Volume 6, Issue 7                                                                                            May 8, 1998


Vegetables

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

Melons.

As melon plants are transplanted in the field, be sure to check for melon aphid populations that may have started in the greenhouse. A treatment should be applied if 10 to 20 percent of the plants are infested and you see leaf curling. Lannate will provide control.

Peas.

Although pea aphid populations have not exploded, we continue to see an increase in activity. Once fields reach the bud stage, fields should be scouted one to two times per week for aphids. The treatment thresholds are 5-10 per plant or 50 per sweep. Dimethoate, Lannate or Penncap will provide control.

Potatoes.

Adult Colorado potato beetle activity remains light except in areas where volunteer potatoes can be found. No adult treatments will be needed unless you find 25 beetles per 50 plants and 20% leaf defoliation. European corn borer activity remains below 5 per night in most areas except in the Bridgeville area where catches have increased to 12 per night. Once moth counts reach 20 per night, fields should be scouted for infested terminals and treatments applied when 25% of the terminals are infested. If you are unable to scout, the first corn borer spray should be applied 7 to 10 days after trap catches reach 20 moths per night in your area.  *

 

Starter Fertilizers for Transplants and Initial Watering When Transplanting - Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

Thousands of vegetable transplants are being set out across Delmarva right now. It is important to water the transplants while still in the flat to help ensure adequate moisture as that plant begins its new life in the soil. Additional water is often applied through the transplanter during transplanting, which is also beneficial. The goal is to make sure the root system can supply the top of the plant with adequate moisture, which goes a long way to reduce transplant shock. Be careful that the shot of water through the transplanter does not wash away soil from the roots, thereby exposing them to the air. This situation hurts the young plant.

We are often asked whether starter fertilizer pays off. It really depends on the conditions. In bare ground, when it’s cold, starters can help the transplant get off to a quicker start. Under plastic, where the fertilizer is right there, the soil is warm, and the soil moisture conditions are excellent, starter may not be a factor. The most important thing is to follow directions listed on the label for commercially prepared starters. Many growers use 30% nitrogen solution as an inexpensive starter to mix with the transplant water. 30% solution should be mixed at 1 pints/ 50 gallons of water.

Starters are often not necessary when transplants have been adequately fertilized while in the greenhouse. Recent work from Florida on tomatoes and peppers indicate yield differences can be achieved with good nitrogen fertilizer programs in the greenhouse. *

 

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

Late Blight Report

May 7, 1998

Location/

Emergence Date

DSV's May 4

DSV's May 7

Recommendations

Baldwin - 4/20

12

21

5-day, low rate

Jackewicz - 4/20

12

21

5-day, low rate

Zimmerman - 4/23

6

23

5-day, low rate

Baker - 5/1

0

18

5-day, low rate

All potatoes in Delaware that have emerged since May 1 and earlier have accumulated 18 DSV’s or more. Fungicide spraying should begin at this time with a low rate of a protectant fungicide such as mancozeb ( Dithane, Penncozeb, Manzate), metiram (Polyram) or chlorothalonil (Bravo, Terranil).

The Late Blight Report is also posted electronically at the UD Extension IPM website: http://www.udel.edu/IPM *

 

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

Cucurbits.

As early transplants of muskmelon, squash or watermelon go the field, they are at risk of developing scab. This fungal disease is favored by cool wet weather. To control, apply a chlorothalonil product (Bravo or Terranil) every 5 to 7 days.

Tomatoes.

Bacterial diseases of tomatoes can be a problem in greenhouses and be carried to the field. If transplants are still in the greenhouse, remember that an infectious disease will start in a pocket of one or a few plants and spread to other plants nearby. Plants that are being hardened off, may appear yellow or even have chlorotic spots. These will not appear in foci, but be more widespread in the house or on the wagon. If you are concerned that bacterial is present, a spray containing copper (such as Bravo C /M or fixed copper ) can be applied shortly after transplanting. *

 

  Field Crops

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

Alfalfa.

Pea aphid activity remains high in many fields; however, beneficial activity appears to be keeping populations below economic levels. Alfalfa weevil populations are light to moderate and in many cases cutting will be the best control option at this time. Once alfalfa reaches 18-inches in height, the treatment threshold is 2 to 2.5 larvae per stem. If a field is in full bud, it is approaching threshold and you plan to cut in the next 3 to 5 days, cutting will be the best control option. If you are unable to cut for the next 7 – 10 days and economic levels are present, Baythroid, Warrior or Imidan will be your best control options. All 3 products have a 7-day wait until harvest for use as hay.

