Volume 8, Issue 4 April 14, 2000


Vegetables

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

 

Cabbage.

Imported cabbageworm butterflies have been laying egg in fields for the last 10 days. You should begin to see diamondback moths laying eggs as soon as the temperatures increase. Young larvae will first mine between the upper and lower leaf surfaces before moving to the heart of the plants. Treatments should be applied when 5% of the plants are infested with larvae and before larvae move to the heart of the plants. Bt insecticides, Proclaim, or Spintor will provide effective control. Proclaim is a new insecticide from Novartis, labeled last fall. It has a novel mode of action so it can be used as an effective resistance management tool. It has provided very effective control of imported cabbageworm, cabbage looper and diamondback larvae. The use rate is 2.4 - 4.8 oz/A for imported cabbageworm and diamondback.

Sweet Corn.

Be sure to check the earliest emerged sweet corn for cutworm and flea beetle activity. Treatments for cutworms should be applied if you find 10% leaf feeding or 3% cut plants in one-two leaf stage corn. Ambush, Asana, Pounce, or Warrior will provide effective control. Fields should be treated early in the morning or in the early evening when cutworms are close to the soil surface to achieve the best control. With the warmer winter conditions and relatively dry soil conditions, the potential exists for heavier than normal flea beetle populations. Fields should be checked mid-day when beetles are active to get an accurate estimate of the population level. A treatment will be needed if 5% of the plants are infested with beetles. Ambush, Asana, Baythroid, Pounce, Sevin or Warrior will provide effective control.

A Section 18 was granted late winter for the use of Gaucho( imidachloprid) as a seed treatment on a limited acreage of processing sweet corn. Its use is limited to varieties that are susceptible to Stewart's Wilt. This product provides excellent control of flea beetles. In addition, there is data supporting its effectiveness on seed corn maggot and wireworm on field corn. However, there is no data for white grub control. If you are planting processing varieties treated with Gaucho into fields with a history of grub problems (especially following soybean) or you can find one grub per square foot of soil, a soil insecticide will be needed for grub control. Counter or Force will provide control.

 

 

 

 

 

Field Crops

 

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

 

Alfalfa.

Economic levels of alfalfa weevils can be found in fields throughout the state. Once you see pin hole feeding in the leaves, a whole field sample should be taken. When sampling for alfalfa weevil, randomly collect 30 stems throughout a field, placing

them upside down in a bucket, and shaking the stems to dislodge larvae from the tips. As a general rule of thumb, a treatment should be applied when 50% or more of the tips show weevil-feeding injury before the full-bud stage. Once alfalfa reaches 12-inches tall, the treatment threshold is one per stem. In 13 to 15-inch tall alfalfa, the threshold is 1.5 per stem.

 

 

Field Corn.

Black cutworm pheromone trap catches are still relatively low throughout Delaware and Maryland. Although trap catches provide an indication of areas of potential cutworm outbreaks, there are other factors that can reduce populations. Adverse weather, lack of adequate food for newly hatched larvae, predation, and disease can reduce larval populations. Cutworm larvae are generally large enough to begin cutting when about 300 base-50 degree days have accumulated since eggs were laid or from peak moth flights. In most years this occurs in early May; however, it could be earlier depending on weather in the next 2 weeks.

Wheat.

We are starting to see low levels of cereal leaf beetle egg laying but no egg hatch has been observed. Using degree-day models, we should start to see the first larvae any day. However, the recent cool temperatures may slow development or reduce populations once egg hatch has occurred. Controls should not be applied too early to avoid the need to re-spray fields. Controls will be needed once you find 25 eggs and/or larvae per 100 tillers with 50 60% egg hatch. The threshold of 0.5 larvae per stem has also been an effective threshold when fields are routinely scouted. True armyworm moth activity and egg laying remains low. A cumulative moth catch of 200 or more moths during the month of April indicates the potential for a true armyworm outbreak in small grains. Moth catch information can be found at the IPM website (www.udel.edu/IPM).

 

 

 

 

 

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

Wheat.

