Reflective mulches boost fruit size, color and yields

08/01/2011 05:37:00 PM
Vicky Boyd

Reflective materials that bounce additional sunlight up into tree canopies from the orchard floor can pay off in higher yields, bigger sizes, and better and more evenly colored fruit.

Tests over the past eight years with reflective fabrics placed in drive rows produced similar results in apples, cherries, pears, peaches and nectarines, says Tory Schmidt, a research associate with the Washington Tree Fruit Research Commission in Wenatchee.

“I was a little surprised at how consistently effective they’ve been at those three qualities,” Schmidt says.

'Pretty substantial' results

Results include a “pretty substantial” impact in size, fruit set and yield. Yields in test plots, for example, have run up to 20 percent to 25 percent higher, he says. Mylar foils used in the tests improved only fruit color.

Higher yields, larger fruit and better color “all put money back in the grower’s pocket,” Schmidt says.

While reflective materials so far are more common in Western orchards, the extra light also is crucial for Michigan cherry growers using high tunnel systems with blush varieties.

“We’re already light-limited [without high tunnels] so every little bit helps,” says Greg Lang, professor of horticulture at Michigan State University in East Lansing.

Adding to the problem, the plastic used in high tunnels partly blocks ultraviolet light.

And without UV light, only the topmost layer of Rainiers and other high-value blush cherries achieve full color. The rest, he says, stay pale yellow.

Convincing results in blush cherries

Lang hasn’t found funding for a full range of controlled experiments with the reflective materials.

But he’s done enough preliminary work with three types—Extenday reflective fabric, Mylar foil and a white weed barrier fabric—to show convincing results with blush cherries.

The jury is still out for the region’s growers with Bings and other sweet red varieties, or for those not using high tunnels, he says.

Any added expense requires careful consideration.

Choices, choices, choices

Which reflective material to use depends on your objectives for a particular block, says Jonathan Toye, founder and chief executive officer of Extenday USA Inc.

The company, based in Yakima, Wash., offers 10 versions of its reflective fabric, varying in weight, durability, reflectivity and weave construction.

Growers’ objectives also affect how they use the material, when they deploy it and whether they shift it later in the growing season to aid a different crop, Toye says. “Think about it as a management tool,” he says.

Washington Fruit & Produce Co. in Yakima, Wash., has used Extenday since 2005, mainly in Gala apple blocks. There, the company sees not only color improvements but also up to a 10 percent increase in yield, says orchard manager Dan Plath.

“If [color] was the only reason it wouldn’t justify the expense,” he says.

For color alone, Mylar foils suffice, he says. The company chooses that material for its older Fuji and Gala varieties.

“We have to work harder on those to get color, so there’s a lot of room for improvement,” he says. “But the newer generations [of those varieties] are where we’re getting 70 to 80 percent premium [fruit].”

If improving fruit color is your main objective, Schmidt says, you can wait until a few weeks before harvest to install reflective foils or fabrics. Laying out the material at bloom helps increase cell division to ultimately boost fruit size and yield.

Hold off early deployment until after any severe frost forecasts, Plath says.

Reflective materials substantially reduce ground warming from spring sunlight, which can translate into a degree or two drop in nighttime orchard temperatures—a potentially crucial difference for frost protection.

Mylar foils cost less up front, Schmidt says, but are less durable and must be replaced after a single season, increasing disposal costs.

Sturdier materials such as Extenday represent a bigger initial investment, but can be used for five or six years before replacement.

And unlike the foils, they also can stand up to being rolled up and moved to a new location partway through the growing season, he says.

Many growers take advantage of that sturdiness, placing the fabric strips in apple blocks early in the season to boost cell division, then transferring them to cherry orchards before harvest.

After finishing up cherries, they return the fabric to apple orchards to boost fruit color, he says.

“The benefits more than pay for all that moving around,” Schmidt says. Growers get three to four uses each year out of the same product rather than investing in three times as much reflective material.

The Extenday fabrics work best raised slightly from the ground to allow air flow, he says. Shock cords secure the material during use.

Plath recommends doubling up shock cords on the windward side of any block, a lesson learned from hard experience. A wind storm blew fabric strips up into tree rows like sails, breaking trees at bud unions.

But avoid tightening the cords too much, he says. The material needs some give, especially to handle equipment traffic.

Careful handling and storage during the off-season—ideally rolled up under a tarp out of the way—will help increase its life, Schmidt says.

Reflective material can help make “the best blocks better,” he says. But it’s not a rescue product. “It may marginally help shaded, struggling blocks, but there has to be light reaching the ground for it to be effective.”



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