Northwest Iowa Crop Update Newsletter by Todd Vagts ISU Extension Crops Specialist Counties Served:  Carroll, Calhoun, Crawford, Ida, Monona, Pocahontas and Sac.
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Volume 2, Number 21

Northwest IA Crop Update, August 12, 2002
(Word Document)

In this issue 
  Western Research Farm Field Day
  Corn beginning to dent
  2nd Generation BLB control strategies
  A new pest in Alfalfa – Cowpea Aphid
  Pasture nitrogen application

Introduction

The Iowa State University Western Research and Demonstration Farm will host the annual fall livestock on forage field day on August 27.  The afternoon sessions will highlight research at the farm addressing current and future livestock and forage issues.   Western bean cutworm moth flight is essentially over, now would be a good time to re-evaluate fields to see if egg lay was missed in any fields.  Not that we don’t have enough new pests to deal with, now the Cowpea aphid has shown up in N.W. Iowa alfalfa fields.  Nitrogen applied in early August to grass pastures can boost fall forage production.

Western Research and Demonstration Farm Livestock and Forage Field Day

Please plan to attend the Iowa State University Western Research and Demonstration Farm

Livestock and Forage Field Day on Tuesday, August 27, 2002 - Castana, Iowa, Time 1:00 – 5:00 p.m.

Session Topics Include:

·        Ethanol Co-products for Beef Cattle. 

Pete Olson and Jerry Weiss, ISU Extension Beef and Swine Specialists

·        Management of Warm-Season Grass Pastures

Indi Braden, ISU Agronomy Department

·        Triticale Research and Potential Production for Western Iowa

Margaret Smith, Extension Sustainable/Value Added Agriculture

·        Cuphea, A New Crop for Western IA?

Russ Gesch, Frank Forcella and Gary Amundson, USDA-ARS, Morris, MN

·        Integration of Pasture into A cattle Finishing Program

Peter Hoffman, ISU Animal Science Department

·        Local Crop and Pest Management Issues and Topics

Todd Vagts, ISU Extension Crop Specialist

·        Prairie Restoration Research Studies

Brian Wilsy, ISU Botany Department (Presented by Todd Vagts)

·        Dead Livestock Disposal Project

Kris Kohl, ISU Extension Ag. Engineer

Location:  The Livestock and forage Field Day will be held at the Western Research and Demonstration Farm, Located four miles east of Castana on county highway E34

Growing Degree Day Accumulation and Crop Development
Corn development is at the R4 (Dough) and is progressing to R5 (Dent).   Just prior to R5, kernels along the length of the ear begin to dent or dry on top.

Estimate corn grain yield

{(Ear #) x (# kernel rows) x (# kernels per row)}/90 = Estimated Yield bu/acre

Pest Management
Bean Leaf Beetle (2^nd Generation) has begun or will be emerging soon in area soybean fields.  If 1^st generation population levels exceeded thresholds (for control of 2^nd generation) begin scouting and make treatments as necessary (1st generation threshold for 2nd generation treatment).  Consider defoliation potential of both Grasshopper and BLB when making control decisions. 

If you did not scout 1^st generation beetles, use the thresholds in Table 1 to make management decisions.  Most damage from 2^nd generation BLB will be from feeding on the pod, look for this when scouting. 

Table 1. Bean leaf beetle economic thresholds in reproductive-stage soybeans.*

A New Insect Identified in NW Iowa - Cowpea Aphids in Alfalfa!  Recently Marlin Rice, ISU Extension Entomologist, unofficially confirmed the presence of Cowpea Aphid in northwest Iowa alfalfa fields.  This pest typically as been a problem in western states.  The immature aphids are dark gray; the mature ones are shiny black.    

OSU Cooperative Extension recommends that on alfalfa less than 10 inches tall, 50 aphids/stem should be used as a threshold. On alfalfa taller than 10 inches, 100 aphids/stem may be used. The Texas website suggests a threshold near or below that of blue alfalfa aphid: Height less than 10 inches: 10-12 aphids per stem or 50 per sweep. Height greater than 10 inches: 40-50 aphids per stem or 200 per sweep. These thresholds have not been verified locally, but may be helpful in making treatment decisions.
Excerpted from the University of Nebraska, August 9, 2002 Crop Watch.  Keith Jarvi Integrated Pest Management Assistant, Northeast REC and Tom Hunt; Extension Entomology Specialist, Haskell Ag Lab, Northeast REC

More information on the Cowpea aphid can be obtained form the following web addresses:

·        Kansas State University: http://www.oznet.ksu.edu/dp_entm/extension/newsltrs/26Apr99.pdf

·        Kansas State University: http://www.oznet.ksu.edu/library/ENTML2/MF809.PDF

·        University of California: http://danr.ucop.edu/news/Jan-June2000/cowpeaaphid.html

·        University of California at Davis: http://www.ipm.ucdavis.edu/PMG/r1301511.html

Pasture Fertility Management
Are you considering fertilizing that pasture after a good rain?  Research at the ISU McNay research farm indicated that nitrogen application can be profitable.  A Nitrogen rate of     40 - 60 lbs/A for K. bluegrass or 60 - 80 lbs/A for S. bromegrass, Orchardgrass and Fescue produced 600 - 1,000 lbs additional forage.  This equals $55 - $33/ton hay as-fed basis or about 2 - 3 weeks extended grazing/cow/A.  Bottom line... early August N application was profitable in a rotational grazing system.

Brian Lang, ISU Extension Crop Specialist, NE Iowa

(Word Document)