Powdery mildew continues to be the primary disease in the field at the present time. Most of the mildew in our variety plots is confined to the lower leaves on some varieties. Baytan has kept powdery mildew in check until growth stage 6-7. Powdery mildew is just beginning to be seen on Southern States 555W and 522W treated with Baytan. Mildew was seen on Jackson and Mason but was not at threshold levels.

 

Clean Straw.

If anyone is selling wheat straw to specialty markets that require a clean, bright appearance, last years test results showed that Quadris treated (6.2 fl oz/A) straw was brighter than Tilt (4 oz/A) treated straw while both treatments were significantly better (brighter) than the non-sprayed plots. Both fungicides were applied at head emergence (GS 10.1) for powdery mildew and Septoria control but the clean straw was an added benefit. The fungicides controlled the sooty molds that were common on last years drought-stressed crop.


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

 

Commodities Struggle to Find Direction
This past week has been a struggle for the corn, soybean and wheat markets as they attempt to bid prices toward equilibrium and are currently struggling to find direction. The big dilemma continues to be the weather forecast, which gives the market the 'rumor' in terms of what to expect for precipitation in the corn belt, and then the actual event occurs which gives the commodity market the 'fact'. The old saying in commodity trading is to 'buy the rumor, sell the fact'. The weather forecast for the week of April 3rd took much of the anticipated weather premium out of the market with widespread rains predicted for much of the corn belt. The forecast began to change by the week of April 11th with weather forecasters turning to a drier forecast, so back in goes the weather premium.That process began on April 12th. No one is predicting a run away market at this time. Therefore, it may become prudent in the near future to consider making initial sales on new crop soybeans. Depending upon local basis offerings, it is now possible to achieve a contract price that is at or above the loan rate of $5.36 per bushel. The lifetime low for the November soybean futures contract is $4.53 per bushel.

Recap of USDA's Supply and Demand Report
By now much has been analyzed regarding the April 11th release of the supply and demand report. However, the market seemingly did not react much to the report. Ending stocks for U.S. corn were increased 20 million bushels from the March report, and are still estimated to be less than last year's carryout. Ending stocks for U.S. corn, now estimated at 1.759 billion bushels, are currently 28 million bushels less than the carryout for the 1998/99 marketing year. Ending stocks for U.S. soybeans were reduced 20 million bushels from the March report, and are currently estimated to be 43 million bushels less than the carryout for last year, at 305 million bushels. Ending stocks for U.S. wheat were reduced 54 million bushels from the March report, and are currently estimated to be 3 million bushels less than the carryout for the 1998/99 marketing year, at 943 million bushels. Estimates for Brazilian soybeans were left at 30.5 mmt, 0.5 mmt less than last year. Estimates for Argentine soybeans were increased to 21 mmt, as compared to 20 mmt estimated in March and 19.5 mmt produced in the 1998/99 marketing year.

 

 

 

 

 


Have Heavy Rains This Spring Affected the Effectiveness of Hay Fertilization Programs? - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

 

I had a question from a hay producer wondering whether he needed to refertilize his hay fields because of nitrogen (N) losses from all the rain this spring. The answer is no unless you are seeing severe yellowing on the hay or pasture grasses.

 

There are several reasons for this. A grass hay crop is a perennial crop that has established roots throughout the upper two to three feet of soil. The deep rooting of perennial grasses will allow them to take up much of the N that might be leaching below the traditional plow layer row crop growers must be concerned with. 

Most of our hay species had begun active growth by the time the heavy rains occurred. The grasses are able to store large quantities of N in this new growth for use later as jointing and heading occur.

 

Most producers split N applications so not all was applied early this spring. If you did apply all the N for the season this spring, you should carefully monitor your hay crop for signs that it needs additional N. Nitrogen is mobile in the plant so when a shortage occurs it is moved from the older leaves into the new actively growing leaves. Watch your crop for a general yellowing of the grass and especially watch for yellowing on older leaves. Nitrogen deficiency often is seen as an inverted V-shaped yellow to orange-yellow pattern with the bottom of the V at the mid-vein and closest to the stem).

 

If these symptoms are seen just before harvest, apply up to 50 lb N/A. If they occur within three weeks after harvest, apply about 25 lb N/A as soon as possible and then up to 50 lb N/A after harvest for the next cutting.

