Grand Rapids area tree fruit update – April 6, 2021
A continuation of warmer than normal temperatures and bud development brings disease and insect potential.
Over the past few weeks, the Grand Rapids, Michigan, region has experienced significantly warmer weather than normal. The Michigan State University Sparta Enviroweather station has accumulated 166.5 growing degree days (GDD) base 42 since Jan. 1, which is approximately 13 days earlier than the average for April 5. Conditions have also been much drier than normal, with a slight reprieve on Friday morning, April 2. Accumulation since Jan. 1 has been between 2-4 inches across the Grand Rapids region. Thundershowers Friday morning brought between 0.25 and 0.6 inches to the region.
Despite the overall warmer-than-average trend, colder temperatures moved into the region during the latter part of last week. The area experienced a severe cold event on Friday morning. Several Enviroweather stations recorded lows of 17 degrees Fahrenheit between the hours of 6 and 8 a.m. These temperatures may have had a very minimal impact on floral buds and the crop, depending on the precise location and growth stage of individual orchards.
Very warm conditions are expected to continue through the week, with highs in the 70s and near 80 F (nearly 20 degrees warmer than normal) and low temperatures not expected to fall much below 50 F in the next five days. Two weather systems in the forecast may provide some precipitation, from Thursday to Friday and again over the weekend.
As a result of the continued rapid accumulation of degree days and warm rain, tree growth is ahead of normal and will continue to move very quickly this week. Depending on the location and variety, most apples are between 0.25- and 0.5-inch green, with early cultivars in southern areas approaching tight cluster at the end of the day Monday. By the end of the week, tight cluster can be expected in many varieties.
The warm weather this week will move tree development along and by the end of the week, all apple varieties in the general Grand Rapids growing area will have some amount of green tissue showing. These small leaves are prime targets for apple scab and the warmer weather and predicted rainfall could result in the first apple scab infections of the season.
Spore rods were set out on March 25. With light rains last week, we found only one spore on the four rods on March 29 and an average of one spore per rod on March 31. There was very little green tissue showing at that time and wetting hours were short with no infections.
With the significant rain on April 5, we found an average of 11 spores per rod. Most area Enviroweather stations topped out between four and five hours of wetting with no apple scab infection period, however, the Grant and Belding stations had additional wetting hours and did end up with scab infections according to data from those areas.
Many have applied early copper sprays this week. This will help with the initial early apple scab infections and can help reduce fire blight bacteria numbers from now until bloom, as long as we don't get heavy rainfall (over 2 inches) between now and bloom.
There has been very little insect activity up until this week, but warmer weather on tap for this week will push their activity. It’s not too early to get traps and lures in place for early season flying insects such as speckled green fruitworm, redbanded leafroller and spotted tentiform leafminer. Oriental fruit moth usually starts to fly in early to mid-May and it could make an appearance earlier than expected this season.
This is a good time to make notes about your problem issues in 2020 to be sure you don’t miss the early management timings for pest such as San Jose scale, obliquebanded leafroller, mites and aphids. We are quickly moving out of the dormant oil window, which is a 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.
There always seems to be some debate about whether pink sprays in apple are necessary given the lack of insect activity in a typical cool, Michigan spring. Perhaps for 2021, insects will get an early start and this pink timing will be more critical to manage early season pests before their populations get too far along.