One of the most common mistakes in crop management of apples is underestimating the crop load, says Kevin Larson, horticulturist with Roche Fruit Company, Yakima, Washington. When the fruit is around 12 millimeters (half an inch) in diameter at thinning time, the crop load probably doesn’t look as heavy as it actually is, Larson explained. “We tend to back off on the chemical thinner a little, and then, around the time we’re hand thinning, we’re wondering why we’re spending $800 per acre for hand thinning and fruit size is small.”

Speaking during a panel discussion at the Washington State Horticultural Association’s annual meeting, Larson said another common problem is to let trees carry too heavy a crop in the third leaf so that they never reach their full growth potential. It might be hard to forego those early crops, but it’s necessary if plantings are going to yield 70 to 80 bins per acre at maturity.

Brett Drescher, orchard manager at Auvil Fruit Company, Orondo, Washington, said growers have five or six tools they can use to manage crop load, but often limit themselves to one or two. “A common mistake is to not look at the end result and the greatest possibility you can get out of the crop—the greatest dollar return to you—and not use all the tools available to you to get there,” he said. However, he’s also seen people make the mistake of putting too much money into a block of the wrong variety, and overestimating what they will get out of it.
Detail pruning is an important element of Drescher’s crop management program. “You can spend very little money and accomplish a lot,” he said.

This is followed up with very aggressive thinning practices as early as possible. With certain high-value varieties, where he wants to guarantee a full crop every year, he resorts to hand thinning of blossoms.

Advantages of blossom thinning are good return bloom, bigger fruit, and maximized packouts, resulting in better returns. And the results are 100 percent guaranteed—unlike with other thinning strategies. Sometimes, with high-value fruit, a grower might chemical thin and then wish they had better-sized fruit and didn’t have to hand thin, he said. “You’re looking at $200 to $300 a bin difference between that and what was blossom thinned and reached the full potential it could get to.” Blossom thinning also helps to assure return bloom to avoid the ­biennial bearing that many Fuji growers struggle with, he added.

Mike Robinson, production manager with Double Diamond Fruit in Quincy, Washington, said there are times and places where it makes sense to do blossom thinning, particularly if it’s a high-value crop and you can’t take the chance of not thinning adequately, but he feels that the chemical thinning tools available now are good enough that he can generally use chemical thinning and save $2,000 to $3,000 per acre on hand blossom thinning. However, he’s excited about the potential for mechanical bloom thinning.

Larson said there’s a place for blossom thinning, as trees tend to crop better when the crop is removed early, but a grower can’t just decide on the spur of the moment to do it because it will require different pruning the ­season before and different nutrient strategies.

“I think there’s a place for it,” he said. “There’s some blocks where you can get more fruit in the target range and it can pay for itself, but if the block is going to peak on 80s and 88s with chemical thinning, I don’t think you can justify the extra expense.”


Larson said he pays close attention to nutrition in all of the blocks. In the past, growers tended to cut back on the nitrogen in an attempt to produce redder fruit. “Eventually, the tree runs out of nutrition, and we get into just horrible alternate-bearing blocks that would be off for two years in a row,” he said. “Nutrition is something we pay strict attention to, and we have some good results coming from that.”

Harold Ostenson, organic program manager with Stemilt Growers, Inc., Wenatchee, Washington, said that over the past 15 years, a range of thinners has become available that work well, but timing the applications correctly for various weather conditions is tricky. A mistake he sees is not taking action soon enough. “You keep waiting to evaluate, and by the time you’re done evaluating, you have too many fruit. The quicker you get the excess off, the bigger and more colored the fruit that’s left.”

He hopes that a model that Virginia Tech scientist Dr. Keith Yoder is developing to help growers time their thinning applications will make results more consistent. The key is to target the narrow window between having the fruit set you want and having too much.
To target that window, Ostenson monitors sample trees and uses a spreadsheet to record the number of king blooms and clusters each day. As the blossoms open up, he removes the side blooms. When the flowers reach the right number to produce the desired crop load, a thinner is applied, after allowing time for fruit set to take place. Ostenson said it doesn’t take long to count the blossoms, because he only counts king blooms.

“This is the way to do it, rather than guessing how much fruit is out there,” he said.

Larson has parameters for each variety. For example, he tends to thin Gala harder because it tends to produce small fruit. He considers how much pollen is in the block and looks at the history of the block to see if it has been easy or hard to thin. That will influence the rates and ­timing somewhat.

Drescher said the history of the block and variety play big roles in his choice of thinning program, as does orchard elevation, but his general philosophy is, “be early, be aggressive, and don’t look back.”

Robinson said the fertilizer ammonium thiosulfate works well for Red Delicious, but he doesn’t see the same benefit with other varieties. Lime sulfur and fish oil is hard to beat for Gala, he said, but he has concerns about applying that combination on Fuji at 80 percent bloom timing because of the risk of fruit marking. On Fuji, he tends to use just lime sulfur.

Ostenson said fish oil and lime sulfur provides benefits in addition to fruit thinning. Research has shown that it is effective also against fireblight when applied during bloom. Moderator Tory Schmidt, horticultural associate with the Washington Tree Fruit Research Commission, said it’s also effective against mildew. Larson said he uses ATS on blocks that are easy to thin, and lime sulfur on others where more thinning is needed. He doesn’t use fish oil because of the fear of marking fruit.