Department of Plant Pathology

Southeastern Apple Production Plant Pathology

Disease Management

Fire Blight Risk - May 5, 2008

The slightly cooler weather has reduced the risk of fire blight through Wednesday, May 7th. However, there is a risk of infection if it rains anytime from Thursday May 8th through Sunday May 11th. Rattail bloom on susceptible variety/rootstock combinations should continue to be protected. In many years most of our infections occur after the full bloom period.

Streptomycin Rate

Questions have arisen lately regarding the rate of streptomycin to use - should it be based on ppm (60 or 100) or rate/acre? I've spoken to colleagues in Virginia and New York and the general feeling is that control is better when about 1.5 lb of streptomycin is used per acre. The rate/100 gal (4.8 to 8.0 oz) listed in the Orchard Management Guide is based on the old dilute 400 gal/acre standard. So if you are using the per 100 gal rate and spraying less water per acre than needed to wet trees to the drip point, you are likely using less streptomycin/acre than needed to satisfactorily control fire blight.

The forecast is based on weather data and forecasts for the Mountain Horticultural Crops Research Station at Fletcher, NC, using the MaryBlyt model.

Turner Sutton
Telephone: 919.871.0798
Email: turner_sutton@ncsu.edu

Web Crafters: Anne S. Napier and Steve Schoof
Email: anne_napier@ncsu.edu

Updated May 5, 2008