West Michigan tree fruit update – May 8, 2018
Tree fruits responded quickly to warmer weather.
Degree-day wise, the general Grand Rapids, Michigan, area is about six days behind average totals for base 42, and only three days behind for base 50. One week ago we were nine days behind, and the jump in degree-day accumulations and the heat have pushed all tree fruits forward in development.
Most apple varieties are in the tight cluster to pink stage with a few early cultivars with open bloom just beginning. Early developing sweet cherry varieties started blooming over the weekend with the major bloom period yet to happen. Peaches will begin bloom any day now too. Plums are beginning bloom and apricots are in full bloom.
The first apple scab infection for 2018 took place with wetting events on May 2 and 3 with most areas seeing a moderate to heavy infection period. Spore numbers started out slowly (12 per rod) with the rain beginning at night, but the next morning’s rain discharged 743 more spores with another 76 spores releasing later in the day, for a total of 831 spores released during the 30-plus hours of wetting. This is a pretty significant number for a first infection and even more should be expected with the next rain event as we move through primary scab season.
I now feel confident I have a good monitoring site and spores are definitely ready. As of this morning, we should be around 25 percent mature spores and looking ahead to potential rain later this week, we will be closer to 40 percent of mature spores, so I am expecting some big spore numbers ejected. The forecast is also calling for potentially heavy rain—upwards of 3 inches in some predictions, so don't skimp for the next rains and use the systemics and a good rate of protectant to be best protected ahead of the wetting period. Winds are predicted to be lower tonight, so take advantage of good coverage conditions.
We are coming into the timing to be concerned about powdery mildew in apples. For most blocks, wait to add mildewcides closer to or in the bloom stage. For any blocks with a history of powdery mildew, begin adding mildewcides right now on the earlier side.
Regarding fire blight, there are a few flowers just beginning to open in pears and the earliest apples. With the warm weather predicted for today, more bloom will open and potentially the rains later in the week could provide the right conditions for blossom blight infections. The temperatures will be on the lower side after today, but keep fire blight on your radar screen and check the MSU Enviroweather fire blight model often for updates.
Consider pink sprays this week before significant bloom opens. Your targets are aphids and other sucking insects as well as a few chewing insects such as various leafrollers and green fruitworm. With rather cooler to average temperatures in the forecast over the next several weeks, it could be a long time before the petal fall timing gets here, so this would be a good year to not skip a pink spray.