Volume 7, Issue 17                                                  July 23, 1999


Vegetables

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

Lima Beans and Snap Beans.
Continue to watch fields for leafhopper adults and nymphs. The treatment threshold is 5 per sweep prebloom and 10 per sweep during bloom. In snap beans, Asana, Lannate or Orthene will provide control. In lima beans, dimethoate or Lannate will provide control. If lima bean fields are in bloom, Lannate would be the material of choice. Beans fields should also be sampled for mites showing up throughout fields. Although we are limited in our control options, Kelthane has provided effective control in recent years. If numerous eggs are present at the time of application, 2 applications spaced 5-7 days apart may be needed. Processing snap beans should still be sprayed at the bud and pin stages with Orthene for corn borer control. A third spray with Lannate will be needed 5-7 days from harvest. Be sure to check the Crop Pest Hotline on Tuesdays and Fridays for the most recent trap catches in your areas (in-state: 1-800-345-7544; out-of state: 1-302-831-8851).

Peppers.

Maintain a 7-10 day schedule for corn borer control. Aphid activity is starting to increase, especially in fields where only a pyrethoid has been used. If aphid populations are starting to increase, Lannate or Orthene should be used to provide both aphid and corn borer control.

Pickling Cucumbers.

Aphid activity has started to increase in seedling stage fields. As temperatures increase, fields should be watched for melon aphid explosions. A treatment will be needed if 20% of the plants are infested with aphids. Lannate will provide melon aphid control. If populations have not exploded, we have also seen good control with Thiodan.

Sweet Corn.
Fresh market silking sweet corn should be sprayed on a 3 day schedule throughout the state. Be sure to check the Crop Pest Hotline on Tuesdays and Fridays for the most recent trap catches in your areas (in-state: 1-800-345-7544; out-of state: 1-302-831-8851). Fall armyworm moth activity still remains light. However, all late-planted fields should still be checked during the whorl stage for fall armyworm feeding. A treatment is recommended if 15 % of the plants are infested. In many cases, 2 applications will be needed to provide effective control. Larvin (30 oz per acre) and Warrior (3.84 oz per acre) have provided the best control in recent years.


Crop Injury from Last Year's Herbicide Program - Ed Kee, Extension Vegetable Crops Specialist, kee@udel.edu

Recently, I have diagnosed two situations in which vegetable crops experienced significant economic damage from the residual of last year's herbicide application. In one case, sweet corn was stunted by carry-over of Scepter on soybeans; in the other pickling cucumbers were stunted by carry-over of Pursuit on lima beans. In another situation, we had to re-plant our sweet corn variety trial because we experienced injury where Classic was overlapped last year on soybeans.

The message is two-fold. First, many vegetables are extremely sensitive to the newer herbicide chemistry represented by the families of these herbicides. The label restrictions are real and need to be followed. Second, keep good records of herbicide applications so inadvertent mistakes are avoided.


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

LATE BLIGHT REPORT

DSV accumulations as of July 19 , 1999 are as follows:

Location/

Emergence Date

DSV’s

July

19

DSV’s

July

14

Recommendation

P-Day

Value for Early Blight Prediction*

Baldwin – 4/19

89

87

10-day, mid rate

622/654

Jackewicz – 4/30

78

78

10-day, mid rate

571/601

Art Wicks – 4/26

76

76

10-day, mid rate

595/622

Ken/Chris Wicks – 5/3

71

71

10-day, mid rate

559/585

*bold is current value/ regular is previous report value.

For early bright susceptible varieties the high rate of a protectant fungicide is recommended Disease pressure from foliar diseases is very low at the present time. Use your judgement when applying fungicides at this time of the season. With many fields getting close to maturity they will not benefit from any more fungicide sprays. I have seen some soft rot in bottoms and sprayer tracks has stood. Continue to manage your irrigation wisely to avoid tuber problems.


Vegetable Diseases - Kate Everts, Extension Vegetable Pathologist, University of Delaware and University of Maryland; everts@udel.edu and Phil Shields University of Maryland; ps136@umail.umd.edu

MELCAST for Fungicide Application on Watermelons.