Small Grains.

In fields that were not treated earlier, we are starting to see any increase in cereal leaf beetle activity. At this time, the treatment threshold is 0.5 larvae per stem. Once fields reach the hard dough stage, no treatment will be needed for cereal leaf beetle. Many people have commented on the increase in "bird activity" over barley fields. In some years and in some cases, it is a good indication of armyworm activity. However, it does not appear to be the case this season. Although we have seen a slight increase in armyworm activity in barley, populations are still well below the economic threshold level of one per foot of row in most fields. You may still find hot spots of economic infestations so all barley and wheat fields should be checked during the next two weeks for armyworm larvae. What we are generally finding in barley are high populations of syrphid fly larvae. These larvae are beneficial insects, which are feeding on any remaining aphids. At first glance they may look like small armyworm larvae because they often have bright colored patterns on the topside of their bodies. However, if you look at them closely you will see that they do not have a head or legs – characteristics typical of fly larvae. In many cases, you can find high numbers in lodged areas so do not confuse them with armyworm larvae. Grass sawfly larval populations have also increased in wheat. Fields should be checked and treatment applied before stem clipping is twice the worm count. The treatment threshold is 0.4 larvae per foot of row. If both worm species are present, Lannate or Warrior can be used on wheat. In barley, only Lannate is labeled. Parathion can be used for both insects in barley and wheat but can only be applied by air and has specific setback restrictions. *

 

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

Small Grains.

Powdery mildew continues to be the most important disease present in wheat. If wheat has flowered, fungicides will not be of much benefit. Some reports of unsatisfactory fungicide performance have surfaced and I wanted to give a few possible reasons why the fungicides may not have lived up to expectations. First of all the weather pattern has been very favorable for disease development. The temperature conditions have been ideal. Powdery mildew does not need free water to be able to germinate and infect leaves like other fungi. The high relative humidity (85-100% RH) is all that is necessary. So the fungus has had an edge from a weather perspective. If fungicides were applied, materials like Tilt are best as protectants not eradicants. Very heavy infection pressure combined with ideal weather conditions for the fungus may overwhelm the fungicide. What is also often overlooked is the fact that at the time of a fungicide application infections can have taken place but no visible symptoms can yet be seen (latent infections). Most of those infections will probably continue or slow down and symptoms may be seen several days later. Tilt applied to infected wheat will slow infections but not kill what is there. It is fungistatic not fungicidal, but it should protect tissue that has not been infected at the time of application. It will slow down the rate of an epidemic in progress. Often powdery mildew that is present at the time of an application will turn from a healthy white to sickly tan color and appear to dry up. Warm (80F or more) and dry weather will also do a lot to slow or stop powdery mildew development.

Other problems in wheat that we are seeing are an increase in the number of fields with symptoms of wheat spindle streak mosaic virus and barley yellow dwarf. These have not been confirmed serologically yet, but are very symptomatic of virus diseases. Fields with wheat spindle streak should be planted to resistant varieties next season. *

 

Pre-Sidedress Nitrogen Testing -Gordon Johnson, Extension Agricultural Agent, Kent County; gcjohn@udel.edu

Now that much of the corn crop is in the ground and many plantings have emerged, it is time to plan for side-dressing season.

In fields that have received recent manure applications or where legume cover crops have been used, the Pre-sidedress Nitrogen Test (PSNT) is a tool that can help corn producers determine how much additional Nitrogen fertilizer (if any) will be needed at sidedressing to produce the desired crop. The PSNT is based on the concept that the soil nitrate level early in the growing season is proportional to the amount of N that will become available during the rest of the growing season from soil organic matter and organic nitrogen sources (such as manure) recently added to the soil.

Soil samples for PSNT’s should be collected from the field immediately before the period of maximum growth rate and nitrogen uptake, approximately 30-40 days after planting, when corn is 10-12 inches high. This is just prior to sidedressing. Samples should not be taken earlier than this (less than 6") as you may get erroneous results: earlier sampling likely will result in underestimating the amount of N available from manure or other materials in the soil. It is also important not to sample just after heavy rainfall as nitrate levels will be temporarily depressed.

