July 19, 2004
 

SOYBEAN INSECTS

Soybean Aphid

Soybean aphids can be found in many fields in the area, but at very low levels. Brian Lang reports an average of 0.5 aphids/plant in the research plots near Decorah.  To put this in perspective, here is a comparison of aphid populations in research plots near Decorah for the last few years.  The 2002 populations never justified treatments.

Average Aphids/Plant at Research Plots Near Decorah
                             2002      2003    2004
Early July                10         300       0.01
Mid-July                110      1,400       0.5

Because of the potential of this insect to populate under the right conditions, no one is saying to ignore aphids this season (not yet), but they will have to come a long way before treatments can be justified.

Japanese Beetles

Some soybean fields have been sprayed for Japanese beetles in the Cedar Rapids area. There is no economic threshold specific for this pest, but the general rule of thumb is to spray during the reproductive stages of soybeans if percent defoliation reaches 20%. Most people tend to overestimate percent defoliation. The following article contains pictures which can aid you in making estimates http://www.ipm.iastate.edu/ipm/icm/2002/7-29-2002/soydefoliation.html

Bean Leaf Beetle

The first of the 1st generation Bean Leaf Beetles are showing up now.  Information on scouting the first generation to make decisions on treating the second generation can be found at http://www.ipm.iastate.edu/ipm/icm/2001/7-16-2001/scoutblb.html.

CORN INSECTS

Corn Rootworm

The rootworm larvae are about done feeding on the roots.  They are pupating and the adult beetles are/will be emerging.  There have been many complaints about fields with significant root injury from rootworm feeding.  The main reason for these problems is probably because of displacement of soil insecticide from the "protection zone" due to excess rainfall.  If you want to rate rootworm control, next week is the best time to do so.  Go to the following web site for the methodology of rating rootworm control.
http://www.ent.iastate.edu/pest/rootworm/nodeinjury/nodeinjury.html

For more information check out the corn rootworm home page:
http://www.ent.iastate.edu/pest/rootworm/

Western Bean Cutworm (WBC)

This is a relatively new insect pest in corn for eastern Iowa.  The following article from the July 19 issue of the ICM Newsletter provides details on WBC and scouting method. 
http://www.ipm.iastate.edu/ipm/icm/2004/7-19-2004/wbc.html

It is time to scout for this insect now and continue as long as scouting reports (linked to the web site above) show high levels of moth flights.  The following link has a photo of an egg mass to help you ID it when scouting.
http://www.ipm.iastate.edu/ipm/icm/2003/7-28-2003/wbc.html
 

White Mold in Soybeans

        Some are reporting finding white mold in soybeans. I would expect this disease to be more widespread this year with the wet weather that we have had. Cobra applications have resulted in less white mold in research conducted by X.B. Yang, but it is likely getting too late in the season for that to be very effective.

Stress Induced Potassium Deficiency in Corn

            There are a number of fields again this year that have areas of stunted corn where the lower leaves are yellow along the leaf margins. This is a symptom of K deficiency, so soil test levels should be checked for future years. Over the past 15 years Ive seen numerous fields that show these symptoms in a haphazard pattern across the field except that the endrows usually look the best. If this endrow pattern is evident, it is likely that the symptoms are not only being caused by a soil fertility problem, but also an environmental phenomenon where slight differences in the soil structure make a big difference in root function.
 
            This year I am seeing this endrow pattern even in fields that don't show these K deficiency symptoms. In some fields it is evident that there is more surface compaction where the corn looks good and the soil is more mellow where the corn looks bad. This was also seen in many fields last year, and I assume has something to do with soil-to-root contact. There are other odd patterns showing up in both corn and soybean fields this year related to traffic patterns, wheel tracks, and past tillage patterns.
 

Upcoming Program

August 4 & 5, CCA Exam Preparation Training, Iowa City

I am offering a course designed to help ag professionals pass the CCA exams on August 4 (1:00-5:00) & 5 (9:00-1:00) in the Johnson County Extension Office at 4265 Oak Crest Hill Rd. SE in Iowa City. The cost for the 2-day course is $85, which includes study materials. The deadline to register for the course is July 20. The CCA test is being offered on Aug. 6, but the deadline has already passed for signing up to take the test this summer.