Volume 6, Issue 14                                                                                          June 26, 1998


Vegetables

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

Crop Pest Hotline.

Be sure to check the Crop Pest Hotline Report for the most recent nightly moth catches to help you time corn borer and corn earworm sprays on peppers, snap beans and sweet corn. You can receive this information by calling in-state: 1-800-345-7544; out-of state: 1-302-831-8851; or on our webpage: www.udel.edu/IPM. Information is updated on Tuesday and Friday by Noon.

Peppers.

In areas where corn borer catches are above 2- 3 per night, peppers should be sprayed on a 7 – 10 day schedule. If Orthene is used, a 10-day schedule will be adequate and it will also provide pepper maggot control. If a pyrethroid or Lannate is used, sprays should be applied on a 7-day schedule. Dimethoate should be added to the mix for pepper maggot control.

Potatoes.

We are starting to see an increase in Colorado potato beetle adult activity. If the predominant life stage is small and large larvae, Kryocide/Cryolite or Agri-Mek should be used. Once you see a significant increase in adult activity (50 per 100 plants), then Provado should be used.

Agri-Mek has received an aerial application label for potatoes.

Potato Leafhoppers Alert.

See comments under the field crop section

Snap Beans.

All processing snap beans should be sprayed at the bud and pin stages for corn borer control. Orthene should be used at a rate of 1 1/3 lb per acre for corn borer control. This rate will also provide potato leafhopper control. Starting at the pin stage, fresh market snap beans should be sprayed on a 7-day schedule with Lannate for corn borer control.

Sweet Corn.

All fresh market silking sweet corn in Kent and Sussex Counties should be sprayed on a 3-4 day schedule and on a 4-5 day schedule in New Castle County. Small fall armyworm larvae continue to be found in the whorls of the latest planted fields. No treatment is needed until you find 15% of the plants infested. In the last 2 years, Larvin (30 oz/acre) or Warrior (3.84 oz/acre) have provided the most consistent control. *

Melons.

Agri-Mek has received an aerial application label for melons.

 

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

Root Knot Nematodes.

Be on the lookout for root knot nematodes. Along with soybean cyst nematode, root knot can be diagnosed in the field by the presence of the nematodes on the roots. Root knot produces swellings on the roots of susceptible crops such as cucumbers, cantaloupes, carrots, beans, and many other vegetable crops. At this time of the season the first indication may be some stunting in irregular areas in an infested field. Digging the plants carefully at this time can reveal the swellings on the roots called galls or knots that form around the developing female root knot nematode. Little can be done after galling is seen. Frequent irrigation can help minimize the damage to the infected root systems. Check for root knot by soil sampling fields to be planted to susceptible vegetables in the fall before planting the crop. Fumigants or insecticide/nematicides such as Vydate can be used before planting to reduce the nematodes. *

 

Late Blight Update

DSV accumulations as of June 22, 1998 are as follows:

Location/Emergence Date

DSV's June 18

DSV's June 22

Recommendations

Baldwin - 4/20

101

116

5-day, mid rate

Jackewicz - 4/20

95

105

5-day, mid rate

Zimmerman - 4/23

65

65

10-day, mid rate

Baker - 5/1

81

93

5-day, mid rate

Note: If you are growing varieties that are susceptible to early blight such as 'Belrus' or 'Conestoga' , you should be using the high rate of the protectant fungicide you are now using. Early blight is starting to show up on the older leaves on susceptible varieties now. We disabled the early blight component of WISDOM to get the spray schedule information for late blight protection only. Early blight is generally not a problem on 'Superior' and many other varieties that are grown here.

Late blight has been identified and confirmed on tomatoes in Caroline County, MD. This should not be a concern if you have been spraying on a regular basis. Also, the late blight genotypes that infect tomato do not do not necessarily infect potato, most do not. At this writing I do not know what genotype they have, but the fungus can spread rapidly geographically from tomato patch to tomato patch if the weather is favorable for late blight development and tomatoes are not protected with fungicides. Stay on the protectant spray program and check your fields regularly. 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 ; Phil Shields, University of Maryland, ps136@umail.umd.edu

Quadris on Cucurbits.

I have been asked about the status of Quadris registration on cucurbits. There is a great deal of misinformation going around. Growers have asked why we don’t have a section 18 for use of this product on cucurbits when Texas, Georgia and South Carolina do. In fact these states do not have Section 18’s. Their request (like ours) has not been approved. Use of Quadris in those states is allowed because the states declared a crisis.

Maryland, Delaware and Virginia submitted Section 18 requests for exemption to allow the use of Quadris and Nova on cucurbits several months ago. Due to lack of staff, the EPA has not completed their review on our request. Because it’s apparent that the EPA is unable to process our request, Maryland has declared a crisis, and as of June 25th, the use of Quadris Flowable and Nova 40W are allowed in the state of Maryland. Delaware is also undergoing this process, however, their exemption has not yet been issued. More information on the status of Delaware’s crisis should be available next week.

Quadris may be used within one day of harvest. Do not apply more than four applications, and alternate applications with a fungicide that has a different mode of action. Nova has a 48 hour PHI. It may be applied six times per season, and should also be alternated with fungicides that have different modes of action.