 

Irrigation on Winter Wheat - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

 

A two-year study of irrigation timing on winter wheat was completed this past harvest season. The studies used a high-yielding, disease resistant wheat variety that was heavily fertilized with split applications of nitrogen including fall-applied nitrogen. Excellent stands were achieved both years. Fungicide was applied to minimize disease impact on yields and insecticides were used when needed. Irrigation treatments began one week after the wheat flowered. The crop was irrigated with 1.5 inches of water per week less the amount of rainfall received. Irrigation treatments were: a control that received no irrigation, and irrigation for one, two, three, and four weeks following flowering. The center of a 30 by 30 foot plot was combine harvested for a yield estimate.

 

No significant differences were observed between the control and any irrigation treatment. Although not significant, the trend both years was for lower yields with longer periods of irrigation and especially when irrigated for three or four weeks. Test weight was not affected significantly by irrigation.

 

Should you irrigate wheat? This question ultimately must be answered by individual producers. Certainly, based on this research and research from the late 1970s and early 1980s, irrigation of wheat will not pay economically.

 

If you intend on irrigating wheat anyway, follow these guidelines.

 

Irrigate only the best fields with high yield potential.

              Limit the number of irrigations while building the soils available water to near maximum.

              Do not irrigate during flowering.

              Stop irrigating by two weeks after flowering.

              Irrigation prior to heading should occur only under extreme drought conditions.

 

 

 

 


Roundup vs. Touchdown - Reprinted Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

 

Bob Hartzler, Weed Science Specialist, Iowa State University wrote the following article. My experiences with Roundup and Touchdown support what Bob says in his article.

 

Almost everyone involved in corn and soybean production is familiar with glyphosate, which is marketed as Roundup Ultra by Monsanto. However, the introduction of Touchdown by Zeneca has created some confusion. Both products contain the same active ingredient, glyphosate. The difference between the two herbicides is that glyphosate is the isopropylamine (IPA) salt of the parent acid, whereas sulfosate is the trimethylsulfonium (TMS) salt of the acid. In my opinion, both products should be referred to as glyphosate, but Zeneca was able to convince the organization that assigns herbicide common names that the TMS salt of N-(phosphonomethyl)glycine deserved a different common name. Thus, the TMS salt of the active ingredient in Touchdown is referred to as sulfosate. There are several herbicides that are marketed as different salts of the same active ingredient, and these salts all have the same common name. Examples of this include Banvel and Clarity (different salts of dicamba) and the many different formulations of 2,4-D.

 

Does the amine salt influence the effectiveness of the herbicide? Touchdown is formulated at 5 lbs sulfosate per gallon (a 6 lb formulation also is available in Florida) whereas Roundup Ultra has 4 lbs glyphosate per gallon. However, it is somewhat misleading to compare the formulated salts on a pound per pound basis since the IPA and TMS salts have different molecular weights.

 

It is more accurate to compare acid equivalents than active ingredients since the acid equivalent takes into account only the herbicidally active portion of the molecule {N-(phosphonomethyl)glycine}. When comparing the performance of the products it is critical to make sure equivalent rates are being used. (For equivalent rates of glyphosate acid, it is 32 oz of Roundup Ultra and 28 oz of Touchdown 5).

Once the herbicide is inside the plant, the salt disassociates from the parent molecule so there is no difference in the two herbicides at the site of action (EPSP synthase). Differences in performance might arise from differences in absorption caused by the different salts or the surfactants present in the formulated product. Monsanto is promoting the advantage of Transorb technology with Roundup Ultra, stating that absorption and translocation of glyphosate in Roundup Ultra is greater than that of sulfosate in Touchdown. While there are conflicting data on differences in absorption between the products, much of the data indicates little, if any, difference between the herbicides. Researchers at the University of Illinois presented results of a study investigating the absorption and translocation of both products at the recent Weed Science Society of America Annual Meeting. (Satchivi, N., L. Wax, E. Stoller, and D. Briskin, USDA/ARS and University of Illinois. 2000. Uptake and translocation of glyphosate and sulfosate in velvetleaf and giant foxtail. WSSA Abstracts 40:32-33). They found no differences in these two traits in either giant foxtail or velvetleaf. For example, 23% of Roundup Ultra was absorbed from the velvetleaf surface 24 hours after application compared to 22% of Touchdown. Addition of AMS to the spray solution increased the amount of herbicide absorbed and translocated, but again there were no differences between formulations.

