August 5, 2005
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 follow are:
Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS)
NOAA NWS Drought Monitor
NOAA NWS 6
10 Day Weather Outlook
NOAA NWS 8
18 Day Weather Outlook
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
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.
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
(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
Pastures August 12, 2005, Lancaster Research Station, Lancaster, WI.
Andrew Jackson 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.
Research and Demonstration Farm (Agronomy) Field Day 1:30 p.m., September 14,
2005, Crawfordsville, IA.