Volume 6, Issue 18                                                                                           July 24, 1998


Vegetables

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

Melons.

The recent weather has been very favorable for the development of mite and melon aphid populations in watermelon fields. Fields should be sprayed for mites when 10-15% of the crown leaves are infested. Agri-Mek continues to provide good control when applied by air and ground. Kelthane has also worked well but should not be over used. If you have been consistently using Kelthane in past years, you may want to switch to Agri-Mek to avoid development of resistance. In addition, you should not use more than 2 applications of Agri-Mek in order to avoid resistance development. Fields should be sprayed for melon aphids when 20% of the plants are infested plants with 5 or more aphids per leaf or runner. Lannate will provide melon aphid control but coverage is important, especially if leaves have begun to curl.

Peppers.

Continue to maintain a 7-10 day spray schedule for corn borer and pepper maggot control. Corn earworm populations are still very low and should not be of concern in peppers at this time.

Snap Beans.

Processing snap beans should be sprayed at the bud and pin stages with Orthene for corn borer control. After the pin spray, a third application with Lannate will be needed within 5 to 7 days from harvest in most fields except in the Bridgeville area where sprays are needed on a 5 day schedule from the pin spray until harvest.

Sweet Corn.

Fresh market silking sweet corn should be sprayed on a 3-4 day schedule in Sussex County and on a 4-5 day schedule in Kent and New Castle Counties. v

Air Pollution Injury on Watermelons - Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

We have seen some watermelon fields showing some air pollution injury. Ozone injury is the predominant type of injury, and watermelons are the most sensitive to ozone of all the cucurbit crops. Ozone (O3) and other photochemical pollutanats are formed by atmospheric chemcial processes. The nitrogen oxides and hydrocarbons released from vehicular fuel combustion interact in dry air with UV light to form ozone. Ozone is the air pollutant with the greatest effect on crop production.

Watermelon injury includes premature chlorosis, chlorotic mottle, bleaching, stippling, and if severe enough, necrosis of the crown leaves. Of course, there is no treatment for ozone injury, other than maintaining proper growing conditions with good management of irrigation and fertility. Watermelon injury should not be confused with fungus diseases. v

Blossom End Rot and Hollow Heart on Watermelons - Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

Blossom-end rot is a disorder caused by calcium dificiency in the fruit. Blossom-end rot frequently occurs after plants have been subjected to a severe drought stress, which interferes with the calcium transport to the fruit. When these deficiencies occur in the fruit, the cells break down. While there are varietal differences in susceptibility to blossom-end rot, when conditions are right blossom-end rot will occur in all varieties. In general, varieties with long fruit will have more of a tendency for blossom-end rot than round or oblong varieties.

Blossom-end rot will also occur when the fruit load is heavy, acting as a sink pulling nutrients into the fruit. We often notice small fruit showing blossom-end rot just before the large fruit are harvested. The calcium is being drawn into the large fruit, sometimes at the expense of the smaller, younger fruit.

Symptons first appear as small, light brown spots at the blossom end of the immature fruit, and then enlarge to form dark, sunken, leathery lesions.

The first management step to avoid blossom-end rot is to maintain a good pH and high calcium levels. Lime is the cheapest, most effective way to achieve this. After the season begins, using calcium nitrate, especially when the pH is marginal (5.9 or less), as a side-dressing or injected through an irrigation system is useful. Foliar sprays can be of some benefit but are expensive.

Hollow heart is the void, or empty area in the internal center of the melon at harvest. Often not notice until harvest and a melon is cut, hollow heart results from extremely high growth rates and expansion of the fruit. Over irrigating and over fertilizing with nitrogen are often associated with hollow heart. 150 to 175 pounds of nitrogen per acre is adequate to achieve excellent yields of watermelons. v

Irrigating Vegetable Crops - Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

Irrigating during the hot, dry conditions is a must to achieve profitability in vegetable crops. When temperatures are in the 90's and crops are in reproductive stage (flowering, blossoming, tasseling, fruit set, etc.), most crops are losing one-third of an inch of water/day/acre through evapotranspiration. Irrigation scheduling becomes problematic and almost a moot point under the conditions we have experienced during the past week. The goal should be to replace and maintain the soil moisture that is lost through evapotranspiration.

