MSU Extension

Weather and growth stages

July 2016 was one of the warmest months on record and the degree accumulations reflect this. August has also been warmer than usual. A month ago, the general Grand Rapids, Michigan, area was settling into nine or 10 days ahead of normal degree-day accumulations. Very warm days and warm nights have moved us even farther ahead in degree-days to about 14 or 15 days ahead of normal for the third week of August – this is highly unusual. Growing degree-day (GDD) totals for the Michigan State University Sparta Enviro-weather station are: 3,214 GDD base 42, 2,790 GDD base 45 and 2,144 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.

A few Zestar were harvested last week. Paula Red harvest began earlier this week in Grand Rapids. Gingergold harvest is just beginning now. Fruit quality for these early varieties has been excellent. Our early maturity testing indicates there is a mixed maturity on major varieties such as Gala and McIntosh, which should be of no surprise given the long, drawn-out bloom period we experienced this spring. When you are testing fruit on your own farms for maturity (starch, pressure and brix), it’s is best to sample from fruits that you expect to harvest next to give you the best data to base harvest decisions upon.

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. 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.

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 adult codling moth flight is declining and we should be well past the peak flight, as well as the peak egglaying. Egg hatch will continue for at least another 10 to 14 days and cover sprays are very important in blocks catching over threshold. Heavy rains have most likely removed all pesticide residues and reapplication is necessary in blocks over threshold.

All stages of European red mite are being found, and quite surprisingly with all the heat in July and August, populations have not exploded. Heavy rains have washed them away and high humidity is not favorable to mites. The August threshold is 7.5 mites per leaf through about mid-August. As harvest approaches, there is little need for miticides as the benefits will not outweigh the expense so late in the season. It would be much better to let the beneficial insects build in any mite populations to help with management for next year.

Obliquebanded leafroller flight for the summer generation has been sporadic with very extreme populations not commonly reported. A few small larvae can be found in blocks with high obliquebanded leafroller pressure, but overall, numbers appear to be quite low for this pest right now. All eggs that were laid in the second generation should now be hatched.

Apple maggot adult flight began in the Grand Rapids area between July 17 and 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 continue covering up in hot spots, particularly near woodlots that serve as a refuge for this pest.

Oriental fruit moth third generation flight is well underway and we should be approaching peak egg hatch this week. Late-season peach varieties need to maintain 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 – oriental fruit moth still have two to three weeks of larvae activity in west Michigan.

Spotted wing Drosophila adult flight has remained quite high since late July. Cover sprays to prevent infestation are highly recommended in susceptible crops near their harvest window.

There have been a few recent 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 suspected stink bugs, please let me know by emailing irisha@anr.msu.edu so we can get them identified correctly.

Japanese beetles started being found in late June and they declined for a week or so and then came back, then declined again and came back again in earnest in late July. In the past two weeks, they have declined significantly, but there are still a few present. They just don’t seem to want to give up this season. Numbers are now so low that they don’t need management, but do note where your high numbers were so you can be ready for them in the hot spots next year.

Final note: Apple fruit quality appears to be excellent this year and a higher percentage of your crop could be going to fresh, which will pay better. Don’t cut corners here at the end to save a few pennies and risk wasting all you have done so far.