PGR helps stone fruit growers hit marketing windows, cut fruit drop

By Vicky Boyd


A plant growth regulator that helps prolong fruit firmness and quality in apples is gaining a following among stone fruit growers, who say it helps them hit profitable marketing windows.

We were looking at it for timing on the marketing end, says Joy Cline, farm manager at Bear Mountain Orchards in Aspers, Pa., who tried the PGR, ReTain, on about 30 acres of peaches and nectarines in 2004. If you can hold that fruit an additional two or three weeks in storage when the market is flooded and then sell it when the people are out, it's going to be a help.

ReTain, from Valent BioSciences, has been federally registered for use on apples since 1997 and gained federal registration for stone fruit, except cherries, in 2004. It is not yet registered for use on stone fruit in California.

AVG, or aminoethoxyvinylglycine, the naturally occurring active ingredient in ReTain, blocks ethylene production in plant tissue. Ethylene, a plant hormone, controls fruit maturity, ripening, firmness and abscission, or fruit drop.

The product is approved by the Organic Materials Review Institute for use in organic production.

Can you hold, please

In apples, growers apply a single spray of ReTain about four weeks before the anticipated start of harvest. Because it prohibits ethylene production, ReTain allows growers to hold apples on the tree longer without softening or dropping. In the meantime, the fruit can color and size.

If apples enter storage firmer, chances are they will be better quality and firmer when removed and repacked, says Ricardo Menendez, Valent BioSciences global business manager for PGR products.

Cline first became acquainted with ReTain when she used it on red delicious, galas and Rome apples.

We use it mostly as a harvesting tool, she says. We wanted to delay the reds long enough to get a little bit better color. With all of our other varieties, we wouldn't get to our Romes quick enough, and we used it for drop-control problems.

Since the Romes remained on the tree two to two and one-half weeks longer, they also increased in size.

With the galas, she used the PGR to help gain size and color and was able to harvest in one picking.

In this case, it's a great harvesting tool, because we don't lose time pulling out of our peach harvest and we gain quality on the gala, Cline says.

Less drop in stone fruit

For stone fruit, ReTain should be applied seven to 14 days before anticipated harvest.

Valent BioSciences has conducted two years of trials on California peaches and nectarines. Although the actual response varies among varieties, environmental conditions and cultural practices, Menendez says he's typically seen ReTain shorten harvest by a couple of days.

When you apply ReTain, what you will see is your first pick will be delayed two to four days, Menendez says. You end up picking fruit that's of better quality, firmer and a bit bigger. It gains size because you're letting it hang two to four days more.

But the last pick will typically occur about the same time in treated and untreated orchards.

With many of the varieties, growers pick two to four times. Typically, the first harvest is based on skin color and may involve 10 percent to 20 percent of the crop. Two to three days later, the crew may return to pick another 40 percent of the crop.

Crews may return for one or two more harvests, cleaning up the remainder of the fruit.

Growers who use the PGR may eliminate one harvest in a stone fruit orchard, reducing picking costs, Menendez says.

The reduced number of harvests also may translate into less crop loss caused by harvesters ladders knocking fruit off the trees.

As harvest approaches, soft fruit tends to drop to the ground. Because the PGR helps maintain fruit firmness, Menendez says growers typically see less fruit drop and less orchard culling as picking crews discard soft fruit.

Although the actual results vary among peach and nectarine varieties, Menendez says it's not uncommon to see fruit drop reduced by 10 percent to 20 percent.

Late-season benefits

Cline used the product on Bounty and Cresthaven peaches as well as Fantasia nectarines in 2004.

On the Bounties, an early variety, she says she didn't see a pronounced benefit.

The market seemed to be pretty good, so we didn't hold them very long, she says.

Although Cresthavens tended to be poor quality across the East Coast in 2004, Cline says the PGR improved quality and produced peaches that appeared to hold better during packing and storage.

The benefits seemed most pronounced on Fantasia, a late-season nectarine.

But Cline was quick to point out that she only had one year's experience with the PGR on stone fruit, and 2004 had atypical weather with an unusually wet growing season. The PGR may produce different results during a more typical season, she says.

I definitely believe on our late variety nectarines, like Fantasia, I wouldn't hesitate to use it again, Cline says. I'm most definitely going to try it again on our nectarines, and I'd like to see what it does on some of our later varieties. But I'll cut out the early-season varieties. G