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9/21/2009 - 9/27/2009

Crop and Weather Report - Sept. 21

By Doug Cooper, Extension Communications

ISU Extension climatologist Elwynn Taylor, integrated pest management specialist Rich Pope and soybean agronomist Palle Pedersen are this week’s crop and weather report guests. Taylor says he expects a normal frost date this year which should benefit most crops. Pope shares how the September weather has been favorable to this year's harvest. Pedersen reports early harvesting is beginning in southwest Iowa; the cool weather earlier in the year may have cut yield potential.

Degree Days - Watching, Waiting and Staying Warm

By Rich Pope, Department of Plant Pathology

A near-perfect week!  Sept.13 - 20 provided seasonally normal temperatures, bright sunshine and some light rain at week's end; all of which are favorable to Iowa's maturing crop. As of Sept. 21, the mid-range forecast is calling for night temperatures that should NOT approach killing temperatures. If this bears out, it will mean no early frost in 2009.   

Degree day accumulation map for September 20, 2009

 

Late-season foliar diseases, especially northern corn leaf blight of corn, flourished on susceptible hybrids, and has likely reduced yields some in spots.  Soybean aphids were still found in some fields close to senescing, and winged aphids and nymphs were eary to find in central Iowa on it's overwintering host, buckthorn.

 

 

Rich Pope is a program specialist with responsibilities with Integrated Pest Management. Pope can be contacted at ropope@iastate.edu or by calling (515) 294-5899.

Manage Soybean Diseases at Harvest Time

XB Yang, Department of Plant Pathology

Two soybean diseases - sudden death syndrome (SDS) and soybean white mold - are wide spread in Iowa this season. In August SDS showed up in almost every Iowa region, with some regions having high disease intensity. Large patches of soybean with SDS symptom are obvious from south to north. White mold, a disease that can drastically cut yields, started to get the attention of producers in late August. This year white mold is so wide spread that agronomists report observing it in many soybean fields in southern Iowa.  In northern Iowa, patches of soybean killed by this disease were so abundant that I found them in nearly every soybean field while attending a field day Sept. 18. Before this year, the highest loss from white mold in my book was about $32K in a farm. This year, a farmer told me he estimated a loss of $40K to his farm from this disease.

In the past, rotation effect made white mold outbreaks an even year occurrence. This year, is the first time we have seen a wide occurrence in an odd year. For most of the fields where white mold was found, the disease was scatted in small patches. To prevent the disease from developing into an every year problem, we should minimize the spread of this disease at harvest by limiting the size of disease patches. When combining a soybean field infested with white molds, harvest the disease patches last so that the combine will not spread infested plant materials to non-infested area. 

As for SDS, the management of its risk for future soybean fields should start when you harvest your corn fields. Our greenhouse and field studies show that corn is a good crop for harboring SDS pathogen, especially corn kernels. We compared the survival of SDS fungus in different crop residues (corn or soybean) which included different parts of a crop (root, seed, straw). We found that treatment that had corn kernel density equal to average harvest loss consistently had the highest SDS fungus population. Our finding is consistent with producers’ observations that severe outbreaks of SDS can occur after a few years of continued corn production. Our results suggest that a nice and clean harvest of corn field should help reduce the risk of SDS, while a high amount of harvest loss increases SDS risk the next time soybean is planted. 

 

XB Yang is a professor of plant pathology with research and extension responsibilities in soybean diseases. Yang can be reached at (515) 294-8826 or by emailing xbyang@iastate.edu.



This article was published originally on 9/28/2009 The information contained within the article may or may not be up to date depending on when you are accessing the information.


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