Integrated Crop Management News

Links to these articles are strongly encouraged. Articles may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If articles are used in any other manner, permission from the author is required.

Preventative vs. Curative Fungicides

July 29, 2008

By Daren Mueller and Alison Robertson, Department of Plant Pathology

We have received several questions about selection of fungicides, especially with regards to deciding between “curative” and “preventative” fungicides. People want to know if they should be applying a strobilurin fungicide, triazole fungicide, or a premix of both. 

More on Fungicide Application Questions

July 24, 2008
Image of a comparison of bacterial blight and brown spot

By XB Yang, Department of Plant Pathology


Near the end of July, a common time for fungicide applications, there are many questions about using fungicides to control soybean diseases. This article responds to questions producers are currently asking about soybean and corn fungicide use.


Here Come the Bean Leaf Beetles!

July 22, 2008
Image of a newly-emerged bean leaf beetle

By Jon Tollefson and Marlin Rice, Department of Entomology


The bean leaf beetle overwinters as an adult that feeds on young soybeans in May and June. They lay eggs that produce the first generation, which attacks beans in July. The subsequent generation, the second, is of most concern when protecting the plant from the beetles feeding because it attacks the pods and beans as well as foliage.


Is that Common or Southern Rust Showing up in Iowa Fields?

July 22, 2008
Image of lesions characteristic of common rust

By Alison Robertson, Department of Plant Pathology


Is that common or southern rust showing up in Iowa fields?  Chances are it is common rust. It has probably been too cool and wet so far this growing season to see southern rust. Symptoms of the two rusts are very similar but there are subtle differences.


Unusual Foliar Diseases Showing up in Iowa Corn

July 19, 2008
Image of light tan, round to oval spots characteristic of Holcus leaf spot

By Alison Robertson, Department of Plant Pathology

Over the past week I have received emails, phone calls and samples of two leaf spots that occur in Iowa from time to time, Holcus leaf spot and Physoderma brown spot.


HOLCUS LEAF SPOT

Holcus leaf spot is caused by the bacterium Pseudomonas syringae. Symptoms are light tan (sometimes almost white), round to oval spots, which may appear water soaked at the margins or have a light brown border occur on the lower leaves (Figure 1 and 2).

Correction to the European Corn Borer Economic Threshold Spreadsheet

July 15, 2008

By Jon Tollefson, Department of Entomology

A user of the revised Economic Threshold that we recently published in the Integrated Crop Management News noticed that there was an incorrect function.  I didn’t see it because it didn’t make a difference with the numbers that I used worked through it.  We have replaced the previous threshold spreadsheet with a corrected one.

Not a Bad Week, All in All

July 15, 2008
Image of base 50 degree F degree days in regions of Iowa from May 1 to July 13, 2008

By Rich Pope, Department of Plant Pathology


The week ending July 13 was close to average in terms of temperature, and crops have generally made slow but steady improvement in condition over the period.



Soybean Cyst Nematode Females now Apparent on Soybean Roots

July 15, 2008
Image of adult SCN females on a soybean root and nitrogen-fixing nodules

by Greg Tylka, Department of Plant Pathology


Many Iowa soybean fields may be infested with the soybean cyst nematode (SCN) but the infestations may not be known because SCN does not always cause obvious, above-ground symptoms. In fact, yield loss of up to 40 percent has been documented without above-ground symptoms occurring.


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