Take 15-20 soil cores to a depth of 12 inches from the field to be tested when corn is 10-12 inches high. Take cores from the middle of the row to avoid any fertilizer bands laid down at planting. Combine the soil cores and mix thoroughly. Spread the soil thinly on a newspaper in warm place to dry. It is very important to dry the samples as soon as possible to minimize any changes in the soil nitrate levels prior to analysis. If samples cannot be dried immediately then refrigerate until they can be dried.

Results from the nitrate test along with realistic yield goals, starter N applied, and adjustments for manure application rate and timing are used to determine the amount of sidedress N needed.

PSNT’s are done by the University of Delaware Soils Lab, the Conservation Districts in Kent and Sussex Counties, and can also be run at your county extension offices. The Conservation Districts have been doing many of these samples for minimal fees for the last several years. If you want to know more about PSNT’s, contact the extension agriculture agent in your county. *

 

Soil-Applied Herbicides Need Water - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

Herbicides applied to the soil surface require rainfall or irrigation to move them into the soil where the plants will absorb them. The amount of water needed to "activate" these herbicides depends on the water solubility of the herbicide and moisture content of the soil. Most soil-applied herbicides require 0.5 to 0.75 inches to be moved in the soil. Princep requires 0.75 to 1.0 inches of water to become "activated". If you have irrigation and your corn herbicides have been applied, but you have not received at least 0.5 inches of water, you should consider applying that amount with your system. This is one situation where spending a little money now could save money later. For instance, if your residual grass herbicide is not moved into the soil and grass control is poor, you are looking at an expensive postemergence application of Accent or Accent-containing pre-mix. Spending the money to irrigate and activate the herbicides could save a high herbicide bill later. *

 

Select Herbicide Label Is Expanded - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

The postemergence grass herbicide Select, from Valent, is now labeled on alfalfa, dry beans, and tomatoes. Select is very good on most annual and perennial grasses. Select does not control any broadleaf weeds. Use rate is typically 8 oz/A and requires the use of crop oil concentrate. Refer to the label for specifics. *

 

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

Wet Weather Poses Near Term Pricing Opportunities for New Crop Corn and Soybeans.

Corn planting progress reports may be somewhat deceiving this week. With 39 % of the 1998 U.S. corn crop reported planted as of May 3rd, we are actually ahead of the 30 % national average for the first of May. The problem is that since these numbers were reported things have slowed a bit due to wet planting conditions. Iowa is the only one of the three "I" States that is slightly ahead, in planting, of their five-year average progress. Private forecasters were calling for heavy rains in the eastern portion of the Midwest corn-belt for the middle of this week.

What does this information imply for grain marketers? Fact is the U.S. corn and soybean crops will be planted. In some areas (Minnesota is 81 % planted, the highest for this date going back to 1956). The wet conditions that have developed in the Midwest as of this week (May 7th) have presented a ‘window’ of opportunity to consider pricing an additional percentage of the 1998 corn and soybean crops. A Chicago Board of Trade market analyst and trader conferred this morning that we may see at least a 10 cent gain in new crop corn and a 20 cent gain in new crop soybeans. Those needing to price some of the 1998 crop will be wise to take advantage of the opportunity presented, by what is likely to be a temporary lull in planting progress. Next week we will be revisiting an old subject, "Agricultural Options: A Marketing Tool for Weather Markets". *

 

Leaf Wrapping Symptoms on Wheat - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

In the past week, I’ve had calls about and seen a number of fields which are showing unusual symptoms. Most growers are spotting it when the wheat head gets partially stuck in the flag leaf collar and becomes bent in almost a U shape. When you examine the plants closely, the flag leaf wraps or spirals around the wheat stem and the flag leaf blade is curled in a cork-screw fashion near the base of the blade. Within a field, plants that were headed or had a nearly fully-emerged flag leaf did not show these symptoms.

