Volume 7, Issue 27                                                                                                                       October 1, 1999

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

 

New Insecticide Registrations :

Admire/Provado - Although not in time for the main use season, we will be able to use this material on all cucurbits next season. It will provide an additional tool for cucumber beetle control and a much needed addition to aphid control.

 

Fulfill - This new insecticide has recently been registered to control aphids on potatoes and other tuberous vegetables. Fulfill represents a new class of chemistry and a new mode of action. It works by causing the insect's mouth parts to "lock up." The

insect stops feeding within hours but remains on the plant for a short time (two to four days). Fulfill stops aphid damage quickly (in two to four hours) and delivers excellent residual control (10 to 14 days in potatoes).  In research trials, it has provided excellent control of our major aphid species including the green peach aphid and the melon aphid.

 

 

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

 

Nematodes in Veggies.

Fall is the best time to soil sample for nematode pests such as root knot, lesion, and other plant parasitic nematodes. After fall harvest but before any fall tillage is done take soil cores six inches deep between plants in the row. Samples should be taken in the root zone of the old crop. Twenty cores/ sample should be taken from random spots in the field and placed in a plastic bucket gently mixed, and a pint of soil submitted for analysis. Nematode test bags and instructions are available for purchase from the county Extension offices. Fall sampling for root knot nematodes is strongly recommended for fields that will be planted in cucumbers, watermelons, cantaloupes, lima beans or other high value vegetables where root knot could reduce production.

 

Root  knot  nematode

 

Spinach.

Cercospora leafspot has been identified in several fields at this time. Spots produced by this fungus are small, circular and often have a reddish brown border. The centers can be tan to brown, but old spots will often have a black to brown felty appearance from the spore bearing structures that are darkly pigmented. Under warm, wet conditions this fungus disease can produce numerous spots that coalesce and can blight entire leaves. Often cutting will remove the infected leaves and copper sprays can be used to protect the new growth from infection.

 

 

Field Crops
 
 

 

 

 


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

 

Wheat.

Each fall I receive numerous calls regarding the value of fall and late winter aphid control in reducing barley yellow dwarf incidence in wheat. We are planning to do 2 to 3 on-farm evaluations this fall but I thought that the following article provided good information on this subject. The entire article was taken from Kentucky Pest News (Sept 13,1999 edition) which is written by Extension Specialists at the University of Kentucky.

 

 

WheatCAN APHID CONTROL REDUCE BARLEY YELLOW DWARF INCIDENCE IN WHEAT?
A case study (Caldwell Co., KY 1998-99)
By Doug Johnson and Lee Townsend

 

Pioneer 2510 wheat was planted using a no-till planter on 22 Oct 1998 following a corn crop on the University of Kentucky Research and Education Center in Caldwell Co. KY. The 4' by 15' plots were arranged in a randomized complete block design with five replications. Fertility was applied as 100 lbs of nitrogen on 26 Feb 99 (Feekes GS 3-4). The treatments included three different insecticide application dates and an untreated control. Two treatments consisted of single applications of Warrior (lambda-cyhalothrin) at 3.2 fl. oz. per acre, made with a backpack sprayer in 26 gal of spray per acre, on 24 Nov 98 (Feekes GS 2-3 ) or 17 Feb 99 (Feekes GS 3). The third set of plots were treated on both dates. These were compared to an untreated control. Regular aphid counts were not made but plots were checked for aphids just before applications were made. Plots were rated for BYD on 5 May 99 (Feekes GS 10) by randomly selecting 50 individual plants and examining them for symptoms. Percent of plants displaying BYD symptoms were analyzed for differences using the SAS GLM. procedure.

 

Significant differences in percentages of plants displaying BYD symptoms, as related to insecticide treatments, were detected (F (3,12 df) = 3.83, Pr>F =0.039) (Table 1). Although very few aphids were seen before the final insecticide application; they were widespread and numerous during the spring.

 

Table 1. Mean percentages (ñ s.e.) of wheat plants showing BYD symptoms in plots treated with Warrior insecticide on selected dates to control aphid vectors of barley yellow dwarf virus.

