Disease Update for May 9th, 2012

Apple Scab

Apple scab ascospore release is now down to 30%. Primary scab infections may still occur; thus continuous and thorough coverage is critical for preventing infection of young fruits.

Fire Blight

The fire blight outlook remains critical with wetting periods and temperatures above 62 degrees F. There are still late blossoms on some cultivars, and any day with wetting from rain, dew, wetting from thinning or maintenance sprays may cause fire blight infection. To manage resistance, it is important to not over-use streptomycin. Also, it is not very effective in controlling the shoot phase of fire blight. Research at FREC has shown that an application of Penncozeb, at 3 lb, + Kocide 3000, at 8 oz, OR Mycoshield, at 1 lb, plus Captan, at 3 lb, provides some fire blight control. 

Powdery Mildew

Powdery mildew pressure remains high this season, with 13 days favorable for infection from April 1 through May 7. Temperatures 50 to 77 degrees F favor powdery mildew infection. Conidia are wind-dispersed and do not require moisture to germinate.

Bacterial Spot on Stone Fruit

Similar to fire blight, bacterial spot is favored by warm temperatures (70 to 85 degrees F) with light rains or heavy dew. Windy weather is most conducive for disease development and spread and infections occur only when the leaves are wet.

The latest apple scab, fire blight, cedar apple rust, powdery mildew, cherry leaf spot, and bacterial spot infection models are now posted.