Central Illinois corn farmers defend against new ‘tar spot’ crop disease

A pathogenic crop illness has formally arrived in central Illinois, with the potential to rival the dreaded corn rootworm as a high corn yield-robber.

Tar spot (Phyllachora Madis) is a fungus that impacts corn leaves, forming black specks that can’t be simply eliminated. So-called “fisheye” lesions — brown or tan lesions with darker borders — also can develop. Robbed of their pure, leafy safety, kernels could not attain full development potential, stifling yields.

In 2018, Purdue College reported a yield-reducing epidemic of tar spot occurred in northern Indiana and in surrounding states. Possible first arriving by way of northern Indiana, Wisconsin or Iowa, tar spot crept into northern Illinois round three years in the past. Moist springtime circumstances the previous couple of years allowed the fungus emigrate downstate so far as Peoria, the place it apparently is there to remain.

“There may be some tar spot starting to floor in space corn fields of Peoria County,” Patrick Kirchhofer, supervisor of the Peoria County Farm Bureau, mentioned in mid-July. “Tar spot is a reasonably new illness in Peoria County because it was first found three years in the past. It’s most likely right here to remain, as a result of it’s an airborne illness and resides in plant residue. Agronomists are nonetheless studying in regards to the illness.”

Above-normal moist climate in springtime in central Illinois together with heavy dews have been conducive to plant ailments corresponding to grey leaf spot and tar spot through the first a part of the rising season, Kirchhofer added.

The fungal illness can overwinter in crop fields, making tillage and crop rotation a near-must for farmers in areas susceptible to the fungus. As well as, research present that crop fields with heavy irrigation use can foster extra tar spot fungal development than in non-irrigated fields.

Holding a eager eye on the unfold of tar spot in Illinois is plant pathologist Chelsea Harbach, a business agriculture educator for the College of Illinois Extension. Along with issuing an enchantment to farmers to report the illness’s presence in corn fields, Harbach is dedicated to updating incidences of tar spot all through the state by way of the U of I farmdoc web site.

“In case you’ve been a sufferer of excessive incidence and/or severity of corn tar spot in your fields, you understand how limiting this illness will be on corn yield,” mentioned Harbach, in an Extension weblog posted July 11. “As this illness will be severely yield-limiting AND the pathogen is comparatively new but in Illinois, now we have been monitoring the unfold of this pathogen by corn IPMPipe.”

Crop seed firms are investing closely in analysis to develop traits that defend towards corn tar spot. Although the analysis is ongoing, college research have proven that sure business corn hybrids are higher at proscribing tar spot development than others.

“In 2015 we have been caught off guard by the presence of this illness, so not one of the hybrids that we had out there to us commercially had any stage of resistance. Breeders needed to be fast to display screen germplasm to search out good candidates for breeding resistance into our commercially out there hybrids,” mentioned Harbach. “Together with creating host resistance, built-in pest administration (IPM) should be saved in thoughts to keep away from overusing completely different sources of resistance. The perfect factor farmers can do is to scout their fields early and infrequently.”

Fastidiously chosen corn hybrids defended with strategically timed functions of fungicides present one of the best recognized protections towards tar spot, in line with Dr. Damon Smith, affiliate professor and Extension plant pathologist for the College of Wisconsin-Madison (UWM). Smith offered the most recent analysis conclusions concerning tar spot to farmers and applicators through the Illinois Fertilizer and Chemical Affiliation’s 2022 conference, held in Peoria final January.

“Tar spot has been remoted as one (solitary) fungus, however as lately as 2018 we weren’t positive. Since then we’ve discovered lots,” mentioned Smith. “For all intents and functions right here within the Midwest, we’re coping with only one organism. However it will possibly transfer shortly, and it’s a big downside that’s taking a whole lot of yields.”

Nevertheless, the tar spot downside in central Illinois seems to have largely abated — no less than for this rising season — with current above-average temperatures, hotter evenings and sporadic drought changing the cool, moist in a single day hours of spring and early summer time.

“Primarily based on stories from the farmer-leaders I’ve talked to in central Illinois, tar spot isn’t an enormous concern for many Illinois corn farmers in 2022. Tar spot thrives in moist circumstances, and the drought-like climate we’ve skilled this rising season has made for an unfavorable local weather for tar spot to trigger a lot of an issue up to now. We are going to maintain watching and dealing with specialists to ensure farmers have the sources they want if and when tar spot turns into a priority,” mentioned Rodney Weinzierl, government director for the Bloomington-based Illinois Corn Growers Affiliation, on July 29.

With its hardy resistance and functionality to overwinter in crop residue, tar spot might be one thing Illinois crop pathologists together with Harbach might be monitoring for many years to return. To learn extra about Harbach’s analysis into tar spot’s prevalence in Illinois, try her Extension weblog Corn tar spot illness monitoring in Illinois: College of Illinois Extension.