Corn beginning to Dent
Estimate corn grain yield
Staging soybean development
Two-spotted spider mites
Stay the course with aphid monitoring
Castana Field Day
Needs assessment survey
Introduction
Area crops are capitalizing on recent precipitation and the milder
temperatures as they fill ears and pods. Corn development is moving
into the dough and early dent stages while soybeans are approaching
R6. Now is a good time to venture into corn fields and get a first
good estimate on grain yields. For most pest situations, soybeans
need to be protected through the R5.5 to R6 stage, use the included
guides to stage your crop. Spider mites can be found in area
soybean fields, be sure to monitor their populations, particularly
if an aphid insecticide was applied to the field. Soybean aphids
remain present, but in most fields, remain below threshold.
|
Table 1. Degree-Day Weekly Accumulation |
|
|
2005 |
2004 |
2003 |
14-Yr Ave |
|
Aug 8-14 |
147 |
77 |
144 |
139 |
|
Forcasted Aug 15-21 |
134 |
90 |
189 |
127 |
Crop Management
Corn Development
is nearing partial or full dent in many fields. At R5 (Dent, 35-42
days after silking) all or nearly all kernels are dented or denting.
The kernels are drying down now beginning at the top where a small
hard white layer of starch is forming. This starch layer appears
shortly after denting.
Estimate
corn grain yield
{(Ear #) x (# kernel
rows) x (# kernels per row)}/90 = Estimated Yield bu/acre
Soybean Development
Criteria for determining soybean developmental stages:
-
R5 = Seed is at least 1/8 inch long in the
pod at 1 of the 4 uppermost nodes on the main stem. About 15
days to R6.
-
R6 = Pod with green seed that fills the
cavity at 1 of the 4 uppermost nodes on the main stem. About 18
days to R7.
Growth rate of
the seeds and whole plant is still very rapid at early R6. This
rapid rate of dry weight and nutrient accumulation begins to slow in
the whole plant shortly after R6 and in the seeds shortly after
R6.5.
Pest
Management
Two-spotted Spider
Mites This is another
pest that has been showing up in NW Iowa soybean fields. Some of
the aphid insecticides should help keep these in check, but some do
not. Know if mites are there in significant numbers before spraying
for aphids, and check the insecticide label for mite control if they
are a problem. The good news is that cooler weather slows them
down. Be sure to check for mite activity and not just the foliar
symptoms. I looked at a field late last week that was crawling with
mites, I rechecked the field today before advising to spray the
field, and the mites were gone. See this 2002 ISU ICM Newsletter
article if you want more info on this pest:
http://www.ipm.iastate.edu/ipm/icm/2002/7-22-2002/spidermites.html.
Soybean
Aphid Aphid populations
continue to remain steady to slightly increasing in most area
soybean fields. Small “hot spots” with 500 to 1000 aphids per plant
continue to be reported. These hotspots generally are very small,
either on field borders or areas less than 20 ft in diameter.
Therefore it is important to scout your entire fields aggressively.
Minnesota’s pest survey (August
12) reports several fields in southern MN have been sprayed, yet
in other fields, aphid populations appear to be declining.
Estimated
aphid population growth rate.
The SAGE model predictions for this week are showing an aphid
population growth potential of doubling every 2 days. But I think
with increasing beneficial populations and increased moisture in the
canopy, most fields will not see population growth any were near
this potential. Be diligent in scouting fields with known
infestations. Refer to my soybean aphid web page for population
growth estimates based on different current populations: http://www.extension.iastate.edu/nwcrops/soybean-aphid.htm.
Crop Update
Live
Join me in the “Crop
Update Live” web meeting to be held on Friday morning at 7:30 am. I
will review and update crop and pest management information
presented in this week’s newsletter. Click on this link
http://breeze.extension.iastate.edu/r52004619/” Friday morning
to join the meting. To view a recording of the meet, browse to my
Crops homepage:
http://www.extension.iastate.edu/nwcrops/.
Fall
Livestock and Crops Field Day
The Iowa State University
Western Research and Demonstration Farm near Castana, IA will be
hosting its annual fall livestock and crops field day on Thursday,
August 25, from 1 – 3:30 pm. Topics covered at the field day
include: Swine Welfare, Animal ID, Producers Role in Meat Quality,
New Value Added Meat Cuts, What has happened with aphids and rust,
Solid Waste Settling March ’06 Compliance and Results of feeding
Condensed Corn Distiller Soluables. For more information contact
the Monona County extension office at 712-423-2175
ISU
Extension Needs Assessment Survey
All
Iowans are encouraged to participate in a statewide needs assessment
for Iowa State University Extension. ISU Extension is in the
process of doing some long range planning for the years 2006-20011,
and your help in identifying what we need to work on is requested.
To do that, a web-based survey designed to obtain input from a broad
base of Iowans is now available at all Iowa county extension web
sites. Results from the survey will be used by local county ISU
Extension councils throughout the state to confirm needs, set
priorities and identify regional issues. We would like your help!
Go to your local county extension web page (go here:
http://www.extension.iastate.edu/Counties/state.html, point and
click on your county), and do the survey found in the top right-hand
corner of the web page of your county Extension Office.
