Volume 6, Issue 24                                                                                  September 4, 1998


Vegetables

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

Lima Beans.

Corn earworm larvae can be found ranging in size from " to one inch long. Controls are needed if you find one larva per 6 foot of row. The rate of Lannate will depend on the larval size at the time of treatment. If worms are small, 1.5 to 2 pts per acre will be adequate. However, if the worm size is mixed at the time of treatment, 3 pts/acre will be needed.

Peppers.

All peppers should be sprayed on a 7-10 day schedule for corn borer, fall armyworm and aphid control except in the Bridgeville area where sprays are needed on a 5-7 day schedule. Be sure to check the Crop Pest Hotline for the most recent trap catches in your area. Lannate or Orthene are the preferred materials at this time.

Snap Beans.

Processing snap beans should still be sprayed at the bud and pin stages with Orthene for corn borer control. Asana should be combined with Orthene at the pin spray to control corn earworm. In Kent County, sprays are needed on a 6-day schedule from the pin stage through harvest. In the Greenwood area, sprays are needed on a 5-day schedule after the pin spray. In the Bridgeville area, sprays are needed on a 4-day schedule from the pin stage through harvest. Be sure to check the Crop Pest Hotline for the most recent trap catches in your area.

Spinach.

Webworms and beet armyworm can both be found feeding in spinach fields throughout the state. In most fields, webworms are the predominant species at this time. Since Spintor may be in short supply, you should consider using Ambush, Pounce or Lannate if webworm is your predominant pest. Remember that Lannate can not be used on spinach that is less than 3 inches in diameter. Controls for webworms should be applied before significant webbing has occurred. If the beet armyworm is the predominant species, Spintor should be used.

Sweet Corn.

Fresh market silking sweet corn should be sprayed on a 2-3 day schedule throughout the state. Be sure to check the Crop Pest Hotline for the most recent trap catches in your area. *

 

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

Spinach.

For fall planting be sure to rotate away from spinach for 2 years to avoid white rust and apply Ridomil Gold as a pre-emergence spray application for control of pre-emergence damping-off and early season control of blue mold and white rust.

Snap beans.

Be on the lookout for bean rust. Rust can be a problem on fall-planted crops. Planting resistant varieties for the fall crop is the best control, but if rust should appear spray with Bravo every 7 days. Rust is easily identified by the presence of small, yellow, circular spots with a reddish-orange, powdery spore mass in the center.

Lima beans.

Remember that favorable weather in the fall can mean downy mildew. If 1.2 inches of rain falls within a 7 day period and the average daily temperature is 78 F, downy mildew can occur on a susceptible variety if the fungus is present. If a period of 90 F occurs during this time, the disease will not develop. Keep an eye on the weather and spray accordingly with tri-basic copper sulfate.

Cucurbits.

Virus diseases have been a problem in late plantings of cucumbers, summer and winter squash and pumpkins. Mottling, strapping and deformities on leaves and fruit have been seen. Avoid planting near other cucurbits and strict aphid control can help, but have not been very effective. Plant breeders are incorporating resistance to more viruses and that will be the key to control in the future. Watermelon mosaic virus is the most common virus that we see in the fall on cucurbits and the one that breeders are trying to develop resistance against.

 

Be on the lookout for foliage diseases on pumpkins. Maintain sprays of chlorothalonil (Bravo, Terranil) for foliage and fruit disease control. Where powdery mildew is a problem spray with Bravo plus Nova and alternate weekly with Quadris. Quadris will give good control of powdery mildew and black rot, but we do not know how effective it may be for downy mildew. The best program for downy mildew is preventative sprays with chlorothalonil or Ridomil/Bravo. The recent hurricane weather may have brought up downy mildew spores from the south. If they survived and we get favorable weather for disease development, growers will want to have a fungicide in place for downy mildew control.

Fall sampling for nematodes in vegetable crops.

Fall is the best time to determine nematode levels in production fields. Nematode levels are usually the highest in the fall following harvest. This is particularly true if root knot nematode is a potential problem. Melon growers particularly are encouraged to sample fields for next years production after fall harvest. Spring samples are not reliable in detecting damaging levels of root knot nematode. Sample directions and nematode test bags are available from each county Extension office. This inexpensive test can pay big dividends, so as the soil test folks say, Don't guess, Soil Test.   *

 

Vegetable Diseases - Kate Everts, Extension Plant Pathologist, University of Maryland and University of Delaware ; everts@udel.edu ; Phil Shields, University of Maryland, ps136@umail.edu

MELCAST for Fungicide Application on Watermelons.

Do not use MELCAST if there is a disease outbreak in your field, it is a preventative program. Below are the EFI values from weather stations located on the Eastern Shore August 25- August 31. Any questions please call Phil Shields at (410) 742-8788 or e-mail: ps136@umail.umd.edu

EFI Values

Location

8/25/98

8/26/98

8/27/98

8/28/98

8/29/98

8/30/98

8/31/98

U of M, LESREC
Salisbury,MD

1

1

6

6

5

4

4

Wootten Farms, Galestown,MD

0

0

3

6

4

3

4

Mark Collins, Laurel, DE

0

3

5

7

4

5

5

U of D, REC Georgetown, DE

1

1

2

3

1

1

1

Vincent Farms Laurel, DE

0

1

6

5

6

4

5

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

Soybeans.

