West Michigan tree fruit regional report – May 20, 2014

Apples are entering the full bloom stage this week in West Michigan.

Daily temperatures have been much lower than average for the past week and tree growth seems to have stopped because of it. The majority of apples across the West Michigan region have been stuck in pink for the last week. There were some cool nights late last week and a few growers ran frost fans, but Michigan State University Extension experts expect little to no bud damage as temperatures stayed at or above 29 degrees Fahrenheit for most locations. In the last day or two, some bloom has begun to open. The major period for full bloom in apples will be near the end of the week and over the weekend.

Sweet cherries are moving out of the full bloom stage. It’s still too early to determine fruit set. It was cool and wet during bloom, so hopefully adequate pollination and fertilization took place. When the weather was nice, bees were working vigorously in sweet cherries. Tart cherries are in full bloom. Peaches are in various stages of full bloom depending on site and variety.

Tree fruit diseases

Over the past two weeks, there have been several rain events resulting in various apple scab infections. Primary scab spore numbers have been steadily declining, but are still being trapped. Lesions from the earliest infections in late April should be found at any time.

Now that some open bloom is present, the risk for fire blight blossom blight needs to be considered. The cooler weather of late has kept the risk low, but it increases by mid-week. Most apples from the Ridge and north did not need blossom blight cover sprays for the rain Monday into Tuesday, May 19-20, due to cool weather and a lack of bacterial build up in blossoms. Only those blocks that have a history with fire blight issues or Gingergolds with open bloom needed to be covered.

The current rain event is only a marginal risk for fire blight blossom infections and very little acreage will need cover sprays. As temperatures warm in the next seven days and more bloom opens, the risk for blossom blight goes up significantly, so watch for heavy dew or light rains. It only takes 0.01 inch of rain or a heavy dew, or even a dilute spray, to trigger a blossom blight situation.

Trauma blight risk is determined a bit differently than blossom blight. Any activity or weather that causes wounds to the tree creates an opening for fire blight bacteria to get into the tree. Pruning and branch manipulation should not be done during wet periods as it can cause trauma blight situations. Keep a close eye on the weather today, May 20, as we are in a slight risk for severe weather (hail and high winds) later this afternoon. A trauma blight situation from hail or high wind would trigger the need for cover sprays in all fire blight-susceptible apple cultivars, regardless of the risk for blossom blight.

Stone fruits now need fungicides for brown rot with open bloom present.

Tree fruit insects

The warm weather a week ago spurred some insect development, but cool weather over the weekend put an end to it temporarily. Spotted tentiform leafminers can be seen flying in the evening hours. A few more aphids are found each week, but numbers still seem lower than usual. European red mite egg hatch was reported by several scouts last week, so start planning your petal fall mite controls. Redbanded leafrollers seem to be a bit higher than usual this year, but very few people trap for this moth.

Many scouts have reported flight of oriental fruit moth and a biofix for the Grand Rapids, Michigan, region is set for May 19. Numbers are low and this generation is of concern in stone fruits, but not in apples.

No reports of codling moth in the region yet, but traps and lures should be in place now. Plum curculio could start moving into stone fruits in the next seven to 10 days, especially if we get nights with temperatures above 60 degrees Fahrenheit. The best place to find early plum curculio activity is in stone fruits near a wooded area.

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