When it comes to defining fruit quality, growers might think a bit differently than consumers.
“Fruit consumers are concerned with flavor, texture, the balance between sugar and acid, and appearance (shape, color, russet),” said Dr. Jim Schupp, pomologist at Penn State’s Fruit Research & Extension Center. “We’ve seen an increase in consumers who say that a locally produced product is a quality attribute they’re after.”
However, fruit marketers might have a different view. “Producers are interested in grade, consistency, traceability, and GAP certification [Good Agricultural Practices],” said Schupp, “and if you’re a retailer, you’re concerned about shrink.”
Both consumers and producers are interested in qualities such as fruit size, firmness, and freedom from defects. Schupp said, “As we move toward fresh markets, we need to recognize that the requirements are very demanding and competition is fierce. We have to focus on quality as an important way of maintaining our competitive edge in the marketplace.”
Schupp said that everything that’s done in the orchard contributes to improving fruit quality. “We use chemical thinners to adjust crop load,” he said. “This has an impact on fruit quality for multiple years, and on return bloom. Products that contain a mixture of 6-BA and GA can make the fruit shape more attractive to consumers or retailers.”
There are several ways in which the crop load can be adjusted. “Our first shot at this is with pruning. We prune to get light into the canopy, to get good return bloom, and get good fruit color and quality throughout the canopy. But when we prune, it’s unavoidable that we remove bearing surface, and by so doing, we set the stage for crop potential for those trees,” explained Schupp.
Other initial fruit quality measures include chemical thinning, rescue thinning, hand thinning and return bloom sprays, which Schupp said are important for adjusting the following year’s crop.
Factors such as tree age, overall vigor, the previous year’s crop and how much stress the tree was exposed to the previous year also influence fruit quality. Weed pressure, mites and mineral deficiencies can have a negative effect on blossoming and blossom strength. Schupp said that because the care and health status of trees varies, it’s challenging to make recommendations to growers.
“We know that there are certain varieties that are relatively easy to thin, like Ginger Gold, so we’ll use lower rates and make a single application in the best thinning window of 10 to 12 millimeters. That’s all we need to do. Other varieties are moderately difficult to thin, so we’re into the middle range of application rates,” noted Schupp. “When we have a strong set, we’re doing a tank mix with carbaryl to increase the thinning activity if necessary. If the set is particularly heavy, we may do a double thinning and put something on at petal fall and follow up later at 10 to 12 millimeters.”
Tree fruit varieties directly influence the grower’s thinning program. “When we thin, we’re thinning not only for fruit quality of this year’s crop but for next year’s crop as well,” said Schupp. “Certain varieties are more prone to AB [alternate bearing] than others.” He added that Ginger Gold, Cortland, Mutsu, and non-spur Rome are easy to thin; McIntosh, Jonagold, spur Rome and Stayman are moderately difficult to thin; and spur Delicious, Fuji, Golden Delicious, and Cameo are difficult to thin.
Both flower density and fruit set have a key role in fruit quality. “We know that trees that have a very heavy snowball bloom often have a lower percentage of setting flowers compared to trees that have a green bloom,” said Schupp. “The presence of so many flowers on creates a high demand for reserves and [the] current season’s carbohydrates. Even if the percent set is low, the sheer number of flowers will still require thinning.”
He said that from year to year, the single most reliable predictor of fruit set and final yield is initial set. He suggests that growers ask themselves how many fruits are there and if they are growing. “What’s happening is that competition for carbohydrates is increasing by petal fall and initial fruit set, the last of the tree’s reserves are being used up to fuel new growth of fruits, shoots, and roots, and it becomes a matter of carbohydrate supply and demand,” explained Schupp. “Our job as managers are to modify that initial fruit set. We’re going to modify, not override, what happens.”
Growers should remember that as a perennial cropping system, the fruit tree’s survival strategy is to keep itself alive, rather than keeping its progeny alive. Much of the regulation of developing fruit and whether it stays or goes is dependent on carbohydrate supply and demand. Under high light conditions and increased photosynthesis, the fruit is harder to thin. Under low light conditions, carbohydrates are reduced, fruits are under more stress, and they’re easier to thin. Temperature also plays a role – low temperatures mean low metabolism and low demand for carbohydrates, and trees are harder to thin. In higher temperatures, the opposite is true – the tree is unable to regulate its metabolism, which creates high demand and easier thinning.
Schupp suggests that growers always consider the weather when selecting chemicals, determining application rates, and timing applications. “There’s a critical time,” he said. “The two days before and the four days after application are the most critical days when it comes to thinners.”
Schupp said, “From the standpoint of fruit set, low light and warm temperatures would be a bad scenario, but cool and sunny weather might be worse. Because we have no control over the weather, chemical thinning will always carry an element of risk. One of your challenges as growers is to find weather prediction that you believe and trust.”