Volume 8, Issue 10 May 26, 2000

 

 

Vegetables

 

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

 

Blacklight and Pheromone Trap Information.

Throughout the summer, timing of insecticide applications and spray intervals for corn earworm and corn borer control on peppers, potatoes, snap beans, lima beans and sweet corn are often based on local trap information. Trap catches are updated three times per week and can be found at our IPM website: http://www.udel.edu/IPM/latestblt.html. You can also call the Crop Pest Hotline at 800-345-7544 (in-state) or 302-831-8851 (out of state).

 

Cabbage.

If you are growing cabbage varieties that are susceptible to thrips, be sure to watch for an increase in feeding activity. A treatment should be applied when 20% of the plants are infested. Dimethoate, Metasystox-R, Spintor or Warrior will provide control.

 

Melons.

As vines begin to run on the earliest plantings, be sure to watch for increases in aphid and mite activity. Spider mites have reached economic levels in a number of fields. 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 1015% of the crowns are infested. If populations of mites have exploded, Capture should be used. A second miticide application may be needed in 7-10 days. Agri-Mek should be used for the second application. In general, dimethoate has provided very poor control. In recent trials, Danitol and Kelthane have also provided good mite control and should be rotated with Capture and Agri-Mek to avoid resistance. Remember Capture and Danitol are both pyrethroids and therefore should not be used in successions. If populations are heavy or numerous eggs are present at the time of treatment, at least 2-3 miticide applications may be needed. As the warm weather returns, be sure to sample melons for aphids. 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.

 

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. If trap catches exceed 20 per night, sprays will be needed on a 5-7 day schedule.

 

Potatoes.

The first infested terminals can be found in the Felton/Harrington areas on the earliest planted potatoes. If BLT trap catches are being used to time ECB sprays, all of the earliest planted potatoes should receive an ECB treatment by May 26 -27. Potato leafhopper activity is starting to increase and adults can be found in the earliest planted fields. Furadan or a pyrethroid will provide leafhopper control. Colorado potato beetle larval activity is starting to increase . 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 has provided effective control of Colorado potato beetles (CPB) and European corn borer. However, it will not provide potato leafhopper control. 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.

 

Snap Beans.

Continue to monitor fresh market and processing snap beans for leafhopper and thrips activity. A treatment is needed if you find 5-6 thrips per leaflet or 5 leafhoppers per sweep. If both insects are present, the threshold of each should be reduced by the level for each insect. In seedling beans, fields should be treated if plants are drought stressed and you can find leafhopper nymphs feeding on plants. Lannate, Capture, Asana or dimethoate can be used on fresh market snap beans. Lannate, Capture, Asana, dimethoate or Orthene can be used on processing snap beans.

 

Sweet Corn.

Corn planted under plastic should be sprayed on a 5-6 day schedule for earworm control. On the earliest planted sweet corn, continue to look for ECB in the whorls. European corn borer whorl infestations range between to 20 30 % infested plants in the earliest planted fresh market sweet corn fields. The treatment threshold is 15% infested whorls or tassels. If you plan to wait and treat just as tassels are emerging, timing of sprays will be important. Treatments must be applied just as tassels are emerging from the whorls to be effective. On later planted corn, flea beetle and cutworm activity has increased. The treatment threshold for flea beetles is 5% infested plants and the cutworm threshold is 3% cut plants in 1-2 leaf stage corn and 5% cut plants in 3-4 leaf stage corn.

 

 

Vegetable Diseases - Kate Everts, Extension Vegetable Pathologist, University of Delaware and University of Maryland; everts@udel.edu

 

Muskmelon and Watermelons.

The weather has been excellent for development of muskmelon and watermelon leaf spots. Apply a protective spray of chlorothalonil (Bravo or Terranil) before the coming rain.

 

We would like to thank everyone who responded to our Melcast survey. We are currently faxing or e-mailing information to 42 respondents.

 

 

 

MELCAST for Watermelons.

The weather based forecasting program MELCAST has begun for 2000. If you signed up to receive a report, it should have started this week. If you have not received any reports please call Mrs. Edna Marvil at (302)856-7303 or Vanessa Fitzmaurice at (410)742-8789 and give us your name and fax number or e-mail address. In addition, the report is available on the web at http://www.agnr.umd.edu/users/vegdisease/vegdisease.htm or http://www.udel.edu/IPM/. (see sample on page 9).

