Volume 6, Issue 27                                                                                    September 25, 1998


Chickweed Control in Spinach This Winter - Ed Kee, Extension Vegetable Crops Specialist ; kee@udel.edu

Chickweed is the most serious weed threat to overwintered spinach. Chlorpropham, sold as Sprout Nip, is no longer available for control of chickweed in spinach. Spin-Aid, a material labeled for post-emergence use on processing spinach only, does have activity on chickweed. However, applications must be made before the stem is three inches long. It may require two or three applications through the winter, as new flushes of the weed comes through, to obtain control. Spin-Aid can be applied at 2 to 4 pints/acre, with no more than 6 pints applied per year. One strategy is to apply the lower rate (2 pints) repeated on young chickweed as required through the winter.

Use 18 to 20 gallons of water/acre and do not add any adjuvants or additives. Too much water may cause precipitation of the herbicide. The spinach must have 4 to 6 true leaves. Spin-aid must be applied no later than 40 days prior to harvest. Spin-aid should be sprayed when temperatures are 75 degrees F or less. Spin-aid may cause injury when rapid climatic changes from cool, overcast days, to hot (75 degrees or higher), bright days. Please read the label for the complete directions and restrictions. v


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

Lima Beans.

Scout lima beans regularly for the presence of downy mildew. It has been identified in several fields now in Delaware and Maryland. The only labeled fungicide for control of downy mildew is copper sulfate. Early detection and fungicide applications can prevent further infections if downy mildew is identified early. (See Issue #23, Aug.28 for more information.) v

Field Crops

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


Controlling diseases in next year's crop. This past season Delaware wheat growers saw and unprecedented outbreak of tan spot caused by the fungus Pyrenophora tritici-repentis. This fungus will overwinter in old, infected wheat debris. The other disease which was favored by wet weather during flowering was head scab. Both these diseases can be controlled by good field sanitation practices that include tillage to bury old crop residues where spores from tan spot, scab, glume blotch, and take-all reside. The other practice is rotation. Don't plant wheat after wheat following soybeans or wheat after corn no-till. This increases the risk of scab, tan spot, and Septoria leafspot and glume blotch. If you are planting saved seed from the 1998 crop be sure to have it well cleaned, test for germination and treat with Raxil-thiram, or Vitavax 200, to cover both loose smut and seedling scab infections. Captan and thiram will protect the seedlings from seedling blight caused by Fusarium graminearum, the cause of scab. For early season powdery mildew and rust control select disease resistant varieties or plant Baytan or Dividend treated seed. Baytan is preferred for powdery mildew and rust control.



Controlling soybean severe stunt virus. Growers in Sussex County that have seen SSSV in their soybean fields have several new resistant varieties. Research work conducted this summer in a SSSV infested field near Millsboro identified three varieties that are resistant to SSSV: Pioneer 9492, Hytest BHS 4500, and Delsoy 5710. All three are resistant to soybean cyst nematode. These three can be added to the resistant variety list that includes Delsoy 4710 (SCN resistant), Corsica, Chesapeake, Stine 4790, Choska (SCN resistant), and Cisne. This work is supported by the Delaware Soybean Board and check-off funds. v


Factsheet for Corn Stalk Testing for Nitrogen Management Available at Your County Extension Offices

An Iowa State University Extension Factsheet is available at the County Extension Offices for using cornstalk testing to evaluate nitrogen management practices used in your corn fields.

Recent studies have shown that the nitrogen (N) status of a corn crop can be accessed by measuring nitrate concentrations in the lower portion of the cornstalks at the end of the growing season. This finding led to the development of a new tissue test that can be used to evaluate N management practices used in any field in any year.

The time for sampling is between one and three weeks after black layers form on about 80% of the kernels of most ears. Growers should collect 15, 8-inch segments of stalk found between 6 and 14 inches above the soil. Leaf sheaths should be removed. Disease or insect damaged stalks should not be used. Areas differing in soil types or management histories should be sampled separately. Samples should be shipped in paper bags to allow drying of the samples and to minimize growth of molds. Samples should be refrigerated (but not frozen) if stored for more than a day before mailing.

A & L Laboratories will analyze cornstalk samples at a cost of $12 per sample. Typical turn-around time is 3-4 days.

Who should consider using this test? All farmers should consider using the test on a few fields each year. Those who learn that their fields usually test in the optimum range need not make larger investments in time or money. Those that learn that they usually apply too much N to some or all of their fields will find it profitable to adjust rates of application. Producers who grow corn on manured soils should consider the stalk test. Recent studies indicate that most producers greatly underestimate the amount of N supplied by animal manures and apply unneeded fertilizer.

Stalk nitrate nitrogen concentrations can be divided into four categories: low (less than 250 ppm N), marginal (250-700 ppm N), optimal (700 to 2,000 ppm N) and excess (greater than 2,000 ppm N). Low indicates a high probability that greater availability of N would have resulted in higher yields. Marginal indicates that the N available to the plant was very close to the minimal amounts needed. The optimal category indicates a high probability that the N available was within the range needed for maximizing profits for producers. The excess category indicates a high probability that N availability was greater than if fertilizer N had been applied at rates that maximize profits for producers.

Because the concentration of nitrate in the stalk at the end of the season reflects all factors that influenced N availability and N needs during the growing season, it is unrealistic to expect to achieve optimal range levels of stalk N in all fields in all years. Weather considerations should be accessed and fertilization rates increased in the low range and decreased in the excess range. The test does not directly indicate how much N to increase or decrease, but continued use of the test for several years enables producers to make adjustments toward optimum rates.

This test is one more tool that producers can use to improve their cost of production.

* Taken from Cornstalk Testing to Evaluate Nitrogen Management; prepared by A.M. Blackmer and A.P. Mallarino, Iowa State University.

                      Weather Summary

Week of September 18 to September 24

0.66 inches: September 22, 1998
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 88 F on September 21 to 68 F on September 23.
Lows Ranged from 67 F on September 18 to 47 F on September 23.
Soil Temperature:
76 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:


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.