Volume 7, Issue 9                                                                                              May 28, 1999


Vegetables

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

New Insecticide Registrations.
SpinTor 2SC (from Dow AgroSciences) received a federal (Section 3) registration for use on potatoes and sweet corn on May 21. In research trials, Spintor has provided effective Colorado potato beetle (CPB) and European corn borer control on potatoes. The use rate is 3 to 6 ounces per acre, depending on size of larvae and population pressure, with a 7-day pre-harvest interval. For resistance management, do not apply to consecutive generations of the CPB and do not make more than two applications per generation of CPB. Spintor is also labeled for corn borer, corn earworm and fall armyworm control on sweet corn. The rate range is 3 to 6 ounces per acre with a one-day pre-harvest interval.

Confirm 2F (from Rohm and Haas Company) has also received a federal (Section 3) registration for use on vegetables in the leafy, fruiting and cole crop groupings. This new insecticide offers a new mode of action and will be an important component of resistance management programs. Pests controlled by Confirm include beet and fall armyworm, garden webworm, cabbage looper, tomato hornworm and European corn borer. The rate range is 6 to 8 ounces per acre with a 7-day pre-harvest interval.

Melons.
As vines begin to run on the earliest plantings, be sure to watch for increases in aphid and mite activity. Both melon aphids and mites have reached economic levels in a number of fields. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Lannate and Thiodan are the only materials labeled on melons that provide melon aphid control. These materials must be applied before aphids explode to be effective. Dimethoate will not control melon aphids. When sampling for mites, be sure to check the entire plant if plants are small or the crown area on larger plants for signs of stippling and the presence of mites. Controls should be applied if 10–15% of the crowns are infested. In recent years, Kelthane and Agri-mek are the only materials that have provided mite control in melons. In general, dimethoate has provided very poor control. Recent applications of Agri-Mek for above threshold population levels have provided good mite control. If populations are heavy or numerous eggs are present at the time of treatment, at least 2 applications of Agri-Mek will be needed.

Peppers.
No corn borer controls will be needed until inch size fruit are present. At that point, sprays will be needed on a 7-10 day schedule when corn borer catches are above 2 per night in local blacklight traps.

Potatoes.
Corn borer moths continue to lay eggs in potato fields and we should begin to see the first larvae tunneling into plants by next week. A treatment should be applied if you find 20 – 25% of the terminals infested with larvae. Since Monitor and Furadan are systemic, these insecticides will provide the best control of larvae once terminals are infested. Two to three applications will be needed to provide control. If the terminals are not infested but moths are actively laying eggs in the field, Ambush, Pounce or Penncap will provide control. Three to four applications of a pyrethroid or Penncap will be needed to provide control. Potato leafhopper activity is starting to increase and adults can be found in Bt potatoes as well as fields that were not treated with Admire at planting. Furadan or a pyrethroid will provide leafhopper control. Colorado potato beetle adult egg laying activity is starting to increase and the first egg hatch has been observed. The treatment threshold for Colorado potato beetle is 4 small larvae per plant or 1.5 large larvae per plant. If both small and large larvae are present, the threshold of each should be reduced by for each. Provado, Agri-Mek or Spintor will provide beetle control. Spintor (a product of Dow AgroSciences) received a federal label on potatoes on May 21. In research trials, Spintor has provided effective control of Colorado potato beetles (CPB) and European corn borer. However, It will not provide potato leafhopper control. The rate range for Spintor is 3 to 6 ounces per acre. In general, 4 oz per acre has provided effective control; however, higher rates will be needed if CPB larvae are large or populations are heavy. Provado will provide control of leafhoppers and Colorado potato beetle but not European corn borer. Agri-Mek will control small and medium CPB larvae but is not very effective on high populations of adults.

Sweet Corn.
With the increase in corn borer moth activity, watch for corn borer larvae feeding in the whorls of the earliest planted fields. Corn borer larvae can be found in the whorls and tassels of the earliest planted fields. Fields should be treated once you find 15% of the plants infested with live larvae. Ambush, Pounce, Penncap or Warrior will provide the best control. If bees are foraging in the area, Penncap should not be used. Fresh market sweet corn that was planted under plastic and is now silking should be treated on a 6-day schedule for corn earworm control. v


Pea Harvest Begins - Ed Kee, Extension Vegetable Crops Specialist, kee@udel.edu

Pea harvest began on Wednesday, May 26, near Milford. Harvest should be in full swing by June 2 or 3. In general, the crop looks good despite the dry weather. Irrigation and cool temperatures appear to have fostered good yields.

Pea aphids are still around, and fields need to be checked.

The Pea Variety Trial Twilight Field Meeting is set for Tuesday, June 8, here at the R & E Center near Georgetown. 22 early varieties and 27 late varieties will be on display. The activities begin at 5 PM.