 

The website provides more detailed information concerning each model and the disease(s) that it is designed for, detailed information regarding each weather station or skybit location, a sample record sheet, as well as a blank record sheet that you can print out for use at your location. If you do not have access to the website, please contact Edna Marvil at the Research and Education Center at 302-856-7303 to request that this information be send to you.

 

To use MELCAST for Watermelons (gummy stem blight and anthracnose), apply the first fungicide spray when the watermelon vines meet within the row. Additional sprays should be applied using MELCAST. Accumulate EFI (environmental favorability index) values beginning the day after your first fungicide spray. Apply a fungicide spray when 30 EFI values have 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, reset the counter to 0 and start over.

 

If, for some reason, a serious disease outbreak occurs in your field, return to a weekly spray schedule.

 

 

Melcast for Watermelons

EFI Values (Environmental Favorability Index)

 

Location

5/17

5/18

5/19

5/20

5/21

5/22

5/23

5/24

Bridgeville, DE

 

0

0

0

2

0

1

1

Laurel, DE

(Collins Farms)

 

0

2

1

2

0

0

2

Galestown, MD

 

0

0

1

1

0

0

1

Georgetown, DE

0

0

0

0

1

0

0

0

Hebron, MD

 

0

0

0

0

0

0

0

Salisbury, MD

0

1

0

1

1

0

0

2

Vienna, MD

 

0

0

0

1

0

0

2

Laurel, DE

(Vincent Farms)

 

0

0

1

2

0

0

1

 

 

 

MELCAST for Cantaloupes and TOMCAST for Tomatoes.

 

In addition to MELCAST for Watermelon, we have added two additional models that are designed to help you make decisions on when to spray for diseases. MELCAST for Cantaloupes is a fungicide application program for (Alternaria leaf blight) that is similar to the watermelon model, but uses a different program to calculate EFIs. It can be used by anyone growing a powdery mildew resistant variety such as Athena. To use MELCAST for Cantaloupe, apply the first fungicide spray when the cantaloupe vines meet within the row. Additional sprays should be applied using MELCAST. Accumulate EFI (environmental favorability index) values beginning the day after your first fungicide spray. Apply a fungicide spray when 20 EFI values have 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 0 and start over.

 

TOMCAST is a spray forecaster for leaf blights and fruit diseases of processing tomato (early blight, septoria leaf spot, anthracnose). In fields that are not rotated away from tomatoes and in late planted fields begin sprays shortly after transplanting. In all other areas begin sprays when crown fruit are one-third their final size. Additional sprays can be scheduled using TOMCAST. Sprays should be applied after accumulating 18 DSVs (disease severity values) since the last fungicide application. TOMCAST does not work for bacterial diseases or late blight. Scout fields for these diseases. If they occur, additional sprays are warranted (see Delaware Extension Bulletin 137).

 

If you are interested in more information about these weather-based models or to sign up to receive information call Mrs. Edna Marvil at (302)856-7303 or Vanessa Fitzmaurice at (410)742-8789 and give us your name and fax number or e-mail address. In addition, the reports are available on the web at http://www.agnr.umd.edu/users/vegdisease/vegdisease.htm or http://www.udel.edu/IPM/. 

 

 

 

Late Blight Update - - Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

 

Disease Severity Value (DSV) Accumulations as of May 24, 2000 are as follows:

Remember that 18 DSVs is the threshold to begin a spray program

 

Emergence

Date

DSVs

May 24

DSVs

May 21

Recommendation

April 14

76

64

5-day, low rate

April 21

49

37

5-day, low rate

April 22

29

17

5-day, low rate

April 27

29

17

5-day, low rate

May 20

16

 

5-day, low rate

 

Accumulated 12 DSVs since the last report.

After todays severity value accumulation all potatoes that have reached greenrow before May 20 will need to be protected with fungicide.

 

Although the predictor is calling for low rates, I would suggest a medium rate for potatoes that are approaching bloom.

 

New fungicides labeled. Agtrol International has recently introduced a new fungicide called Flouronil, and expanded the label for UltraFlouish. Flouronil is a wettable powder that contains two fungicides, mefenoxam and chlorothalonil. Mefanoxam is the active ingredient of Ridomil Gold and UltraFlourish. You probably recognize chlorothalonil as the active ingredient in Bravo. Flouronil contains the same active ingredients as Ridomil Gold Bravo. ltraFlourish is now labeled as an in-row treatment at planting for pink rot and leak just like Ridomil Gold. UltraFlourish is a two lb./gallon formulation of mefanoxam while Ridomil Gold EC contains 4 lb./gallon.

