Source: AgAnswers - An Ohio State Extension and Purdue Extension partnership

In the garden world, apple of Peru is known for its beautiful purple flowers and its ability to repel insects. In agricultural fields, however, it shows a different face — a nasty, invasive one — and it could become the next weed nightmare for field and vegetable crops in Ohio and other areas of the United States.

Apple of Peru, or shoo-fly, has been known to exist in the United States for a long time. But it wasn't until the past few years that the weed made its way into farmland, invading fields in Georgia, North Carolina, Tennessee, Virginia and Ohio.

"Some of our most common and problematic weeds today, such as velvetleaf, giant ragweed and giant foxtail, were not found or were rare in this region 40 or 50 years ago but now cost Ohio farmers millions of dollars to control every year," said Doug Doohan, a weed ecologist with the Ohio Agricultural Research and Development Center (OARDC) in Wooster, Ohio.

"We think that apple of Peru is following that same trajectory, but not as slowly. Five years ago we didn’t even know of its existence in farm fields, and we now already have at least 2,000 acres infested in Ohio."

Apple of Peru was discovered by OARDC researchers in a Sandusky County, Ohio, pepper field in the summer of 2002. Subsequent field surveys have found the weed in at least 20 farms in Sandusky and Seneca counties, affecting corn, soybeans, bell peppers and tomatoes.

A native of the Andes region in South America, apple of Peru belongs to the same family, Solanaceae, as tomatoes, peppers and potatoes. Leaves are arrowhead-shaped and pointed at the tip, with irregularly toothed margins. During July and August, the plant produces light-purple (occasionally white), trumpet-shaped flowers that develop into papery bladder-like structures encasing a single berry. It can grow up to six feet tall.

Doohan said the real extent of the weed in Ohio is unknown because it can be easily mistaken for other plants. At an early stage, apple of Peru is similar to eastern black nightshade, a common weed in vegetable crops. In its later stages, it looks like common ground cherry and bears similar fruits, the only difference being the brittle fruit of the weed versus the pliable fruit of the ground cherry.

Gardeners share and trade apple of Peru for its attractive flowers and its "shoo-fly" ability. The plant serves as an insect repellent, and some people grow it in their gardens and rub it on their skin.

But while apple of Peru may be good at keeping bugs away, it also can attract a swarm of problems.

"What makes the situation with apple of Peru potentially serious is that it is more difficult to control than most weeds," Doohan explained. "It produces a very persistent seed that can survive in the soil in the dormant phase for many years, always waiting for that opportunity to come along and grow and produce seed on its own. And while we have herbicides that will control giant ragweed or velvetleaf, we have not been successful at finding many herbicides that are effective on apple of Peru."

Doohan and collaborators have tested some 25 herbicides for their effectiveness to control apple of Peru. Of those, only four show any promise — but they have their shortcomings, too.

"The herbicides that are effective on apple of Peru are older-type materials, like atrazine, which have greater environmental impact when used than more modern products," Doohan said. "So the most likely scenario is that farmers that have apple of Peru will have to go back to using older types of herbicides. They may have to use a rate of atrazine higher than we would like to see farmers using. This creates greater hazard to the environment."

For farmers who grow vegetables in rotation with corn, the situation is bleaker. Doohan said the rate of atrazine that is required to control apple of Peru would prohibit the planting of vegetables the following year because the residue left by the herbicide in the soil would seriously damage, if not kill, the vegetable crop.

"This also means that farmers would have to grow more high-volume, low-value crops like corn and soybeans in preference to the high-value, low-acreage crops like tomatoes and peppers simply because they can't control apple of Peru in those vegetable crops like they can in corn," he pointed out.

Apple of Peru has quickly caught the attention of vegetable growers. Elwood, Ind.-based Red Gold Inc., the nation's largest tomato processor outside California, has looked into what the weed would do to the industry if it becomes established in the Great Lakes' tomato-processing acreage.

"Their analysis indicates that it would take a money-making enterprise and turn it into a money-losing business," Doohan said. "That's a worst-case scenario, but it has happened before with weeds, and it could happen again."

Apple of Peru is bad news for soybeans, too. In recent studies, Doohan found that a relatively small population of the weed — about 1,400 per acre, "which you'd be able to see but wouldn't think of as a terribly big weed problem" — reduced soybean production between 15 percent and 25 percent.

The damage caused by this weed in other parts of the globe has Doohan concerned about what it could do to Ohio. Apple of Peru has become the worst weed problem for soybean farmers in Brazil, one of the world's leading soybean producers. It also affects crops in Africa, Asia and Australia.

"We've been meeting with farmers, landowners and crop consultants to educate them about apple of Peru," Doohan said. "We'd like to contain this weed and, even better, eradicate it from the areas where it's currently found. If that doesn't happen, we are afraid it will become a huge problem for farmers."

Doohan and his team will conduct field trials this summer to further test herbicides and their effectiveness against the weed. The researchers also are seeking funding to study the populations of apple of Peru present in Ohio and compare them with those found elsewhere in the United States and in other countries. Such a study would allow them to pinpoint the origin of the population affecting Ohio, which is still unknown.

For more information about apple of Peru or to obtain a laminated pocket identification card, contact OARDC's Weed Ecology Lab at (330) 202-3593 or the Sandusky County office of OSU Extension at (419) 334-6340.