Southern corn leaf rust (SCLR), caused by the fungus Puccinia polysora, was confirmed in Caldwell, Daviess, and Ohio counties last week.

Dr. Kiersten Wise, extension plant pathologist at the Grain and Forage Center for Excellence at Princeton, compiled the following thoughts concerning this important disease of corn.

The timing of these discoveries in mid-July is on schedule for when we usually see the disease appear in Kentucky. These confirmations indicate that SCLR is likely present across western Kentucky. The fungus, which causes SCLR, does not overwinter in Kentucky; it requires a living corn host to survive.

Spores are carried on wind currents from Central America and Mexico known as the Puccinia pathway. Initial deposits cause infection in the southern U.S. and from there are transported north in wind and weather. It will be important to scout and monitor fields. Submit samples to the Plant Disease Diagnostic Laboratory through the Extension Office if you suspect you have SCLR in a field.

Southern rust is first observed as raised, dusty orange pustules on the upper surface of the leaf. The disease is easily confused with common rust, which produces pustules on both sides of the leaf whereas SCLR pustules are typically only on the upper side.

Common rust, caused by the fungus Puccinia sorghi, is present in many Kentucky cornfields and is not economically necessary to manage. It is important to distinguish between the two diseases before applying fungicide.

Key takeaways are that to date, all confirmations in this area have been at low incidence and severity, but recent heat, humidity, and rain are favorable for disease development. Farmers may need to spray corn to protect yield from southern rust. The potential impact of SCLR depends on the crop growth stage of a field when infection occurs.

Any corn that is already at the milk stage will likely not need a fungicide application. Corn that had a fungicide application at VT or later will not need a second fungicide application, if it has reached blister (R2) when southern rust is present. Farmers with corn still in vegetative growth stages should wait to spray until the disease is detected in a field, and try to get as close to VT as possible to apply a fungicide.

Research in the southern U.S. has shown corn is able to keep SCLR in check in the vegetative stages. There are less expensive fungicides that are rated as equally effective for southern rust management as more expensive products. If farmers are concerned about input costs or hadn’t planned to apply fungicides this year, they can choose less expensive products and expect to see similar levels of protection. A list of the current ratings for fungicides for southern rust efficacy can be found on my website at http://daviess.ca.uky.edu/ANR.

Asian longhorned tickAsian longhorned tick is confirmed in Floyd, Martin, and Metcalfe Counties on black bear, elk, and cattle. This is an exotic tick native to China, Korea, and Japan. Asian longhorned ticks are small, reddish-brown ticks with no distinctive markings to aid in quick recognition. The unfed adults are smaller than the other adult hard ticks that we commonly encounter.

This species is an aggressive biter and frequently builds intense infestations on domestic hosts that can cause stress, reduced growth, and severe blood loss. One reason for their rapid buildup on hosts is that the female ticks can lay eggs without mating.

It only takes a single fed female tick to create a population of ticks. Potentially, thousands can be found on an animal. You should protect yourself from tick bites when in tick habitat. Personal protective measures such as the use of EPA-approved insect repellents and 0.5% permethrin-treated light-colored clothing are effective against Asian longhorned ticks.

Crossing Through This

Nearly 150 participants attended Crossing Though via Zoom last week. Kentucky farms are experiencing unprecedented financial stress. Managing lower gross income while meeting financial obligations is a challenge. The next meeting is Thursday at 6 p.m. Mark Barker with Farm Credit Mid-America will discuss why now, more than ever, open dialogue with your lender is important. There are still some spots open and registration is required. Signup at https://bit.ly/2020FarmFamily.

 

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