Operators of center-pivots and other overhead systems generally have a accurate estimate of how much water they are applying. With drip irrigation, it is a little more difficult. However, a drip system designed to deliver 25 gallons per minute per acre will apply 0.44 acre inches in 8 hours. A system designed to deliver 50 gallons per minute per acre will apply 0.88 acre inches in 8 hours. In a 12 hour day, each system will deliver 0.66 or 1.33 acre inches, respectively. v

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

Ozone Damage.

Cucurbits - The recent heat and humidity have produced increased levels of ozone. Watermelon and squash are the most sensitive of the cucurbits followed by cantaloupe, cucumber and pumpkin. Icebox types of watermelon traditionally have been the most sensitive watermelon cultivars and sensitivity varies from cultivar to cultivar. Look for bleaching, mottling of upper leaf surfaces and/or dark stippling. The oldest leaves at the crown are the most susceptible. These leaves will eventually become necrotic. Irrigated acreage will exhibit more damage if the cultivar is sensitive. Increased humidity usually favors symptom development as well. Unfortunately there are no controls except select cultivars that are resistant to ozone damage.

Beans - Ozone can also damage sensitive snap and lima beans cultivars. On beans ozone injury or bronzing appears on the upper leaf surface as small water-soaked or necrotic lesions that coalesce and become bronze or reddish brown, resembling sunscald injury. Premature senescence and defoliation can occur following prolonged exposure to damaging levels of ozone.


Late Blight Update

DSV accumulations as of July 20, 1998 are as follows:

Location/Emergence Date

DSV's July 17

DSV's July 20

Recommendations

Baldwin - 4/20

147

147

10-day, low rate

Jackewicz - 4/20

142

144

10-day, low rate

Zimmerman - 4/23

92

121

10-day, low rate

Baker - 5/1

140

141

10-day, low rate

The Zimmerman site had a dramatic increase due to its location near the water, which is the opposite of what it has been doing all season. With the projected high temperatures this week and the stage of growth, I am over-riding the recommendation at that location.

If you are growing early blight susceptible cultivars and you are not ready to dig them yet, the high rate of a protectant fungicide is suggested. The Late Blight Report is also posted electronically at the UD Extension IPM website: http://www.udel.edu/IPM v

 

Vegetable Diseases - Kate Everts, Extension Plant Pathologist, University of Maryland and University of Delaware ; everts@udel.edu, 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 8-15. Any questions please call Phil Shields at (410) 742-8788 or e-mail: ps136@umail.umd.edu

EFI Values

Location

7/15/98

7/16/98

7/17/98

7/18/98

7/19/98

7/20/98

7/21/98

7/22/98

U of M, LESREC
Salisbury,MD

4

3

5

2

3

2

4

1

Wootten Farms, Galestown,MD

1

0

3

0

3

2

3

1

Mark Collins, Laurel, DE

2

0

3

2

2

0

3

2

U of D, REC Georgetown, DE

1

2

1

1

1

1

3

 
Vincent Farms Laurel, DE

3

0

4

2

2

1

3

1

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. v


Laurel Farmer's Auction Market Report

July 16 - 22, 1998

Quantity Produce Price
61,776 Cantaloupes  
 

Athena

0.25-2.40
 

Super Star

0.45-2.20
 

Eclipse

0.55-0.85
 

Passport

0.60-2.00
 

Savor

0.25-1.20
512 Honeydews 0.75-1.90
29 Crenshaws 0.85
9385 Sugar Babies 0.40-2.00
  Watermelons  
 

Crimson Sweet

 
 

12 up

0.80-1.35
 

15 up

1.50-2.50
 

20 up

1.70-3.20
 

25 up

2.60-3.35
 

Sangria

 
 

12 up

1.15-1.80
 

15up

1.30-2.30
 

20 up

2.20-3.50
 

25 up

3.20
 

Royal Majesty

 
 

15 up

2.15-2.50
 

20 up

2.10
 

Fiesta

 
 

12 up

0.75-1.25
 

15 up

1.60
 

Royal Star

 
 

