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Distinguish Gray Leaf Spot from Bacterial Leaf Streak

Categories: GROWING, CORN

Gray leaf spot (GLS) has challenged farmers for years, but several states should watch out for a new corn leaf disease that has strikingly similar symptoms. Originating from South Africa, bacterial leaf streak (BLS) was first identified in Nebraska in 2016 and has now been confirmed in Colorado, Kansas, Iowa, Minnesota, South Dakota, Illinois, Oklahoma and Texas. Sightings have not only been reported in field corn but in sweet corn, seed corn, and popcorn as well.

A. BLS with wavy margins  B. GLS with rectangular lesions that move down leaf veins 

BLS and GLS can appear quite similar at first glance, making it difficult to distinguish the 2 diseases. But due to different management practices requirements, it’s critical to know which infection your crop has – there are subtle differences between GLS and BLS. Here are a few ways to help identify the 2 different diseases:

  • Lesions: As pictured to the right above, GLS usually produces more rectangular or blocky lesions with smoother margins. In contrast, the BLS lesions depicted on the left typically have a wavier mark. BLS may first show lower on the plant and work their way up the canopy, and the lesions may be yellow, tan, brown or orange. The disease is also observed to infect via natural openings in corn leaves, which is often where lesions are first to appear.
  • Timing: If lesions first emerge in June, the disease is likely BLS, which tends to develop in cooler conditions. GLS usually occurs in July and August as temperatures rise.
  • Lab identification: If you’re still unsure whether your corn is infected with BLS or GLS after scouting, send a sample to the lab. Microscopes enable researchers to test BLS from GLS by looking at magnified leaf tissues.

As for disease treatment, there are a number of fungicides and tolerant hybrids that can help manage GLS. But since BLS is a bacteria rather than fungal disease, there are NO Fungicides that can control it.  However, several general management practices can help reduce BLS presence in future years.

  • Crop rotation: Instead of growing continuous corn, a type of environment in which BLS is known to thrive, rotate to soybeans or another crop to help break infection buildup.
  • ​​​​​​​Tillage: Deep tillage is another way to prevent bacterial growth, as BLS has been shown to overwinter in infected crop debris. Tillage further buries and degrades infected plant matter by reducing its ability to carry over into the following season.
  • Cleaning equipment: If part of your crop is infected by BLS, slow the spread of disease by washing combines, tractors, planters and sprayers before entering a new field.

Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.

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