MSU Extension Apples

General harvest comments

We are in the midst of another outstanding week for color development on apples. While the cool nights and temperate days will help with red color, the temperature is only one factor in biosynthesis of anthocyanin (the pigment responsible for red color in apples). Another important factor is sunlight contact with fruit. Fruit must be exposed to light to develop sufficient red color, and this is particularly critical for earlier varieties that won’t have as long in the field to pick up color in coming weeks.

Hedging and leaf thinning are valuable practices for exposing fruit to more sunlight, but bright sun on the forecast should also be handled with caution because photo-oxidative sunburn can occur when fruits that were previously shaded are suddenly exposed to direct sunlight. This type of sunburn can occur even when temperatures are mild, so another cool week does not alleviate the risk of this happening. Growers who aggressively hedge or leaf thin should make sure that sunburn protection material is out immediately following the pruning.

Photo-oxidative burns that I have seen so far this season are most common on the east sides of trees in the days immediately following an aggressive leaf or shoot thinning, especially in situations where an application of sunburn protection material was delayed after the thinning was conducted. This likely is because fruits on the east side of the tree don’t face the intense afternoon sun coming from the west throughout the growing season. Since cuticle formation in fruits takes time and responds gradually throughout the season to the environment around the fruit, the cuticle can be a little bit less well developed in this situation and fruit can burn more easily

The timing for ReTain applications is either upon us or quickly approaching, so make sure you are coming up with a game plan on timing and rates. You can check out a few good ReTain reminders by reading the Michigan State University Extension article, “ReTain and NAA as a standard practice for apples.”

For those looking at short range applications (14 days before harvest or shorter), remember that NAA can be added at 10 ppm to help with stop-drop. NAA delays the formation of the abscission zone (the spot where the stem separates from the spur), but also stimulates biosynthesis of ethylene. For this reason, combining NAA with ReTain gives us the best of both worlds. The NAA slows the formation of the abscission zone leading to less fruit drop, and the ReTain shuts down the biosynthesis of ethylene, allowing us to capitalize on the advantages of NAA as well as the other benefits of ReTain (delaying harvest, improving firmness, less greasiness, less cracking, etc.).

Growers using ReTain 30 days before harvest at full rates do not need to add NAA to this application, but NAA is helpful at the 30 day pre harvest interval when using a reduced rate (one-half, one-third or one-fourth pouch) on varieties with high sensitivity (Gala, Jonagold) or moderately high sensitivity (Honeycrisp).

Growers spraying a preharvest fungicide to protect against pin point scab and/or storage rot fungi are reminded that strobilurin fungicides (Flint Extra) as well as first generation SI fungicides (Indar, Rally) do not provide reliable apple scab control in Michigan. SDHI fungicides are a good choice for a pre-harvest spray since they provide excellent broad-spectrum disease control on fruit and will take care of any apple scab spores that might be around to cause pin point scab.

Insect update

We are near the end of the insect management season, but lower than average degree day accumulations mean that several insect pests are likely to start later and hang around longer than we would tend to expect. Apple maggot is still active at this time. Bait red sphere traps with apple volatile to improve efficacy, and the threshold for these traps is five apple maggot flies.

Second generation codling moth is underway. Closely monitor individual orchards to determine a biofix. After a biofix is established, target an application of insecticide at about 250 growing degree days base 50 from that catch date, as this will coincide with the start of egg hatch. Be cautious in setting second generation biofix across your acreage this year for codling moth, a sporadic start to first generation flight will likely mean an equally sporadic start to second generation. A late start to the season and low growing degree day accumulations mean we do not anticipate a third generation of codling moth this year.

Brown marmorated stink bug pressure continues to be low so far this season, with only two individuals having been captured in traps in the region so far. We will continue to monitor for brown marmorated stink bugs until harvest is concluded, but risk for the west central region looks low at this time.

Second generation obliquebanded leafroller is flying, and timing for treatment is 400-450 growing degree days base 42 after you biofix an orchard. European red mites are low this year in most orchards; the August threshold is 10-15 mites per leaf and we are nearly into September at this point, so mites will be falling off the management radar for the season. Third generation of oriental fruit moth is in flight. The timing for an application targeting oriental fruit moth is 200 growing degree days base 50 after you biofix an orchard.

