Vol. 5 No. 4 April 25, 1997

Weekly Crop Update

University of Delaware Cooperative Extension

Volume 5, Issue 10

June 6, 1997


Field Crops:

Field Crop Insects -

Derby Walker, Extension Agricultural Agent.

derby@udel.edu

Continue to monitor for cutworms and armyworms. Corn fields near wheat should be monitored for armyworms migrating from drying down small grains. Although economic levels of armyworms may not have been present in wheat, continue to monitor for them in field corn. A treatment would be needed if 35% or more of the plants are infested and 50% or more on damaged plants and worms are less than : A long. Armyworms larger than 13" long are usually done feeding. Spot or edge treatments may be all that is necessary.

 

Forage Fertilization -

Richard W. Taylor, Extension Agronomist

rtaylor@udel.edu

Potash or potassium promotes forage growth, stand longevity, helps forages tolerate stress conditions, and improves winter survival. Phosphorus improves root growth, forage production, and stand longevity. Alfalfa removes from 10 to 13 lbs. of phosphorus (P2O5) per harvested ton and from 40 to 60 lbs. of potash (K2O) per harvested ton depending on stage of maturity. Orchardgrass removes from 14 to 16 lbs. of phosphorus per ton and 60 to 70 lbs. of potash per ton. Timothy removes from 9 to 12 lbs. of phosphorus and 40 lbs. of potash per harvested ton. If you harvest 3 to 5 tons per acre per year, you remove large amounts of phosphorus and potash.

First, as with any crop, use a soil test to determine the amount available to the crop from the soil and to get a recommendation of how much additional fertilizer your crop will need. If the recommended rate of potash is greater than 90 lbs. per acre, it is best to split the potash into two equal applications. Apply one after the first or second cutting and the second after the final summer harvest (late August or September). If the phosphorus level is low-medium or higher, topdress with phosphorus. Phosphorus can be applied in one application with the first potash application or, if convenient, as a mixed fertilizer along with the potash.

If you are growing alfalfa, add 20 to 40 lbs. per acre of sulfur plus 2 lbs. of boron per acre. Keep in mind that boron is very toxic to plants if overapplied. For clovers, add 0.5 to 1 lb. of boron per acre. Boron is more safely applied if blended with potash or phosphorus fertilizer.

 

Irrigating Full-Season Beans -

Richard W. Taylor, Extension Agronomist, and Bob Uniatowski, Extension Associate--Field Crops

rtaylor@udel.edu

bobuni@udel.edu

Unlike corn, full-season beans require a different irrigation strategy and management system. Stress during the vegetative growth phase of the crop (planting to first bloom) can improve yield potential. In a study sponsored one year by the Delaware Soybean Board and conducted at the University of Delaware Research and Education Center, soybeans irrigated from planting to near maturity yielded no better and, for some varieties, worse than the non-irrigated controls. Full-season beans irrigated only during the reproductive growth phase yielded 10 to 20 bu/A more than the non-irrigated controls which that year yielded 50 to 55 bu/A.

However, there are circumstances when full-season beans should be irrigated during the vegetative growth stage. Apply just the quantity of water necessary to solve these problems when or if they occur.

1. Emergence of the crop is threatened by drought or soil crusting.

2. Herbicide activity may become severely reduced because of lack of rainfall.

3. The soybean stand is in eminent danger of total loss from drought.

4. Drought conditions have reduced growth to such a point that canopy closure is unlikely to occur by first bloom. Ideally, canopy closure should occur two weeks before the crop reaches the bloom stage of growth.

Once the beans begin to bloom, apply enough water to prevent any water stress until the first pods begin to change to their mature pod color and the leaves begin to drop. When the first pod on the main stem turns the mature pod color, the crop has reached physiological maturity and additional yield increases will not occur. Irrigation after this point will only delay dry-down and possibly reduce seed quality.

Later this month, I will discuss irrigation of double-crop beans which is considerably different from the irrigation of full-season beans.

 

Field Crops Diseases -

Bob Mulrooney, Extension Plant Pathologist, University of Delaware.

bobmul@udel.edu

Wheat.

So far the crop is looking very good from a plant disease viewpoint. We did have a confirmed report of barley yellow dwarf mosaic virus last week. Late infection of BYDM will produce yellow to red flag leaves. These late infections should not affect yields. In most areas, flowering was completed before the rainy period, which should reduce the chances that scab infection occurred. We will have to wait and see what develops. More take-all was also seen last week, see last week's report for details.

 

Double-cropped Soybean Herbicide Options -

Mark VanGessel, Extension Weed Specialist.

mjv@udel.edu

It appears that stocks of Canopy may be tight this year for soybeans planted behind barley. If you are considering alternatives to Canopy do not forget about Lorox, Sencor, or Lexone. These three are effective on many of the broadleaf weeds we combat each year. Furthermore, Lorox has a 4 month recropping interval for almost all rotational crops, and Sencor/Lexone fit well with most of our vegetables (be sure to check the label for specifics). Either of these broadleaf herbicides should be tankmixed with a grass herbicide. Finally, it is best to start with a good burn down program. Even though many of the broadleaf herbicides have some burndown activity, it is often not enough. One to two pints of Gramoxone Extra or Roundup should be added for burndown activity.

