Apple scab and rust infection period Apr 14-15

We recorded another apple scab and rust infection period at Winchester Apr 14-15: 14 hr wet at 62° with 0.53 inches of rain. This was another critical cedar-apple rust and quince rust infection period with many spores released during the extended wetting period, and flowers highly susceptible to quince rust infection. Considering this infection period following the recent one Apr 12-13, it is prudent to include an SI (DMI) fungicide for after-infection control of rusts in the next spray application. More rainfall and infection is expected Apr 19-20. 

Infection conditions were similar southward to Roanoke and east of the Blue Ridge from Manassas to Central Virginia. Rainfall amounts since Apr 12 ranged from 1.5 to nearly 2 inches. This was enough to deplete protective fungicide residue, and fungicides with after-infection control are suggested.

Previously, I posted a picture of a large quince rust canker, which illustrates the perennial nature of quince rust inoculum levels. Thus, serious quince rust epidemics are dependent on the release of spores while the blossoms are susceptible, the condition that has just occurred over the past several days. Below is a contrasting picture that shows a small quince rust canker on third year growth and tiny cedar-apple rust galls (upper left) with a single spore horn protruding. These were obviously produced on last years new green foliage on the cedar tree. However, both contribute to overall rust inoculum levels.

Sporulating quince rust canker (lower right), and small cedar-apple rust galls (upper left).