Volume 6, Issue 4                                                                                                April 17, 1998


Vegetables

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

New Insecticide Label.

On April 15, EPA granted a federal label for SpinTor 2SC, a "naturalyte" insect control product produced by Dow Agro Sciences for control of worms, leafminers, and thrips in apples, cole crops, tomatoes, peppers, eggplant, and leafy vegetables. Insecticide trials in Delaware and the Mid-Atlantic region in 1997 indicated that SpinTor provides excellent control of diamondback moth in cabbage. It is effective in both cool and warm temperatures. Once we receive a label from EPA, we will have more information on the use rate.

Potatoes.

Since we may see the earliest planted potatoes emerging from the ground by next week, begin looking for colorado potato beetle adults feeding on plants, especially where Admire was not used at planting. No insecticides will be needed until you find 25 beetles per 50 plants and defoliation has reached 10%. Provado at 3.75 oz per acre will provide good control. *

IPM Web Page               http://www.udel.edu/IPM

 

Watermelon and Cantaloupe Weed Control - Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

Watermelons.

Watermelon weed control is best achieved with the use of herbicides in combination with several cultivations. Even when black plastic mulch is used, herbicides are often used to control weeds that may come through the opening in the plastic and in the middles between the rows. Cultivation is also used to control weeds in the middles.

For Direct Seeded plantings into bare ground (no mulches) - A three-way combination of Command 4EC (4 to 6 ounces/acre) plus Curbit (1.5 to 2.0 pints/acre) plus Sinbar (3 ounces/acre) will provide the widest spectrum of weed control at a reasonable cost. This combination is applied preemergence. Command and Curbit control grasses and each controls certain broadleaf weeds. Command is weak on redroot pigweed, while Curbit is weak on ragweed. Sinbar is very effective on most broadleaves, although weak on pigweed. It is possible to achieve good weed control if either the Command or the Curbit is omitted, especially with multiple cultivations.

When transplants are used on bare-ground, Curbit cannot be used. A Command and Sinbar combination can be applied 3 to 5 days prior to transplanting to avoid the temporary chlorosis that occurs with Command. A Prefar (1 gallon/acre) plus Alanap (1 gallon/acre) combination pre-plant incorporated can also be used, although it is very expensive and results are often less than satisfying.

For transplants on plastic mulches, the choices become complicated. Curbit cannot be used on or under the plastic. Successful use of Curbit, Command, and Sinbar combinations has been accomplished when sprayed on the middles only. This must also be done 3 to 5 days prior to transplanting. Again, cultivation of the middles is necessary. We recommend leaving the Command out of this mix to avoid the chlorosis, especially with seedless transplants, which are very expensive. The Prefar/Alanap mix can also be used prior to laying the plastic.

If a herbicide application is necessary to provide some control of the grasses that may come through the opening for the transplant, Prefar at 6 quarts/acre preplant incorporated prior to laying the plastic is recommended, although this is a very expensive treatment. Recent experience has shown that making small openings when transplanting and rapid early growth of the watermelon plant will compete against weeds quite well.

Poast is labeled for post-emergence grass control, if necessary.

Cantaloupes.

Virtually all of the cantaloupe acreage is planted on plastic, much of it uses transplants. If clear plastic is used, soil fumigants are necessary to control weeds under the plastic. If black plastic is used, Curbit can be used for the middles only. Command cannot be used in any situation on cantaloupes, and Curbit cannot be used under or on the plastic. The Prefar/Alanap combination can be used prior to laying the plastic.

Poast is labeled for post-emergence grass control. *

 

Field Crops

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

IPM Web Page            http://www.udel.edu/IPM

Field Corn.

Black cutworm moth activity continues to increase in a number of areas throughout the region (see table at end of newsletter provided by Terra). As indicated in the last newsletter, moth catches ranging from 7 to 15 moths per 7 day period have been associated with a moderate to high potential for cutworm outbreaks. Once moth catches in an area reach this level, the first larvae are generally seen 300 degree days (using a temperature base of 50) after the peak. Although the degree model has not been worked out specifically for our region, it can be used as a general guideline for predicting larval activity in the field.

Grubs continue to be readily found in fields, especially if you are planting into a small grain/soybean stubble. Even though insect development is ahead of schedule because of warmer temperatures, grubs generally feed on corn roots through mid-May. If you have started planting and economic levels of grubs are now present , they will be able to feed for at least one month. Damage from grubs usually appears as long skips in the row or in circular patches. If threshold levels of 1 – 2 grubs per square foot are being found, a soil insecticide placed in-furrow will be needed.