 

Adjuvants for Postemergence Corn Herbicides -

Mark VanGessel, Extension Weed Specialist.

mjv@udel.edu

Most of the postemergence herbicides require an adjuvant for effective weed control. Adjuvants cover a broad category of products that can be added to the spray tank to improve a herbicide=s performance. Non-ionic surfactants (NIS) reduce the surface tension of water and as a result increase the wetting and spreading of the spray solution on the leaf surface. Crop oil concentrates (COC) also increase the wetting and spreading of the spray solution on the leaf surface as well as dissolve the waxy surface of the leaf and increases the time the leaf surface remain wet. Liquid fertilizers also increases the penetration of the herbicide into the plant, but it is unclear how this happens.

NIS is recommended on a percent volume basis, usually 0.25 to 0.5% (1 to 2 qts/100 gallons of spray). COC is recommended on an amount per acre basis, usually 1 to 2 qts/A. Common rates of liquid nitrogen are 1 gallon per acre of 28, 30, or 32% UAN, 1 quart per acre of 10-34-0, or 17 pounds/100 gallons of dry ammonium sulfate (AMS).

Postemergence herbicides cause the greatest amount of crop injury when plants are growing under stressful conditions, such as the past week, or under conditions of very rapid growth. Using the lower rate of the surfactant, or using NIS when either NIS or COC can be used will reduce the amount of crop injury.

 

 

Herbicide

 

Rainfast

Interval

 

Maximum Corn Size

 

Adjuvants

 

Accent

 

4

 

brdcst: 6 collars or 24" tall

direct: 10 collars or 36" tall

 

COC or NIS

UAN or AMS optional

 

Accent+Atrazine

 

4

 

12" tall

 

COC

UAN or AMS recommended

 

Accent+Buctril

 

4

 

brdcst: 6 collars or 24" tall

direct: 10 collars or 36" tall

 

NIS

UAN or AMS recommended

 

Accent+Banvel

 

6-8

 

brdcst: 8" tall

direct: 24" tall

 

NIS

UAN or AMS recommended

 

Accent+Marksman

 

6-8

 

8" tall

 

NIS

UAN or AMS recommended

 

Atrazine

 

2

 

12" tall

 

COC

 

Banvel

 

6-8

 

more than 2 pt/A:

brdcst: 5 lvs or 8" tall

direct: 36" tall

2 pt/A or less:

36" tall

 

COC or NIS

Do not use COC if >5" tall

 

Basagran

 

8

 

No restrictions listed

 

COC, UAN or both

 

Basis

 

4

 

2 collars or 6" tall

 

COC or NIS

UAN is required

 

Basis Gold

 

4

 

5 collars or 12" tall

 

COC

UAN is recommended

 

Beacon

 

4

 

brdcst: 20" tall

direct: pre-tassel

 

COC or NIS

UAN is optional

 

Beacon+Atrazine

 

4

 

12" tall

 

COC or NIS

UAN is optional

 

Beacon+2,4-D

 

6-8

 

brdcst: 8" tall

direct: pre-tassel

 

NIS

 

Beacon+Marksman

 

6-8

 

8" tall

 

NIS

 

Bladex

 

2-3

 

prior to when 5th leaf is visible

 

NIS if dry

DO NOT USE COC

 

Buctril

 

1

 

pre-tassel

 

None recommended

 

2,4-D Amine

 

6-8

 

brdcst: 8" tall

direct: pre-tassel

 

None recommended

 

2,4-D Ester

 

2-3

 

brdcst: 8" tall

direct: pre-tassel

 

None recommended

 

Exceed

 

4

 

brdcst: 24" tall

(minimum ht. 4" tall)

direct: 48" tall

 

COC or NIS (Use only NIS if tankmixing - except Accent or atrazine)

UAN or AMS optional

 

Hornet

 

6

 

brdcst: 24" tall

direct: until 85 days pre-harvest

 

NIS

UAN is optional

 

Laddok

 

8

 

12" tall

 

COC, UAN, AMS, Dash or any combination

 

Marksman

 

6-8

 

brdcst: 5 lf stage or 8" tall

 

COC, NIS, or UAN if dry.

Do not use COC if corn >5" tall

 

Permit

 

4

 

until layby

 

COC or NIS (Use only NIS if tankmixing - except atrazine)

UAN is optional

 

Resource

 

1

 

No specific stage given - Use of drop nozzle is suggested when corn leaves interfere with spray

 

COC

UAN or AMS optional

w/ Banvel or 2,4-D ester no adjuvants

w/ 2,4-D amine only NIS

 

Scorpion III

 

6

 

brdcst: 8" tall

direct: pre-tassel

 

NIS

UAN is optional

 

Shotgun

 

24

 

brdcst: 8" tall

direct: 12" tall

or if rate >2 pts

 

None recommended

 

Stinger

 

6-8

 

24" tall

 

None recommended

 

Tough

 

1-2

 

until 68 days pre-harvest

 

None recommended (except when tankmixed with other postemergence products)

 

COC= Crop Oil Concentrate

NIS= Non-ionic Surfactant

UAN= 28% nitrogen solution

AMS= ammonium sulfate

Dash= BASF spray adjuvant

 

 

Vegetable Crops:

Vegetable Crop Insects -

Derby Walker, Extension Agricultural Agent.

derby@udel,edu

Watermelons.

