It’s difficult to breed for genetic resistance to corn diseases. By the time plant breeders develop resistant hybrids, new mutations or even new diseases, such as tar spot, show up. Old disease organisms mutate fast, and new diseases blow in from other areas.
Lots of pathogenic residue exists from last year. With the wet spring that occurred this year, you can expect more diseases in 2019. You must be proactive in scouting and ready to apply foliar fungicides, if needed.
Several new fungicides are available this year that you might want to try, assuming they’re cost-effective. Contact your chemical supplier and be proactive in making reservations as needed. Hopefully, Mother Nature will be kinder this year during the growing season and won’t favor disease organisms. However, as noted, there is a lot of inoculum of disease organisms on the ground, ready to attack if conditions are conducive. You must be ready to protect crops.
What steps should you take to defend crops from diseases? First, definitely rotate and avoid planting corn after corn this year. Second, plan on using foliar fungicides, if needed.
In 2018, fungicides that were applied on time certainly paid off. Some growers in central and southern Indiana reported that fields where foliar fungicide was applied after pollination was complete yielded 15 to 20 bushels per acre more compared to where no fungicide was used.
The ear leaf, which is the leaf attached to the topmost ear, is the largest and most important leaf on the corn plant. You need to be proactive in the use of foliar fungicides, and protect the ear leaf and all leaves above it, if possible. However, make sure fungicide spraying doesn’t interfere with the pollination process.
Different disease organisms become more prevalent in certain growing conditions. Northern corn leaf blight likes cooler temperatures, and gray leaf spot likes high humidity and high temperatures. Conservation tillage has also increased the incidence of many diseases. Some popular corn hybrids on the market have very high yield potential but are very susceptible to certain pathogens. That increases the probability of disease development.
Scout each field
These susceptible but otherwise high-yielding hybrids help create more disease inoculum for the following year since they’re grown on many acres. Try to select more tolerant hybrids while inspecting seed company demonstration plots during summer. Planting date and relative maturity of the hybrids can also affect the development of certain diseases. Earlier-maturity hybrids can sometimes escape disease.
You may not have to apply fungicides to all hybrids or even all fields planted on different dates. Some fields might escape the disease. But it’s very important to keep scouting during the pollination periods for leaf diseases. The ideal time to apply fungicides on corn is after the ear leaf is fully developed. However, spray after the pollen-shed period is complete and the silks have turned brown. We want to protect leaves during the grain-fill period.
Nanda is director of genetics for Seed Genetics-Direct, Jeffersonville, Ohio. Email him at [email protected] or call 317-910-9876.