Do not use MELCAST if there is a disease outbreak in your field, it is a preventative program. Below are the EFI values from weather stations located on the Eastern Shore July 14 – July 21. Any questions please call Phil Shields at (410) 742-8788 or e-mail: ps136@umail.umd.edu

EFI Values for 1999

Location

7/14

7/15

7/16

7/17

7/18

7/19

7/20

7/21

U of M, LESREC
Salisbury,MD

2

2

3

4

4

4

2

4

Wootten Farms, Galestown,MD

1

1

2

3

2

3

1

3

Mark Collins,
Laurel, DE

1

2

3

4

4

4

2

4

Vincent Farms Laurel, DE

1

1

3

3

3

4

2

4

D C Farms,
Bridgeville, DE

1

1

2

2

3

4

2

4

Balvin Brinsfield,
Vienna, MD

1

1

2

2

2

4

1

3

Charles Wright,
Mardela Springs, MD

1

1

3

3

3

4

2

3

U of D, REC Georgetown, DE1

1

1

2

2

3

4

3

2

Watermelon Fields should be sprayed with a fungicide when 30 EFI values have been accumulated by the weather station nearest your fields. Add 2 points for every overhead irrigation. After a fungicide spray, reset your counter to 0 and start over. If a spray has NOT been applied in 14 days, apply a fungicide and reset the counter to zero. The first and last day above can be partial days so use the larger EFI value of this report and other reports for any specific day.


Cucurbits.

The EPA has granted a specific exemption (Section 18) for the use of Nova to control powdery mildew on cucurbits in Delaware and Maryland. Nova 40W may be applied by ground or air at a rate of 2.5 oz. product/acre. A maximum of six applications can be made this season and a 48 hour preharvest interval should be observed. Alternate Nova 40W with fungicides that have a different mode of action. Care should be taken that Nova does not enter the groundwater, and the label stipulates that Nova should not be mixed/loaded or used within 50 feet of sink holes or wells. Direct application to bare soil should be avoided and treated fields should not be over irrigated.

Nova is a systemic product that provides very good control of powdery mildew. It is specific to powdery mildew and should be used with a broad spectrum fungicide such as Bravo, Terranil or Dithane. In research plots on pumpkins at LESREC in 1998, our best treatment was Quadris alternated with Nova combined with a chlorothalonil product.


Laurel Farmer's Auction Market Report

July 15 – July 21, 1999

Quantity Produce Price
65136 Cantaloupes  
 

Athena

0.25-0.80
 

Super Star

0.25-0.60

Passport

0.35-0.90
11581 Sugar Babies 0.60-1.60
267 Honeydews 0.65-1.25
44769 Watermelons  
 

Crimson Sweet

 
 

12up

0.85
 

15 up

0.75-2.00
 

20 up

1.00-2.30
 

25 up

0.85-2.50
 

Sangria

 
 

15up

0.70-2.00
 

20up

1.10-1.80
 

25up

1.80-2.05
 

30up

3.35
 

Royal Sweet

 
 

15 up

1.05
 

Mardi Gras

 
 

20 up

1.55-2.15
 

25up

2.40
 

Royal Majesty

 
 

15up

1.90
 

20up

1.35
  Seedless 1.10-3.95
16 Peppers  
 

Green

5.50-10.50
12 Banana 3.00-5.00
2 Eggplant 5.00
2262 Tomatoes  
 

Red

3.00-13.00
 

Pink

3.50-13.00
5 Cherry Tomatoes 7.00
1564 Sweet Corn Doz. 0.60-1.65
72 Cucumbers 3.00-8.00
171 Squash  
 

Yellow

3.00-10.50
 

Green

3.00-11.50
35 Potatoes  
 

Red

3.00-7.00
20 Blackberries 1.70
13 String Beans 7.50-15.00
25 Lima Beans 17.00-32.00

Field Crops

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

Alfalfa.

Potato leafhopper adults and nymphs are still active in many fields. Fields should be scouted from one week after harvest until 60% of the field is in the bud stage. Ambush, Baythroid, Dimethoate, Pounce or Warrior will provide effective control. If fields are treated after a cutting, the best control will be achieved if there is at least 1-2 inches of regrowth before application.

Soybeans.

Spider mites can readily be found in many fields. Infestation levels range from a few patches in a field to high populations throughout fields. If threshold levels are present – that is 20-30 mites per leaflet and/or 10% of the plants exhibiting mite damage (light stippling not severe damage) over more than one-third of the leaves, a treatment should be applied. If dimethoate has worked in the past, then it will be worth using again this year. When applied by ground, the addition of a material like LI-700 or AD-100 (acidifying/penetrant) has improved control with dimethoate. If you did not get control with dimethoate last year and/or you have already sprayed dimethoate this year and it has not worked, the Sect 18 material Danitol, at 16 0z per acre, should be considered. Parathion can still be used but it can only be applied by air and there are number of setback restrictions.


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

I recently saw a field of irrigated corn in brown silk with gray leafspot. This is very early given the weather conditions to be seeing gray leafspot. Many of the leafspots were very small, but produced abundant spores in a moist chamber. Growers should be checking irrigated fields for possible infection. From the road the problem looks worse because the fungus produces more toxin in full sunlight so the first few rows can look pretty bad. Be sure to check the whole field to try and get an idea of how much infection is present.