 

Time of Application

% of plants showing BYD Symptoms +/- SE(1)

No Insecticide

13.2 +/- 5.0 a

24 Nov 98

5.6 +/- 1.0 ab

24 Nov 98 and 17 Feb 99

1.6 +/- 0.4 b

17 Feb 99

3.2 +/- 1.2 b

(1) Means followed by the same letter are not significantly different. p = 0.05. Ryan-Einot-Gabriel- Welsch Multiple range test.

 

Variations in plant stands among plots due to establishment problems prevented valid yield comparisons. The variation due to stand difficulties would not have allowed a fair comparison of the yield effects.

 

The November treatment, often made as an 'insecticide only' application, costs about $11.00 per acre. The February insecticide application is often made in conjunction with other inputs, so the application cost may be saved. Therefore, in this location and in this year, the fall, winter, and combination treatments would have cost $11.00, $ 6.00 and $17.00 respectively.

 

Assuming the entire difference in percentage of plants showing BYD symptoms was a result of insecticide timing, and that a damaged plant would have about a 20% yield loss, we can compare the relative merits of treating -vs- not treating.

 

No Insecticide Treatment

Using an estimate of 13.2 % damaged plants with a 20% yield reduction for each damaged plant, the effective yield loss was calculated to be 2.64%. If this were 100 bu/acre wheat, the resulting loss would be 2.6 bushels. At a price of $2.50/bushel, the untreated acre of wheat would bring about (97.4 bu at $2.50/bu) $243.50 or a loss of $6.60 per acre due to this aphid-vectored disease.

 

24 Nov & 17 Feb Insecticide Treatment

The best insecticide treatment (two applications) contained an average of 1.65 % damaged plants. This indicates that about 88% of the loss to BYD was prevented by the two treatments. As calculated above, this is a 0.3% yield loss per acre. For 100 bu / acre wheat, this loss would be 0.3 bushel, leaving a per acre yield of 99.7 bushels. At $2.50 / bu the resulting loss would be $0.75, bringing a per acre return of (99.7 bu at $2.50 /bu) $249.25. However, this level of protection was obtained by making two insecticide applications, at a cost of about $17.00 per acre. Reducing the per acre return by this cost leaves a net return of ($249.25 - $17.00) $232.25.

 

24 Nov. Only Insecticide Treatment

The 24 Nov. treatment had 5.6% damaged plants. Assuming the standard plant yield loss, this is the equivalent of a 1.1% yield loss per acre. For 100 bu/acre wheat, this loss would be 1.1 bushels, leaving a per acre yield of 98.9 bushels. At $2.50 /bu the resulting loss would be $ 2.75, bringing a per acre return of (98.9 bu at $2.50/bu) $247.25. However, this level of protection was obtained by making an insecticide applications which would cost about $11.00 per acre. Reducing the per acre return by this cost leaves a net return of ($247.25 - $11.00) $236.25.

 

17 Feb. Only Insecticide Treatment

The incidence of damaged plants in the 17 Feb. treatment was 3.2 %. For 100 bu/acre wheat, this loss would be 0.6 bushels, leaving a per acre yield of 99.4 bushels. At $2.50/bu the resulting loss would be $1.50 bringing a per acre return of (99.4 bu at $2.50/bu) $248.50. However, this level of protection was obtained by making an insecticide applications which would cost about $6.00 per acre. Reducing the per acre return by this cost leaves a net return of ($248.50 - $6.00) $242.50.

 

 

Summary

Under these test conditions, the insecticide applications did cause statistically significant differences in BYDV symptom expression. However, it is clear that the assumed associated protection of yields resulting from this level of symptom reduction was not cost effective. If all other things are equal, the cost of the insecticide applications was greater than the reduction in damage (Table 2).

 

Table 2. Net return ($/ac) from plots treated at selected times with an insecticide application to control aphid vectors of BYDV in Caldwell County, KY, 1999

 

Treatment

No-Insecticide

24 Nov &

17 Feb

24 Nov

17 Feb

Net return per acre

$243.50

$232.25

$236.25

$242.50

 

The circumstances and yield potential on your farm will alter these figures. As prices and yields decline and treatment costs increase, the insecticide treatments will look even less appealing. However, a rise in prices and yields coupled with a lower treatment costs will make the returns from insecticide applications look much more favorable.

