Less plum curculio damage was seen

In a Michigan State University research project, young pigs were efficient grazers, cleaning up the orchard of dropped apples.

The results of a pilot project conducted by Michigan State University scientists show that Jim Koan’s idea of using pigs to eat the June-dropped apples containing plum curculio larvae in
his organic orchard has potential and may be –applicable to other pests and diseases.

Koan, an apple grower in Flushing, Michigan, is interested in integrating organic pork production into his –current organic apple production. He is hoping to solve two issues by producing organic pork. Many of his organic apple customers ask for organic meat when they visit his orchard. And, as an organic grower, he struggles with controlling plum curculio.

The first year of the apple-hog project answered –several questions. It turns out that:

• Young pigs will eat the apples, leaving few behind;
• Smaller pigs work better than large ones;
• Plum curculio larvae do not survive after ingestion by pigs; and
• Fewer plum curculio were found in August in the grazed plots than in the control plots.

"It’s preliminary data, but very encouraging," said Dr. David Epstein of Michigan State University’s Integrated Pest Management Program for tree fruit. Epstein served as the project’s entomologist and was assisted by Dale Rozeboom of MSU’s animal science department. The first-year pilot project was funded through a grant by the U.S. Department of Agriculture’s Integrated Organic –Project. Epstein is hopeful they will receive funding for a second phase of the project for the next three years.

June drop

Plum curculio, a beetle that lays eggs on apples in the spring, was the initial pest targeted for control by the pigs. Hatching plum curculio larvae burrow into apples. Undeveloped fruit fall in June and July during what is called "June drop." Larvae then exit the dropped fruit, migrate into the soil and pupate, later to emerge as adults to –reenter the tree canopy and feed on fruit in the summer months.

Earlier work done by MSU showed that larvae begin exiting the fruit at about 480 degree days post egg laying, with the base at 50°F. Epstein stated that by scouting the orchard for the first appearance of egg laying, they were able to predict when to introduce the hogs into the orchard to consume dropped apples. Timing is important because the pigs must eat the apples before plum curculio larvae exit.

Three trial replicates were set up in Idared and McIntosh orchards. Fruit that dropped during the June-drop period were monitored and quantified. During the three-week period, each tree averaged a drop of about 123 apples. The pigs were eight weeks old when they began grazing the orchards for pest control. With little scientific literature to guide them, the researchers were unsure that the pigs were even big enough to be effective –grazers.

"But it turned out that these little guys moved through the orchard like a team, like mini-Hoovers," Epstein said. "They picked up every apple that was dropped. We went from over 120 apples per tree to only two. And that was 27 hogs in a one-acre plot in just two to three days."

The pigs also rooted enough to provide excellent weed control, rooting about six inches deep around the trees.

Koan also learned about fencing and hogs. The pigs learned to get through a single wire electric fence, which ultimately reduced their trial to two replicates of grazed and ungrazed plots. In the future, it will be necessary to use more secure fencing materials, such as hog wire.

They also learned that the larger hogs did too much rooting and mostly lay around in the shade of the trees instead of eating apples.

In a controlled laboratory setting, MSU animal scientist Rozeboom confirmed that no plum curculio larvae survived the swine gut after ingestion.

Initially, plum curculio traps in the two plots showed no real differences in populations between the two treatments, Epstein said. But the researchers also looked at insect feeding injury in June and in August. Some 600 fruit were evaluated each time, 30 fruit per tree, 20 trees per treatment. During the August fruit evaluation, the ungrazed plot had five times more feeding injury than the grazed plots with the pigs.

"This is extremely encouraging –preliminary information," he said.

Challenges

One of the future challenges will be to supplement the pigs’ apple diet with additional protein. The pigs were fed only apple pomace in addition to the orchard vegetation and were slow to gain weight, reaching only about 70 pounds at 5 months. The sows were slower to breed back than conventionally raised hogs. Researchers will need to consider adequate protein amounts and sources in future research.

Scientists are especially interested in learning if other pests can be controlled from swine grazing, such as codling moth that can overwinter in the ground. Running the hogs to eat leaves and orchard debris could also be helpful in controlling scab.

Epstein said they would also like to look at the demographics of an organic pork market and see if there is a quality difference between organic pork and –conventional pork. He noted that the hogs must be out of the organic orchard by 90 days before harvest to comply with rules developed by the Organic Materials Review Institute.