Washington State University Warning Of 2nd Generation Leafhoppers

The tree fruit industry across the Evergreen state is being warned that 2nd generation leafhoppers are now active in area orchards.  WSU said these 2nd generation adult leafhoppers are known to transmit X-disease phytoplasma, meaning this is a critical period for monitoring and management.

After harvest, both leafhopper populations and phytoplasma levels within trees tend to increase.  As phytoplasma concentration rises, the likelihood that leafhoppers will acquire and transmit the disease also goes up.

Leafhoppers are the only known vectors of X-disease phytoplasma. Seven species are currently known to transmit the disease: 

• Colladonus reductus
• Colladonus geminatus
• Euscelidius variegatus
• Colladonus montanus
• Fiebriella florii
• Scaphytopius acutus
• Paraphlepsius irroratus.  

In Washington, C. reductus and C. geminatus are the most commonly trapped carrying the pathogen.

Growers Reminded To Check Their Orchards

When it comes to monitoring, WSU offers the following tips: 

• Use yellow sticky cards or sweep nets to monitor leafhopper populations
• Place traps a row or two in from orchard borders, in areas of concern in your block, and throughout blocks
• Mount traps 2-4 feet above the ground, using about 1 trap per 2 acres
• Check traps weekly. 

School officials add growers should use an average of one leafhopper per trap as a spray threshold.

When it comes to management Strategies:

• Rotate products when applying insecticides to reduce resistance risk
• Target sprays after harvest through October, when populations and transmission risk are typically highest. 

How Often Should Growers Spray?

And growers are asked to remember, it takes several weeks for a leafhopper to become infectious after feeding on an infected tree. The phytoplasma must move from the gut to the salivary glands before the insect can transmit it to a healthy tree. Therefore, well-timed sprays every 2-3 weeks are typically sufficient and more sustainable than shorter intervals.

Additional Resources

Visit WSU's Tree Fruit Website for efficacy tables and product rotation information.

WSU also encourages growers to use the Little Cherry Scouting Guide mobile app to help identify symptoms and insect vectors of X-disease phytoplasma and Little cherry virus (available on Apple and Android), Apple version click here or for Android version click here. 

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