Small Grains.

Aphid populations continue to be moderate in most wheat fields with higher populations being found in some barley fields. Although aphid populations are higher than in 1997, they have not reached the economic levels encountered in 1996. At this time, the chance for vectoring barley yellow dwarf virus is very slim. The next opportunity for aphids to cause damage is from feeding on the developing grain heads. Aphids feeding on the grain heads can reduce yields as well as test weight. Once fields reach the early dough stage, it is no longer necessary to be concerned with aphids. Cereal leaf beetle egg laying activity continues to increase but no egg hatch has been observed. We should start to see hatch in the southern part of the state by next week (week of April 20) if temperatures remain warm. The threshold of 0.5 larvae per stem will result in economic levels of control if fields are scouted routinely and sprays applied in a timely manner. In high management fields and/or where significant egg laying has occurred, the lower threshold of 25 eggs and/or larvae should be used, especially if a fungicide application is needed. However, no sprays should be applied before 50% of the eggs have hatched. At this time, true armyworm moths have begun to fly but have not reached peak flights. In areas where wheat is in the boot stage and/or will be in head by next week, begin sampling for grass sawflies and true armyworm. The extremely warm temperatures a few weeks ago followed by cooler temperatures is generally favorable for grass sawfly outbreaks. Since larvae are often difficult to detect when they are small, a sweep net can be used to detect the first small larvae. You should include field margins and rank areas in your sample because adult sawflies will be attracted to those areas. Once larvae are detected, fields should be sampled by shaking 3 to 5 linear feet of row in 5-10 locations and counting the number of larvae found in the innerspace between 2 rows. A treatment is recommended if you find 0.4 larvae per foot of row. *

 

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

Special Local Need (24c) Registration Approved for Tilt Fungicide on Wheat.

On April 6, 1998, the Delaware Department of Agriculture, Pesticide Division, approved a Special Local Need (24c) application from Novartis for the use of Tilt 3.6E fungicide on wheat up to and including Feekes growth stage 10.5 (full head emergence) for the control of powdery mildew and rust. Prior to this approval Tilt had to be applied to wheat prior to complete flag leaf emergence (Feekes GS 8).

The 24c label gives farmers the flexibility to use Tilt when it is most needed, usually during the period of wheat head emergence. If scouting indicates an earlier application, the label still provides for that use. The problem I often had with the previous label, was that Tilt had to be applied before the full extent of the disease situation was known. This sometimes resulted in unnecessary applications of Tilt. Farmers with high yield potential wheat crops felt that the crop had to be protected and had little choice. Now the disease situation can be determined at a later crop development stage and make applications when needed.

The 24c label for Tilt was made possible because new residue data showed that an application of 4 ounces, made up to Feekes growth stage 10.5 and 40 or more days before harvest, did not result in illegal residues in harvested grain or grain fractions.

Label restrictions are: 1) do not apply Tilt after Feekes growth stage 10.5, 2) do not apply more than 4 fl.oz. of Tilt per acre per season, 3) do not apply within 40 days of harvest, 4) do not cut the green crop for hay or silage. After harvest, the straw from treated crops may be used for bedding purposes. The user must have a copy of the 24c label at the time of application.

Wheat Diseases.

Powdery mildew continues to be the most common disease present. The amount varies considerably depending on the amount of nitrogen applied and varietal susceptibility. The cool weather pattern favors continued development, so continue to scout fields often. Consider fungicide applications if 5-10% of the leaf area of the uppermost fully expanded leaves is infected. Fungicide applications will be most economically feasible when yield potential for the crop is in the 60 bushels/A and above range. *

 

Questions To Ask Before Choosing a Herbicide - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Below is a list of considerations when deciding what herbicides to use. Asking the questions in the order they are given here will help to formulate an effective herbicide program without getting caught by critical questions that were not asked.

1. What weeds need to be controlled?

(This is the overriding consideration)

2. Is more than one herbicide needed for acceptable weed control?

( If more than one herbicide will be needed, can the herbicides be tank-mixed? Is there a pre-mix available for the herbicides you need?)

