Grand Rapids area tree fruit update – April 13, 2021
Cooler weather predicted for the coming week expected could slow apple development.
In the past week, the Grand Rapids, Michigan, region has continued to experience significantly warmer weather than normal. The Michigan State University Sparta Enviroweather station has accumulated 279 growing degree days (GDD) base 42 since Jan. 1, which is approximately 19 days earlier than the average for April 12. This corresponds to the normal GDD accumulation for May 1. This spring, conditions have also been much drier than normal throughout the state, but this was alleviated by several rain events last week. Over 1.5 inches of precipitation was recorded in most locations across the Grand Rapids region from Thursday, April 8, through the weekend.
Cooler and drier conditions are expected in the coming week. High temperatures are expected to be in the 50s (degrees Fahrenheit). Low temperatures are predicted to be in the mid-30s. A few showers are expected, primarily overnight Wednesday into Thursday (April 14-15), but minimal precipitation is likely (less than 0.1 inch).
As a result of the warm weather and rainfall, tree growth is well ahead of normal. Depending on the location and variety, most apples are between tight cluster to open tight cluster, with the first pink tissue visible in many varieties. Early varieties in more advanced locations are at pink stage this week.
The cool fronts moving in next week have the potential to cause temperature drops overnight and should be watched closely for potential frost damage. However, forecasting tools are not accurate enough for any definitive predictions this far in advance. At this time we do not expect significant damage.
With temperatures predicted to be more in the normal range, insect activity will likely follow a normal development as well in the next few weeks. Early flyers such as speckled green fruitworm, redbanded leafroller and spotted tentiform leafminer have been active in the past week or more. We found small overwintering obliquebanded leafroller larvae in a known hot spot and you should be scouting for them as well—obliquebanded leafroller numbers have been slowly increasing in the past few years overall.
Traps should be in place for major pests such as oriental fruit moth and perhaps codling moth. Oriental fruit moth adults could begin to fly this week in light numbers, but we should wait for a true sustained flight before setting a biofix—a cooler week should curb their activity, delaying the need to set a biofix just yet. Even codling moth might become active earlier and it wouldn’t hurt to have traps up in any high-pressure blocks to be sure you don’t miss a sustained flight biofix event.
Start thinking about your pink sprays—it’s time to have a plan in place. This is a good time to go over last year’s problem issues to be sure you don’t miss the early management timings for pest such as San Jose scale, obliquebanded leafroller, mites and aphids. 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.
With a good deal of fresh, green tissue showing in apples, the risk for primary apple scab infections is a concern with any rain event. Most MSU Enviroweather station data in the general Grand Rapids area indicates the first scab infection over the past weekend. Spore numbers were a bit lower than expected—a further indication that perhaps they are delayed in development a bit due to the drier than average winter and spring so far. The forecast is calling for cooler and dryer conditions in the next week. All wetting events from now until mid-June will be potential scab infections and a tight scab fungicide program is needed. Don’t be tempted to stretch your fungicide covers too much. It’s much more effective to manage diseases preventively than after the fact.