Soybean Aphid Update

Soybean aphids continue to be present in soybean fields across northeast Nebraska but overall have not appeared to increase in numbers. In our sentinel fields, the aphids are present on more plants in each field, but the overall population has not change significantly. The hot weather early last week may have slowed their reproductive rate, and the hot weather early this week will hopefully continue the trend. As with many insects, aphid populations are very weather dependent, and will fluctuate widely depending on conditions. Some economic thresholds are being circulated that are much lower than the 250 aphids per plant that we recommend. We feel that the 250 aphid per plant threshold (with populations also increasing) is much more realistic, and still gives growers about a week’s time to spray the field. This also allows time for weather and natural enemies to help slow the population increase. The lower threshold numbers being used by some are based on some very preliminary data and we feel it is not a realistic threshold to use at this time, until more research is conducted. Therefore, we strongly discourage treating for soybean aphids until the 250 per plant threshold is reached and populations are still on the increase. Take the time to scout your fields thoroughly before making a treatment decision, it will be time (not necessarily money) well spent.

Bean Leaf Beetles in Soybean

The true first generation of bean leaf beetles has been working on soybean foliage for a couple of weeks. Beetle numbers appear to be below thresholds in all fields. During this time beetles are working on leaf tissue and the soybeans have plenty to spare. Numbers will be decreasing as females lay eggs and die off. The more serious second generation will be emerging in late August and will be feeding on the developing pods. More information will come on that later.

Second Generation European Corn Borers

Second generation European corn borers are flying and scouting should be underway in non-Bt corn. Numbers across the state appear to be low but the flight is not yet done, so here is a review of ECB management.

Fields that have green silks and are shedding pollen during the peak period of moth flight are most susceptible to second generation infestation. Scout fields regularly, at least once every three to five days, especially during the early half of the moth flight period. Select a minimum of 50 plants per field, choosing plants from several different parts of the field. Examine the underside of leaves for white borer egg masses. These masses, usually found on leaves in the middle third of the plant (frequently near the midrib), normally hatch in about five days. Each egg develops a black spot just before hatching.

Application timing is critical to reasonable control. Best control (approximately 50-70 percent, depending on timing, application method and product choice) is realized when application is timed to first significant egg hatch and when young larvae are still located in the leaf axils. Larvae that have bored behind the leaf axils, into the sheath or are in or on the ear are not likely to be controlled. As the plant approaches blister stage and beyond, potential economic benefits of an insecticide application rapidly decline.

A worksheet has been developed to help determine whether treatment of second generation European corn borers in corn is economical. For this worksheet you need to know:

1. Average number of egg masses per plant in field
2. Crop stage
3. Expected yield
4. Expected value of corn
5. Expected percent control with insecticide
6. Cost of control (product plus application costs)

This worksheet may be useful in closely evaluating the many factors influencing the cost/benefit relationships involved in treating second generation European corn borers. Average values are suggested in the worksheet and may need to be modified in certain situations:

· Borer survival is suggested to be three borers per egg mass. On average, European corn borer egg masses contain 20 eggs, although this may vary from 10 to 40. Three borers per 20 eggs equal a 15 percent survival rate. Larval survival will vary with weather conditions and field type (dry land versus irrigated). In irrigated corn, larval survival is likely to be 20 percent or more, but in dryland corn it's likely to be 10 percent or less. Exposure to hot, dry weather greatly decreases egg survival.
· Yield loss per borer is suggested to be 4 percent per borer for infestations before silks turn brown, and 3 percent per borer after silks turn brown, but before blister stage. These values only account for physiological yield loss (reduced yield from corn borer damage to water and nutrient uptake through the stalk) and do not consider the potential for yield loss due to stalk breakage or ear drop.
· Percent control with insecticides is suggested to be equal to 70 percent. This is a good average value for second generation European corn borer control, although if you have data to suggest higher or lower control levels under your conditions, change this value.