 

Watermelon Transplant Problems - Ed Kee, Extension Vegetable Crops Specialist, kee@udel.edu

Seed corn maggot, high winds, and poor germination of seedless varieties in the greenhouse have given some watermelon growers the transplant blues. Hindsight is 20-20, but it is a good time for growers to note the problems and resolve to not get caught next year. There is nothing more frustrating or scary for growers to have the investment in plastic, drip irrigation, and all the rest and then not have enough plants, or enough good plants of the desired variety. Our extension publication, The Watermelon Growers Handbook is available from county extension offices in Delaware and Maryland. v


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

Cantaloupes.

It is very important to control cucumber beetles to prevent transmission of bacterial wilt. Plants are most susceptible from transplanting until they begin to vine.

Beans (snap and lima).

To avoid root rots plow down previous crop debris and have a clean seedbed. Apply Ridomil Gold in a 7-inch band over the row after seeding, or apply Ridomil Gold PC 11G in-furrow at seeding to control Pythium damping-off and root rots.

 

LATE BLIGHT REPORT

DSV accumulations as of May 23, 1999 are as follows:

Location/

Emergence Date

DSV’s

May

23

DSV’s

May

20

Recommendation

Baldwin – 4/19

30

28

7-day, low rate

Jackewicz – 4/30

31

29

7 day, low rate

Art Wicks – 4/26

31

29

7-day, low rate

Ken/Chris Wicks – 5/3

28

26

7 day, low rate

This report does not include rainfall on Monday. For any potatoes that emerged after May 6 or 7 your severity values range from 9 to 11, still below the threshold of 18 DSV’s. For all the other potatoes we have accumulated enough DSV’s to warrant a 7-day spray interval. Most areas received some much-needed rainfall. Newark received some unwanted hail with the rain, Monday afternoon. Hail-damaged leaves are easily infected by many fungi, so if you got any hail damage ignore the prediction and apply a protectant fungicide as soon as possible. v


Vegetable Diseases - Kate Everts, Extension Vegetable Pathologist, University of Delaware and University of Maryland; everts@udel.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 May 19-26. Any questions please call Phil Shields at (410) 742-8788 or e-mail: ps136@umail.umd.edu

EFI Values for 1999

Location

5/19

5/20

5/21

5/22

5/23

5/24

5/25

5/26

U of M, LESREC
Salisbury, MD

-

3

0

1

2

3

0

0

Wootten Farms, Galestown, MD

1

2

0

0

2

4

0

1

Mark Collins,
Laurel, DE

1

3

0

0

1

3

0

0

Vincent Farms
Laurel, DE

2

4

0

0

2

2

0

0

D C Farms,
Bridgeville, DE

1

2

0

0

2

1

0

0

Balvin Brinsfield,
Vienna, MD

0

0

0

0

2

4

1

0

Charles Wright,
Mardela Springs, MD

1

3

0

0

2

3

0

0

U of D, REC
Georgetown, DE

1

2

0

0

1

1

 

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


Reflex and Basagran in Snap BeansMark VanGessel, Extension Weed Specialist; mjv@udel.edu

Below is a quick summary of common weed species in our area and relative control you can expect with Basagran or Reflex. These ratings are based on small weeds (less than 4") that are actively growing.

Weed (< 4 inches) Basagran Reflex
Nightshade Poor Fair-Good
Cocklebur Good-Exc. Fair
Jimsonweed Excellent Good
Lambsquarters Poor-Fair Poor
Morningglory Poor Fair-Good
Pigweed Poor Good-Exc.
Common ragweed Fair-Good Good-Exc.
Smartweed Good Fair
Velvetleaf Good Poor

v


Twilight Pea Variety Trial Field Meeting  - Ed Kee, Extension Vegetable Crops Specialist, kee@udel.edu

Tuesday, June 8, 1999

5:00 p.m. – Dusk

Research & Education Center, Georgetown, Delaware

The 1999 University of Delaware Pea Variety Trials are planted, the stands look good and the early trial was in full bloom as of May 15. We are looking forward to harvest and another year of generating good data for the industry.

The early trial, with 22 varieties, was planted March 19. This trial is located at the Dill Farm, approximately 1.5 miles west of the main entrance to the REC on route 9. The late trial was planted on April 27 and has 27 varieties. Come visit the trials, evaluate new varieties and interact with processors, growers, seedsmen and University folks.

Dinner will be provided. Please contact Edna Marvil at 302-856-7303 if you plan to attend, so that we can have an accurate count for dinner.

We hope you can join us on the 8th. Look for the blue and gold tent at the U of D Dill Farm on Route 9. v


Field Crops

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

Alfalfa.

Now that many fields have been harvested for the first time, it is time to start sampling for leafhoppers. Although we have only detected adults while sampling, be sure to watch fields carefully within one week of harvest for both adults and nymphs. Leafhopper adults are laying eggs in fields and populations can explode quickly if the weather turns hot and dry. When alfalfa is 3-inches or less in height, the treatment threshold is 20 per 100 sweeps. In four to six-inch tall alfalfa, the treatment threshold is 50 per 100 sweeps. Ambush, Baythroid, Dimethoate, Pounce or Warrior will provide effective control.