 

Choosing a 100 bushel per acre yield as a basis for comparison may be misleading. 'Intensive Wheat Management' has used 100 bushels as a benchmark; however, many fields will not support this level of production. When yields change so do the level of expenses that can be supported. Using the percent damage estimates, and assumed costs of control from the previous examples we have calculated the necessary value of a bushel of wheat needed to support the three treatments at various yield levels, using the BYD intensity seen in the 1998 experiment (Table 3).

 

Table 3. The value ($) of a bushel of wheat required to offset the costs of various insecticide treatments.

 

Potential Yield (Bu/AC)

Fall Treatment @ $11/ac

Winter Treatment @ $6/ac

Fall & Winter Treatment @ $17/ac

100

7.23

3.00

7.35

90

8.03

3.33

8.17

80

9.04

3.75

9.19

70

10.33

4.29

10.49

60

12.06

5.00

12.23

50

14.47

6.00

14.66

40

18.09

7.50

18.47

30

24.12

10.00

24.64

 

There is no consistently successful strategy to reduce losses to BYD virus by trying to control their aphid vectors with insecticidal sprays. While sprays may kill many aphids and reduce the percentage of infected plants, potential yield savings may not pay for the chemical and application. There are many other factors that impact the relative effect of BYDV infections.

 

BYDV infections developed very late in the 1998- 1999 crop, probably because of very low aphid numbers during the fall. The aphids that were present did not arrive until December. The late aphid flight probably resulted from the late summer-early fall drought that affected Kentucky. The lateness of the aphid / BYDV infections is illustrated by the fact that the late winter (Feb. 17) application was just as effective at reducing BYDV symptoms as either of the other two applications (Table 1.). A larger than "normal" portion of the infections occurred after Feekes GS 3. Because of this, the data presented in Table 3 must be used very carefully. If you consider only Table 3, it appears that the most appropriate time to make an insecticide application is in the late winter. While this was true in 1998-99, this may not be the case in most years. If both aphids and BYDV had been present very early in the fall, the percentage of infected plants and the relative damage to each would have been much greater. While late infections may be important in a year of good prices and low costs, an early fall infection is always a more important consideration.

 

Acknowledgments

The authors express their gratitude to Dr.'s Don Hershman (Plant Pathology) and Lloyd Murdock (Agronomy) for their review of this publication. We also especially appreciate the time and work of Dr. Dick Trimble (Ag-Economic) in proofing and challenging our economic arguments.

 

 

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

 

Small Grains.

Be sure that you plant wheat varieties with high levels of disease resistance. Seed should be treated to protect them from loose smut and common bunt. Varieties that are susceptible to powdery mildew should be treated with Baytan or other seed treatment that will protect them from early infection.

 

Soybeans.

As I have mentioned before, premature death of soybeans should not be blamed on the drought unless you check for possible diseases such as charcoal rot. I visited several more fields this past week that were infected and the disease caused large circular areas of dead plants. I thought I would pass along comments from Don Hershman from Kentucky where they experienced charcoal rot as well.

 

A soil-borne fungal disease, charcoal rot, is very widespread and will cause significant yield losses in many soybean fields throughout Kentucky this season. Charcoal rot, caused by Macrophomina phaseolina, is favored by mid to late season drought stress that, obviously, has been a serious problem statewide this summer. This disease was also very damaging last year because of the late season drought stress, which existed during the latter part of the growing season.

 

Macrophomina phaseolina is present in many of Kentucky's (and Delaware’s) agricultural soils at rather high populations. However, because drought stress is not a problem in soybean in most years, charcoal rot is not an annual problem. In fact, it is unusual to have back-to-back years where charcoal rot is a problem, but that has been the case for the 1998-99 seasons.