There has been some speculation that the problem is a copper (Cu) or manganese (Mn) deficiency. I do not think that is the cause for the symptoms. I will describe Cu and Mn deficiency symptoms below and explain why I do not think that they fit the situation. But first, what do I think is the cause. Early last week we had some very cold night temperatures and in some areas at least pockets of frost. I have seen this combination of symptoms once before and they were associated with frosted fields or frost pockets at or near flag leaf development. My answer then is that this is frost or cold damage that occurred during flag leaf development and growth. It appears that the cold damages one side of the leaf’s growing point and this causes the spiraling growth of the flag leaf’s leaf sheath and the rolling or curling of the leaf blade. The twisted growth makes it difficult for the head to emerge from the boot and results in the U-shaped crook in the emerged head where the tip is stuck in the leaf collar of the flag leaf.

You should also know one other thing. The tendency for the head to get stuck in the leaf collar of the flag leaf is variety dependent and not always associated with cold damage. I checked in the variety trials and found a number of wheat varieties that show this symptom. These included Northrup King brand Coker 9663, Southern States brand FFR-555W, Jackson, and several more. Is this a problem? No, the varieties grow out of it usually before you see the anthers emerge (when the pollen is released). It has not been associated with reduced yields since the above listed varieties always do very well in the variety trials and often are among the top-yielders.

What isn’t it? First, let me describe Cu deficiency. Copper deficient plants are light green, with dry and twisted leaf tips. Chlorosis or yellowing and bleaching are followed by death and further curling and twisting of the leaf tips and margins. Delayed maturity, shriveled grain, and distorted, twisted, incompletely emerged heads and awns (meaning they are not fully emerged from the boot) may be seen. Roots of affected plants are stunted, excessively branched, and rosetted. Nodes may be darkened.

How do these symptoms differ from those we see in the field? The leaf curl has been primarily near the leaf base NOT at the leaf tip. In the plant’s I’ve seen with the leaf rolling, the color has been good and not the very light green of Cu deficiency and the leaf tips were not burned, dry, and twisted. The heads although caught for a while in the flag leaf’s collar continue to grow and emerge completely out of the boot. Another thing to keep in mind is that Cu deficiency is extremely rare and, with the wide spread use of poultry manure, our soils are not likely to be deficient in Cu.

What about Mn? Manganese deficient plants are chlorotic and slow to mature. The plants develop small, roughly circular, gray-white spots on the older leaves. When the deficiency is severe, these may coalesce forming gray-white streaks between the veins and can even be on the younger leaves. Leaves may kink or droop at the base of the blade or wherever the spotting is intense. The only possible similarity with the symptoms I’ve seen is the word kink. By kink, the description means that the leaf bends down not twists into curls. Obviously, Mn deficiency is not the cause of the symptoms I have been seeing. *

 

Sulfur and Magnesium Deficiencies on Wheat - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

I was called by a county ag agent to look at a wheat field that suddenly turned yellow after a second nitrogen application. He had taken a tissue test but the results indicated only that sulfur (S) was a little below the normal range (about 5 percent) and magnesium (Mg) was 20 percent below the bottom end of the normal range. The nitrogen (N) concentration was very good. What had been overlooked by the lab was the nitrogen to sulfur (N:S) ratio. This was over 50 percent higher than the maximum expected in normal wheat samples.

On walking through the field, we saw that the soil was a very fine sand with very little clay in it. A section of the field that was a heavier soil did not show the same level of symptoms although there were scattered spots evident. In the lighter portion of the field, we could see areas that were more severely affected as well as some striping across the field in the direction the sprayer had run. In one stripe where the sprayer had failed to overlap and little to no additional N was applied, the wheat was still green. In the severely affected areas, the wheat was generally yellow in color, stunted, and delayed in development. The symptoms were classical S deficiency. To complicate the problem, ammonium sulfate at 100 lbs per acre had been applied to the wheat in the fall. I speculated that the combination of heavy fall, winter, and spring rainfall and the very sandy nature of the soil moved the S below the rooting zone of the wheat. When the second shot of N was applied, it caused an imbalance in the N:S ratio and lead to the development of the symptoms we saw.

In a few areas where the symptoms were not as severe, we also saw evidence of Mg deficiency. This shows up as very distinct interveinal chlorosis (yellowing) usually on the older leaves first. The veins remain very dark green giving the leaf a distinct banded (green:yellow:green:yellow) appearance. It also can causes stunted plants. Both the soil test and tissue test indicated, Mg levels were low in the field. The next time the field is limed, dolomitic limestone should be used.

When we discussed the conclusions with the farmer, he offered some confirmation of the diagnosis. In an area with similar symptoms but located near potatoes, wheat that had recently received some ammonium sulfate when fertilizer was spread on the potatoes looked green and healthy.

