Scab and rust infection period Apr 12-13

We recorded 27 hr wetting with 1.6 in of rainfall from 6 AM Apr 12- 9 AM Apr 13 with the first 10 hr at 53, then gradually dropping to 49. This wetting was plenty long for an apple scab infection period and likely also an infection period for cedar-apple and quince rusts although it was a bit on the cool side for rusts. Rust spores were discharged during this wetting and blossoms are now susceptible to quince rust which results in distorted fruit at harvest. Quince rust inoculum is produced by cankers (shown below) that can survive for many years, resulting in consistently high local inoculum levels from year to year (to year). Because an inch and a half of rainfall would have eroded most of EBDC residue applied this week before the rain, a follow-up application including an SI fungicide is suggested for after-infection control. Strobilurin (QoI) fungicides are notably weak for quince rust control.

The fire blight graphic will be updated tomorrow. Temperatures yesterday and today have been too cool for fire blight infection, although infection could have occurred as predicted with the rain early Tuesday morning on bloom that was open Monday.

Quince rust inoculum source, a perennial canker in red cedar.

  

Two-celled quince rust teliospores germinating in the exuding mass (click on the picture to enlarge it). Orange-colored ones have not yet germinated but those that are clear have germinated and the resulting basidiospores (the smaller, more rounded ones, top, center above) are carried away by wind currents.