3. Does the herbicide(s) of choice have application restrictions or unacceptable risks associated with its use?

4. Does the herbicide(s) of choice require a genetically enhanced variety?

5. Does the herbicide have rotational restrictions?

6. Are there other restrictions (such as soil type, pH, etc.) that could limit its use?

7. Can I mix this herbicide with other pesticides? (Are there limitations if other pesticides were used earlier?)

8. Will I need a surfactant?

9. Have you considered resistance management?

10. Are there still more than one herbicide that will have similar performance for your situation?

11. What is the cost of your available options?

12. What is your experience with the available options? *

 

Reminder of Restrictions Associated with the Use of Acetachlor - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Acetachlor is a preemergence herbicide for corn that controls annual grasses and some broadleaf weeds. It is in the following products: Harness, Harness Extra, Surpass, Surpass 100, Topnotch, and Fultime. It has received a lot of advertisement in the past few months, but most of this advertisement does not mention the restrictions that are important in our area. The restrictions pertain to groundwater quality. The restrictions are based on depth of groundwater within one month of planting and the combination of soil type and organic matter. Do not apply acetachlor if the groundwater depth is 30 feet and you have sands with less than 3% organic matter, or loamy sands with less than 2% organic matter, or sandy loam with less than 1% organic matter. *

 

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

U.S. Export Sales Highlights.

Cumulative exports for all wheat for the current marketing year are running 794,000 metric tons behind last year. For the current week, wheat exports were up 5% from the previous week, but down 5% from the 4-week average.

Cumulative exports for corn are running 7.085 million metric tons behind last year. For the current week, corn exports were 16% below the previous week, but 15% above the 4-week average.

Cumulative exports for soybeans are running 1.188 million metric tons ahead of last year. For the current week, soybean exports were 18% below the prior week and 39% below the 4-week average.

Planting Progress Reported to be Slow in Mid-west.

Cool temperatures and wet conditions are expected to keep field work from making much progress in the corn belt for the next few days. Market traders will be watching forecasts closely in the next few weeks to gauge potential planting delay impacts. One anticipated impact would be the switching of some corn acres to soybeans, if plantings are delayed. Currently, that development does not appear to be happening in the Southeast, where planting progress is lagging, but catching up. Traders attention will be turning toward watching mid-west planting progress.

Market Strategy.

Much depends upon an individual's price objectives, when deciding whether commodity sales should be made at given points in time. Lately, there have been many price negatives reported that have driven commodity prices to current levels e.g., U.S. Planting Intentions, U.S. Grain Stocks, Southern Hemisphere soybean crop size, and now a reminder on where U. S. exports stack up for corn, wheat, and soybeans. Current projections for new crop corn, wheat, and soybean prices are around $2.45 for corn, $2.85-$3.00 for wheat, and $5.75 for soybeans (basis Chicago), assuming normal crop development. *

 

Frost/Freeze Symptoms on Winter Wheat - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

This continues an article on the effects of frost on winter wheat that I began last week. I will cover symptoms of damage to wheat heads, wheat stems, and finally leaves.

Head Damage: Wait at least 5 to 7 days after the frost or freeze to make a valid assessment of the damage to the head. If the weather remains very cold, it could be as much as two weeks before an accurate assessment can be made.

For heads (the growing point) still in the boot (surrounded by the leaf sheaths), you will need to either cut with a sharp blade into the stem lengthwise to find the growing point or you will have to carefully unroll the leaf tissue that surrounds the growing point. Examine the tissue and locate the last node or swollen stem section. The head is located just above the uppermost node. For wheat still early in the reproductive cycle (early jointing), a hand lens may be needed to see the developing wheat head that will be very small.

An undamaged head will be yellow-green, turgid or firm, glossy in appearance, and plump. A damaged or killed head is initially white in color but becomes pale white, tan or cream colored later. It will be limp, dehydrated, have a flatter shape and when compared with undamaged heads, it will appear to not be developing in size. Stem growth will stop if the growing point has been killed. After two weeks, these stems with killed growing points will be readily visible. A stem or tiller with a live, developing head will have new green leaf tissue emerged at the top of the stem. Otherwise, the young growth at the top of the stem will be chlorotic (yellowed) and necrotic (dead/dying) or be absent.

Stem Damage: Most often this occurs to the lower stem area so to check for this type of damage, remove the lower leaves and leaf sheaths to expose the stem. Damage symptoms include discoloration, lesions, rotting, splitting, collapsed internodes, and either stem bending or lodging. The nodes may enlarge and turn a brownish color. When the lowest most node above the soil level bends to form an elbow shape, the symptom of freeze damage is called bent elbow syndrome.

If severe damage occurs to the stem, the disruption in water and nutrient movement can kill the growing point. Lodging or bending will occur within a few days after a freeze.

Less severely damaged stems may not lodge for 2 to 3 weeks. These stems at first will appear whitish to bleached in color but turn brownish to a darker discoloration as stems deteriorate. Often the stem will collapse giving a flatten look.

