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Healthy Fruit 2010 Vol. 18:15

Jul 27, 2010

Orchard Radar preliminary McIntosh harvest date forecasts (for Belchertown)

Date to apply ReTain to delay harvest for apples which without treatment would be ready for storage harvest on August 25 is Wednesday, July 28

Begin measuring actual McIntosh starch-iodine index no later than Wednesday, August 18

The Michigan formula estimate for standard (i.e. non-spur) McIntosh starch index 4.0 and beginning of optimum McIntosh harvest for CA storage is Wednesday, August 25. Estimate adjusted to lessen influence of unusual bloom date is Tuesday, August 31

Cornell Bulletin 221 provides formulas for different locations to estimate date when non-spur McIntosh reach starch index 6.0 and the end of optimum harvest for CA storage. Using the Hudson Valley formula, the estimated end of McIntosh CA harvest for Belchertown MA is Wednesday, September 15

The way I see it and ReTain timing

The 'early' apple harvest and timing of ReTain application seems to be the topic of choice right now. Clearly, Mac harvest is going to be about a week ahead of average, but don't take that as gospel. A cool August could really move it along or a hot August could retard it some. (Mostly due to lack of color development.) Frankly, I have no real indication how early 'early' apples are right now, largely because we don't have particularly good harvest date records on them and they have a tendency to be variable. (Plus I have been travelling a lot!) But I expect they are at least 10 days early. Peach maturity right now looks to be about a week to two weeks (depending who you talk to) ahead of 'average' but I am not sure how much that means.

I would suggest you think about applying ReTain about a week earlier than you might most years. To me, that means the first or second week in August for the brunt of growers who will be well into McIntosh harvest by Labor Day and want to delay some blocks. That is 21-28 days before anticipated harvest. U-pick growers might be looking at the 3rd week of August as a better timing window, because they are looking to hold fruit on the trees a little longer into the growing season than (for example) the wholesale grower with a lot of fruit going into storage. But again, use your gut feel regarding the weather, fruit condition, fruit color, and early variety harvest as we go along. Every block and variety have different destinations and purposes are -- ReTain application should be tailored to the individual situation and desired result(s).

All that being said, here are some ReTain application reminders:

  • Use one pouch ReTain (full rate) per acre with organosilicone surfactant (0.05 to 0.1% or app. 6-12 oz. per 100 gallons) per ALL label directions
  • Do not apply to stressed trees -- it will not work well
  • Apply 2-4 weeks before anticipated harvest, however, the 2-3 week window being best for most
  • Apply in a water volume of 100 gallons per acre, and ideally in the morning or evening under slower drying conditions; ReTain is rainfast in 8 hours
  • ReTain has a 7 day pre-harvest interval
  • ReTain can be used on Gala and Honeycrisp at half-rate to even-out ripening

Good luck. JC

Time to collect leaves for foliar analysis

It's not too early to start collecting leaves for foliar (plant tissue) analysis to determine nutrient status. Foliar/leaf analysis is the best way to get a snapshot of the nutrient content of your trees, and thus tailor fertilizer programs to address deficiencies or excess of nutrients as indicated by the leaf analysis results. Complete directions for collecting and submitting the leaves can be found on the UMass Soil and Plant Nutrient Testing Laboratory. Consider sampling every block every three years of so you can best address the nutrient needs of your trees. Note that you can analysis can be done for apples, peaches, pears, cherries, etc. If you have any questions let me know. JC

Guest article

TIPS FOR STORING PEACHES AND NECTARINES Mosbah Kushad, Crop Sciences, University of Illinois Extension. Reprinted from Ohio Fruit ICM News, Issue 12, July 21, 2010.

