July 10, 2009
Twisted Whorls & Pale Yellow Leaves
Every year we see some fields where corn whorls become twisted up for a while, and then when the leaves pop out they are pale yellow or almost white. This year it appears to be especially widespread in the area. It is usually seen when we go through a big temperature change, such as from cool to warm, causing spurts of growth where the corn doesn’t unfurl properly. This year it appears to be especially common in areas where corn was stunted due to wet soils. Once the leaves are exposed to the sun for a day or two they green up. Usually the phenomenon does not affect the yield. Some herbicides, such as 2,4-D and dicamba, can also cause whorls to wrap up, but usually that occurs in an earlier stage of growth than what we are seeing now. See Roger Elmore’s recent article for more information and a picture at http://www.extension.iastate.edu/CropNews/2009/0709elmoreabendroth.htm.
Will Fungicide Applications Pay?
Some common rust and gray leaf spot is starting to show up on the lower leaves in some corn fields. Extensive trials, both in small plots and large field scale trials, conducted by universities and also by the Soybean Association in the past few years have shown an average yield increase of about 3-4 bu/A from applying foliar fungicides on corn, which would not likely pay for a treatment. However, averages don’t tell the whole story, since very large increases are sometimes found, especially on corn ground, where hybrids with low tolerance to diseases are grown. Pioneer has seen larger yield increases in the range of 7-8 bu/A.
When corn is near or at tasseling is the best time to scout for corn diseases. If disease lesions are found on or near the ear leaf on a majority of plants, a fungicide application may pay. Yield decreases do sometimes occur with fungicide applications, especially if made before tasseling. With all of the uneven corn out there due to the wet soils, it is important to wait until all of the corn has tasseled before making an application. See Alison Robertson’s recent article for more information at http://www.extension.iastate.edu/CropNews/2009/0706robertsonmueller.htm. Pictures of some corn disease symptoms can be found at http://www.ipm.iastate.edu/ipm/icm/2007/7-2/cornfungicides.html. The new corn field guide is also an excellent reference for corn disease symptoms and can be ordered at https://www.extension.iastate.edu/store/ItemDetail.aspx?ProductID=13118&SeriesCode=&CategoryID=&Keyword=CSI%20001.
I have not seen any soybean aphids in the area yet. Brian Lang reported this week that he is finding an average of 3-4 aphids per plant with about 70% of the plants infested in NE Iowa on research plots. This is lower than what was found in 2007, but higher than the “off-aphid” years of 2002, 2004, and 2006. The recent cool weather is ideal for aphid reproduction. National aphid activity can be tracked by viewing the following USDA web site: http://sba.ipmpipe.org/cgi-bin/sbr/public.cgi?host=All%20Legumes/Kudzu&pest=soybean_aphid
The risk of an epidemic in Iowa remains very low. Rust development can be monitored at the following USDA web site: http://sbr.ipmpipe.org/cgi-bin/sbr/public.cgi
Foliar diseases, including lepto leaf spot and common leaf spot, have been showing up in alfalfa due to the excess rainfall. Fields with extensive leaf disease problems may benefit from harvesting early to try to prevent as much leaf drop as possible. Alfalfa has also been stunted in some fields due to waterlogged soils.
Potato leafhopper damage has been extensive in some fields. A sweepnet is still the best way to scout for potato leafhoppers. Once the stunting and “hopperburn” is seen, a lot of potential yield has already been lost. A general rule of thumb for conventional alfalfa is to treat when there is 0.1 leafhoppers per sweep per inch of alfalfa growth (1 leafhopper per sweep with 10” alfalfa). As alfalfa prices go up, the action threshold goes down.
FOR YOUR CALENDAR
Crop Management and Diagnostic Clinics
July-September – Ames
The Field Extension Education Laboratory is a 43-acre teaching and demonstration facility dedicated to providing a hands-on learning experience for crop production professionals. The demonstration plots are used to show a wide range of management problems, solutions, and diagnostic challenges. “We make the mistakes on these plots so you won't in the future!” The clinics and programs are taught by Iowa State University staff and faculty and invited specialists from other institutions and industry. Modern, air-conditioned classroom facilities complement the in-field sessions, all of which are within walking distance. Current open programs for this summer include the following:
July 13-14, Field Diagnostic Clinic
July 15-16, Crop Management Clinic
Aug 25-27, Iowa Drainage School
September 2, Alfalfa Production Clinic
September 3, Corn Disease Diagnostics and Management
September 15, Soil Management Clinic
For other Agribusiness Education program information, check out the Homepage at: http://www.aep.iastate.edu/homepage.html
New Crop Technology Tour
July 28 6:00 p.m.
Jeff Bermel Farm – Keota
(corner of W15 & G32)
Erin Hodgson, ISU Extension Entomologist, will discuss soybean aphid management at the field day. The new soybean aphid resistant variety can be viewed. Other soybean pest topics, as well nitrogen and manure management topics will be discussed. Free meal sponsored by DOW.
Advances in Precision Ag Expo
ISU SE Iowa Research & Demonstration Farm – Crawfordsville
September 17 10:30 a.m. - 4:30 p.m.
Come see the latest in precision ag technology, including RTK guidance systems, auto-steer, automatic shut-off planters and sprayers. The expo will feature field demonstrations and industry exhibits on the latest technology. More details will be available soon.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
Nondiscrimination Statement and Information Disclosures