Preharvest orchard management

By Terence Bradshaw

First things first: I’m going off-line later today for a rare, two-week, no-work vacation. Please note that I won’t be responding to emails that come in during that time.

Harvest for early apple varieties is just around the corner. That brings in a few management items that should be tended to:

1. Now is the time to collect plant tissue samples for nutrient analysis in apples to best tweak fertility programs next year. If you’re applying fertilizers without tissue samples, you are doing it blind. Samples collected every two, up to three years should be sufficient, unless you are noticing or correcting a particular deficiency. Samples should be collected separately by cultivar, rootstock, and planting system/block- basically, the sample should come from a uniform set of trees. I’ve given instructions on sample collection, and refer to those now if you need them. As for timing, apples leaves are typically collected July 15 – August 15, so now’s the time.

2. Pest management: keep an eye on apple maggot and second-generation codling moth. Some orchards may also have populations of obliquebanded leafroller that warrant treatment. Each of these is really best managed on an orchard-by orchard basis, so check your traps and check NEWA for models for the lepidopteran pests.

3. It’s dry out there, so if you have the ability to water, plan on doing so. Dry hot weather also increases mite incidence, so keep an eye out for them.

4. Approaching harvest means thinking about preharvest drop control. Dr. Duane Green at UMASS recently offered some tips on drop management strategies in an issue of Healthy Fruit:
“The time is rapidly approaching for choosing the preharvest drop control strategy you will use this harvest season. The approach for each variety will undoubtedly be different. There are a number of factors to consider in making this decision including the variety, the product to use, the weather before and after application, the time from application to harvest and the intended use of the apples (immediate sale, short storage period, long storage period). A successful preharvest drop control strategy requires consideration of all of these factors.

As an apple matures and approaches the time of harvest it starts to produce the gas ethylene. The ethylene generat­ed by the ripening apple further stimulates fruit ripening. The ethylene moves through the intercellular spaces in the apple to the abscission zone which connects the spur of the apple with the pedicel of the fruit. The ethylene weakens the abscission by stimulating synthesis enzymes that destroy cells in the abscission zone and the enzymes that hold cells together. Ethylene plays a significant role in the fruit abscission process and controlling it is a key component for drop control and regulation of ripening.
Orchardist have the choice among three currently-available preharvest drop control compounds: ReTain (aminoe­thoxyvinylglycine, AVG), NAA (naphthaleneacetic acid and its many formulations) and Harvista (1-aminocyclopro­pane-1-carboxylic acid). Each compound is different. Their modes of action are different which determines in part how they are use and the responses you can expect following application.

Harvista

This is the newest drop control compound to be made available. It influences physiological responses in the apple by inhibiting the action of ethylene. As a fruit starts to ripen it produces ethylene receptor sites. In order for ethylene to in­fluence any response in an apple (ripening, fruit drop etc.) it must bind to a receptor site. Harvista works by irreversibly binding to these ethylene binding sites. As apple ripens it continues to produce new binding sites. Loss of preharvest drop control activity from Harvista is not due to Harvista being inactivate or metabolized but rather the apple continues to produce new ethylene binding sites which are then available for ethylene to attach to and stimulate fruit ripening and preharvest drop. In initial research using a different method of Harvista application we found that application of more than one low rate of Harvista was able to extend the period of drop control of Harvista. Two to 3 applications of low rates of Harvista, equal to the sum of one application at a higher rate, resulted in longer drop control. Another observation made during the early evaluation of Harvista was that loss of drop control of Harvista can occur very rapidly, within 2-3 days. The current application of this compound made is through a proprietary in-line injection system where sprayers are retrofitted to make this specialized application. Recommendations for the use of Harvista are being handled and overseen by Agrofresh.

ReTain

ReTain (AVG) has been available to growers for over 20 years. During that time it was the main drop control com­pound used by growers. The mode of action of ReTain is by blocking a key enzyme in the biosynthetic pathway, thus in­hibiting production of ethylene in apples. It requires at least 10 days following application for the drop control of ReTain to become effective.

There are several factors that growers should keep in mind when using ReTain as a drop control compound.

· The more ReTain you apply the greater the response (more drop control and a greater delay in fruit maturity) you can expect. In general the response to ReTain is linear with the amount you apply.

· The earlier you apply ReTain in the season the greater the retardation of ripening and red color development will occur.

