August 5, 2005
The cooler temperatures will provide
some relief for the crops, but, unfortunately, most got little rainfall. Although corn pollinated well in many fields, some
kernel abortion has occurred causing tips of ears to be barren. Some fields, on the other hand, had very poor
pollination. Corn rootworm beetle populations
have also been very high in some fields and silk clipping occurred prior to pollination
further reducing yield potential. Continued
dry weather will take its toll on the soybean crop as well.
A few web sites that you may want to
Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS) Drought
NOAA NWS Drought Monitor
NOAA NWS 6 10 Day
NOAA NWS 8 18 Day
For those wanting to estimate corn
yields, its just a matter of counting kernels:
Pull several ears of corn at random and count the number of rows of kernels and the number
of kernels per row. Ignore kernels less than
half size at the tip of the ear. Also measure
off 1/1000 acre along one row in several places in the field and count the number of ears:
1/1000 acre = 17
ft 5" in 30" rows
14 ft 6" in 36"
13 ft 9" in 38" rows
(For 20" rows, count 2 rows 13' 1" long)
Number of kernels per 1/1000 acre =
kernels per row X rows per ear X ears per 1/1000 acre.
Divide this number by about 90 to get bu/A (since there are
about 90,000 kernels per bushel). If you think
kernel size and weight will be smaller than normal, divide by a larger number (100+).
Two Spotted Spider Mites Theyre Back
Many fields that have been treated
with chlorpyrifos (Lorsban 4E,
Eraser, Nufos, etc.) once again have spider mite infestations.
An insecticide is recommended if spider mite
damage is occurring in the field, mites are present, and hot, dry conditions are expected
to continue. If a second insecticidal
treatment for spider mites is needed, use a different active ingredient than was used in
the first application. The Lorsban 4E label states that, if follow-up applications are needed,
make a follow-up application with a non-chlorpyrifos product that is effective against mites. Essentially that sugegsts a dimethoate product, such as Dimethoate 400, Dimate, etc. Continue to monitor fields for two spotted spider
mites until the field reaches maturity stage R7, which is when one normal pod on the main
stem has reached its normal mature color, usually brown or tan. For more information see the July 22, 2002 ICM
Newsletter at http://www.ipm.iastate.edu/ipm/icm/2002/7-22-2002/spidermites.html
and the July 18, 2005 article at http://www.ipm.iastate.edu/ipm/icm/2005/7-18/spidermite.html.
Soybean aphid numbers have increased
above the economic threshold in some fields. Aphid
numbers usually peak in mid-late July and then have a second peak in August. Numbers have declined in some fields in the past
week even when they are increasing in nearby fields. Every
field is different, so fields need to be monitored closely for at least a couple of more
weeks. Usually aphid numbers drop off rapidly
sometime after mid-August. Treatment is
recommended if aphid numbers are increasing and surpass 250
aphids/plant. The cooler temperatures
will decrease moisture stress to the soybeans, but unfortunately may result in greater
soybean aphid reproduction. Under the right
conditions, populations can double in 2-3 days, so 250/plant can increase to 1000/plant in
less than a week. For more information on
soybean aphids, see http://www.ent.iastate.edu/soybeanaphid/
and the July 11, 2005 ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2005/7-11/aphids.html.
Asian Soybean Rust
There have been more finds in the far
southern U.S. Almost all of the finds have
been on sentinel plots, research plots, or on kudzu. For the latest see http://sbrusa.net/.
Other Soybean Foliar Diseases
For some reason, downy mildew, a
disease favored by cool, humid conditions, has been common this year in many soybean
fields. Frogeye leafspot
is also showing up in some fields. Photos of common soybean diseases can be found at: http://www.extension.iastate.edu/Publications/PM1989.pdf.
Soybean Cyst Nematode
With all of the attention on aphids
and rust, don't forget the soybean pest in Iowa that still causes the most yield lost state-wide. Damage from the pest is more evident in
dry years. The July 25 ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2005/7-25/scn.html
provides photos and scouting information to help deal with this pest.
Potato Leafhopper numbers continue to
be high in many fields, so scouting of hay fields continues to be an important
activity. For information on managing potato leafhopper, see pages 107 - 110 of the
June 21, 1999 Iowa State University Integrated Crop Management Newsletter or http://www.extension.iastate.edu/Pages/eccrops/potatoleafhopper.html
. A couple of sources for sweep nets are http://www.gemplers.com/a/shop/product.asp?T1=R13101&src=21SM001
Late Summer (Fall) Seeding of Forages
Most likely, it will be too dry to
attempt a late summer (fall) seeding of forage crops unless the weather becomes more moist and we can get the seeding done by August 20. For more information, see Late
Summer (Fall) Seeding of Forages.
FOR YOUR CALENDAR
Profitable Pastures August
12, 2005, Lancaster Research Station, Lancaster, WI.
Demonstration Farm Field Day 4:00 p.m., August 17, 2005, Andrew, IA.
Research and Demonstration Farm (Horticulture) Field Day 3:00 p.m., September 13,
2005, Fruitland, IA.
Southeast Research and
Demonstration Farm (Agronomy) Field Day 1:30 p.m., September 14, 2005,