Tar Spot. This seven letter word is causing headaches to many farmers across the nation. Tar Spot Disease has been on a non-stop track of multiplying since its first appearance in the corn belt back in 2015.
Originating from South America, this disease is quite a ways from “home,” so what keeps it sticking around year after year? Let’s find out.
When conditions are right
Summer months bring much more than watermelon, pool days and bonfires. Not only are people more active, but these warmer days and cool, dewy nights create the perfect environment for Tar Spot to become active in your fields too.
The sweet-spot for this fungus to grow is when temperatures average around 60-70ºF at night with high humidity levels (we’re talking 75% plus!). Not only are these temperatures and humidity levels ideal for Tar Spot, but the corn leaves seem to be quite the resting place for this disease to develop — especially if the leaves are dewy for an average of seven hours per night.
On average, we see Tar Spot pop up in corn fields starting at V10, but if the conditions are right, this disease is able to infest fields at earlier growth stages too. Having the ability to identify and manage Tar Spot in a timely manner not only impacts your crops, but your economic payback at harvest too.
Putting Tar Spot under the microscope
Tar Spot is commonly mistaken as Southern Rust or Common Rust, but what makes it different? Tar Spot shows up as black spots within the leaf, whereas rust is commonly found on top of the surface. Plus, rust is able to be scraped away, but not Tar Spot. Tar Spot lesions are also dark brown to black in color, whereas rust has more red-orange toned specks on the leaf surface.
Though individual Tar Spot lesions might not look too deadly on your crop, they quickly multiply. Each speck has over 10,000 spores infected with this disease, and once you get it, it is quite a pain to get rid of.
In fact, Tar Spot is able to overwinter in fields and be passed down from crop generation to generation—not to mention the ease of infestation through wind transfer. Another reason why it is important to monitor your fields and take action quickly if the disease starts to appear.
Tar Spot is commonly found near the ear leaf on the plant, both on the upper and lower sides of the leaves. From the ear leaf up on the plant, sugars are being developed to help build yield as the crop progresses towards harvest. Thus, it is important to identify and manage this disease early on. As it works its way up the plant, you may see the ends of some leaves start to turn brown and die off.
To ensure you identify this disease properly—and a proper plan of action is implemented—talk with your local Liqui-Grow agronomist.
Impacting your crop
Though these tiny specks might not seem too detrimental to your crop, Tar Spot has been proven to result in poor grain fill, kernel abortion, reduced kernel weight and can even cause the stalks to fold over in half – literally bringing them to their “knees.”
In more severe cases, Tar Spot has reduced yield by more than 100 bushels per acre!
Management practices to consider
Though tar spot may already be infesting your fields, it is hard to see the visual impact until around 20 days after the infestation has started. As time progresses, you will start to see the black lesions appear, and you’ll want to ensure you have a timely fungicide application to reduce crop risk as the season continues.
A fungicide application at VT with multiple modes of action such as RevyTech®, Veltyma® or Delaro® Complete is preferred, but depending on the time of year, product availability may be limited.
We’re here to help! Contact your local Liqui-Grow office for assistance in scouting your fields for Tar Spot and other diseases and determining the right fungicide application, to help protect the yield you’ve been generating this season.
Questions? Give us a shout!
Text us at 564-220-2508 or email firstname.lastname@example.org.