15 up

1.25-2.20
 

20 up

2.00-2.75
 

25 up

2.70-3.35
 

Seedless

0.90-4.20
155

Yellow Dolls

2.80
93 Peppers  
 

Banana

3.00-5.50
 

Green

3.00-13.00
 

Sweet

6.00
2239 Tomatoes  
 

Red

3.00-35.00
 

Pink

3.00-26.00
9

Cherry Tomatoes

4.00-7.00
 

Plum Tomatoes

6.50-11.00
2337 Sweet Corn Doz. 0.65-2.00
42 String Beans 9.00-14.00
208 Cucumbers 3.00-7.50
307 Squash  
 

Yellow

3.00-8.50
 

Green

3.00-7.00
187 Potatoes  
 

White

4.00-6.00
 

Red

3.00-6.50
2 Eggplant 6.50

Field Crops

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

Field Corn.

Japanese beetles and corn rootworm adult beetles continue to be found feeding on the silking corn. The decision to treat should be based on the number of beetles per silk as well as how far you are in the pollination period. In northern areas where you can find "clouds" of rootworm beetles in the field and on the silks, yield losses have occurred, especially along field edges, from beetles feeding on silks before 50% pollination has occurred. A treatment is recommended on silking corn if you can find 4-5 beetles per plant, they are clipping silks to less than inch long, AND it is before 50% pollination has occurred.

Soybeans.

With the current hot, dry weather, all fields should be watched carefully for spider mites. Economic levels are showing up in neighboring counties in Maryland. Damage will first appear at the base of leaves as white stippling on the top surface of leaves. Since we do not have any good miticides available for mite control in soybeans, early detection and application of control materials is critical. If dimethoate is used, high storage temperatures (greater than 95 degrees F) can reduce the effectiveness and it is very susceptible to degradation if the pH and/or iron content of the spray water are high. Buffering agents can be added to the mix to adjust for high pH and iron content. The buffering agent should be added to the spray tank before dimethoate is added. There have already been mite control failures with dimethoate, especially in fields where it did not work in 1997. In these situations, the only other options would be multiple applications (2-3) of parathion by air only and very few applicators are able to apply it. We are in the process of working on a Crisis Exemption for Danitol for mite control in soybeans. Research from Virginia shows good control on peanuts. We also just used it in a mite control trial in watermelons and it worked well. After 3 months of searching for a product that both a registrant and EPA would support, this is the material that both parties would support. We will hopefully have a Crisis Exemption by Friday, July 24. It will cost between $15 and $ 20 per acre but will be better than spraying dimethoate 3-4 times as was done in 1997 and get no control. Since there is no available aerial application data, the label will state ground application only. We will keep posted on the progress of this label. v

 

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

Keeping Barley Seed.

There have been several questions concerning keeping barley for seed that was infected with bacterial kernel blight. If the barley crop had good test weight and yield and germination is high it is safe to assume that it can be kept for seed purposes. If infections levels were very high and yields were reduced it is not worth the risk. There are no seed treatments currently available that can be used to control this disease. v


Upcoming Events…

August 12, 1998

Farm & Home Field Day

Time: 8:30 a.m. - 1:00 p.m.

Location: U of D Research & Education Center, Georgetown

For More Information: Contact the REC at 303-856-7303.

August 12, 1998

Watermelon Twilight Meeting

Time: 5:30 p.m.

Location: U of D REC

For More Information Contact Edna Marvel at 302-856-7303.

August 26, 1998

Irrigation Field Day

Time: 9:00 a.m. - Noon.

Location: Thurman Adam's Farm

For More Information: Contact Mabel Hough at 302-856-7303.

September 15, 1998

Recycling of Pesticide Jugs

Time: 1:00 p.m. - 4:00 p.m.

Location: Sussex County Soil Conservation District Equipment Yard

For More Information: Contact DDA Pesticide Section at 1-800-282-8685


Weather Summary

Week of July 17 to July 23

Rainfall:
None.
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 96 F on July 21 & 22 to 83 F on July 19.
Lows Ranged from 85 F on July 22 to 61 F on July 19.
Soil Temperature:
78 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:

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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