Big cherries require big commitment

Left: Before pruning: Bing on Mazzard rootstock. Right: After pruning: The same Bing on Mazzard tree. Notice that the small, weak wood was removed.

Growing big cherries doesn’t just happen. It takes commitment, attention to macro and micro details, and crop load management. But with larger cherry crops forecast in the future, having a 65 to 75 percent packout due to small size may no longer be profitable.   

In sharing insights on how to produce cherries that peak at 10-row or larger, a panel of cherry growers stressed during the 2010 meeting of the Northwest Cherry Institute held in Yakima, Washington, that size is becoming ever important. Growers need to do all they can to produce large, firm, sweet cherries.

“In the past, I thought that the 11-row cherry had a place,” said Travis Allan of Allan Brothers, Yakima, Washington. “It paid for picking, it paid for packing, and we made money on it. But last year, it was such a drag on what we did.” His company is now ­looking at ways to eliminate 11-row cherries from the operation.

Start off right

The Dalles, Oregon, orchardist Tim Dahle said that growing large fruit is a complex equation, involving such factors as light interception, adequate branch diameter and angle, proper leaf-to-fruit ratio, and adequate root system, nutrition, and irrigation. “It begins with orchard establishment and choosing the proper rootstock,” he said. “Even in the best of orchards, you’ll have trees that aren’t performing, which means that there’s an imbalance from something.”

The imbalance could be from roots that are impaired, a tree that’s diseased from crown gall (or other viruses), damage from gophers, roots that were killed from a water leak, or other maladies, Dahle said. But it’s important to identify those trees and take corrective action, removing enough of the top of the tree to allow it to grow ­pencil-sized wood, he noted.

Precise irrigation plays a major role in fruit size, said Dahle. “If there’s not quite enough irrigation, fruit is small and stressed. Too much, and fruit is soft and low in sugar. It’s difficult to hit it right all of the time.”

Once the crop is harvested, the tree doesn’t need as much soil moisture, and reduced levels can actually encourage deeper rooting.
Dahle warned growers not to depend on a calendar to schedule irrigation. Good soil moisture data is needed to make good irrigation decisions.

Pruning

Cherry grower Norm Gutzwiler of Wenatchee, ­Washington, has been part of field demonstrations and workshops for years, helping others learn the importance of pruning in cherries. He encouraged orchardists to get rid of big wood, opening up the tree to capture energy through light interception.

“It’s a continual process—remove and replace wood every year,” he said.

Gutzwiler said growers  should think in terms of pounds or boxes of fruit per tree. In a block of Bing on Gisela 6, planted with 8 feet between trees and 16 feet between rows, heavy pruning was done to the two-leader structure to bring production levels down to two boxes of fruit (one box per leader) per tree. At that spacing, there were 340 trees per acre, he said, which equates to about 20,400 pounds of fruit or 10.2 tons per acre. “If you put five more pounds of fruit on each tree, you’ll come up to more than 11 tons per acre.”

In another example of central leader Skeena trees on Mazzard rootstock, spaced 5 by 14 feet apart, the trees only need 30 pounds of fruit per tree to total 9.5 tons per acre. Branches need to be continually tipped, he said. The closer spacing results in 628 trees per acre. “If you add five pounds of fruit per tree, it puts another 2.5 tons of fruit per acre on the trees.”

Pruning should be approached differently depending on the rootstock, he added. For Gisela, a very precocious rootstock and one that sets a lot of fruit on one-year wood, he recommends tipping all of the shoots and leaving less wood in the trees than on Mazzard rootstocks. “In Mazzard, if you take one-year wood and tip, you’ll get too much vigorous wood,” Gutzwiler said.

Fruit per foot

Thinning at the green fruit stage is one way to eliminate 11-row fruit, Allan said. But how do you know if you’ve thinned enough?
Allan has been working with grower-shipper Jason Matson of Selah, Washington, to develop guidelines based on the number of fruit per foot of fruiting limbs.

“We trying to boil it down to a small area,” he said, adding that a guide is needed so that growers don’t just have a “look” that they’re after when thinning, but some real numbers as well.

If target tonnage is around ten tons per acre, with 228 trees per acre that would equal about 87 pounds of fruit per tree, he explained, and that would be about 3.6 to 4.3 pounds of fruit per limb in the fruiting area (20 to 24 branches) on a multiple-leader tree. Because the average weight of a 10-row cherry is approximately one-third ounce, it would take about 40 individual cherries to equal 13.2 ounces for each foot of fruiting area on the limb.

Allan is still working on many variables to the formula. Data showed that one-year wood is key to producing large fruit and should comprise 30 to 50 percent of the total length of the fruiting branch.

Data that Allan and Matson have collected thus far show that for a heavy crop of ten-plus tons per acre with 228 trees per acre, a grower should aim for 40 to 45 cherries per foot of a fruiting limb. If the crop was thought to be on the light side, say six to eight tons per acre, a few more fruit could be left on the fruiting branches. The grower would then target 45 to 55 cherries per foot of fruiting limb.

Nutrition

When it comes to tree nutrition, the three grower panelists follow new recommendations from university researchers to apply nitrogen (urea) in the fall to boost spur development the following spring. They also take leaf and soil samples to identify nutrient deficiencies.
Dahle noted that trees that are being pruned hard need adequate levels of nutrition to produce his goal of pencil-sized, 18-inch-long wood.
Growers also need to observe tree growth to gauge how vigorous the orchard is growing, said Gutzwiler. Tree vigor can be a clue to the nitrogen status.