 

 

 

Section 18 Labels Approved in Delaware for Sinbar on Watermelons & Reflex on Snap Beans - Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

 

The EPA granted a Section 18 Emergency Use Label for Sinbar on Watermelons as a pre-emergence treatment at 2-3 ounces.

 

Also granted was the use of Reflex on Snap Beans as a post-emergence treatment for control of many broadleaf weeds. Please check the label for the correct rate, which is dependent on the size of the weed.

 

 

 

 

Field Crops

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

 

Field Corn.

Cutworms are still active so be sure to continue to scout for leaf feeding and cut plants. In addition, slug activity can be found as a result of the recent cool weather. Deadline bullets and liquid N are still the only available control measures. If nitrogen is used to reduce slug populations, you should apply 20 gallons per acre of 30 % N in the evening when slugs are active. The best results are obtained when applied on spike to 1-leaf stage corn. Deadline bullets banded at 6-8 pounds per acre has given fair to good control. It can also be applied on larger corn. True 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.

Although sawfly larvae are still present and clipping heads in wheat, activity has generally peaked in most areas of the state. Fields should be checked one last time for this insect pest. The treatment threshold is 2 per 5 foot of row innerspace. It is generally too late to treat for sawflies if the number of clipped heads is 3 to 4 times the average worm count and most caterpillars are greater than one-inch long. Armyworms are still active, especially in barley. Continue to watch for larvae feeding on the leaves and grain kernels. Remember that armyworms like to clip heads just before the grain matures. The treatment threshold in barley is one per foot of row and 2 per foot of row in wheat. On barley, Parathion or Lannate will provide armyworm control. On wheat, Warrior, Parathion or Lannate will provide armyworm control. Although parathion can still be used on wheat and barley, it has a number of restrictions including: (1) aerial application only, (2) set back restrictions, and (3) closed system requirements.

 

Soybeans.

Bean leaf beetles and Mexican bean beetles can be found in the earliest emerged soybean fields. Bean leaf beetle damage appears as small circular holes in the leaves. In comparison, Mexican bean beetle feeding will appear as a lacey pattern on the leaves. No controls are needed unless you find at least 2 beetles per plant and they are reducing the stand by 25 percent. A pyrethroid or Sevin will provide control. Grasshopper nymphs continue to be found in no-till fields and along field edges. Treatment of non-crop areas may also help to prevent whole field infestations at a later date. As a general guideline, non-crop areas should be treated if you find 20 or more grasshoppers per square yard. As we approach barley harvest, soybeans planted after barley harvest should be checked carefully for grasshopper activity. Early control of nymphs will provide the best control. Once grasshoppers are found in a field, a treatment is needed if you find one grasshopper per sweep and 30% defoliation. Asana, Sevin or Warrior have provided the most consistent control. Slugs can also be found feeding on newly emerged fields. Unfortunatley, there are no effective controls for slugs in soybeans.

 

 

 

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

 

Normal Trade Relations Bill for China Passes House 

The U.S. House of Representatives strongly passed the Permanent Normal Trade Relations bill this week (237-197). The next stop is the Senate where easy passage is expected. This is good news for the grain markets, not so much in the short run but passage of the bill is likely to have a very positive impact on commodity prices in the not too distant future. China, with a population of 1 billion, is the largest market in the world. House passage will not provide much impetus for a rally in the commodities markets, however, a down vote would have resulted in immediate negative pressure on commodity prices.

 

That turns our attention to the driving force behind this week's market, strong export sales and the weather. The weekly export sales report was viewed by traders as strong for corn, good for new crop wheat, and strong for soybeans.  Commodity traders will be positioning themselves for a long Memorial Day weekend, with futures markets closed Monday. Great interest is being shown in the weekend forecast, especially for the western corn belt, which now calls for precipitation amounts to be pared back from previous guestimates. The current level of commodity prices and the 'still too early to tell' status for 2000 crop development, continues the grain sellers "wait and see mode". Due to extremely early row crop planting in the midwest, the size of this year's corn crop will be determined in the month of June. June is widely perceived as the month that will 'make or break' the corn crop. Overnight trade placed December corn at $2.52, November beans at $5.50, and July wheat at $2.80 per bushel. These price levels are likely to result in tight farmer holding.

 

 

 

 

Experiences With Roundup Ready Soybean Weed Control - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

The Delaware Soybean Board has funded a series of studies for weed control in Roundup Ready soybeans. A summary of the results follows.

