Production Blog: Tar Spot
Spooky Spots on Fall Decor Pose Potential Issue for Corn Farmers
JEFFERSON CITY, Mo. (DTN) -- Halloween is less than a week away, and stores across the country are filled with scary sights. Yet among all the ghosts, goblins, witches and warlocks, an even spookier spectacle lurks on some store shelves, going unnoticed by most shoppers.
Over the past few weeks, reports of decorative cornstalks infected with tar spot, a fungal disease of corn, have been reported in box retail chain stores in several states, including Alabama, Arkansas, Louisiana, Mississippi, Oklahoma and Tennessee. The primary concern for farmers is that the disease has not been found in cornfields in these states during the growing season previously. Tar spot spores from these fall decorations could be released unknowingly and overwinter in these new areas, potentially driving the spread of the disease farther south.
"It is never a good thing to introduce an aggressive corn pathogen to new regions," said Mandy Bish, University of Missouri Extension plant pathologist. "We do not know exactly how the pathogen will respond in these warmer environments."
Tar spot is caused by the fungus Phyllachora maydis and was first reported in the United States in Indiana and Illinois in 2015. Since then, it has been found in 19 states and Canada. Tar spot infections were discovered early this year. Read more here: https://www.dtnpf.com/…
The fungus infects the upper side of corn leaves and appears as raised hard, black spots, known as stromata. The spots are typically one-sixteenth to three-quarters of an inch in diameter and can protrude through the tissue, becoming visible on the bottom side of leaves. Within each stroma, the fungus produces spores that continue to infect corn plants throughout the growing season.
Even after corn plant senescence, the stromata remain. Inoculum overwinters in corn residue and can survive extreme temperatures. Spores are dispersed via wind and rain splash.
With long periods of favorable environmental conditions -- such as morning dews, lingering fogs and rainy days -- high disease severity can reduce yield and test weight and result in plant lodging. Yield losses to tar spot can vary depending on the time of disease onset, weather conditions and hybrid susceptibility. Losses of 50 bushels per acre (bpa) or greater have been observed in previous seasons.
The exact origins of the infected decorative cornstalks are unclear. In a press release, Terry Spurlock, University of Arkansas Extension plant pathologist, said some of the plants he found appeared to have originated at a farm in Illinois. Other decor carried labels noting "product of the USA" or "product of Canada."
Bish said that she herself has found tar spot on decorations for sale in Columbia, Missouri, located in the center of the state. She noted that because the disease is endemic in Missouri with sufficient levels of the fungus present across the northern and central portions of the state, her concern is for Missouri's southern counties and states to the south where the disease has yet to be detected during the growing season.
Extension specialists in several states recommend that those who have purchased decorative cornstalks examine them for the telltale black spots. If they find the fungus, place the stalks in a garbage bag and dispose of them through their trash collection service. Infected stalks should not be thrown out in a commercial field or backyard garden, as doing so may inadvertently introduce the pathogen into the environment. It only takes one case for the disease to gain a foothold.
"In order to delay the challenges of tar spot, it is important to consider how the corn is disposed of," Bish noted.
To learn more about tar spot and its distribution, go here: https://cropprotectionnetwork.org/…
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Jason Jenkins can be reached at jason.jenkins@dtn.com
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