 

Charcoal rot is evident at this time as dead plants scattered throughout the dryer portions of a field or it may be evident field-wide. Confirmation that the plants were killed by charcoal rot is based on cutting into the surface of the lower stem and upper taproot area and finding a gray discoloration with many extremely small black specks embedded throughout the tissue. Leaves generally die and remain attached to plants rather than falling to the ground. (Here many young, infected plants did lose their leaves)

 

Unfortunately, in a dry year there is no control for charcoal rot if irrigation is not an option. All soybean varieties are susceptible and no management practices will be of much help where soil conditions are highly favorable for charcoal rot development. My purpose in writing this article is simply to inform you that low yields in many soybean fields will be the result of more than just drought conditions.

 

 

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

 

General Commodity Market Observations

U.S. corn harvest is nearing 30% complete, with soybean harvest reported to be near 20% done.  Russia is asking for U.S. soybeans, soy oil, and soy meal as part of a food aid package from the U.S. Talks between the two countries are to be held in October.  USDA recently signed a $10 million PL480 agreement with Uzbekistan for the sale of nearly 37,000 tons of U.S. soybeans under a fiscal 1999 (Oct.-Sept.) supply period.  This news coupled with rain showers that have held up harvest in the Midwest for a few days and some possibility of cooler temperatures expected for Nebraska and Dakotas later this week have bolstered the corn and soybean markets slightly.

 

General LDP Observations

Two things have happened this week:  First, depending upon location, deficiency payments for soybeans were running around 85 to 95 cents per bushel in respective county FSA offices.  Second, many of the nation’s farmers experienced harvest delays due to rain and could not get beans out of the fields to take advantage of the payment rate.  Crop maturity prevented others from being able to take any LDP at the current rate.  Providing farmers would get their beans harvested, then this type of payment rate could be taken advantage of either by opting for the Field Direct or the Stored LDP.  What needs to be understood is that the beans have to be harvested before any option for loan deficiency payments (LDP) can be taken.  For those experiencing harvest delays, a third option, the 9-month loan program may need to be considered.  This option is likely to appeal mostly to producers who have on farm storage and long cash positions at harvest.

 

Grain Marketing Highlights Available on the Internet

Producers can continue to receive “Grain Marketing Highlights” by subscribing to the Grain Marketing Discussion Group, available on the Internet.  Contact Carl German at 302-831-1317 or e-mail clgerman@udel.edu  to obtain instructions on subscribing to the discussion group.

 

 

Options for Harvest Aid Treatment  Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

 

A harvest-aid may be a consideration to dry down vegetation prior to harvesting to reduce foreign matter in the harvested grain.  For corn, Defol (sodium chlorate) is labeled for applications 14 days prior to harvest and it can be applied by air.    Defol will dry down plants but it does not have herbicide activity.  Dry down is slow, expect at least 14 days.  Also, 2,4-D is labeled but it must be applied by ground rig which provides challenges for getting it where it is needed.  In soybeans, Gramoxone Extra, Touchdown, and Roundup are labeled.  Gramoxone can be applied by air after at least one-half of the soybeans have dropped their leaves.  Touchdown is labeled for an application of 1.6 pts/A with either ground rig or aerial equipment.  Apply Touchdown to soybeans when pods have lost their color and wait 7 days before harvesting.  Roundup must be applied with a ground rig after the pods have lost their color and a 7day period between application and harvesting.  For sorghum, Defol and Roundup are labeled.  Apply Roundup, Touchdown, and 2,4-D with extreme caution because spray drift can be very damaging to trees, shrubs, and lawns at this time of year.

 

 

Fall Control of Perennial Weeds  Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

 

