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| This newsletter, and previous issues from this year, can be found on-line at:
http://www.extension.iastate.edu/plymouth/info/cropupdate.htm
Crop Stress Update
Rain actually fell in almost all of NW and WC Iowa this week! This rain certainly helped a lot with both corn and soybeans – but exceptions occur to this statement. Many crop producers attended the drought meetings in Holstein and Mapleton this week (over 200), indicating the amount of problems that exist. A lot of these producers had fields, or at least parts of fields, that never pollinated due to moisture stress. Rainfall cannot help these fields. But the rain will fill kernel that are still present. We also did quite a bit of nitrate testing of cornstalks. At the Holstein site about 2/3 indicated free nitrates in the stalk – but over 90% in Mapleton. This could cause some feeding problems if this forage is fed to livestock.
For lots of good feeding information in a drought year, check out this web page at the Iowa Beef Center: http://www.iowabeefcenter.org/content/drought.htm. Also, in very dry years, aflatoxin can become a problem. Grain buyers and all producers should be familiar with this potential problem – and ways to look for it’s existence in your fields. See this ISU aflatoxin publication and review it before harvest: http://www.extension.iastate.edu/Publications/PM1800.pdf.
Lodged Corn Yield Losses
Significant portions of Plymouth and Cherokee County received high winds with the storms that passed through on Tuesday evening. Other areas probably had some of the same, too. There are a lot of acres where corn is about 2 feet tall right now. The question of the last two days – at least for me – is “What will this do to corn yield?” I tried to look for research data that discussed yield losses from lodging at this time, but all I could really find was data from pollination time and before. The worst case scenario, I suspect, is lodging at pollination. Some Wisconsin data would indicate yield losses of 12 – 25+% when lodged at pollination – depending on the year. Interference with pollination led to quite a few barren plants. But, these plants were already pollinated, so I would suspect yield loss to from this storm.
Although no data exists, I would suspect it might be more similar to the data from lodging at V-14 – maybe about a 10% loss. However, if very dry conditions return, we now have fewer good roots to sustain the stress. Also, stalk rot can be greatly increased in these damaged plants – creating a “wild card” to predicting yield. One thing we do know, harvesting corn has become a much bigger challenge in these areas!
Roger Elmore, the ISU Extension Corn Specialist, printed an ISU ICM Newsletter article on this topic last year. To read it, go to this web site: http://www.ipm.iastate.edu/ipm/icm/2005/8-1/rootlodge.html.
Soybean Aphids
Our soybean aphid monitoring is still showing aphids in most NW Iowa counties – some have had slowly increasing numbers in the past week – others hardly find any. All of our reporters have indicated that numbers remain below the treatment threshold; other reports indicate that some areas have reached the threshold and some treatments have occurred. Keep scouting. Remember, the treatment threshold is 250 per plant and rising, with 1000 per plant as an economic injury level. For the Minnesota Speed Scouting method – which reduces the time needed per field for analysis yet still looks quite accurate for population assessment based on the 250/plant trigger level - go to this 2004 ISU ICM Newsletter article: http://www.ipm.iastate.edu/ipm/icm/2004/7-26-2004/sampleaphids.html . Spider mites might be of concern in some neighborhoods due to the moisture stress that has been experienced. If spider mites are a concern and the aphid threshold is reached, then consider using Lorsban (or generic chlorpyrifos). The synthetic pyrethroids will not control spider mites, and may allow mite populations to increase rapidly.
Bean Leaf Beetles
Bean leaf beetle damage can be found. Remember that defoliation from this generation isn’t that big of a yield robber. Instead, ISU entomologists would suggest scouting your bean fields this week and to evaluate the population in your fields – then use this to determine if you should treat the NEXT generation in mid to late August. See threshold numbers and more details in this 2004 ICM Newsletter article: http://www.ipm.iastate.edu/ipm/icm/2004/7-12-2004/predictblb.html.
The 2006 Manure Management Clinic will be held on August 22-23, 2006, at the Field Extension Education Laboratory- located west of Ames. This clinic will focus on open lot manure management issues. Agenda and registration information can be found at: http://www.aep.iastate.edu/index.php?option=com_content&task=view&i... CCA credits are available.
Thanks for "Subscribing!" For more information contact:
Joel DeJong, ISUE FS/Crops
24 1st St, NW, LeMars, IA 51031
Phone 712-546-7835, FAX 712-546-7837
E-mail: [email protected]
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