July 7, 2005

Insect Update

Soybean Aphids

Soybean aphids are now being found in EC Iowa in some soybean fields, especially in the northern part of the area. A few fields have been sprayed, but aphid numbers have been very low so far in most fields where they have been found. Aphid reproduction is greatest during dry, cool weather, so the current weather may increase aphid numbers in areas that have missed the rains. Brian Lang has monitored aphid numbers during the last four years in NE Iowa. Although the numbers are higher this year than last, they are still much lower than they were in 2003. You can see his counts in the last ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2005/6-27/aphids.html. The economic threshold is considered to be 250 aphids per plant. For more information on soybean aphids see http://www.ent.iastate.edu/soybeanaphid/.

Potato Leafhoppers

 Potato leafhoppers have been causing problems again this year in many alfalfa fields. The best way to make decisions on managing potato leafhoppers is to use a sweep net. A rough rule of thumb is that a treatment is justified when 0.1 leafhoppers per sweep per inch of alfalfa height is found (for example 5 leafhoppers per 10 sweeps if the alfalfa is 5 inches tall). A couple of sources for sweep nets are  http://www.gemplers.com/a/shop/product.asp?T1=R13101&src=21SM001 and http://www.forestry-suppliers.com/product_pages/view_catalog_page.asp?id=5280 . A treatment can either be an insecticide or cutting the alfalfa. Cutting the crop will kill many of the nymphs and cause the adults to fly to another field. The regrowth should be monitored to see if an insecticide is still needed. Dry weather usually increases potato leafhopper problems. It is also common to find leafhoppers in soybeans. Some are confusing these with soybean aphids. It takes more leafhoppers to cause an economic problem in soybeans, with a treatment usually not justified unless damage to the beans is obvious. For more information on potato leafhoppers see http://www.ipm.iastate.edu/ipm/icm/1999/6-21-1999/potlhmang.html.

 

Disease Update

Asian Soybean Rust

The first observation of soybean rust in soybeans planted this year was made recently in southern Alabama and Florida. In both cases the rust was found in sentinel plots. Despite extensive scouting for the disease, there have been no reports further north. Brown spot can now be found in many soybean fields in SE Iowa. Like soybean rust it also first shows up on the lowest leaves. You need to look for pustules with a 15X or 20X magnifier in order to differentiate between brown spot and soybean rust. Pocket magnifiers can be found at the same 2 sources given above for sweep nets. If you think you see a pustule, make sure it is not a piece of dirt. It is not likely that we will see soybean rust in Iowa until it is confirmed further north in the U.S. To see the latest visit http://sbrusa.net/.

FOR YOUR CALENDAR

July 8, Ag Professional Tour, NE ISU Research Farm, Nashua.
Program runs 9:30 to Noon.  We will discuss "hot" topics at the time, including the latest developments of soybean aphid, rust, more results from the alfalfa S fertilization trials, herbicides trials, and any other observations and experiences from the group.  A $10 registration fee will be charged at the door, $25 for CCA credits (2.5 CCA credits available). Pre-registration is not required.

July 12, Grazing Field Day, Andrew Jackson Demonstration Farm, Andrew.
Starts at 6:30.  Discuss stockers and cow-calf; new forage seedings for pasture, and grazing corn.  Directions: N of Andrew in Jackson County on Hwy 62 to County Rd Y-61.