MSU Extension Fruit & Nuts

Horticultural concerns

Despite the lack of overall rainfall, apple size is normal or even slightly ahead of average for this date. Irrigation should continue until this dry pattern breaks. We are approaching about 3 inches behind tree needs right now, so hopefully you are making up for it with irrigation.

Harvest of early apples has started—Paula Red, Gingergold, Premier Honeycrisp and Wildfire Gala are of good quality. At this time, we feel the predicted apple harvest dates are still accurate with the data collected so far. We have begun testing a few early ripening apple varieties in our Michigan State University Ridge Apple Lab and in general, fruits are reading out at slightly farther along than expected, but not by more than a day or so right now.

We really need to get into Macs and Galas to know if we should tweak the dates for later varieties. Our predicted harvest dates are a general guide to help you plan ahead for harvest and your harvest management plan for AVG—ReTain, 1-MCP (Harvista) and Blush.

Tree fruit diseases

The very dry weather has lessened the need for summer disease fungicides in apples, but a second application for sooty blotch and fly speck should be considered once this next chance for rain moves by. A few examples of lenticel rot in Honeycrisp have come to my attention and hot, humid weather conditions are perfect for summer diseases and fruit rots to flourish. Keep those fungicides applied as necessary.

If the weather turns to a more wet pattern, fruit rots and secondary apple scab could become a concern. Pinpoint scab is a problem best taken care of in the orchard, especially in late August and into September if rainfall becomes heavy. There is some lenticel rot present in Honeycrisp; please refer to the 2012 article from MSU Extension, “Lenticel infections and bitter rot of apples,” when hot and dry conditions caused similar fruit damage.

Tree fruit insects

Adult trap numbers of codling moth continue to be very low in most blocks, but there was a bit of an overall spike in trap numbers in the last week or two. There are also a few problem blocks with higher than normal numbers. I set a regional second generation biofix for July 20 (1,465 GDD50) and there have been 635 growing degree-days (GDD) base 50 accumulated since that date using Sparta Enviroweather data. This indicates we are at a peak or 50 percent egg hatch for that biofix date.

A good rule of thumb for second generation is to use your 1X trap numbers to guide you. If you get trap catches over threshold, go out about 10 days from there and be ready to apply a cover spray. It’s best to use your own orchard trap numbers for decision making. Overall, codling moth pressure is not high for second generation. Second generation activity should come to an end in the first week of September for low pressure blocks. High pressure blocks might need another week beyond that to get through all egg hatch.

Adult flight of summer generation obliquebanded leafroller is underway with not very high numbers overall. I set a biofix for the summer flight for Aug. 1 (2,517 GDD42) and 560 GDD base 42 have been accumulated since that date. We should be at about 50 percent egg hatch and small larvae will become visible at any time.

San Jose scale crawlers for second generation should begin to appear this week in blocks with scale problems. I set a new regional biofix for July 20 (1,382 GDD51) with 605 GDD base 51 accumulated since that date for Sparta. The model indicates crawlers should begin to hatch at any time with cover sprays going on this week to prevent scale damage to fruits and shoots.

Apple maggots continue to fly in the Grand Rapids, Michigan, area with numbers from some blocks being very high. We have had red sphere traps with volatiles catching four or five flies per week with a few catching well over 25 per trap—per week! Overall, numbers seem to be higher than in years past. The threshold for non-baited red spheres or yellow boards with ammonium is one adult fly means you better spray in seven to 10 days. For red spheres with the volatiles added, it’s four to six flies and you can use an accumulation from week to week. The recommended trapping density is four traps per 10 acres.

If you are not trapping at all or have only one trap up for a 20 or 40 acre block, you can’t really know what’s going on with apple maggot. If you are going to skimp on traps, at least put one or two along a wooded area to be sure you are choosing the most likely location to catch apple maggot.

Apple maggot can be active well into September and it is likely that the next rain event, if we get more than a half-inch of rain, will create another flush of maggot flies. Phil Schwallier and I are concerned that we have become complacent about this “old” pest, but we have trapped it in what we consider very clean blocks, so it’s around. You typically have about a week from the trap catch to get something on to prevent egglaying damage and maggot larvae in fruits. Apple maggot damage can also be confused with brown marmorated stink bug damage.

Japanese beetles continue to be present and are declining.

All stages of European red mite and twospotted spider mite are now present. There seems to have been an uptick in mite populations in the last month, and more twospotted spider mites this summer than ever. The threshold for all mites is 7.5 mites per leaf for August. Now that we are halfway through August, it is likely that mite populations over threshold will not compromise photosynthesis, which could lead to a reduction in overall apple fruit size. We are tight on the bubble of if there would be economic value to offset the cost of a miticide spray. There is an abundance of predators in mite populations, which is a good thing.

From my early biofix for oriental fruit moth on May 10, 2,425 GDD45 have been accumulated. This indicates third generation egg hatch is underway and will reach a peak later this week. Consider cover sprays in peaches and apples where trap numbers have been high (over 20 in peaches and over 50 in apples). Generations start to run together and overlap in late summer, so use your traps numbers as a guide; if you hit a week with some high trap numbers, go out seven to 10 days from there and apply an insecticide over to prevent larvae damage to fruits.

Brown marmorated stink bug can be found on various favored hosts in all stages. You may have seen reports from New York and other eastern states that second generation egglaying is happening there. We are much behind their degree-day accumulations and it doesn’t appear Michigan will have a second generation for brown marmorated stink bugs—hurray! The population is still increasing and it is highly suggested you add something to your cover sprays now or very soon, if you haven’t already, to reduce the presence of brown marmorated stink bugs in your apple blocks.

In low pressure areas, future cover sprays should be able to consist of perimeter sprays or sprays targeted to where brown marmorated stink bug habitat is present—wooded areas and soybeans in particular. High pressure blocks might need a whole cover again in two weeks to fully prevent fruit damage.

This is going to be a tough insect to manage, so stay calm and spray on. There is also some bitter pit and lenticel rot showing up, which can easily be confused with brown marmorated stink bug damage or even apple maggot damage. If you have questions about any damage you are seeing, please feel free to call for help (517-353-3272 or 616-693-2193).