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Serving: IA
a fungus on a soybean leaf
WILL IT PAY? Plant pathologists offer timely guidelines to help determine if applying a fungicide will be a sound investment this year.

Deciding on foliar fungicide tougher for late-planted crops

Lower yield potential of late crops complicates fungicide application decision-making.

Many farmers are wondering if applying foliar fungicide will provide an adequate return on investment for their late-planted corn and soybeans this year. A record number of corn and soybean acres were planted late and have reduced yield potential.

A new article released through the Crop Protection Network (CPN) discusses how to make fungicide decisions for corn and soybeans, given the delayed planting scenarios across the Midwest in 2019. The article considers yield potential at various planting times in the north-central region, as well as the previous wet and cool conditions when evaluating for a positive return on investment.

Also considered is the potential damage a frost can do to overall yield, which can impact return on investment. Of interest to Iowa farmers and crop consultants is the threat of diseases during reproductive growth stages, as much of Iowa's corn and soybeans are now entering those stages.

Scout prior to reproductive stages

Iowa State University plant pathologists Daren Mueller and Alison Robertson, along with their colleagues from other universities in the Midwest, co-authored the CPN article.

The article states: "Disease development prior to grain fill will have a greater impact on yield reduction than when disease develops later in the cropping season. In a typical year, crops are usually at a more mature stage of development when diseases become prevalent, and thus there is less impact on yield. This year, however, with delayed planting and reduced growing degree day accumulation, corn and soybean development in many areas is two to four weeks behind normal.”

Disease development prior to or during early grain fill could significantly affect yield, the article notes. “Thus, scouting fields for yield-limiting diseases prior to reproductive stages will be crucial in determining whether or not to apply a fungicide.” 

Corn diseases already showing up

Diseases like gray leaf spot and northern corn leaf blight have already been confirmed on corn prior to tassel in some areas. Gray leaf spot is favored by warm temperatures, high humidity and heavy dews. Northern corn leaf blight is favored by cool temperatures and wet leaves. Both of these diseases typically start in the lower canopy, and if favorable conditions continue, can quickly spread to the upper canopy and be very damaging.

Similarly, development of tar spot before R2 to R3 growth stage may cause considerable damage and yield loss. University research indicates that fungicide applications occurring at tasseling or silking (VT to R1) are most effective at minimizing the impact of gray leaf spot and northern corn leaf blight, and protecting yield in susceptible hybrids.

Southern rust could also be problematic in late-planted corn in 2019. This disease moves northward each year and may impact yields in late-planted corn. Fungicide applications prior to milk stage (R3) may be needed to limit yield impact in certain cases. 

Watch for these soybean diseases

Frogeye leaf spot and septoria brown spot are two soybean foliar diseases that are prevalent in wet and humid weather. Septoria brown spot generally is not an economic threat to soybeans but may cause yield reductions if infection reaches the upper canopy. It’s important to begin scouting bean fields for frogeye leaf spot and septoria brown spot around beginning flower (R1 growth stage) to help make a foliar fungicide decision.

Generally, fungicide applications for management of frogeye leaf spot on susceptible bean varieties are made at beginning pod (R3). It’s not likely that foliar fungicide applications to soybeans prior to reproductive stages will be economical. If using foliar fungicides to manage these diseases, use products that contain multiple fungicide classes, as resistance to strobilurin (quinone outside inhibitor) fungicides has been observed in multiple states by both frogeye leaf spot and septoria brown spot fungi.

In the northern soybean-production regions (I-80 and north) white mold (sclerotinia stem rot) may be of concern. All stages of soybeans are susceptible to infection by the white mold fungus, but most infection occurs through open flowers during periods of cool and wet weather. If Iowa continues in a cool, wet weather pattern this year, late-planted soybeans will flower further into the growing season due to less accumulated growth days. Plants will be more susceptible to infection for a longer period of time when the weather is very conducive to disease. 

Make fungicide decision field by field

Whether or not to use a foliar fungicide will have to be considered on a field-by-field basis. The Crop Production Network article goes further in depth, explaining what field conditions have the potential for higher returns on investments. View the full article here.

CPN also has valuable resources available such as disease encyclopedias, disease management publications and CCA exams for continuing credits — all for free.

Source: Iowa State University, which is responsible for information provided and is wholly owned by the source. Informa Business Media and subsidiaries aren’t responsible for any content in this information asset.



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