Tar Spot

Managing Tar Spot This Season

Posted on by Liqui-Grow

 

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 questions@liqui-grow.com.

 

Resources: 

https://corn.ipmpipe.org/tarspot/

https://crop-protection-network.s3.amazonaws.com/publications/tar-spot-filename-2019-03-25-120313.pdf 

Tar Spot Update

Posted on by Liqui-Grow

Summary

Last week Dr. Damon Smith, with the University of Wisconsin, gave an update on Tar Spot and I thought his findings were extremely valuable and the most relevant information I have seen to date.

Tiny black spots against a brown lesion are a symptom of the tar spot complex in corn.

Two corn kernels graphic

Keynotes

- Tar Spot can overwinter and has been in WI for 3 years. It is also in Eastern IA. The first two years Tar Spot was in Wisconsin, it did not infect plants until late August. This year it arrived Mid-June.

- There hasn’t been a single plant found with the Monographella version (the really bad type only found in Mexico so far)

- Tar spot is causing yield loss in the absence of any another disease, such as grey leaf spot.

- Hybrid tolerance incredibly variable. Some can handle it, some take a huge yield hit with this disease.

- Early hybrids take less of a hit. Research is showing that at 10% of the leaf area covered with Tar Spot yields are reduced by 8 bu/ac. Longer maturity (103-113 day) hybrids lost 15 bu/ac when 10% of the leaf area was infected.

- University plant pathologist are creating a phone app (the TarCaster) that will hopefully be able to predict the arrival of the disease based on the weather. They already have a similar program for predicting white mold. They expect that to be out for testing this upcoming year.

- Yield losses appear to be dependent on when the plants become infected with Tar Spot. For example, this year infection started between V8 and VT is some regions but in previous years infection did not start until after milk stage.  There is barely a hit on yield if it arrives during the Milk stage.

-Fungicide does help if timed properly, and at least Headline Amp and Delaro are labeled for Tar Spot.

-University plant pathologist plan on releasing a fungicide update around the end of December to show when the optimum time will be for applying fungicides to control/suppress Tar Spot.