Fire blight risk reduced temporarily

Current weather conditions have reduced the risk of fire blight infection, but it is still essential to keep shoot blight under control.

With the sudden change to weather conditions similar to those in Scotland, one of my favorite places, the fire blight risk has been significantly reduced. However, risk of fire blight infection is not gone. Let’s recap where we are currently as of May 17, 2011.

In regions with orchards near full bloom last week when temperatures hit the high 70s to low to mid-80s (Southwest Michigan, Southeast Michigan, early blooming varieties on the Ridge), it is possible to likely that these orchards will have sustained some level of blossom blight infection. The expression of symptoms will be delayed by the cooler weather, but will eventually become visible.

Blossom blight provides an extensive amount of inoculum for further shoot blight infections. It is cycles of shoot blight infection that can result in serious epidemics. Apogee should be used in these at-risk orchards for shoot blight control (see my previous article, APOGEE FOR FIRE BLIGHT (shoot blight) MANAGEMENT!!!!!). In addition, as temperatures warm back up this week, if open bloom is still present in orchards, another application of Kasumin (in counties where it can be used) or streptomycin (where resistance is not confirmed) should be applied to protect trees coming out of bloom.

In regions with limited bloom open between May 11-13, blossom blight risk is currently reduced due to low temperatures. However, I think inoculum levels will be elevated in any orchard blocks that had fire blight infection last year due to activation of the pathogen in cankers. Thus, growers need to be vigilant and protect blossoms that will open this week as the temperatures warm back up. Observe the Maryblyt model on the Enviro-weather web site. Growers should be a bit more conservative in these at-risk orchards and consider antibiotic applications even when EIP values are lower (between 60 and 100).

In Northwest Michigan, where trees have not begun blooming yet, it is business as usual. In orchards where blight was prevalent last year, growers must be active, spraying antibiotics in a protective mode to limit blossom blight infection. If Maryblyt EIP values are high (more than 100) during bloom, the application of Apogee will be essential to keep shoot blight under control.

Dr. Sundin’s work is funded in part by MSU’s AgBioResearch.

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