Dealing with heavy fruit set

Lynn Long believes that Gisela rootstock can consistently produce 10-row cherries with good tonnage (10 tons per acre).

Are Gisela rootstocks a viable option for cherry growers and capable of consistently producing high-quality fruit? Oregon State University’s Lynn Long believes the productive Gisela rootstocks can yield large fruit with good tonnage, despite the experiences of 2009.

Long, OSU Extension educator for Wasco County, has worked with a grower in The Dalles, Oregon, in a pruning trial comparing fruit quality from trees on Mazzard and Gisela rootstocks. In 2008, the grower’s largest fruit came from the Gisela blocks, with 70 percent of Bing on Gisela peaking on 9.5 row. None of the Bing cherries grown on Mazzard even came close, he noted during the 2010 Northwest Cherry Institute in Yakima, Washington.

“But that was in a year with frost,” Long said, adding that just about anybody can prune a Gisela tree under frost conditions. Last year, the Bing on Mazzard fruit peaked at 11- to 11.5-row, while Bing on Gisela peaked at 10-row.

“I think that’s where you want to be—you can get 10 tons per acre of 10-row cherries—and make good money, even in a year like 2009,” he said  “That’s what we need to be doing, year in and year out, and have large fruit on our Gisela trees.”

In another pruning trial focused on the effect of tipping, Long found that in a block of Skeena on Gisela, fruit size increased two millimeters after the second year of tipping all branches compared with trees in the same orchard that were not tipped or only tipped slightly to keep trees to eight feet all.

He acknowledged that some yield is sacrificed when all of the branches are tipped. “But after last year, we’ve learned that we don’t need a lot of fruit on the market. We need good-quality fruit on the market.”

Heavy fruit set

In some years, like 2009, even with proper pruning, growers with trees on Gisela rootstocks can find they are headed into a heavy fruit set with the potential for small fruit. Long saw problems developing relatively early—by shuck fall—last season and suggested several practices to help growers avert poor fruit size.

Eliminate weak wood—As he went around the district, he saw weak, pendant wood. “If you have Gisela rootstock, you have got to prune out the weak and pendant wood, even if you’re pruning at shuck fall, or you’ll have no new growth and it will be hard to size fruit,” he said. Fruit on small wood, with only a few leaves, become what he calls parasitic fruit. The fruit don’t have enough leaf area to support them and must draw ­carbohydrates from the rest of the tree.

“One thing you must do when you’re pruning Gisela cherry trees is to always think in the back of your mind, ‘How do I reduce the crop load on this tree,’” he said. “Look for opportunities to remove weak shoots that aren’t 18 to 24 inches long.”

Hand thin—He’s usually not a fan of hand thinning because it’s difficult to recoup costs, but in emergency situations, thinning can be a good investment, especially in high-return cherries like Rainier, Sweetheart, and Chelan. But he warned growers to avoid hand thinning in midseason varieties, unless it’s an emergency. “There’s no way that you can economically thin Bing cherries if you’re receiving 75 cents a pound return. But in an emergency situation, it may pay.”

He suggests thinning by using the fingers to rake fruit out of clusters. Using scissors is too slow. “You need to get fruit off the tree as quickly as possible.”

Extra nutrients—Big crops require extra nutrients. He advised growers to apply extra nitrogen if they have a big crop. If 80 pounds of nitrogen is your normal rate, he recommends applying 120 pounds and considering foliar applications.

Long is a proponent of applying urea (nitrogen) in the fall to encourage spur leaf development the next spring. Dr. Greg Lang of Michigan State University found that two applications of 15 to 20 pounds each of nitrogen in 25 to 75 gallons of water, made around the first week of September and a week later, increased winter bud hardiness and increased spur leaf development by 20 percent.

“I encourage every grower in Oregon to put on the fall spray every year,” he said. “If spur leaves are larger, potentially they are producing more carbohydrates, and more carbohydrates flowing into the fruit means larger cherries.” Growers making fall applications can reduce the amount of nitrogen they apply earlier in the year to avoid a vigorously growing tree.

Higher GA rates—He also encouraged growers to use higher rates of gibberrellic acid when trees are overset. Higher rates of GA will not take the place of good pruning, but can help with fruit quality, Long explained. However, putting on the standard 20 parts per million will be a waste of money as the tree won’t respond. “You need to kick it up to 30 to 35 ppm to get a response.” But he cautions that higher rates of GA will affect the finish and return bloom for Lapins and Lambert varieties, so lower rates around 20 ppm for those varieties must be used.