Earn CEUs and Improve Your Knowledge of Phytophthora and Pythium

Oomycetes are some of the most devastating plant pathogens. Some of you may have family who settled in the United States as a result of the Irish Potato Famine in which over one million people died, while another one million emigrated. The pathogen that devastated Ireland\u27s potato crop in the mid-1800s is an oomycete calledPhytophthora infestans. Some oomycetes that are likely more familiar to us here in Iowa are Phytophththora sojae and Pythium species. These pathogens are usually associated with seedling blights on corn and soybean, although P. sojae can affect soybeans throughout the growing season. Some of you may have experienced devastating losses to these pathogens in your corn or soybean field

Know Your Spots as Foliar Diseases Show up in Corn

Several foliar diseases are being reported in corn at this time, and it is important to be able to differentiate between the various leaf spots because management options will vary. Some leaf spots are caused by bacteria and therefore cannot be managed with a foliar fungicide. Development of other leaf spots will slow considerably in the extreme hot temperatures we are currently having. However, there are some leaf spots that favor these hot, humid conditions and, depending on disease pressure and hybrid susceptibility, management with a foliar fungicide may be warranted

Diseases Showing Up in Iowa Corn

Northern corn leaf blight (NCLB) (Figure 1) has been reported from several fields in southern Iowa. You will remember that this disease was widespread in Iowa in 2014, and severe on susceptible hybrids. Since the fungus survives the winter in corn residue, we likely have above normal inoculum present. Cool weather with frequent precipitation favors infection of corn by the fungus and disease development. New lesions may develop every 4 days (Muiro et al., 2010) when conditions are favorable (susceptible hybrid, cool and wet weather). Warm dry conditions will slow or halt disease development until favorable conditions return

Remember to scout for corn stalk rots

Stalk rot occurs to some extent in every cornfield in Iowa each year because as corn stalks mature, they naturally decay. However, stalk rot can occur prior to physiological maturity and is considered a disease problem, which reduces yields in two ways. First, affected plants die prematurely (Fig. 1) and therefore produce lightweight ears with poorly filled kernels. Second, and this is more common, plants with stalk rot easily lodge (Fig. 2), which makes harvesting difficult, and many ears are left in the field

Don’t Stop Now!

Now is not the time to stop scouting. It may not be pleasant out there (think pollen and hot), but the weather the past couple of weeks has been favorable for gray leaf spot development. Gray leaf spot development is favored by mean daily temperatures between 72 F and 85 F, and high humidity (higher than 90%). I have had several reports this past week of fields in which the gray leaf spot has developed up to the ear leaf. Northern leaf blight development has also been progressing in several fields in central Iowa. I have been scouting my field plots the past couple of days and also have noticed that gray leaf spot and northern leaf blight have developed rapidly in the past two weeks. One thing I noted was disease severity was hybrid specific. I have several hybrids in my plots, but only one or two may be at threshold for a fungicide application (disease present on the third leaf below the ear leaf or higher). The affected hybrids always are rated more susceptible to disease

Time to Scout for Stalk and Ear Rots

When corn reaches black layer, the crop should be scouted for stalk and ear rots. Anthracnose stalk rot is apparent in many fields across the state andDiplodia ear rot has been reported. The incidence of corn ear rot should be determined before harvest since ear rot diseases can reduce yield and quality of the corn harvest. Furthermore, some of the fungi that infect corn ears may produce mycotoxins, which are harmful, and can be fatal, to livestock

Eyespot and Gray Leaf Spot Severity Continue to Increase in Iowa

Gray leaf spot (GLS) has reached threshold levels in some corn fields in southwestern Iowa and a fungicide application should be considered for these fields. As many as 5-20 gray leaf spot lesions are present on the ear leaf and, in some fields GLS lesions are also present on the leaf above the ear leaf. Approximately one in two plants are infected, and corn is at growth stage VT/R1. A couple of weeks ago, I summarized data from Greg Shaner at Purdue University, that showed fungicide applications can be profitable when disease pressure is high and the infected hybrid is susceptible to gray leaf spot

Wheat scab prediction model available to growers

Wheat in southern Iowa has now headed. Wheat is most susceptible to Fusarium head blight (scab) during flowering growth stages; however, some infection can occur during kernel development. Although scab often is not a problem in Iowa, if weather conditions are wet the disease can threaten wheat crops as it did in 1996

Corn Disease Publication Now Available

Corn producers and other professionals in the agriculture industry depend on the Iowa State University Extension publication Corn Diseases, PM 596. It is always in high demand, and after a revision, is back on the shelf to be ordered from the Extension online store

Assess Seedling Health When Doing Stand Counts

Corn planting is virtually done, and across Iowa small green spikes are becoming visible as seed germinates. Now is the time to start assessing stands. Doing stand counts involves more than just counting the number of seedlings that have emerged. Seedling health should also be assessed. ISU Extension field agronomists Virgil Schmitt and Mark Carlton have reported that seedling rots are prevalent in southeast Iowa