. Sevin and Warrior are labeled on all three crops and have provided good control. Asana has also provided good control but is only labeled on corn and soybeans. Pounce and Ambush have provided poor control of grasshoppers in past years.



As soybeans begin to flower, be sure to check carefully for mites feeding on the undersides of the leaves. When weather conditions are hot and dry at flowering, populations can quickly explode . Damage is first noticed at the base of the leaves appearing as white stippling on the top surface of the leaves. The treatment is 20-30 mites per leaflet and 10% of the leaves with feeding damage. Dimethoate, Lorsban, Penncap and Parathion will provide control. Although dimethoate is the only systemic insecticide available for mite control in soybeans, it should be applied before populations explode and is generally less effective on drought stressed beans. The addition of crop oil or an organosilicone has greatly improved control, especially when using aerial application.


Soybeans or Grain Sorghum?

Richard Taylor, Extension Agronomist, and Bob Uniatowski, Extension Associate-Field Crops




Which crop should you choose to plant following a winter wheat crop when it's getting late in the season? Under dryland conditions, the choice should be soybeans anytime after the first week of July. In our grain sorghum variety trials conducted from 1990 to 1995, we found that there is at least a one in five chance that the sorghum crop will be a total failure when planted from July 10 to 20. In a date of planting trial on soybeans sponsored by the Delaware Soybean Board, we found that soybeans planted on July 15 produced from 15 to 20 bu/A dryland and 30 to 35 bu/A under excellent moisture conditions (ideal rainfall or irrigation).


If the field can be irrigated, the question is more difficult to answer. Generally, under irrigation, soybeans have the advantage of greater economic return when planted in mid- to late-July.


Yield Expectations for Late Planted Double-Crop Beans -

Richard Taylor, Extension Agronomist, and Bob Uniatowski, Extension Associate-Field Crops




When planting beans late in the season, its useful to know what yield potential to expect. In a four-year project sponsored by the Delaware Soybean Board, yields averaged over eight varieties representing four maturity groups indicated the following yield potentials:


Dryland conditions:

July 1 = 30 bu/A

July 15 = 15 to 20 bu/A

August 1 = 5 to 8 bu/A


Irrigated conditions:

July 1 = 45 to 50 bu/A

July 15 = 30 to 35 bu/A

August 1 = 15 bu/A


Especially under dryland conditions, yield expectations can fluctuate widely based on weather patterns but the above yield goals can give you a good starting point when calculating whether to consider certain inputs.


Vegetable Crops:

Vegetable Crop Insects -

Joanne Whalen, Extension IPM Specialist.



Lima beans and Snap Beans.

Potato leafhopper adults and nymphs continue to be active in beans throughout the state. Weather conditions continue to be favorable for damage, especially in drought stressed fields. The treatment threshold is 5 per sweep during prebloom and 10 per sweep during bloom. In snap beans, this threshold should be reduced by one-half if thrips are also present, especially if the field is drought stressed. Asana, Lannate or Orthene will provide control of both pests.



Mite activity has increased with the hot, dry weather. The treatment threshold is 10-15% infested leaves. Dimethoate is still the first choice for mite control but needs to be applied before mites explode. If treating by air, the addition of an organosilicone has improved control.


Be sure to check the Crop Pest Hotline for the most recent corn borer blacklight trap (BLT) catches and spray schedules. At the present time, BLT catches are extremely low (0-1 per night); however, sprays are still needed on a 10 day schedule for pepper maggot control (dimethoate or Orthene). Once trap catches reach 3-5 per night, sprays should be applied on a 7-10 day schedule for corn borer control. If a pyrethroid or Lannate is used, sprays should be applied on a 7 day schedule. If Orthene is used, sprays should be applied on a 10 day schedule.


Snap Beans.

Be sure to check the Crop Pest Hotline for the most recent corn borer blacklight trap (BLT) catches and spray schedules. At the present time, no additional sprays should be needed on processing snap beans if Orthene was applied at the bud and pin stages. If trap catches increase to 3-5 per night within one week of harvest, Lannate should be applied within 5 days from harvest. Penncap will also provide control but should not be used if bees are foraging in the area.


Sweet Corn.

Corn earworm catches remain relatively low but be sure to check the Crop Pest Hotline for the most recent trap catches and spray schedules. Fresh market silking sweet corn should be sprayed on a 4 day schedule in Kent and Sussex counties and on a 5 day schedule in New Castle County. Fall armyworm activity has also started to increase in seedling and whorl stage corn. Infestations are ranging from 5 to 10% infested plants. The treatment threshold is 15% infested plants. Insecticides must be directed into the whorls using a minimum of 30 gallons per acre of water to get effective control. Two sprays are often needed, especially if infestations increase beyond 15% infested plants.