Field Corn.

Along with cutworms, no-till fields should be scouted for true armyworm larvae. Armyworm larvae can be found in fields that were planted into a burned down small grain cover or where a small grain cover was not completely plowed under before planting. The treatment threshold is 20 – 25% infested plants. A pyrethroid will provide control of cutworms and armyworms.

Small Grains.

Armyworms continue to be found sporadically in barley and wheat fields. In some cases, the economic threshold level has been reached but no head clipping has been observed. Since armyworms prefer to feed on the vegetation in the lower part of the canopy, no sprays should be needed in wheat until you begin to see head clipping or if larvae begin to move up the plants feeding extensively on the foliage. We should be at the peak in sawfly activity and head-clipping damage should be over in the next 7-day period.

Soybeans.

As early-planted soybeans emerge, be sure to watch for bean leaf beetle and Mexican bean beetle adults and feeding damage. Control will not be needed until you find 40% defoliation or they are feeding on the cotyledons and the stand count is being reduced by 25%. A pyrethroid or Sevin will provide control of both insects.  v


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

Wheat.

Barley yellow dwarf virus continues to be seen on wheat. Some stunting is occurring as well as yellowing of the upper leaves. Rust is beginning to appear but is very light at the present time. Septoria leafspot (Septoria nodorum ) is also beginning to appear. The wheat crop is advanced enough that no or very little effect will be seen on the crop from these two diseases. The dry weather and low humidity will not favor glume blotch unless it begins to rain often. Wheat and barley look very good at the present time. v


Corn Injury Symptomology Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

There are a number of residual grass herbicides labeled for corn. All of these products are sold alone or in combination with atrazine. The list includes metolachor (Dual and Bicep), alachlor (Partner, Lasso MT, Bullet), dimethanamid (Frontier, Guardsman, Leadoff), and acetachlor (Harness, Fultime, Surpass, Harness Extra, and TopNotch). Although these active ingredients are slightly different, the type of corn injury is the same. Problems with leaves unrolling and plants "leafing out" before emerging from the soil.

 

Soybean Preemergence Herbicide Rates Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Three years of research supported by the Delaware Soybean Board has shown that reduced rates of soil-applied herbicides can be a cost-effective approach in many situations. Rates as low as one-half the labeled rate for the soil type were used alone and in combination with postemergence herbicides. When used alone, the reduced rates often did not provide as good of weed control as the full rate. However, if the population of difficult to control weeds is high (cocklebur, morningglory, ragweed etc.), a postemergence spray is needed. When the postemergence herbicide is used, treatments with the lower soil-applied herbicide rates were as good as the full rate. If you know there are fields that will require a postemergence spray, lower your costs by reducing the rate of soil-applied herbicides. Be sure to keep an eye on those fields with reduced soil-applied herbicides to get a timely postemergence spray. v


Improving Forage Productivity - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

Many producers have finished or will shortly finish their first harvest hay. One of the best and easiest ways to increase yields and improve forage quality is to fertilize the crop properly. After the first hay harvest is an ideal time to apply additional nitrogen (N) fertilizer on hay fields consisting primarily of grass species. It is also ideal timing for application of needed phosphorus (P) and potassium (K) fertilizer on hay fields of all types (legume, grass, and mixed legume and grass). Nitrogen should be applied after each cutting on grass or predominately grass hay fields. Nitrogen promotes more leafy growth, increases the protein content of the grass, and is needed to boost second and third cut yields on grass fields. P and K are usually applied either in one shot or split with one half after the first cutting and the other half in August or early September after the late summer harvest.

Since hay removes many nutrients and can quickly lower the P and K soil test levels, hay producers with access to poultry manure have an ideal opportunity to use all the nutrients manure provides. Keep in mind that the manure will be surface applied so application should be timed to minimize the risk of heavy rains that might move the manure off site soon after application. Also, a substantial portion of the urea or ammonium nitrogen will be lost, since on hay fields, it can’t be incorporated. This should be accounted for in your calculations of how much N will be available to the growing hay crop. v


Viewing Small Grain Varieties - Bob Unitowski, Extension Associate,University of Delaware; bobuni@udel.edu

This year 6 barley and 62 wheat varieties are being tested in three locations in Delaware. Signs to identify the varieties have been placed in the first replication at all three sites. Growers and crop advisers are welcome to visit the small grain plots to see how your favorite varieties and some of the newer varieties are doing.

The trials are located at the following sites from north to south:

Week of May 20 to May 26

Rainfall:
0.04 inches: May 23, 1999
0.45 inches: May 24, 1999
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 86F on May 22 to 72 F on May 25.
Lows Ranged from 64F on May 23 to 44F on May 21.
Soil Temperature:
71 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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