· When one pouch of ReTain per acre is applied on McIntosh effective drop control (less than 20%) will generally last for 30 to 35 days. Supplemental application of ½ to 1 333g pouch will extend the period of drop control and contin­ued retardation of ripening.

· Split applications of ½ pouch of ReTain will have much more drop control than 1 application of 1 pouch.

· Trees under water stress, heat stress or severe mite damage do not respond to ReTain well and its use on these trees is not recommended.

· This use of an organosilicate surfactant (Silwet L-77 or Sylguard 309, 6-12 oz/100 gal) is strongly suggested. It im­proves the performance of ReTain and it imparts a certain amount of rain fastness.

· The maximum amount of ReTain that can be used per year is two 333g pouches. Maximum drop control will be achieved using this amount.

Naphthaleneacetic acid (NAA)

Since the discovery of auxins (including NAA) in the 1930s, this group of has been known to retard preharvest drop. NAA is available in many commercial formulations. It is generally applied at a rate of 10 ppm. One can expect drop control to last 7-10 days from one application. A second NAA application of 10 ppm will extend the drop control to about 14 days. Generally, it requires 2-3 days for the drop control of NAA to take effect. NAA is most effective if it is applied just prior to the start of drop. Determining this time may be difficult. The label suggests that NAA should be applied when the first few sound fruit are found under a tree. NAA is most effective when applied prior to the start of drop. Careful monitoring of the orchard is recommended. Unlike ReTain and Harvista, NAA is known to have the abil­ity to advance ripening and shorten the storage life of fruit. Advanced ripening can be accentuated when warm to hot weather follows application, harvest is delayed, used on stressed trees or applied at rates higher than 10 ppm.

NAA may be useful when applied with other drop control compounds. NAA can be used in conjunction with ReTain. Some researchers have reported that it can enhance the drop control of Retain. Some growers wish to delay the applica­tion of ReTain to 10 to 14 days prior to anticipated harvest to minimize the influence that ReTain may have on delaying red color development and ripening. In this case NAA can provide near term drop control until the drop control prop­erties of ReTain can start to take effect. There are no reports on the use of NAA in conjunction with Harvista. Another frequent use of NAA is when it is applied with ethephon to increase red color and advance the ripening of apples early in the season. In this case, NAA can be tank mixed with ethephon or it may be applied separately 2-3 days after ethephon application.

Specific Drop Control Recommendations Differ with Cultivar

Suggestions for preharvest drop control in New England were initially developed to be used on traditional New En­gland cultivars that had a preharvest drop control problem, most notably McIntosh and Macoun. However, recently the popularity and the extensive planting of Honeycrisp and Gala have presented new challenges. Both of these cultivars are low ethylene producing cultivars, thus rates used on these cultivars must be lower to minimize the inhibitory effect of ReTain on red color development.

-Honeycrisp.

Honeycrisp has a significant drop control problem that if not countered with a drop control compound, could result in preharvest drop losses of up to 50% before harvest. Frequently, 1/3 to ½ a pouch per acre is applied to minimize the reduction in red color development. The timing of this could be 2 to 3 weeks before harvest or a split application of 1/3 to ½ 333g pouch at 3 week and 1 week before harvest. Depending on the situation, a low rate of NAA may be included with the ReTain to enhance drop control. Low rates of NAA applied on Honeycrisp will probably have a limited influ­ence on adversely influencing flesh firmness and fruit quality. There is limited information available to document the effects of Harvista on Honeycrisp drop and fruit quality.

More recently we have published work that documents the advantages of making a split application of one pouch of ReTain 3.5 weeks prior to anticipated harvest and a second 1 333g pouch application 2 weeks later. This results in a sig­nificant the delay of preharvest drop until early October. Under this scenario fruit ripen under more favorable weather conditions and red color at harvest was excellent.

-Gala.

While preharvest drop is not a malady suffered by Gala, fruit frequently experience stem-end split as they ripen, develop an undesirable “greasy” feel and internal browning may develop in storage. Under warm to hot conditions this can occur very rapidly. ReTain can delay ripening and thus reduce these maladies, but it comes at the expense of retard­ed red color development. Low rates of ReTain (1/3 to ½ pouch/ acre should be used to minimize the delay in red color development. NAA is not useful here since it does have the tendency of advancing ripening and aggravate the problem. Little information is available for the use of Harvista on the delay ripening on Gala.”

Enjoy the end of summer, this looks to be a busy harvest season ahead.

Best,

Terry

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