The best control that can be achieved usually will prevent much of the stalk and leaf sheath tunneling, but will not necessarily prevent invasion of the ear tip. This is especially true if the borer flight period is extended or a partial third generation occurs. Stalk protection is critical for the plant to fully develop the ear. While late worms that attack the ear tip do reduce grain quality, they do not reduce yields as seriously as borers that tunnel in stalks. Early harvest and selection of a corn variety that has good ear retention should minimize ear drop.

Generally, liquid and granular formulations of the same insecticide are equally effective against second-generation European corn borer larvae. However, if other insects (except spider mites) are present and/or European corn borer moth numbers are high, liquid formulations are preferred over granules because of their broader spectrum of activity and the added advantage of obtaining some moth control. If spider mites are present, Capture is probably your best choice. Lorsban, Penncap M, Pounce (permethrin), Asana, Warrior, Capture, Mustang Max, and Baythroid will all control European corn borers.

Management Worksheet for Second Generation European Corn Borers

An interactive web version of this worksheet is also available at http://www.ianr.unl.edu/forms/forms.skp/ecb_2nd.html

_______________ Number of egg masses per plant x 3 borers per egg mass* = _______________ borers per plant

_______________ Borers per plant x 4% yield loss per borer** = _______________ percent yield loss

_______________ Percent yield loss x _______________ expected yield (bu per acre) = _______________ bushels per acre loss

_______________ Bushels per acre loss x $_______________ sale price per bu = $_______________ loss per acre

$_______________ loss per acre x 70% control*** = $_______________ preventable loss per acre

$_______________ preventable loss per acre

-$_______________ cost of control (product + application costs)

=$_______________ profit (+) or loss (-) per acre if treatment is applied

If preventable loss exceeds cost of control, insecticide treatment is likely to result in economic benefit.

* Assumes survival rate of three borers per egg mass; may vary with weather and egg mass size. ** Use 3 percent loss per borer per plant if infestation occurs after silks are brown. The potential economic benefits of treatments decline rapidly if infestations occur after the corn reaches the blister stage. *** 70% is an average, you may use another value if desired.

 

IRRIGATION AND NITROGEN FIELD DAY
Dennis Jarecke Farm
12:30 p.m. August 17, 2004

Best Management Practices are becoming and essential part of every farming operation. Learn some of the latest technologies and practices involved with irrigation and nitrogen management.

12:30 p.m. Lunch

1:00 p.m. Managing Nitrates In The Irrigation Water - Charles Shapiro, Cooperative Extension

1:20 p.m. Well and Water levels/Management Area Update - LLNRD

1:40 p.m. Soil Moisture and Water Monitoring Technologies - Bill Kranz, Cooperative Extension

2:00 p.m. Demonstration Plot Update - Eric Smith, LLNRD

Directions:
Jarecke Field – From the Loup River Inn South of Fullerton, go 3 miles east, ½ mile north, 3 miles east, 1 mile north and ½ mile east. The field is on the north side of the road.

MANURE MANAGEMENT FIELD DAY
Mahoney Farms
6:30 p.m. August 17, 2004

Manure Management and Best Management Practices are an essential part of every livestock operation. With the increasing regulatory side of manure management it is essential to keep up to date on the latest information.

Agenda

6:30 p.m. Food and Drinks

7:00 p.m. Well and Water levels, and Management Area Update - LLNRD

7:15 p.m. Update on Livestock Regulations – Rick Koelsch, University of Nebraska

8:00 p.m. Soluble Salts in the Soil and in the Water- Charles Shapiro, Cooperative Extension

8:20 p.m. Demonstration Plot Update - Eric Smith, LLNRD

Directions:
To Mahoney Demonstration Site: Using Highway 39 travel northwest of Genoa or southeast of St. Ed to 535 Ave. Turn south at 535 Ave. for about 2 miles. You will cross the Beaver Creek bridge and the Railroad tracks, then turn west and go 3 miles, then 1/2 mile north.