 

Both Monsanto and Zeneca are claiming that their formulation is safer and less likely to affect yields. Recent research has shown that traditional postemergence herbicides occasionally may reduce soybean yields. However, this research has indicated that when yield losses occur, they are relatively small and that the crop response shortly after application is not a good predictor of the likelihood of a yield response. Touchdown is more likely to cause a foliar response in soybeans than is Roundup Ultra, but this damage is due to either the trimethylsulfonium salt, surfactants, or inert ingredients present in the formulated product. It is unlikely that the minor burning caused by these compounds induces a response that persists long enough to influence the yield potential of Roundup Ready soybeans.

 

In summary, the difference between glyphosate and sulfosate is that they are different salts of the same molecule. As with different amine salts of 2,4-D, we do not expect significant differences in performance of the two herbicides. Users should keep in mind the differences in surfactant needs, use rates, and labeled uses. 

 

 

 

 

 

Be Sure to Consider Last Year Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

 

I wrote last week about when planning your weed management consider what happened last year in that field. In it, I talked about reducing soil-applied herbicides when you think you will need to spray postemergence. An exception to this in corn is crabgrass. Postemergence control of crabgrass is very difficult at best. Basis Gold is the only option available and it needs to be sprayed before the crabgrass is one inch tall. With heavy crabgrass pressure, Fultime, Bicep Magnum, or Harness Xtra with 1 qt of Princep is the best option.

 

 

Field Pansy (Johnny Jump Up) Control Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

 

This weed is difficult to control. Our results with field pansy control show that rates of 1.5 qts of Roundup Ultra or Gramoxone at 1.5 pts plus 2,4-D are the best options.

 

 

 

 

 

 


Weather Summary

Week of April 6 to April 12

Rainfall:

0.21 inches: April 8, 2000

0.46 inches: April 9, 2000

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

Air Temperature:

Highs Ranged from 76F on April 8 to 52 F on April 9.

Lows Ranged from 45F on April 8 to 32F on April 9.

Soil Temperature:

52 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 2000 Season

Trap Counts Provided by UAP Inc., Seaford, DE

April 3 - 9, 2000

 

Location

# Moths per 7 Days

Location

# Moths per 7 Days

Bridgeville, DE

1

Leipsic, DE

5

Cheswold, DE

0

Lincoln, DE

0

Cordova, MD

0

Little Creek, DE

5

Crumpton. MD

2

Magnolia, DE

1

Delmar, MD

1

Mardela, MD

0

Denton, MD

0

Marydel, DE

0

Dover/Wyoming, DE

0

Middletown, DE

0

East New Market, MD

0

Milford, DE

0

Easton, MD

0

Millsboro, DE

0

Eldorado, MD

0

Milton, DE

1

Ellendale, DE

0

Newark, MD

1

Farmington, DE

0

Pocomoke, MD

0

Federalsburg, MD

0

Preston, MD

1

Felton, DE

1

Princess Anne, MD

1

Frederica, DE

4

Queen Anne, MD

1

Georgetown/ReddenDE

0

Rhodesdale, MD

2

Goldsboro, MD

1

Salisbury, MD

0

Greensboro, MD

3

Seaford, DE

1

Greenwood, DE

3

Selbyville, DE

0

Harbeson, DE

0

Smyrna, DE

2

Harmony,MD

0

Snowhill, MD

4

Hebron, MD

3

Sudlersville, MD

0

Hickory Hill, DE

0

Trappe, MD

0

Hurlock, MD

0

Vernon, MD

1

Kenton, DE

0

Vienna, MD

1

Laurel, DE

1

Westover, MD

0

 

 

Willards, MD

0

         Moth catches of 9-15 moths per 7 day period have been associated with a moderate to high potential for cutworm outbreaks.

         Moth catches of 5 per night for at least 2 consecutive nights have also indicated a high potential for problems

         You can expect to see cutting activity approx. 300 degree days from peak moth activity (9-15 per week or 5 per night for at least 2 consecutive nights)


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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