What could be done about it? Small grains that are deficient in S yield poorly so even a late application to provide S may improve yields. However, the expected yield improvement needs to be evaluated against the price of wheat, the cost of another trip across the field, and the cost of fertilizer. The most effective way to apply both S and Mg is a foliar application of calcium and magnesium sulfates (Epsom salts but industrial or fertilizer grade) at about a 2 percent solution (weight to weight). The solution should be applied at a very high gallonage. Yes, ammonium sulfate will also work but to prevent burn it needs to be supplied as a solid material, the rate raises your costs, and the addition of more nitrogen is not useful or environmentally responsible. *


UpComing Events:

Strawberry Twilight Meeting

University of Maryland Wye Research and Education Center

Cheston Lane

Queenstown, Maryland

Thursday, May 14, 1998

6:00 p.m.

What You Will See:

Annual Plasticulture, 10 varieties and 15 breeding lines; June Matted Row Trial,12 varieties and 11 breeding lines

Who Will Be With Us:

Plant Breeders: Dr. Joseph Fiola, Rutgers; Dr. Stan Hokenson, USDA; Dr. Gene Galletta, USDA (retired) plus University of Maryland Specialists

 

Small Grains Diagnostic Field Day

University of Delaware Research and Education Center

May 21, 1998

7:30 a.m. - 1:00 p.m.

Three Certified Crop Advisor Continuing Education Units (CEU) earned.

Pesticide recertification credits earned.

Prior registration required 302-856-7303.

Registration deadline: May 15.

 

Small Grain Troubleshooting for Producers

University of Delaware Research and Education Center

May 21, 1998

3:00 p.m. - 5:00 p.m.

Prior registration required 302-856-7303.

Registration deadline: May 15.

Pesticide recertification credits earned.


Weather Summary 

Week of May 1 to May 7

Rainfall:
0.25 inches: May 2
0.05 inches: May 4
0.20 inches: May 5
0.15 inches: May 6
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 77 F on May 4 to 62 F on May 2.
Lows Ranged from 58 F on May 2 to 50 F on May 7.
Soil Temperature:
63 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


Black Cutworm – Pheromone Trap Catches – 1998 Season

Data Provided by Terra Inc., Bridgeville, DE

Trapping Period : April 24 – May 1

UD Extension IPM website: http://www.udel.edu/IPM *

Location

#Moths/7Days

Location # Moths/7Days
American Corner, MD

6

Lewistown, MD

5

Argos Corner, DE

8

Magnolia, DE

2

Atlanta, DE

1

Mardela Springs, MD

4

Berlin, MD

2

Marydel, MD

5

Bethel, DE

0

Milford, DE #1

21

Bridgetown, MD

3

Milford, DE #2

0

Bucktown, MD

8

Millsboro, DE

7

Burrisville. MD

0

Milton, DE

4

Cambridge, MD

6

Newark, MD #1

2

Clarksville, MD

2

Newark, MD #2

7

Dagsboro, DE #1

12

New Church, VA

26

Dagsboro, DE #2

2

Oak Orchard, DE

2

Delmar, DE

9

Pocomoke, MD #1

13

Denton, MD

6

Pocomoke, MD #2

4

Easton, MD

5

Preston, MD

5

Eldorado, MD

2

Public Landing, MD

4

Ellendale, DE

0

Queen Anne, MD

0

Farmington, DE

0

Redden, DE

4

Federalsburg, MD

1

Reeds Grove, MD

2

Frankford, DE

16

Reliance, MD

1

Georgetown, DE

3

Rhodesdale, MD

17

Goldsboro, MD

8

Ridgely, MD

0

Greenwood, DE

0

Seaford, DE #1

0

Harmony, MD

14

Seaford, DE #2

6

Hurlock, MD #1

2

Selbyville, DE #1

5

Hurlock, MD #2

4

Selbyville, DE #2

6

Laurel, DE # 1

4

Snow Hill, MD #1

0

Laurel, DE # 2

3

Snow Hill, MD #2

13

Laurel, DE # 3

5

Snow Hill, MD #3

9

Leipsic, DE

2

Trappe, MD

1

Lewes, DE

3

Vernon, DE

2

    Wyoming, DE

1


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.


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