With peach and nectarine harvest nearing full swing, some fruits will likely be kept in storage for later sales. Unlike apples, peaches and nec- tarines do not store for a long time at low temperature. The alternative for many is to plant varieties of different maturity dates in order to extend the season. One of the biggest problems with storing peaches and nectarines at low temperature, below 40°F, is that they develop a mealy or wooly texture. Wooliness or stringiness is a chilling injury response to low temperature storage. It is well known that during normal ripening of peaches, enzymes that break the cell wall, causing the fruits to soften, such as polygalacturonases and pectinmethylesterase, are activated. However, when fruits are stored at 32 to 36°F, the activity of some of these enzymes is reduced substantially. Without these cell wall breaking enzymes, peach and nectarine fruits will not soften properly even when kept at room tempera- ture for a long time; instead the fruit becomes stringy or mealy. Several methods have been used to avoid wooliness or stringiness in peaches, including harvest- ing fruits at full maturity or early ripe stages, intermit- tently warming the fruits during storage, treating the fruits with ethylene, and spraying fruits in the field with gibberellic acid, GA3.

Harvesting fruit at full maturity is somewhat difficult to predict precisely because most peach and nectarine varieties on the market are high coloring. One of the methods used to estimate fruit ma- turity is to use ground color as an indicator of when to harvest. Ground color is the color of the skin away from the sun on the shaded side of the fruit. If the color has any tinge of green, then the fruit has not reached full maturity. In the photo below you can distinguish the sunny side from the shaded side. Fruits will store 10 to 14 days longer (develop less wooliness) when they are picked when the shaded side has turned yellow or deep orange. For high coloring cultivars, it is difficult to use ground color as an indicator of early ripening or full maturity. You might use either days from full bloom or degree-day models to decide when to harvest. If the fruits are picked too soon, you can expect between 20 to 35% of the fruit to be wooly after 3 weeks in storage.

Intermittent warming during cold storage is another way to reduce wooliness of peaches and nectarines. Warm Fruits coming from the field should not be put in storage immedi- ately after harvest. Fruit should be kept in a shed or in a cool storage (65 to 70°F) for several hours, before they are placed in cold storage. Chilling injury is much worse when fruits are put in cold storage immediately (when they are hot) than when they have cooled. For this reason it is best to harvest fruit very early in the morning than in the middle or late in the day. You can also reduce chilling injury by washing fruit with cold water 55 to 60°F before it is placed in storage. Studies have shown that fruits that have been picked early in the morning, cooled for a few hours in a shed or by drenching with cold water may be placed in cold storage at 35 to 40°F for up to four weeks without de- veloping significant wooliness, especially if the fruit are taken out of storage every two week for 12 to 18 hours, placed in a cool place (65 to 70°F), then returned back to the cold storage at 35 to 40°F. In other words, by taking the fruits out of storage for a few hours every two weeks they will not likely be stringy when they soften. It is a tedious process, but it seems to help the fruit ripen after storage.

Another method that has been used to reduce wooliness is to treat fruit after harvest with 10 to 15 ppm ethylene. Ethylene is the hormone that causes the fruits to ripen. Peaches are classified as climacteric fruits. Climacteric fruits are those that need ethylene to ripen (such as bananas and tomatoes). Peaches produce some ethylene, but when the fruits are kept at low temperature the ethylene synthesis process is damaged. By treating the fruit in storage with ethylene, the enzymes that cause the fruits to soften are stimulated and wooliness is reduced. I have not seen this being applied commercially, but it is worth experimenting with if you have the tools to inject ethylene. You may also store fruits that produce higher levels ethylene with peaches and nectarines, like apples. Unfortunately apples mature at later dates than peaches and nectarines.

Storing peaches under controlled atmosphere has also been shown to have some positive effect on reducing wooliness in peaches, but the effect is not consistent. Controlled atmosphere is used extensively to store apples, but has little effect on extending the storage of peaches. One experiment have shown that treating fruits with gibberellic acid delayed ripening of peach and reduced wooliness, but the results have not been confirmed.

Last year, I bought fruits from our local grocery store in mid-August that were stringy and never softened. Here are a few tips on how to avoid this. Harvest fruits during the cold part of the day (early morning); avoid putting fruit in storage when they are hot; acclimate the fruit at 60 to 70°F for a few hours before storage or at least keep them in a cool shed; store fruits at 35 to 40°F but take them out of storage for a few hours every two weeks.

Useful links

UMass Extension Fruit Program

UMass Cold Spring Orchard

Scaffolds Fruit Journal

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