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Corn+Soybean Digest

Bad Apple

Apple of Peru (AOP) may sound like an enticing fruit, but it's a weed — a very competitive, prolific seed producing and hard-to-kill weed.

In fact, Joel Felix, research associate for The Ohio State University (OSU) says his trials indicate a “differential tolerance to glyphosate.”

He says,“We had mixed results in greenhouse studies. We sprayed Apple of Peru with Roundup and in some cases, it survived. The tops of the plants looked dead, but then it sent out shoots.” Felix says the approximately 10% survival rate is unacceptable because just one plant can produce thousands of seeds.

“The most important thing is not to let the plant go to seed,” he says. “The seeds can be dormant for a long time. That means once they get into the seed bank, they're hard to get rid of.”

Felix has found that AOP is sensitive to atrazine, PPO inhibitors, triazines and Callisto. But ALS inhibitors such as Pursuit, Scepter and Raptor and chloroacetamides such as Dual II Magnum, Lasso, Harness and Outlook, exhibit poor to moderate control. He says it also tolerates bleaching herbicides such as Command.

Felix discovered AOP, an annual in the nightshade family, while he was looking for samples of groundcherry, another nightshade relative. It's a problem weed in Asia, Australia, East and Southern Africa and South America. In fact, the researcher says it's one of the worst weeds in soybean growing areas of Brazil.

AOP is sometimes called shoofly for its supposed insect-repellent properties, and it's been found increasingly in fields across Ohio, Tennessee, Georgia, Virginia and North Carolina.

“There are only slight differences in appearance between Apple of Peru and groundcherry. Mature seeds are enclosed by a papery, leathery cover on both plants,” Felix says. “However, on groundcherry you would have to open up the seed cover to see the berry and get to the seeds. On Apple of Peru, the covering is open at maturity and the berry will shatter, scattering the seed. The berries don't shatter easily on groundcherry.”

The other difference is that AOP can grow more than 7 ft. tall, while groundcherry rarely exceeds heights of 2 ft. However, AOP can range dramatically in size depending upon competition and crop canopy. The one sure thing is an AOP plant of any size will produce at least one berry containing hundreds of seeds, he says.

The seeds need slight incorporation — anywhere from ¼- to 2-in. deep — to germinate, Felix says. Any deeper and the seeds will stay dormant. He says that may explain why he's noticed less AOP in no-till fields.

The seeds germinate as soon as adequate moisture is available in the spring. AOP will produce flowers and berries throughout the summer. A single plant is capable of bearing thousands of seeds and will continue to mature until frost.

This summer, the weed was found to be an alternate host to cucumber mosaic virus, formerly known as soybean stunt virus. Researchers are unsure how this will alter virus infections in soybeans.

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