Late blight on Tomatoes

Late blight is present on tomatoes in both Dorchester and Caroline Counties, MD. The disease can affect foliage and fruit. It appears as large brown areas on the leaves. White fungal growth can be observed at the margins of the lesion on the underside of the leaf. This disease can devastate a field in very short time under ideal weather conditions, so apply fungicides immediately to protect plants. Chlorothalonil (Bravo or Terranil), and Quadris can provide control. In Maryland, Tattoo C can be used under a Section 18 specific exemption. EPA recently approved a 24 C request to reduce the PHI of Quadris from seven days to one day (Maryland and Delaware). To control late blight in tomatoes in Delaware, apply Bravo or Terranil at 2 pts/A on a 7 day schedule. Switch to Quadris when a reduced PHI is needed for harvest. In Maryland, apply two applications of Tattoo C at 7 day intervals. Then apply a chlorothalonil product or Quadris alternated with chlorothalonil for additional sprays.

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 June 18 - 24. Any questions please call Phil Shields at (410) 742-8788 or e-mail: ps136@umail.umd.edu

EFI Values

Location

6/18/98

6/19/98

6/20/98

6/21/98

6/22/98

6/23/98

6/24/98

U of M, LESREC
Salisbury,MD

3

4

3

4

6

3

2

Wootten Farms, Galestown,MD

1

4

2

4

6

2

2

Mark Collins, Laurel, DE

1

5

2

2

6

2

2

U of D, REC Georgetown, DE

3

4

3

4

7

4

0

Vincent Farms Laurel, DE

1

3

3

3

5

2

2

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. *


Field Crops

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

Potato Leafhoppers.

Economic levels of potato leafhoppers continue to be found in a number of crops. Alfalfa, lima beans, potatoes, snap beans, and soybeans are all susceptible to attack, especially those in the early growth stage. Both nymphs and adults can be found in fields, with nymphs doing the greatest damage. This insect will shut down plant growth and make the plants appear "scorched". A sweep net is needed to get an accurate estimate of the population level in all crops. Depending on the crop and labeling restriction, dimethoate or a pyrethroid will provide control.

Soybeans.

Potato leafhoppers continue to be a problem in the latest planted fields. If fields are stressed, leafhoppers are active and you can easily find leaf curling and /or hopper burn, a treatment is recommended. A pyrethroid will provide effective control. Begin to watch fields for spider mites, especially in early-planted fields. Look for early signs of mite damage which appears as white stippling at the base of the leaves. Treatment should be considered if you find 20-30 mites per leaflet and 10 % of the leaves show damage. Unfortunately, we still have a limited selection of miticides available for use on soybeans. Dimethoate gave approximately 2 weeks of control in our field trials in 1997 as well as in commercial fields when applied before mites were out of control. Multiple applications (at least 2 if applied early enough) are generally needed when mite populations have exploded. If you plan to use dimethoate, remember you should check the pH and the iron level of the water. Dimethoate breaks down very quickly if the pH and iron content of the water is high. Parathion is still labeled and worked as a contact material in 1997. However, it can only be applied by air and by a limited number of aerial applicators in the area. If we see that mite populations are building like in 1997, we will be ready to apply for a Section 18 for mite control on soybeans. The available Section 18 products will cost at least $20 per application but should provide up to 4 weeks of control. *

 

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

Soybeans.

Soybean cyst nematodes can be seen on the roots of susceptible varieties from 28-34 days after emergence. If you see stunting or irregular patterns in a field, you may want to check for the presence of SCN. White and yellow females can be seen if the stunted plants are dug and not pulled from the soil. The females are attached to the root and can be seen with the unaided eye. They are small, only 3/4 of millimeter, smaller than the nitrogen fixing nodules, but are often very numerous. The females will turn from white to yellow, then dark brown. Once they turn brown, they fall easily from the roots and are much harder to see without the help of a hand lens. They will usually produce three generations here in Delaware. Fact sheets are available from the county offices on SCN, taking soil samples for nematode detection, and selecting SCN resistant varieties.

Septoria brown spot can also be seen on the unifoliate leaves now. This is usually a minor fungus leafspot especially when seasons are dry. Septoria usually causes defoliation of the unifoliate leaves.

Soybean severe stunt virus was also diagnosed this week in a field with a history of SSSV. This is a unique virus of soybeans that is only known to occur in Sussex County, Delaware. Infected plants are very stunted in irregular areas in the field, the leaves will be abnormal, and often superficial reddish-brown lesions can be seen on the stems. Planting resistant varieties or rotating away from soybeans are the only controls. We are evaluating more varieties for resistance to this virus again this season, with a grant from the Delaware Soybean Board. *

 

Not All Buggy Whipping in Corn is Due to Herbicides - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

Buggy-whipping in corn is a common sight early in the growing and season, and later under certain environmental conditions. The cause of buggy whipping is the formation of abnormal waxy leaf layers, and leaves do not unfurl properly. Both agrichemicals and environment can cause this condition. The chloroacetamides (Dual, Harness, Surpass, Topnotch, Frontier, Partner, etc) can all cause this problem. Even with the safeners added to these products, bugging whipping can occur. The common scenario is that the first rain event after application is a heavy rain storm followed by a few days of cool and overcast weather. Corn that has emerged (up to 2-3 collars), before the rain event can also develop this buggy whipping, but the taller the corn becomes the less likely it is to occur. Banvel or 2,4-D in the whorl can cause buggy-whipping.