U of D Crop Pest Hotline:

In State: 1-800-345-7544

Out-of-State: 302-831-8851


Pickle Harvest Begins -

Ed Kee, Extension Vegetable Specialist



Pickle harvest began on July 2. The first three plantings exhibited for most growers some internal pickle quality problems associated with hollow centers, known as carpel separation or placenta hollows. This problem is associated with incomplete pollination. The extraordinary cool spring kept bees from being active and also impacted the proper growth of the developing pickle. As harvest proceeded to the later plantings, the problem was no longer evident.


Careful Pesticide Container Handling -

Derby Walker, Extension Agricultural Agent and Ed Kee, Extension Vegetable Specialist




Make sure pesticide containers are secure on trucks, trailers, and wagons as you move to the field. Dropping a container and breaking it open is costly and can create a potential environmental problem. Similarly, make sure all lines and connections are secure to avoid costly breaks and leaks.



Upcoming Events at the University of Delaware Research & Education Center...


Weed Twilight Tour

July 21, 1997

6:30 p.m. in the grove

( 1 pesticide re-certification credit will be given)


Crop Diagnostic Field Day

July 31, 1997

7:30 a.m. - 1:00 p.m.

(Includes Lunch, pre-registration is required, participants can earn 3 CCA continuing education credits, contact Mabel Hough at 856-7303 or 856-2585, ext. 304)


Corn Trouble Shooting for Growers Field Meeting

July 31, 1997

3:00 p.m. - 5:30 p.m.

(Includes Dinner, pre-registration is required, contact Mabel Hough at 856-7303 or 856-2585, ext. 304)


University of Delaware

Farm & Home Field Day

August 13, 1997

8:30 a.m. - 1:30 p.m.



The University of Delaware Research & Education Center Has Voice Mail


The phone system at the Research & Education Center now includes Voice Mail. This option will give callers the ability to go directly to a professional’s office and talk directly to them or to leave a message on their voice mail. The secretaries at the REC will still be answering the phones from 8 a.m. to 5 p.m. Monday through Friday at the 856-7303 number, but will be transferring you to the professionals voice mail to leave messages. If you are not sure who you need to talk to, they can of course direct you to the correct individual. If you know the extension of the professional you are trying to reach, you can go directly to their office ( at anytime ) without interception by the secretaries by calling 856-2585 and then entering the individuals extension. The following is a listing of extensions of some of the professionals at the REC:


Mary Argo 325

Diaz Bonville 302

Rhonda Bundick 383

Dean Dey 324

Diagnostic Lab 317

Lisa Dorey 305

Kate Everts 327

Vic Green 328

Ward Harris 384

Charlotte Headley 301

Mabel Hough 304

Mark Isaacs 308

Ron Jester 310

Quintin Johnson 332

Jeanie Johnson 348

Ed Kee 311

Bud Malone 309

Jack Martin 347

Edna Marvil 306

Master Gardner 318

Bill McGowan 320

Ed Odor 346

Mariano Salem 316

Sujatha Sankula 380

Barb Stephens 307

Mark VanGessel 312

Helen Waite 313

Derby Walker 321

Marlyn Webb 303

Mary Wilcoxon 323

Jay Windsor 322

Tracy Wootten 341


(This is not a complete listing)




Late Blight Report.


DSV accumulation as of July 7, 1997 are as follows:



Location/ Emergence date


DSV’s June 30


DSV’s July 7



Baldwin - 4/20



7-day, high rate

Jackewicz - 4/26



7-day, high rate

Zimmerman - 4/28



7-day, high-rate

Baker - 5/7 -5/9



7-day, high-rate


The increase in spray schedule itnerval is for early blight control and disease severity values that have increased since the last report. As a comparison, this time last year 1996 severity values for the four sites were : Baldwin, 87; Jackewicz, 80; Bergold 58; Maghan, 84. Weather conditions continue to be unfavorable for late blight. Late blight information hotline number 1-888-831-SPUD.



Weather Summary

University of Delaware,


Week of July 4 to July 10, 1997



0.35 inches: July 10

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




Ranged from 92 F on July 4 & 10 to 82 F on July 6.


Ranged from 73 F on July 9 to 59 F on July 6.


Soil Temperature:

74 F. Average for the week.




Complied & 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. 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.