Corn earworm pressure remains below threshold level in most fields with larvae ranging in size from to one inch long. In most cases, very little pod feeding has been found. Corn earworm trap catches continue to increase so you can expect to see an increase in larval activity during the next week to 10-day period. Controls will not be needed until you see the first signs of pod feeding and you find 3 larvae per 25 sweeps in narrow row beans or 5 per 25 sweeps in wide row soybeans. We have received a number of questions regarding whitefly activity in soybeans. Although they can be a significant pest in snap beans and lima beans, we have not seen any problems in soybeans.  *

 

Alfalfa’s Critical Cutoff Date for Harvest - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

Following the rains some received from the hurricane/tropical storm last week, enough alfalfa regrowth can occur in the next two weeks to justify one more harvest. Growers should keep in mind that alfalfa requires about a period of six weeks of regrowth before a killing frost. This means that in the northern and central portion of the state, the last harvest should occur no later than September 15 and, in the southern portion of the state, no later  than September 20. This rest period is necessary for alfalfa to store enough energy reserves to survive the winter and begin growth next spring.

Sometimes when temperatures are favorable enough regrowth occurs that an additional harvest after a killing frost can be obtained. Research at the Delaware State University has shown that, in general, the amount of forage harvested in this dormant season harvest is the amount of reduction seen in the first spring harvest or, to put it another way, the amount that is left after a killing frost (no additional harvest) is added to the expected first harvest the next spring.

Another critical factor in alfalfa survival is the late-summer or early-fall application of potash (K2O) as suggested by your soil test results. Potash helps the plants resist the effects of sub-freezing temperatures during the winter. Whenever possible split potash applications with the first half applied after either the first or second harvest and the last half applied after the August or early September harvest. Remember that alfalfa is a very heavy user of potash fertilizer. Soil test potash values should be closely monitored to be certain you have adequate potash available to the crop. *

 

Small Grain and Cover Crop Planting Season - Richard W. Taylor, Extension Agronomist, rtaylor@udel.edu; Bob Uniatowski, Extension Associate-Field Crops, bobuni@udel.edu

Already we are seeing some corn fields being harvested and especially where drought severely damaged the corn. Some of these fields will be planted into small grains and some may be planted with small grains as a cover crop. For a cover crop, cereal rye is most frequently used. You should keep in mind though that rye is a host crop for Hessian fly just as is wheat, barley, and triticale. To minimize the chances of damage from Hessian fly, these crops should not be planted until after the fly-free date. The only crops that can be planted in September without encouraging this pest are winter and spring oats and the cole crops such as winter rape. Both oats and winter rape if planted by mid-September will grow enough to tie up a significant amount of nitrogen fertilizer that may remain in the soil. In most winters, spring oats will be winter killed during the winter and will form a nice mulch to no-till into next spring. Winter oats will usually survive unless the winter is unusually severe and will need to be killed with herbicide or plowed under next spring. Winter rape will react similarly to the winter oats.

For small grain planting, our research has shown that barley should be planted between the first and second week of October for maximum yields. Planting in late-September actually resulted in slightly lower yields. After the second week of October, barley yields decreased rapidly (from 1 to 2 bu/A/day) until mid-November. Barley survival is problematical by late-November. Wheat does best when planted as near as possible to the fly-free date but yield reductions from delayed planting are not as dramatic as with barley. Still by November, yield potential is declining rapidly and the decision to plant that late should take that into account to determine if it makes economic sense to plant late. 

Variety selection is an important consideration. In the 1998 Small Grain Variety Performance Trial report we found that for barley across locations for long-term yields, the best varieties were Starling, Pennbar 66, and Pennco. Acton did well in all but the middle of the state. Callao did especially well at the Kent County location but also at the Georgetown location. Nomini still does well at the Middletown location. For wheat across locations, the best varieties for long-term yields were Jackson and Northrup King brand Coker 9663. Varieties new to the trials that did well at all three locations were Southern States brand FFREXP3409D, Quantum brand 706 and 7203, Pioneer brand 2540, and Roane.

Finally and maybe most importantly, check small grain bags or certification tags for the germination percentage and whether the seed was treated with one of the fungicides. Small grain seed from many areas is showing poor germination especially for untreated seed. Test weights were also very low last year and the seed may not flow through drills as it does in more normal years. Be certain your seeding rate is correct and takes into account the germination rate and purity percentage. If you save your seed, a germination test will be critical to know if the seed will be acceptable or not. Sometimes germination can be improved with seed treatments but do not use saved seed if the germination is below about 70 percent. When germination is low, plant vigor is often low too and can adversely affect the crop. Instead of using poor quality saved seed, buy new seed of proven quality this year.  *


Weather Summary

Week of August 27 to September 2

Rainfall:
0.41 inches: August 27

0.25 inches: August 28

Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 91F on August 29 to 82 F on August 28.
Lows Ranged from 75 F on August 27 to 64 F on September 1.
Soil Temperature:
80 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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