Plastic Fantastic

A simple barrier technology prevents Andean potato weevil infestations, benefiting farmers while also yielding important environmental and biodiversity dividends as a result of reduced insecticide applications.

An ordinary sheet of plastic is proving to be a simple and effective alternative to expensive, harmful insecticides for controlling a major potato pest. That is what International Potato Center (CIP) researchers working in the high Andes have discovered. The results are not only helping farmers but also protecting biodiversity and the environment.

Andean potato weevils (Premnotrypes suturicallus) pose a major problem for farmers at altitudes of between 2,800 and 4,200 meters, where potato is an important staple and cash crop. The weevils, which are very common at these altitudes, crawl into potato fields at the beginning of the growing season and breed, and when the larvae hatch they move into the soil, feeding underground on tubers. To date no crop resistance to the weevil has been detected. Farmers attempt to control weevils mainly by using 2-4 applications of insecticides, which are expensive, highly toxic, and often ineffective because the dosages are wrong or mistimed. From 15% to 40% of tubers are commonly infested at harvest, even with the use of insecticides. When no control measures are taken, the weevil can destroy half of the crop or more.

But the Andean potato weevil has an Achilles heel: it is flightless.

"Erecting a simple plastic barrier just 30-50 centimeters high and 10 centimeters into the ground is very effective in stopping weevil migration to potato fields and consequently tuber damage," explained CIP entomologist Jürgen Kroschel. "What's more, it's an idea that has been tested collaboratively with local farmers to assess its impact, ease of use and acceptability."

Under CIP's integrated pest management program, more than 60 individual field experiments were carried out over 4 years with farmers in the high Andean villages of Ñuñunhuayo and Aymara. The experiments set out to determine the efficiency of plastic barriers, farmer receptivity and the potential economic benefits to farmers.

The results are very positive. Barriers were found to reduce Andean potato weevil damage by up to 70% more than did insecticide applications. They were tested against other Andean weevil species in locations throughout Peru, Bolivia, and Ecuador and, in all cases, were found to be equally as effective as insecticides or more so.

Comparing increased yields and higher prices for undamaged tubers to costs, the plastic barriers proved to be an excellent investment. Average net benefits for farmers were US$147 per hectare in one of the test villages and $807 per hectare in the other.

Local opinion on the alternative technology was very positive. More than 90% of the farmers participating in the project considered the barriers a very useful and easy-to-install tool, and they were interested in promoting them further among other farmers. Farmers are now being encouraged to experiment with the barriers, expanding their use in communal rotation systems. The technology is being taken up by national agricultural institutes in Peru to further promote its use in smallholder agriculture.

Farmers are not the only ones to benefit, as there are important environmental and biodiversity dividends.

Not surprisingly, the method scores high on the environmental impact quotient (EIQ). The EIQ uses a formula to calculate the impact of a pesticide on wildlife, farmers, consumers and agroecologies. Including fungicide applications for the control of late blight disease, the EIQ of 32.9 for the plastic barriers was less than a fifth of the EIQ of 191.5 recorded for farmers' traditional spraying practices. The plastic sheeting is good for at least two seasons, after which it can be recycled.

"The plastic barriers reduce the weevil population enormously," said Kroschel. "So if an entire village applies this method for several seasons, we can effectively minimize the weevil population and ultimately could get to a point where farmers can produce potatoes without needing any special weevil control."

Also important is the technology's potential impact on insect biodiversity. The application of broad-spectrum insecticides affects not only weevils but also their natural enemies, upsetting species' natural balance and diversity. Prolonged insecticide use in the Andes has degraded populations of parasitoid and predator insect species, such as ladybirds and hoverflies, which help control other potato pest populations such as potato tuber moth and aphids.

"We study how we can influence agricultural systems by bringing in more biodiversity to augment natural enemies and get a more stabilized agroecosystem," explained Kroschel. "The plastic barrier is a simple but effective tool that we can use toward that goal."