Organic Apple Production is Possible With Management Techniques That Apply to All Orchardists

Posted: September 29, 2009

Six years ago, producing certified organic apples in Pennsylvania might have seemed impossible given the wide range of pests and diseases that apple trees are susceptible to. But with increasing input costs and a market flooded with imported apples, Pennsylvania orchardists were hurting and some wondered if the organic option was worth a look.
Liberty apples at the Rock Springs orchard in transition to organic production.

Liberty apples at the Rock Springs orchard in transition to organic production.

The project that ensued, named PROFIT, for Pennsylvania Regional Organic Fruit Industry Transition, started with a 2 acre block of “Enterprise” and “GoldRush” apples planted at the Fruit Research and Extension Center in Biglerville. “Researching organic production made a lot of sense because it recognizes the ecological balance that occurs in an orchard,” said Dr. Jim Travis, Professor of Plant Pathology, who helped start the project. Over time the project expanded and now there are 5 acres of certified organic apple trees at Biglerville and acreage in transition to organic at the Russell Larson Research and Education Center at Rock Springs.

To beat the complex of apple pests and diseases, the Penn State researchers integrate a range of management practices that include selecting disease resistant varieties, mating disruption to reduce pest populations, biological control of pests using natural enemies, and a line-up of naturally derived fungicides and pesticides that are allowed under the National Organic Program.

crassweller resistant variety
Dr. Rob Crassweller stands with a scab resistant apple variety from the Czech Republic in the Rock Springs Orchard.

According to Dr. Rob Crassweller, Professor of Tree Fruit, “starting with disease resistant varieties puts you ahead of the eight ball from the beginning.” Crassweller’s research has focused on testing new apple varieties collected from around the world that are resistant to diseases such as scab, powdery mildew, and fire blight. Particularly promising are varieties originating from the Czech Republic and Germany, including several varieties in the ReZista series. In a consumer sampling survey, two scab resistant varieties, Topaz and Crimson Crisp, even scored higher than the non-resistant variety Jonagold.

At the Rock Springs Orchard, Crassweller points to a block of Liberty apples, a scab resistant variety, that is managed organically.  The trees are loaded with picture perfect fruit ready to be harvested.  Mixed into the block though, is a tree of Fuji apples, a non-resistant variety.  Apple scab, a fungal disease common in humid regions, has resulted in lesions on the fruit and leaves, reducing the yield and marketability of the fruit.

In addition to selecting disease resistant varieties, Travis points out that proper site selection, pruning, and trellising are all important factors in reducing disease pressure as well.  Good airflow within the tree helps to keep the leaves dry and allowing sunlight to penetrate the canopy kills fungal spores with ultraviolet radiation.  Trees that are over fertilized and grow too fast are more susceptible to fireblight, so in an organic orchard, the trees are managed to grow at a slower pace. “We’re stacking control strategies on top of each other. You can’t think that there will be one silver bullet spray that will do it all,” said Travis.

fuji scab
Fuji apples in the organic orchard at Rock Springs get scab because they are a relatively susceptible variety.

Although spraying to control diseases is still a necessity in organic production, the number of sprayings can be dramatically reduced with proper cultural management. “With a scab susceptible variety of apple, you would have to spray 15 to 20 times a season, but with a resistant variety, you can easily cut that down to only 4 or 5 times,” said Travis. The primary fungicides approved for organic production are sulfur and lime sulfur, but Armicarb (potassium bicarbonate), and stylet oil are also available.

Controlling diseases in apple trees is only one part of the equation, though. Managing insect pests is equally critical. “There are over 20 insect pests that could destroy the crop at any point during the growing season,” said Dr. Greg Krawczyk, Extension Tree Fruit Entomologist at the Fruit Research and Extension Center in Biglerville. “An orchard is a monoculture that is in place essentially forever. And since various insect and spider mite pests can have between one to eight generations per year, there is always a pest around that is in peak fitness, and they know exactly where the fruit is.”

apple pheremone
The white card at the top of this apple tree emits sex pheremones throughout the orchard, making it difficult for male insects to hone in on a mate.

Organic apple growers have several methods for controlling pests.  One is mating disruption, which is achieved by dispersing a cloud of sex pheromones throughout the orchard.  Normally, male insects use the pheromone plume released by a female insect to locate a mate.  But when the entire orchard is overwhelmed with the pheremones released by the commercially available dispensers, the males lose their ability to track females.  The mating disruption technique is effective in reducing the pest population, but it is not foolproof, as male and female insects can still locate each other by chance, especially when populations are high to begin with.

Biological control, where beneficial insects predate and parasitize the pests, is another method for managing pests.  There are dozens of species of wasps that parasitize the eggs, larvae, and pupae of codling moth and oriental fruit moth, two of the major apple pests.  Predatory mites, ants, and beetles also contribute to controlling pests such as aphids and mites.  The downside to biological control, however, is that to get the beneficial insects into the orchard, you have to let the pest population build up to a certain extent.  “Here on the research station, we can let the pest populations build up and wait for the beneficials to arrive.  But for the commercial orchardist, that is a very uncomfortable process to go through,” said Krawczyk.

Effective monitoring is the most important part of pest management in any orchard, conventional or organic.  Krawczyk sets out traps for dozens of insect species throughout an orchard and checks them frequently to track pest populations.  This lets him know how well the mating disruption and biological control is working, and allows him to make decisions about when an organically approved pesticide should be sprayed. 

A range of organically approved pesticides are available, including those based on oils, soaps, spinosad, Bacillus thuringiensis (Bt), neem, pyrethrum, and kaolin clay.  The kaolin clay acts as a physical barrier to pests and as a natural repellent, but when applied anytime after June often results in a faint gray film on the apple.  Krawczyk reminds us that for some of these products, “they are organically approved- but they are still pesticides.”

Many of the techniques that are used in an organic apple orchard are also used by conventional orchardists. Krawczyk manages a whole-farm mating disruption project on more than 20 farms throughout Pennsylvania.  The farms participating in the project have often reduced the number of insecticide applications they use by more than 50% and sometimes spray even less than an organic orchardist would.  Conventional orchardists are also planting disease resistant cultivars just as an organic grower would. Crassweller points out that “eventually, conventional orchards will probably be managed very similarly to the way organic orchards have to be managed.”

Travis said that the Pennsylvania apple industry “hasn’t split over the organic issue.” In the first few years of the PROFIT project most of the research dollars that the industry provided went toward developing organic practices. “Even if orchardists don’t go organic, they would still like to adopt some of the practices,” Travis added.

The research team also has some projects underway that show potential to improve the sustainability of apple production, but aren’t approved under the National Organic Program. Krawczyk recently received a grant from Northeast SARE to investigate the use of entomopathogenic nematodes to control dogwood borer, which can kill young trees. “The problem is that the nematodes need to be applied with a barrier that will conserve moisture so they don’t die, and the barrier is not approved for use in organic systems,” he said.

The research team considers the project a success. “When we started, the general perception was that we could not do it,” said Krawczyk. “But now, growers are doing it with good results.” Perhaps the most important success of the project is that many of the methods developed for organic production are also being adopted by the conventional orchardists, resulting in a more sustainable apple industry across the state.

Editors Note: Apples grown with organic methods at the Rock Springs Orchard will be available this fall at the Horticulture Cellar Market on the University Park campus.

For more information on organic and sustainable apple production see: