Grand Rapids area tree fruit update – March 30, 2021
Warmer than normal temperatures have led to an early spring.
After a very cold trend in February, warmer than normal temperatures over the past week have led to early spring conditions. The Michigan State University Sparta Enviroweather station has accumulated 118 degree days base 42 since Jan. 1, which is approximately 16 days earlier than the average for March 29. Conditions have also been much drier than normal. Accumulation since Jan. 1 has been between 2-3 inches across the Grand Rapids, Michigan, region. Despite the rain that was expected over the past five days, the Sparta and Grand Rapids region only received about 0.5 inch Friday evening, March 26, and less than 0.1 inch over the weekend.
The short-term forecast indicates there will be a return to late winter conditions over the next few days, with a crash in temperatures. Highs will only reach into the 40s and low temperatures may dip into the upper teens in the evenings. Unfortunately, there is little moisture associated with the incoming cold fronts, with only scattered showers and less than 0.1 inch of rain predicted, and very windy conditions. By the weekend, however, temperatures are expected to return to warmer-than-seasonal conditions.
As a result of the rapid accumulation of degree days, tree growth is also ahead of normal. The first green tissue on early apple varieties, such as Idared and Ginger Gold, was observed in Sparta in the middle of last week (around March 25). First green for the Sparta area was observed in Gala and Fuji over the weekend, while areas in southern Grand Rapids are reporting green tip across most apple varieties yesterday, and areas to the north (Grant, Kent City) are just reaching first green today.
With the cooler temperatures coming in the next few days, degree day accumulation and bud development will slow dramatically. Low temperatures are not expected to cause any significant damage to buds at this time. More information about critical temperatures and evaluating buds for cold damage can be found in the Michigan State University Extension article, “Freeze damage depends on tree fruit stage of development.”
Spore rods are set up to monitor in two locations on the Ridge for 2021. With the most recent rain events, there was only one spore on one, which works out to 0.25 spores on the four rods being monitored. Don’t worry, apple scab spores will be ready when green tissue is ready—they always are. In 2020, there were quite a few of the highly susceptible apple varieties with a good amount of scab, so overwintering inoculum is likely to be higher than typical and your early season management applications will be more important in 2021. Early season copper sprays for fire blight will also help for apple scab.
There is very little happening this last week of March in the insect arena, but warmer weather on tap for next week will push their activity. This is a good time to make notes about your problem issues in 2020, so be sure you don’t miss the early management timings for pest such as San Jose scale, obliquebanded leafroller, mites and aphids.
Very little dormant oil us used in commercial apples these days, but it is still your best first management tactic for mites, scale and aphids. There were some apple blocks with higher levels of mites in 2020 than we have seen for some years and this will need to be monitored carefully early in the season. The weather forecasts keep calling for a hot summer, which could push mites to high levels if they are not managed well early in the growing season.