West central Michigan tree fruit update – May 16, 2017

The extent of frost damage is starting to become clearer as young fruit continue to develop.

Dead blossom (left) next to two healthy blossoms on a tart cherry cluster on May 16, 2017. All photos by David Jones, MSU Extension.

Dead blossom (left) next to two healthy blossoms on a tart cherry cluster on May 16, 2017. All photos by David Jones, MSU Extension.

Warmer weather across west central Michigan over the past several days has moved tree fruit development along rapidly. Apples are in full to late bloom, tart cherries are in full to late bloom and peaches and sweet cherries are in the shuck throughout most of the region.

Warm weather has allowed for excellent pollinator activity for several days, which growers were encouraged to see following the previous week’s cool weather and generally poor pollinator activity.

Growing degree-days (GDD) for west central Michigan Jan. 1– May 16, 2017

Enviroweather station

GDD 42 Current

GDD 45 Current

GDD 50 Current

Benona / Shelby

359

251

128

Elbridge / Hart

459

341

195

Fremont

519

392

232

Hart

459

339

192

Ludington

428

313

174

The extent of frost damage is starting to become more clear as young fruit continues to develop. Generally speaking, the take away thus far has been that damage is still extremely spotty. Within blocks, the general pattern that hilltop fruit is good, valley fruit tends to be quite poor and everything in between has been highly variable.

Early on, apples look to have been hit particularly hard. Many growers assumed that late blooming cultivars that were at full pink during the frost events would have fared better than those that were in full bloom, but unfortunately this was not the case. Apple flowers in bad sites have been damaged uniformly, regardless of developmental stage. This is likely due to the extreme duration of these cold events. Direct exposure to the night sky was clearly a major factor during the frost, as sky-facing blossoms are consistently the most severely damaged blooms across the region.

Dead stigma, styles and ovaries

Dead stigmas, styles and ovaries on ‘Gold’ sweet cherry, May 16, 2017.

Rains on May 15–16 brought concerns of fire blight on apple blossoms as EIP (Epiphytic Infection Potential) went into the moderate to high range throughout the area. Growers did a good job of making sure applications of streptomycin or kasumin and oxytetracyclene went out ahead of the rains. Many growers have questioned blossom blight management on frost-damaged blocks in light of the extensive frost kill suffered throughout much of the region last week, under the assumption that fire blight cannot infect a dead flower. While it is true that blossom blight is not a concern on a flower killed by frost, growers need to consider the following.

It takes only a small fraction of healthy open blooms during conducive weather to get an epidemic started in an orchard. While many blocks have significant damage (more than 90 percent), remember that only 100 percent flower death would truly mean 0 percent risk for blossom blight, and wholesale loss of every blossom in a block is extreme. Dead blossoms are not a risk for infection sites, but the few healthy flowers that likely remain in many frosted blocks certainly do. Be in management mode even if the majority of blossoms in a block have been damaged. The next three days will be warm and humid, and it rained on the night of May 15–16, with more scattered showers on the way on the 16th. As such, coming days are looking to be a critical window of fire blight management this season.

Additionally, the long, cold period over the past two weeks followed by the frost make it likely that we will have significant scattered bloom following the period of full bloom, often called “ragtag” bloom. These late-opening blossoms are perennial culprits in sourcing a fire blight epidemic in a block because they often open up outside of the full bloom sprays that we put out, and thus escape management.

Rains on May 15 and 16 also brought another apple scab spore release. While the majority of scab spores are likely released at this point, we still have a few weeks of primary scab left. Michigan State University Extension advises growers to be vigilant, and keep covered before rain events.

Oriental fruit moth is flying right now throughout the west central region. Most growers have mating disruption out at this time. Management is ongoing. The first codling moths were also trapped at the Trevor Nichols Research Center over the past weekend. Traps and mating disruption should be out.

As stone fruit emerges from the shuck and apple fruitlets begin to emerge, growers also need to be thinking about plum curculio. Scouts should be keeping an eye out for this pest in coming weeks. Plum curculio has been spotted on the ridge and other areas nearby, so it is likely that early plum curculio will arrive in the next few days.

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