MSU Extension

Weather and growth stages

July and August 2016 were the warmest on record and the degree accumulations reflect this. Very warm days and warm nights have moved us even farther ahead in degree-days to about 18 or 26 days ahead of normal for the first week of September. Growing degree-day (GDD) totals for the Michigan State University Sparta Enviro-weather station are: 3,595 GDD base 42, 3,129 GDD base 45 and 2,413 GDD base 50.

Even though the accumulated degree-days have jumped ahead of normal, the predicted apple harvest dates are calculated based on weather two to six weeks after bloom, so they have not changed for these formula-based predictions. Some varieties, such as Gala, will develop faster with warm July weather, but most do not. Please refer to “Predicted 2016 apple harvest dates” by MSU Extension to help with the proper timing for end of season applications and pre-harvest interval determination as well as your harvest management needs.

Early apple varieties are picked. Paula Red and Gingergold harvest was complete on the Ridge prior to Labor Day, Sept. 5. Our early maturity testing indicates the predicted harvest dates seem to be right on target for Gala and McIntosh, Sept. 5 and 7 respectively. Ideal Honeycrisp harvest is also very near. When you are testing fruit on your own farms for maturity (starch, pressure and brix), it’s best to sample from fruits that you expect to harvest next to give you the best data to base harvest decisions upon.

Some fruit drop can be seen in McIntosh and Honeycrisp, and is due to the fruits pushing themselves off as they enlarge. The very warm weather conditions could make fruit drop due to high ethylene, an issue this year as well.

Diseases

Some areas have seen really high amounts of rainfall in the past month and very humid conditions have significantly added to the number of wetting hours needed to move the summer apple disease model forward. Some areas have remained relatively dry. Summer diseases in apples are a complex of fungi that include sooty blotch and flyspeck. These diseases require about 240 hours of leaf wetness starting after 2 inches of rain has accumulated on your last fungicide spray. The sooty blotch and flyspeck Enviro-weather model can help you time re-applications if needed based on your last fungicide spray on your farm and the nearest MSU Enviro-weather station data. Some sooty blotch and flyspeck is being found in early apple sampling.

Fruit rots in storage. Rainy summer months can also increase the potential for fruit rot fungi to get established. For the 2016 season, it is highly recommended that a fungicide application be made to any apple blocks you intend to store for more than a few months to lower the incidence of fruit rots coming out of storage.

Insects

Second generation codling moth activity should be ended now that 2,100 DD50 have been accumulated. If you have high pressure blocks, use your trap numbers from 10 to 14 days ago to determine if you might need one final insecticide for the season.

Obliquebanded leafroller activity should be ending. This is a good time to do a thorough scout for obliquebanded leafrollers and make notes of problem areas that will be addressed in early 2017.

Apple maggot adult flight began in the Grand Rapids, Michigan, area July 17-20, and has continued steadily in some blocks since. The MSU fruit team trap line has seen numbers in the double digits for several weeks in early August. Numbers seem to be declining over the past two weeks, but they are still higher than in previous years and indicate apple maggot numbers are increasing each year. Recent heavy rainfall totals will reduce your protection. If you are still catching adult apple maggots, you should stay covered up in the hot spots, particularly near woodlots that serve as a refuge for this pest. There is no good threshold for maggot adult traps, and if you are still catching them, they could still sting fruits.

Oriental fruit moth third generation flight continues and is declining. Egg hatch should also be past peak, but will taper off over the next 10 to 14 days. Late-season peach varieties should have maintained insecticide cover sprays for oriental fruit moth. This third generation can cause unexpected stings in apples where numbers are high (40 moths per trap), and is of particular concern in codling moth disrupted blocks where insecticide cover sprays are not routine. Don’t get caught with oriental fruit moth damage as you let pesticide covers wane now that codling moth is ending.

There continues to be a few reports of brown marmorated stink bug adults and nymphs in the Grand Rapids area in known hot spots. While this invasive pest is now present, we are still in the watchful waiting stage for the general Grand Rapids area fruit production region. If you find suspect stink bugs, please email Amy Irish-Brown at irisha@msu.edu so we can get them identified correctly.