 

For full-season soybean with annual weeds, start with a clean field using either tillage or a good burndown program. Although we have tried to time our Roundup Ultra sprays for both burndown and in-crop weed control for no-till soybeans, we have not been successful with this approach. Time your postemergence spray during the period 3 to 4 weeks after planting with conventional tillage soybeans or 3 to 5 weeks after planting with no-till soybeans. The moisture conservation with no-till allows for the wider window of application. If you foresee problems with spraying during this window, consider using a reduced rate of a preemergence herbicide or spraying prior to 3 weeks after planting and including a residual herbicide.

 

Spraying earlier than 3 weeks after planting often requires either a second Roundup Ultra application or tank-mixing a residual herbicide to reduce the need for a second application. Three tank mix options we have tried include FirstRate, Classic, or Pursuit. However, our research has not shown a benefit to tankmixing another herbicide with Roundup Ultra if sprayed 3 to 4 weeks (after planting) for conventional tillage or 3 to 5 weeks for no-till.

 

Morningglory control with Roundup Ultra will be reduced if the morningglories have begun to vine. However, tankmixing with other herbicides has not improved control. For maximum morningglory control, either spray Roundup Ultra at 3 weeks after planting (when the weeds are the smallest) or apply two applications of Roundup Ultra.

 

For perennial weeds (horsenettle, Canada thistle, hemp dogbane, common milkweed, johnsongrass, and bermudagrass), our research has shown applying Roundup Ultra late as possible (4 to 6 weeks after planting) has given better control than early applications. There has been no advantage to two applications. It is difficult to achieve 100 percent control with most perennial weeds, regardless of the weed control program used. We often achieve 80 to 85 percent control with the program described here.

Finally, we have not seen differences in weed control or yield when using Touchdown in place of Roundup Ultra, and there are generic formulations of Roundup available.

 

 

 

Height Restrictions and Rainfastness For Postemergence Corn Herbicides - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

 

Rainfastness is number of hours needed between time of application and rainfall or irrigation to ensure sufficient absorption in the plant.

 

Broadcast applications refer to an over the top application and directed refers to use of special spray equipment to direct the spray and avoiding the spray coming in contact with the whorl of the corn. When using corn height or collar number to base your decision to spray on, use whichever feature is first attained. 

 

 

 

 

Herbicides

 

Rainfast

interval (hr)

Maximum corn size

Accent

4

broadcast: 6 collars or 24" 

directed: 10 collars or 36"

Aim

1

broadcast: up to 8 collars

directed: when necessary

Atrazine

2

12" tall

Banvel 

Clarity

4

more than pt/A:

broadcast: 5 lvs or 8" 

directed: 36" tall

pt/A or less: 36" tall

Basagran

8

No restrictions listed

Beacon

4

broadcast: min- 4" tall

max- 20" tall or 6 collar

directed: pre-tassel

Bladex 90 DF

4

prior to when 5th leaf is visible

Buctril

1

pre-tassel

2,4-D Amine

6-8

broadcast: 8" tall

directed: pre-tassel

2,4-D Ester

2-3

broadcast: 8" tall

directed: pre-tassel

Evik

-

directed only: 12" tall do not apply 3 weeks before tasseling

Liberty

4

broadcast: 24" tall or 7collars max

directed: 20" to 36" tall

Lorox

-

directed only

Permit

4

broadcast: 48" tall

directed: when necessary

Poast

Poast Plus

1

broadcast: emergence to start of pollen shed

directed: when necessary (depending on corn canopy and weed ht.)

Resource

1

broadcast: 2-lf to 10-lf stage (collars must be visible)

directed: when necessary; when corn leaves interfere w/ spray 

Roundup Ultra

1-6

up to 30" or 8 collars max

Stinger

6-8

24" tall

Tough

1-2

until 68 days pre-harvest

Premixes

Basis

4

2 collars or 6" tall

Basis Gold

4

5 collars or 12" tall

Celebrity Plus

4

broadcast: 4 to 24" tall

Distinct

4

6 oz rate: 4 to 10 tall

4 oz rate: up to 24 talll

Exceed

4

broadcast: min- 4" tall

max- 20" tall or 6 collar

directed: 20" to 30" tall

Field Master

2

Do not apply to emerged corn

Hornet

6

broadcast: 24" tall

directed: until 85 days pre-harvest

Laddok

8

12" tall

Liberty ATZ

4

12" tall

Lightning

1

broadcast: 12" tall

directed: 20" tall 

Marksman

4

broadcast: 5-lf stage or 8" tall

Northstar

4

broadcast: min- 4" tall

max- 20" tall or 6 collar

directed: 20" to 30" tall

Scorpion III

6

broadcast: 8" tall

directed: pre-tassel

Shotgun

24

broadcast: 8" tall

directed: 12" tall 

or if rate >2 pts

Spirit

4

broadcast: 20" tall or 6 collars (minimum ht. 4" tall)

directed: 20" to 24" tall (before tassel emerg.) 