Melon aphids have been seen in a few fields in Sussex County. Look for cupped leaves on the plant. Melon aphids can be distinguished from other aphids by their black cornicles (tailpipes). A treatment should be considered when 10-20% of the runners are infested with 5 or more aphids per leaf and beneficial activity is low. Lannate is the only material labeled on cucurbits for melon aphid control. Good coverage is needed to reach the aphids on the underside of the leaf.

Reminder for Sprayer Cleanout -

Derby Walker, Extension Agricultural Agent

derby@udel.edu

As you switch from herbicides to insecticides and fungicides, take the extra time to thoroughly clean your sprayer. Safety equipment and extra precautions should be used because pesticides will be present. Consider a tank cleaner to loosen any pesticide residues in the tank. The tank and lines should be thoroughly flushed out. Remove and clean all the screens in the system, as well as the nozzles. Although, this may take a little extra time, it will pay for itself in the long run. Vegetable crops are more sensitive to pesticide injury this season due to the cloudy, cool weather.

Pea Harvest Begins -

Ed Kee, Extension Vegetable Crops Specialist.

walter.kee@mvs.udel.edu

Pea yields to date have been very good, with fields going over 4,000 and 5,000 pounds per acre. Cool conditions have favored pod set, although a few fields show where frost has touched them up. Harvest is proceeding in an orderly fashion.

Post-emergence Weed Control in Snap and Lima Beans -

Ed Kee, Extension Vegetable Crops Specialist

walter.kee@mvs.udel.edu

As plantings are reaching the early trifoliate stages, take a good look and scout your snap and lima bean fields for broadleaf weeds and grasses. Poast will control grasses in both crops. Assure II is now labeled for use in snap beans, but not lima beans. Basagran will control many broadleaf weeds, but works much better if sprayed when the weeds are small. Check the label for instructions on crop oil and surfactants.

Vegetable Crop Diseases-

Bob Mulrooney, Extension Plant Pathologist, University of Delaware

bobmul@udel.edu

Cucumbers.

Just a reminder to keep plantings protected from scab during this cool weather. Many scab resistant varieties are available, and should be used. Apply chlorothalonil every 5-7 days.


Late Blight Update

June 3, 1997

Weather conditions for late blight development are favorable after the rain and humidity of the past several days. 18 disease severity values have been reached or will be reached today.

 

DSV Accumulations as of the June 2 are as follows:

Baldwin

emergence date 4/20: 18

Spray at low rate on 5 day schedule

 

Jackewicz

emergence date 4/26: 16

By today, June 3, 18 severity values will be reached. Spray as above.

 

Zimmerman

emergence date 4/28: 14

This site will probably reach 18 DSV=s today also. Spray as above.

 

Baker

Emergence date 5/7: 27

after 5/9: 19

Spray as above.

 

 

Vegetable Crop Diseases -

Kate Everts, Extension Plant Pathologist, Universities of Maryland and Delaware.

everts@udel.edu

Strawberries.

Some growers are seeing gray mold on the fruit during harvest because of the wet weather. The best control for this disease begins early in the season with cultural tactics such as straw mulch and avoiding excessive nitrogen (See Weekly Crop Update Vol. 5 No. 6). Early sprays are more effective than late sprays since gray mold gets established on the flower petals. If this disease is present and a rescue spray is required, Ronilan + captan, or Rovral + captan may be used. However, be aware that pre-harvest intervals and re-entry intervals must be observed. For example, captan 50WP has a restricted entry interval of 24 hours.

Watermelon.

Vines have begun to run on some early plantings of watermelons. While disease pressure has been low, preventative sprays for control of gummy stem blight, anthracnose, and alternaria will be needed as the weather warms up. Begin spraying a chlorothalonil product (Terranil or Bravo) on a seven day schedule. Use the low rate early in the growing season, while disease pressure is less intense.


Upcoming Events:

 

1997 University of Delaware Weed Day

June 25, 1997

University of Delaware Research & Education Center, Route 9, Georgetown, Delaware

Opening Remarks at 8:30 a.m. in the Grove near the farm buildings.

 

Crop Diagnostic Field Day

July 31, 1997

7:30 a.m. - 1:00 p.m. University of Delaware

Research & Education Center, Georgetown, Delaware

 

 

Complied & Edited By:

Tracy Wootten

Extension Associate - Vegetable Crops


Weather Summary

University of Delaware,

Georgetown

Week of May 30 to June 5, 1997


Rainfall:

0.01 inches: May 31

0.01 inches: June 1

0.02 inches: June 2

0.37 inches: June 3

0.10 inches: June 4

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


Temperature:

Highs

Ranged from 72EF on June 2 to 56EF on June 4.

Lows

Ranged from 60EF on June 1 to 42EF on June 5.


Soil Temperature:

59.6EF Average for the week.

 


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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. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age or national origin.