Spot Form of Net Blotch (SFNB)

By Kenny Rounds /  May 2019

Kenny is a Barley Agronomist based in Twin Falls, ID. Kenny has a bachelor’s degree in Agribusiness Management and has worked for Anheuser-Busch since May 2014.

 

Net blotch is a common disease of barley and is caused by the fungus Pyrenophora teres. It is favored by high humidity and rainfall, including sprinkler irrigation. It has two forms: the spot form (SFNB) and the net form (NFNB). Both forms have similar effects and treatments but are pronounced in different forms.  

 

What to look for when diagnosing SFNB

Symptoms are most commonly found on leaves but can occasionally be found on leaf sheaths. They develop as small circular or elliptical dark brown spots becoming surrounded by a yellowing zone of varying width. These spots do not elongate to the net-like pattern characteristic of the net form. The spots may grow to 3-6 mm in diameter.

 

Issues caused by SFNB?

A severe infection of SFNB may cause premature leaf death and reduce the seed weight. It may also reduce the number of heads and the number of grains per head.  If yield losses do occur from SFNB infection, they generally range between 0 and 10 per cent, but in severe outbreaks can exceed 20 per cent. SFNB more commonly causes reductions to grain quality through reduced grain size.

 

How do you control SFNB?

SFNB can be effectively controlled with the following strategies:

• Use resistant cultivars.
• Bury crop residue and destroy volunteers.
• Use balanced applications of nitrogen and phosphorus. Heavy nitrogen applications generally produce conditions favorable to outbreaks of this disease.
• Follow a crop rotation for at least two years with non-susceptible hosts. Barley should not follow barley, particularly if disease levels were high the previous year.
• Use pathogen-free seed if possible.
• Use seed treated with a fungicide.

 

Summary

SFNB complete control is not economically feasible.  Three top things that will help minimize the chance of infection:

• Removal of residue
• Crop rotation
• Use a fungicide seed treatment on your seed

Always scout fields for diseases and disease pressure. This cannot be said enough. If you see something that is concerning or if you have any questions, please contact your agronomist.