 

 

Be Mindful of Surfactants- Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

.

The rainfall and cloudy skies this past week has resulted in less leaf waxes than usual. Follow this with projected warm weather and growing conditions should be optimal. But this also means that using a crop oil concentrate and/or liquid nitrogen can increase injury for postemergence sprays. To minimize crop injury, consider using only a non-ionic surfactant for postemergence sprays under these optimal growing conditions.

 

 

 

 

Nutrient Deficiencies on Corn Appear - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu

 

Recently, I have noticed several corn fields showing problems which may be manganese (Mn) deficiency. The corn is at the 5 to 7 leaf stage and was planted in early April. The fields were limed this past spring or last fall. The texture varies from a loam to loamy sand. The percentage organic matter is 1 to 1.5 and the soil pH is only slightly elevated (mid-6s).

 

The symptoms began as interveinal chlorosis with the veins a dark green but in between the veins a light green or yellowish color. Symptoms progressed rapidly from the slight interveinal chlorotic cast to areas of bleached white to slightly yellow around the leaf margins about mid way up the leaf blade. The oldest leaves appear to be the most affected. Some necrosis or dead spots are appearing along the margins of the leaf blade and at the leaf tips.

 

The crop has been declining so rapidly that I had a foliar application of 1 to 2 lb Mn/A applied without waiting for a tissue test. Whole plant samples would allow you to make a more definitive diagnosis if your scouting program helps you spot such problems in the early stages.

 

 

Soybean Fields and Soil Crusting - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu

 

The strong storms that occurred during the past week could be impacting soybean stands. When heavy raindrops impact the soil surface, they break soil aggregates apart. This allows clay particles to move downward a short distance and leaves a concentration of sand and silt particles on the soil surface. The sand and silt can then combine to form a nearly impenetrable layer to some plants, especially broadleaf crops such as soybeans and alfalfa. Raindrop-impact crusts are typically only 1/4-inch thick but can severely impact emergence of soybeans.

 

Why be concerned with crust formation? Not only does a crust impact seedling emergence but it also reduces rainfall infiltration, increases runoff, reduces oxygen diffusion to seedlings by as much as 50 percent, reduces surface water evaporation, lowers soil surface temperatures, and increases wind erosion on sandy soils.

 

Soil crusting is most often a problem for growers with low organic matter soils or those who frequently use clean tillage (moldboard plow and frequent diskings to prepare a weed-free, residue-free finely worked seedbed). The impact of crusting is greatest for drill or broadcast planted beans but can become a problem even for row beans. Growers using no-till or conservation tillage practices will seldom experience crusting problems.

The most frequent solution to soil crust problems is the use of the rotary hoe or row cultivator. This equipment is used to shatter the crust and allow seedlings to emerge. When operated correctly, less than five percent (often only one or two percent) seedling loss will be attributable to the action of the rotary hoe. If done in a timely fashion, soybean emergence will be adequate to avoid the need for replanting. The row cultivator will likely result in higher seedling losses but also some weed control activity. Only the rotary hoe should be used on drilled beans.

 

 

 

Weather Summary  

Week of May 4 to May 11

Rainfall:

0.14 inches: May 20, 2000

0.56 inches May 21, 2000

1.11 inches May 22, 2000

0.10 inches May 24, 2000

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

Air Temperature:

Highs Ranged from 85F on May 19 to 58 F on May 20.

Lows Ranged from 61F on May 24 to 53 F on May 20.

Soil Temperature:

68F 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

 

 

 

Maryland Cooperative Extension

Vegetable Disease Forecasting Page
   Welcome to the weather-based disease forecasting page from Maryland Cooperative Extension.  It contains information on how to schedule fungicide applications for watermelon, muskmelon and tomato crops.  If you are using one of these models for the first time, you may want to apply it on a limited area to become comfortable with the model.  As always be sure to scout your field regularly, and if a disease outbreak occurs, revert to a calendar spray.

                                                        
Melcast Watermelon EFI                             Melcast Muskmelon EFI
 

                                                



                                             TOMCAST Processing
                                                     Tomato DSV


Detailed Information on Weather Station Locations

Questions about weather-based models

Sample Record Sheet

Blank Record Sheet

 

 

 

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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