Grand Rapids area tree fruit update – July 26, 2022
Rainfall last weekend and cooler conditions this week gave growers a much-needed break. Expect a return to hot, dry weather beginning this weekend.
Weather and phenology update
Over the past week, conditions in the Grand Rapids, Michigan, area have continued to be very hot. Temperatures were in the 80s (degrees Fahrenheit) most days with overnight lows in the 60s. As of July 25, the Michigan State University Sparta Enviroweather station has accumulated 2248.4 degree days base 42 F (DD42). This is slightly above average, which is 2103.5 DD42, and approximately five days ahead of normal.
Across most of the area, there were severe thunderstorms late last week and over the weekend. Thursday’s weather included high winds and isolated hail. Saturday and Sunday there was a significant amount of rainfall, ranging from approximately 1.5-2.5 inches in accumulation. This was much needed precipitation; by the end of the week, parts of the area were in a D0 or D1 (abnormally dry or moderate drought) according to the US Drought Monitor, but most of this has been relieved in this part of the state.
Expect a much more mild week, with temperatures only in the 70s and overnight lows in the upper 50s. There is a low chance of scattered to isolated showers Wednesday into Thursday morning, but very little rainfall is expected, with less than 0.1 inch possible. Potential evapotranspiration and associated water needs will be lower, due to the cooler temperatures. However, very hot, dry temperatures will return at the end of the week. The warmer and drier than normal conditions are projected to persist in the long term forecast through August and September.
Tree fruit is continuing to put on size. Apples are sizing well and there is a very good potential crop. Hand thinning and summer pruning is underway in most places. Some very minor sunburn and early lenticel damage has been observed.
Peaches have begun harvest on early varieties. Predicted harvest dates can be found on the Enviroweather model. In general, predicted dates are close to average harvest dates this year, with earliest varieties expected to begin harvest at the end of July, other varieties beginning early-mid August.
|Degree day accumulation at Enviroweather stations in the Grand Rapids area|
|Weather Station||Degree Days Base 32 from Jan. 1||Degree Days Base 42 from Jan. 1||Degree Days Base 50 from Jan. 1|
|Aetna - Fremont||3382.1||2191.2||1423.3|
|Sparta 20m Tower||3473.9||2252.1||1468.1|
|Sparta - North||3489.9||2269.6||1482.9|
|Average DD from Sparta historical data for Jan. 1 to date||3363.5||2103.5||1328.7|
|Comparative Date of Averages @ Sparta||28-Jul||30-Jul||1-Aug|
|Days +/- Average @ Sparta||+3 days||+5 days||+7 days|
More information and reports on normal weather conditions and departures from normal can be found on the NOAA Climate Prediction Center website, NOAA U.S. Climate Normals website, NOAA Climate Normals Quick Access Page (which may be searched by region) and Midwest Regional Climate Center website.
Tree fruit diseases
Fire blight risk should be lower as we move into the hotter and dryer months of summer, especially in blocks with no active blight present. Some varieties are setting terminal buds which also reduces blight potential. In the recent storms that brought some isolated hail and high winds that tore foliage, trauma blight would only be a risk in blocks that have active blight in them, so keep a keen eye out for strikes and remove them quickly.
Summer disease management in apples should be considered in areas where the MSU Enviroweather model indicates adequate wetting hours for disease expression. The wetting hour totals vary greatly from station to station this year. Be sure to check the summer disease model on Enviroweather for the weather station nearest you for guidance.
With terminal bud set, powdery mildew infections should lessen. While mildew is low overall, there are still blocks that seem to have more than expected. Take note of these blocks for the 2023 season so mildewcides will be added in earlier in these potentially high inoculum blocks.
Tree fruit insects
With codling moth trap numbers declining to zero for two weeks in some blocks, we can set a new biofix for second generation on July 19 (1330 DD50) with 138 degree days accumulated since. This indicates egg laying for second generation is happening and early egg hatch is expected for July 31 when cover sprays will become more important to protect fruit from infestation. In high pressure blocks with no zeros in trap numbers, that early egg hatch timing will be five to seven days earlier and cover sprays to address hatching larvae need to be maintained continuously to prevent fruit stings.
A Grand Rapids regional biofix for obliquebanded leafroller was set for June 14 (1076 DD42) with 1199 degree days accumulated since. Adult moth numbers have increased slightly in the past week and the model indicates they should reach a peak this week. Egg hatch for the summer generation will begin in about 10 days and small larvae will be visible again by mid-August – just in time for Paula Red harvest, per usual.
A Grand Rapids regional biofix for oriental fruit moth was set for May 12 (312 DD45) with 1626 degree days base 45 accumulated since. Adult flight has increased from last week as second generation ramps up. Early second generation egg hatch should begin the week of Aug. 8 and cover sprays in stone fruits are again critical to prevent shoot and fruit infestation. Monitor for shoot flagging in apples, particularly non-bearing and nursery trees where oriental fruit moth can do a lot of damage.
Green apple aphid populations continue to be highly variable by block and variety and they are lessening as terminal buds set and shoot growth slows. There are many beneficials present in green apple aphid populations.
As green apple aphids decline, woolly apple aphids are becoming easier to find across several apple varieties. Woollies are an old pest that wants to be new again. It was likely managed with broad spectrum pesticides and resistant rootstocks over the past 40 years. Use of both these tools have changed in recent years and woolly apple aphids seems to be enjoying a comeback. They do have favorite varieties – Red Delicious, Empire, Jonagold, Gala, Golden Delicious and more – but they can be found in almost all cultivars is populations are high. When managing woolly apple aphids, excellent coverage is the key to a successful spray program. Slow down, use more water and a penetrant to break through the waxy coating this insect creates.
A regional biofix for the general Grand Rapids area for San Jose Scale was set for May 20 (288 DD51) with 1149 degree days accumulated since the regional biofix. In high pressure areas, adult males continue to be trapped with an uptick in numbers in the past week, indicating the likely start of second generation. Second generation crawlers are expected to appear around Aug. 10 in the Grand Rapids area. When targeting scale, slow down and use more water to deliver management products to all plant surfaces where this tiny insect resides.
All stages of European red mite are present. Predatory mites continue to be found in European red mite populations. There are a few two-spotted spider mites in some areas. Summer miticides should be considered in blocks over the July threshold of five mites per leaf.
Adult Japanese beetles continue to be active and appear to be decreasing a bit. Perhaps there will be an increase in number with the recent heavy rain pushing any remaining adults from overwintering sites in the soil.
Apple maggot adult emergence continues and a jump in trap catch is expected with the heavy rains in the past week. Traps need to be in place if you want to monitor apple maggot effectively for decision making.