Individual variety maturity results

The scales used to rate these different metrics on these charts are as follows:

• Background color: scale 1-4, 1 is fully yellow and 4 is fully green.
• Russet: 1-4, 1 is no russet and 4 is severe russet.
• Pressure: always listed in pounds, and two pressure scores are recorded for each apple tested.
• Watercore: 0-4, 1 is no watercore and 4 is severe watercore.
• Bleeding: 0-4, 0 is no bleeding of red color into flesh and 4 is severe bleeding of red color in to flesh.
• Red: listed as a percentage of the whole fruit with red color.

Ginger Gold

Gowers on the Ridge started picking Ginger Gold this week, and although starch index indicates that fruits are still starchy, they are starting to eat nicely this week in west central. This was particularly true for the Hart location that was sampled. Ginger Gold tends to still test at starch indices of 1s and 2s when it starts to taste nice to farm market consumers, and most growers are picking the variety with this purpose in mind. As a result, the variety will probably be spot-picked for farm market usage in most Oceana County orchards in the next couple of days, and in late Oceana County sites and throughout Mason County by the weekend and early part of next week. This variety has developed a nice side of blush in the past two weeks with the conducive weather. 

McIntosh

Growers always harvest this variety early in west central Michigan, but even the most ambitious harvesters of McIntosh need to wait at least another week. The target starch index for this variety for long-term controlled atmosphere (CA) storage is 5, and fruits this week are still well shy of this mark. Fruit quality coming out of storage will be compromised if they are harvested at the normal west central calendar date this year.

Wildfire Gala

This is an early Gala strain, so the results should NOT be viewed as representative of other Gala strains in the region. Gala fruits are considered mature for CA storage at a starch index of 3, so Wildfire Gala is very close to being ready for CA storage harvest. The color on this strain is outstanding, particularly when we consider that it’s running about two full weeks ahead of other normal season strain Gala. Growers wondering about color in this strain given how early it is should note that fruits are over 90% red at this time, so the variety does color up early. Fruit eat well, this is a nice Gala. This strain will be ready for CA storage harvest early next week.

SweeTango

This club variety is not represented on most area farms, but it provides a valuable benchmark for the timing of maturity on other prominent varieties in west central Michigan. SweeTango should be ready for harvest in Oceana County in the first half of next week and in Mason County by the end of next week. It is getting close to being ready, but could use a few more days to finish up before growers get into picking in the Hart area.

Fruits were still testing (and eating) on the starchy side as of Wednesday morning, and background color still tends towards a yellow-green instead of a golden yellow. Red color is looking very good at this time, and will look even better early next week given the weather on the forecast in coming days. Growers that leaf-thin this variety should use sunburn protectant immediately following the thinning to help avoid photo-oxidative burn, this variety has very sensitive skin.

Premier Honeycrisp

This is an early-maturing Honeycrisp strain that runs roughly two weeks ahead of other Honeycrisp strains. Growers on the Ridge started spot-picking Premier Honeycrisp in the first half of this week, but Premiers in west central still need at least another week, probably longer. Red color on this variety is not very good yet, but should improve with another week of great coloring weather coming up. Background color is still very green, so combined with the lack of red color, they are not looking market-ready yet. Fruits are still extremely starchy.

Zestar!

This is largely a farm market variety in west central Michigan and can be spot-picked at this time. Fruits are eating nicely and starch index values indicate that they have moved in to the acceptable range. Size is acceptable and fruits have a good side of red color this year.

Gala

We are at least two full weeks away from peak Gala harvest in west central Michigan. Most fruits that were tested this week have not moved past starch index values of one and are small, hard and green. This is the case even in the earliest sites in the region. In some years, growers in this area will pick in the first week of September, but this should not be one of those years. Be particularly cautious of picking Gala based on calendar date as it starts to color up in coming days, Gala can achieve outstanding color and size a week or more before it is mature. Gala is considered mature for CA storage at a starch index value of three, with suggested firmness between 16 and 18 pounds.

*Firmness is measured with a mechanical 11-mm wide probe inserted into the pared flesh of a fruit to a distance of 8 mm. Starch index is measured on equatorial cross section of an apple stained with iodine solution and rated using the Cornell University starch-iodine index chart for apples on a 1-8 scale (Predicting Harvest Date Window for Apples by Blanpied and Silsbey, Cornell Extension Bulletin 221.)