Fall is the best time to treat perennial weeds because it is the time that plants are best able to move the herbicide to the roots where it will do the most good.  When considering fall weed control the emphasis should be on what the patch of weeds will look like next spring or summer not the amount of dead stems this fall.  Also, it is important to consider that a fall application will not eradicate a stand of perennial weeds; the fall application will reduce the stand size or the stand vigor.   Fall applications of Roundup Ultra or Touchdown is the most flexible treatment for most perennial weeds such as artichoke, bermudagrass, Canada thistle, common milkweed, common pokeweed, dock, hemp dogbane, horsenettle and johnsongrass.  Rates of 1 to 2 quarts/A of Roundup or 1.6 to 3.2 pints/A Touchdown are consistently the most economical.  Allow at least 7 days after treatment before tilling, mowing, or planting through the treated area.  Banvel at 2 to 4 pints is also labeled for artichoke, bindweeds, dock, hemp dogbane, horsenettle, milkweeds, pokeweed or Canada thistle.  Allow 10 days after treatment before disturbing the treated plants.  Planting small grains must be delayed after Banvel application 20 days per pint of Banvel applied.  Fall herbicide applications should be made to actively growing plants.  Allow plants to recover after harvest before treating them.  Consider the options of spot treating in a standing crop; keeping the combine header as high as possible so the weeds are quicker to recover; or combining around the weed patches and then spraying those patches immediately after harvesting.  Weed species differ in their sensitivity to frost; some are easily killed by frost (i.e. horsenettle) others can withstand relatively heavy frosts.   Check the weeds prior to application to be sure they are actively growing.

 

 

Weed Management Considerations for Small Grains  Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

 

As wheat and barley season quickly approaches just a few reminders for weed control.  For no-till small grains be sure to use a burndown herbicide.  Winter annuals like chickweed have begun to emerge and a non-selective herbicide will control them and reduce the weed competition.  If you are going to be spraying for perennial weeds, spray Roundup 10 to 14 days before planting.  Planting will damage and stress the perennials so you want the Roundup to have plenty of time to translocate.  Do not apply Banvel or 2,4-D in the fall prior to planting small grains.

 

After the crop is planted, the earliest labeled treatment is Harmony Extra at the 2 leaf stage of the small grains.  Fall treatments in small grains often are not adequate for full-season control and a second application in the spring is often necessary.  However, many no-tilled small grain fields do require a fall treatment.

 

Ryegrass is one winter annual that needs to be treated in the fall.  Applications of Hoelon by mid-November have had the most consistent results in the Mid-Atlantic region.

 

Two weeds on the increase that are particularly troublesome are bromes (cheatgrass and downy brome type grasses) and bulbous oatgrass.  They are winter grasses that have the same life-cycle as wheat and barley.  There are currently no products registered that provide control of these weeds.  The best advice is avoid planting winter grains in those fields heavily infested with these weeds, and in the spring do not let them go to seed.

Upcoming  Meetings…

 

Southeast Strawberry Expo

November 3-5, 1999

Raleigh, North Carolina

For More Information: 919-542-3687 or e-mail ncstrawberry@mindspring.com

 

16th Delmarva Forestry Seminar

Saturday, November 6, 1999

Delaware Technical & Community College, Georgetown, Delaware

For More Information: see Issue 25 of Weekly Crop Update or call 302-697-4000 to register for the program.

 

Spinach Meeting

December 14, 1999

Location: Rutgers Research & Development Center, Bridgeton, New Jersey

The emphasis will be on processing spinach, but fresh market spinach will be discussed

For More Information: Contact Steve Garrison at 856-455-3100.  Registration is required.

 

Delaware Vegetable Growers Meeting

January 13, 14 & 15, 2000

13th - Fresh Market Vegetable Crops & Potato Session; Felton Fire Hall, Felton, Delaware

14th – Processing Vegetable Crops Session, Carlisle Fire Hall, Milford, Delaware

15th – Vine Crops Session, Laurel High School, Laurel, Delaware

For More Information: Contact Ed Kee or Tracy Wootten at 302-856-7303.

 

Corn & Soybean Technology Conference

February 10, 11, 12, 2000

Locations: to be announced

For More Information: Contact Gordon Johnson at 302-697-4000.

 

Text Box: This is the last issue of Weekly Crop Update for 1999.
I would like to thank all the contributors for the information that they provide each week during the growing season.   I appreciate their efforts and hope that the information you received this season has been informative and useful to you. 

Best Wishes for a prosperous harvest season.  

Regards,
Tracy


 

Text Box: Weather Summary

Week of September 23 to September 29

Rainfall:

None

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

Air Temperature:

Highs Ranged from 82°F on September 25 to 72° F on September 23.

Lows Ranged from 65°F on September 28 to 45°F on September 23.

Soil Temperature:

70 °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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