Stems that are only slightly damaged can easily be overlooked. These plants do not often recover well and the stem will continue to weaken and deteriorate. Lodging may not occur until near maturity as the head increases in weight. The continued decline in stem health may cause the head to die or may interfere with translocation of nutrients and water to the developing grain. To identify these stems, look for small areas of discolored lesions on the internodes or discoloration at the nodes. Secondary infection with microorganisms can increase the damage.

Leaf Damage: This can occur at any growth stage but is most likely on lush, rapidly growing wheat. Leaf damage symptoms are very visible and can be seen shortly after a freeze. For a severe freeze, leaves show a dark, water-soaked appearance. When temperatures were marginal, leaves may only show a whitish cast. Most damaged leaves will become chlorotic (light green to yellow), twisted, crinkled, and necrotic or burned at the tip within a few days.

Leaf damage may slow growth for a short period; but, with warmer temperatures, new leaves will emerge if the growing point is not damaged. Leaf burn itself has only slight or no effect on yield. If damage has been extensive at the top of the canopy, new leaves may have difficulty emerging although the new growth should break through the damaged tissue. Leaves will appear to be crinkled. *

 

Reminders for Readers of Weekly Crop Update Who Are Accessing From The Web - Tracy Wootten, Extension Associate - Vegetable Crops; wootten@udel.edu

We will send an e-mail reminder that the current issue of Weekly Crop Update is on the website each week to those of you who wish to receive one. I know that those who do get the Weekly Crop Update from the webpage have concerns that in the middle of the season you may forget to access the newsletter. I have set up an e-mail mailing list for those who would like a reminder. If you are interested in being placed on this list, please call me at 302-856-7303 ext. 312 or e-mail me at wootten@udel.edu with your current e-mail address. *

 

Black Cutworm – Pheromone Trap Catches – 1998 Season

Data Provided by Terra Inc., Bridgeville, DE

Data also available at www.udel.edu/IPM

Trapping Period : April 3 – April 10. 1998

Location

#Moths/7 Days

Location

#Moths/7Days

American Corner, MD

4

Lewistown, MD

9

Argos Corner, DE

0

Magnolia, DE

5

Atlanta, DE

4

Mardela Springs, MD

0

Berlin, MD

0

Marydel, MD

0

Bethel, DE

2

Milford, DE #1

12

Bridgetown, MD

3

Milford, DE #2

0

Bucktown, MD

6

Millsboro, DE

1

Burrsville. MD

0

Milton, DE

0

Cambridge, MD

1

Newark, MD #1

3

Clarksville, MD

1

Newark, MD #2

0

Dagsboro, DE #1

2

New Church, VA

8

Dagsboro, DE #2

0

Oak Orchard, DE

0

Delmar, DE

6

Pocomoke, MD #1

4

Denton, MD

5

Pocomoke, MD #2

2

Easton, MD

6

Preston, MD

3

Eldorado, MD

1

Public Landing, MD

0

Ellendale, DE

0

Queen Anne, MD

4

Farmington, DE

0

Redden, DE

0

Federalsburg, MD

4

Reeds Grove, MD

2

Frankford, DE

1

Reliance, MD

6

Georgetown, DE

5

Rhodesdale, MD

7

Goldsboro, MD

7

Ridgely, MD

1

Greenwood, DE

3

Seaford, DE #1

5

Harmony, MD

8

Seaford, DE #2

5

Hurlock, MD #1

3

Selbyville, DE #1

2

Hurlock, MD #2

8

Selbyville, DE #2

1

Laurel, DE # 1

5

Snow Hill, MD #1

0

Laurel, DE # 2

9

Snow Hill, MD #2

5

Laurel, DE # 3

6

Snow Hill, MD #3

7

Leipsic, DE

6

Trappe, MD

2

Lewes, DE

0

Vernon, DE

6

   

Wyoming, DE

4

 

Weather Summary

Week of April 10 to April 16

Rainfall:

0.65 inches: April 10

0.13 inches: April 15

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

Air Temperature:

Highs Ranged from 76 F on April 16 to 49 F on April 10.

Lows Ranged from 53 F on April 15 & 16 to 31 F on April 12 & 13.

Soil Temperature:

52.3F average for the week.

(Soil temperature taken at a 2 inch depth, under sod)

 

Compiled & 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.


University of Delaware Research & Education Center Website:     http://www.rec.udel.edu

IPM Web Page:   http://www.udel.edu/IPM

Hit Counter