Gray leafspot produces small necrotic spots with yellow halos at first. As the lesions grow they become tan and turn gray. The larger mature lesions will have sharp parallel edges and will be opaque when held up to the light.

Soybean cyst nematode has been seen in several fields recently. Irregular yellow stunted areas in your field can be SCN, but digging a few root systems can help to identify the problem. Look for the small yellow or white female SCN on the affected plants. They are smaller than the nitrogen-fixing nodules. Remember they are still around and can cause serious yield reductions. You may not be able to see the cysts if they are brown, so a soil test would be recommended. Nematode test bags are available in all three county Extension offices.


Manganese Deficiency and Drought Stress on Soybeans - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

In many fields, manganese deficiency symptoms are showing up. Manganese deficiency is characterized by dark green veins and light green (mild deficiency) to yellow (moderately severe deficiency) to white (severe deficiency) interveinal leaf tissue. The symptoms often are most severe on the most recently emerged leaves. Manganese deficiency symptoms are similar to the deficiency and toxicity symptoms of some of the other micronutrients.

Some folks have raised the question of why we are seeing so many areas showing these symptoms this year. Whenever root growth is restricted, we can have problems with manganese deficiency since manganese is often present in our soils at barely adequate levels. This year the drought conditions that have persisted almost since corn planting time have limited the root growth in our dryland soybean plantings. In areas of the field where manganese is critically low, the limited root growth causes manganese deficiency symptoms to appear.

Should you treat your fields with either manganese sulfate (techmangam) or chelated manganese? In most cases, the answer is yes since this will reduce at least one stress on the beans. If the beans are under extreme drought stress and are possibly dying, there may not be enough leaf area exposed to adsorb adequate amounts of foliar-applied manganese. In that case, you may be better off to wait until the crop recovers enough (if and when the rains come) to treat. However, where drought has contributed to the appearance of the problem but the beans still show enough leaf area for a foliar application to be effective, manganese should be applied to alleviate that portion of the stress. Often, the application of foliar manganese will make the difference in whether you obtain a soybean crop.

What else should you consider? As with many problems, you need to know why the problem exists and if manganese deficiency is really the problem. Manganese deficiency often can be confused with soybean cyst nematode (SCN) damaged since SCN feeds on the roots and effectively restricts root growth causing symptoms similar to manganese. Compaction is another problem that can induce manganese deficiency. In this case although you may get temporary relief with foliar-applied manganese, there may not be much yield increase because the compaction restricts root uptake of many nutrients and not just manganese. Other factors that restrict root growth (deep cultivation near the plant, pH imbalances in the subsoil or in the surface layer, herbicide injury to the roots, etc) also can cause manganese deficiency symptoms. Always try to learn what are the underlying factors contributing to the problem.


Upcoming Meetings…

Agronomic Crops Field Day

July 27, 1999

9:15 a.m.- 1:30 p.m. (includes lunch)

Marl Pit Road (Rd. 429)Look for the University of Delaware Signs on the left.

Pesticide and CCA credits awarded.

For More Information, contact Carl Davis at the New Castle County Extension Office at 302-831-2506.

 

Crop Diagnostic Field Day

July 29, 1999

8:15 a.m.

U of D Research and Education Center

Three Continuing Education Unit Credits will be awarded for Certified Crop Advisors. The field day is designed to improve diagnostic skills and will focus on commercial vegetables and fruit. Pre-registration is required along with a $25 registration fee. For more information, contact Mabel Hough at 302/856-7303.

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Soybean and Agronomic Crops Twilight Tour

August 2, 1999

U of D Research & Education Center

5:00 p.m. Dinner

6:00-8:00 p.m. Tour

* The Novartis Technology Van will be available for viewing. Further details to follow. For more information, contact Mabel Hough at 302/856-7303.

 

University of Delaware Farm and Home Field Day

August 11, 1999

8:30 a.m. – 1:30 p.m.

For more information: contact

Mark Isaacs or Jay Windsor at

(302) 856-7303.

 

Watermelon Twilight Meeting

August 11, 1999

5:30 p.m.

University of Delaware Research & Education Center

Seedless Variety, Fungicide, and Miticide Trials on display. Dinner will be provided. More information to follow next week. For more information, contact Edna Marvil at 302-856-7303.

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Weather Summary

Rainfall:
0.04 inches: July 14, 1999
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 94F on July 19 to 73 F on July 14.
Lows Ranged from 64F on July 21 to 71F on July 19.
Soil Temperature:
76F average for the week.
(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

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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