There is a phenomenon called "accelerated growth syndrome" that Bob Nielson at Purdue University identified as early as 1995, if not earlier. Basically it is unusual twisted growth where the affected plants are tightly twisted, often bent over severely and do not unfurl on a timely basis. Young leaves deep in the whorl continue to grow rapidly, but are unable to emerge from the unfurled upper leaves. The growth stage where this seems to occur is around 5 to 6 visible leaf collars. After the whorls unroll, you may see "yellow tops" across the field. The younger leaves that had been trapped inside the twisted upper leaves are yellow because they had been shaded for quite some time. After a day or two the plants will green up and the problem will not be visible. Yield effects will be minimal, if any. This problem often occurs following a sudden return to optimum growing conditions preceded by a period of poor growing conditions. In the Delmarva region, it appears this is more of a problem with short-season hybrids.*

 

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

Writing vs. Buying Options Alert.

Eastern Shore farmers need to be alerted to the difference between buying versus writing (selling) options. The reason for the alert is the current market situation that appears to be developing into a declining to flat price mode. Typically, when this happens commodity brokers and traders will begin to advocate selling call options. There is a world of difference in buying an option vs. selling or writing an option. In the case of buying an option, the buyer knows the total cost of the option trade when the option is purchased. The maximum loss is equal to the option premium times the number of units purchased in the underlying futures contract. When buying options to acquire price risk protection, there are no margin calls. The worst scenario that can develop is that the option expires worthless and the buyer (farmer) loses the amount of the premium (insurance) paid. Hence, when a farmer buys options the maximum loss is known while the potential gain from favorable price movements is not known.

When farmers sell or write options, the exact opposite is true. The maximum gain is equal to the option premium received from the option buyer and the potential losses are unlimited. If the option moves deep-in-the-money, the amount paid to the option buyer may far exceed the premium, resulting in a large loss to the seller or writer of the option. Option writers must make margin calls if the option premium increases. Option selling or writing only works in the event of a flat commodity price, between the time the option is sold (written) and the time the option expires.

Option writing and buying are very different. Option writing (selling) is only a speculative method of generating additional revenue, and is directly comparable to selling someone insurance. Conversely, option buying is a method of obtaining price risk protection against adverse price changes. Option buying is directly comparable to buying insurance. Option writing generates premium income, while exposing the seller to the potential of large losses. Option buying permits the buyer to benefit from favorable price developments while providing protection against unfavorable price moves. The maximum loss is equal to the option premium.*

Brittle-Snap in Corn: Are You At Risk? Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

Although brittle-snap is most frequently seen in the Corn Belt states where strong frontal systems create intense winds, we sometimes see isolated areas in the East associated with intense thunderstorms that occur during mid-season. In brittle-snap of corn, the stalk breaks near the primary ear node at the lower portion of the rapidly elongating internode. Damage is most likely to be seen in fields that are not well protected from high winds and are oriented in the direction that the intense summer thunderstorms usually travel in your location. The area affected by the storms is often small but damage can be severe often with a third or more of the plants broken off. Susceptibility to the injury is greatest at about mid-season, after side-dressing time and when moisture conditions are favorable for very rapid growth. By tasseling time, the risk of this type of injury is past. In fact, observations from the western Corn Belt indicate that there may only be a window of a few days to a week when the corn is most susceptible to the injury so two fields side by side can be affected differently if planted at different times.

What cultural conditions favor brittle-snap of corn? High commercial nitrogen fertilization rates and heavily manured fields with very high PSNT (Presidedress Nitrogen Test) values are at increased risk. Fields with good growing conditions (i.e. irrigated fields or fields that have received ideal amounts of rainfall) are vulnerable. It is thought that hybrid selection may impact susceptibility but because of the difficulty in evaluating hybrids for brittle-snap susceptibility, this observation may be more strongly related to maturity or at what stage of growth the hybrid is in when winds hit. Planting date also has an effect but can be managed by spreading out the planting dates in fields that may be at risk (unprotected on the side where prevailing winds and thunderstorms frequently come from). Finally, rotation has an effect. Continuous corn seems to be less susceptible than corn grown in rotation with soybeans but this effect is likely explained by the fact that there is more residual soil nitrogen available when corn is rotated with soybeans. If this extra residual soil nitrogen is accounted for in your nutrient management plan, there is less chance that rotation will play a role. *


Weather Summary

Week of June 19 to June 25

Rainfall:
0.30 inches: June 20
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 90 F on June 21 and 22 to 82F on June 20 and 23.
Lows Ranged from 70 F on June 24 to 63 F on June 19.
Soil Temperature:
72 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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