West Michigan tree fruit regional report – July 12, 2016

Tree fruit harvest is underway for sweet and tart cherries and apricots.

Weather and growth stages

As July gets settled in, drier weather becomes the usual pattern. Some areas received rain over the past few days, but many sites did not. The need for irrigation for all fruits is becoming very important.

Growing degree-day (GDD) totals for the Michigan State University Sparta Enviro-weather station are 1,920 GDD base 42, 1,498 GDD base 45 and 1,186 GDD base 50. On average, degree-day totals put this area seven to eight days ahead of normal average accumulations.

Diseases

Fire blight is finally slowing down as many trees are now setting terminal buds. Young, non-bearing blocks still have terminals growing, and any storms that rip or tear foliage would still likely require fire blight prevention cover sprays for another week or so.

Summer diseases of apple include sooty blotch and flyspeck fungi. These diseases require about 240 hours of leaf wetness starting 10 days past petal fall to begin sporulation. This model uses 220 hours of wetting as a timing to start fungicide programs for these two diseases – you spray ahead of the sporulation to prevent they fungal signs on the fruit. In checking the MSU Enviro-weather stations for the region, the accumulated hours of leaf wetting due to rain and dew differ greatly from site to site. For the 2016 season, it has been quite dry and hours of wetting are not where they typically are, so summer disease fungicides can be delayed. For example, as of July 11, the accumulated wet hours are Sparta 207, Standale 285, Kent City 289, Belding 250, Fremont 310 and Hart 216. These totals indicate that all west Michigan apple blocks should now have at least one fungicide on for summer diseases.

Powdery mildew has been less of an issue so far in the 2016 season, but it is starting to be found more readily in the last few weeks. As terminal buds set, the need for mildew fungicides should be lessened.

Insects

Codling moth adult flight has declined as first generation should be ending. Most blocks should be just past peak egg hatch. A regional biofix was set for May 23 (302 GDD50) and 900 GDD50 have been accumulated since that date, indicating that egg hatch should be nearly over for first generation. This is a good time to change out lures in monitoring traps to be sure to accurately catch the beginning of second generation codling moth flight.

All stages of European red mite are being found. A few beneficial mites have also been found, but they seem to be in low numbers overall to help with high European red mite populations at this time. The July threshold is five mites per leaf. Mite populations can grow quickly in dry conditions.

Adult flight of obliquebanded leafroller is declining rapidly as first generation flight winds down. A regional biofix was set for June 12 (1,132 GDD42) and 800 GDD42 have been accumulated since that date. Small to mid-size larvae can now be found and cover sprays are needed in high pressure blocks. All eggs should be hatched in the next week or so.

Apple maggot adult flight has not been reported yet in the Grand Rapids, Michigan, area, but traps should be in place in known hot spots and along orchard edges near wooded areas with alternate hosts present. Numbers have been creeping higher each year. You only know what is happening with apple maggot if you are trapping for it correctly.

Second generation of oriental fruit moth flight is underway with adult numbers increasing. A regional biofix was set for May 6 (308 GDD45), and 1,325 GDD45 have been added since then. Enviro-weather’s oriental fruit moth model indicates that second generation larvae will be at 10 percent hatch anytime now and need to be targeted in stone fruits and perhaps apples with very high trap numbers (more than 60 per trap per week).

Various species of aphids can be found in all tree fruits, and numbers seem to be building now each week. There are syrphid fly larvae and lady bug larvae present in some populations. MSU Extension advises growers and scouts to continue monitoring for all aphid species in all tree fruits as well as the beneficials that attack them.

Dogwood borer adult flight began three weeks ago and we should be nearing peak flight – this insect seems a bit delayed this year. Target trunks at peak adult flight, which is right now.

Adult flight of spotted wing Drosophila continues with numbers showing increases in early developing fruits (strawberries, sweet cherries and summer raspberries). Cover sprays to prevent infestation are highly recommended in crops near their harvest window.

No reports yet of brown marmorated stink bug adults or nymphs in the Grand Rapids, Michigan, area.

Japanese beetles started to be found nearly a month ago, but they sort of left the scene for a week or so and now they are back – not sure why that happened. They can be found commonly in pairs which means more Japanese beetles, so target them now.

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