Teryl Roper likes a good apple just as much as the next guy, but he also appreciates the value of an apple tree’s root system. As a University of Wisconsin-Madison Extension fruit crop specialist, Roper evaluates new apples in Wisconsin, and the different rootstocks to which they will be grafted.
All the Red Delicious and McIntosh apple trees available for planting are clones from two different original trees. They get their flavor and color from their parent tree. But you can’t plant seeds from a cultivated variety – cultivar – of an apple and grow trees that produce apples just like the parent tree.
For centuries, apple growers have multiplied and perpetuated a tree with desirable fruit by taking a small branch, called a scion, and grafting it to a rootstock. That little operation is now repeated many thousands of times each year to produce trees for commercial and home orchards.
However, the scions of different cultivars only partly determine a particular tree”s qualities, according to Roper. The rootstock determines other important traits, such as how large the tree gets and when it starts bearing fruit.
The rootstocks that produce dwarf trees, for example, have transformed the appearance of apple orchards and made picking apples much easier. Dwarf trees begin to fruit in three years while standard trees take six to 10 years, Roper says. Partly because growers plant the dwarf trees close together, those trees also produce more fruit each year per acre and produce more fruit over the life of the planting than the same apple cultivar on a standard rootstock.
Consumers will have lots of opportunities to sample Wisconsin apples this year at roadside stands, farmers” markets and in stores. Wisconsin ranks 12th in the nation in apple production. However, Wisconsin produces just half a percent of the nation”s apples. With its long summers and mild climate, Washington State is far and away the leader. Wisconsin”s apple industry has become more concentrated over the years. Roper says that there are 36 large orchards with more than 5,000 trees. These orchards produce more than half the state”s crop. By comparison, there are 119 orchards with more than 100 but less than 500 trees.
A great rootstock, like a great apple, is rare, Roper says. But consumers wouldn”t recognize any of the rootstocks by name. Apples get names such as Ambrosia, Ginger Gold and Silken. The no-frills names for rootstocks – M.9, CG 1707, and M.27 – evoke no rosy images.
For commercial growers, choosing the right rootstock as well as the right cultivar affects profits. That”s where Roper”s research comes in. In collaboration with two networks of U.S. and Canadian scientists, Roper tests how well different rootstocks and cultivars perform in Wisconsin. The network that evaluates rootstocks is most interested in finding rootstock cultivars that promote apple production at a young age and produce a large apple crop over the productive lifetime of trees.
Independently, Roper has also studied rootstocks to see if some need less fertilizer than others and if rootstocks influence apple size.
Roper grows, evaluates and studies apples on 10 acres at the College of Agricultural and Life Sciences research station at Sturgeon Bay. The independent evaluations done there help growers decide if the advertising claims that nurseries make in national trade magazines hold true in Wisconsin.
“The trials perform an especially valuable function in weeding out rootstocks that perform poorly,” Roper says. One trial, for example, showed that Royal Gala and a particular rootstock (M.26) were not compatible. They produced a tree that snapped at the graft in a strong wind, even when the trees were staked.
Shoppers at farmers” markets and even grocery stores have a larger selection of apples than just 20 years ago. Red Delicious, Golden Delicious, and McIntosh apples dominated the market through much of the last century. They displaced hundreds of cultivars that were available locally in the early 1900s. Now specialty growers are bringing back some of those heirloom apples, such as Wolf River, Golden Russet and Northwest Greening. Meanwhile, apple breeders are turning out many new cultivars.
“In terms of apples, we”re in sort of a renaissance,” Roper says. “Some small growers continue to plant heirloom varieties. But there”s also been a burst of new cultivars.”
Among the new cultivated varieties evaluated at Sturgeon Bay, Roper is a big fan of Honeycrisp, which Minnesota breeders released in the 1990s. He likes its combination of sweetness and acidity, or tartness, plus its explosive crispness. Compared to growers in the South and Northwest, Midwestern growers have an edge with Honeycrisp because they can produce a higher quality apple than growers in those other regions. Roper also suggests that consumers try Suncrisp and Zestar if they can find these still-rare cultivars.
For homeowners who want to plant an apple tree or two, Roper suggests one of the disease-resistant varieties. These include Liberty, Redfree and Nova Easygro.
Roper”s research was supported by state funding to the College of Agricultural and Life Sciences and the University of Wisconsin-Extension, and by grants from the Wisconsin Apple Growers Association, the College and the USDA.