In Peru's Cañete River valley, 150 kilometers south of Lima, hundreds of bright yellow plastic signs and cards began appearing in irrigated potato fields. At the same time, farmers could be seen carrying large rectangular yellow banners up and down the rows. Some people thought the farmers were protesting against an unknown but obviously unpopular government policy. Others thought they were practicing for an upcoming parade. The reality was quite different: the farmers were enrolled in a pilot program to control an insect pest that was reducing their potato yields by up to a third.

The cards and banners, coated with adhesives, were being used to attract, catch, and kill the leafminer fly, Liriomyza huidobrensis. The traps are part of a package of integrated pest management (IPM) techniques designed by CIP entomologists to help growers protect their crops with a minimum amount of insecticides.

Leafminer larvae damage crops by burrowing (or "mining") into the foliage. Adult females also do damage by puncturing the leaves to lay their eggs. First identified in Brazil in 1926, the insect is becoming an increasingly important pest worldwide.

Natural enemies fall

The leafminer became a major problem for Peru's coastal potato growers in the 1970s after massive doses of insecticides wiped out the fly's natural enemies. By the early 1990s, leafminer damage had reached a point where farmers were spraying extremely concentrated doses of insecticides up to 12 times per season.

CIP field tested leafminer IPM in 1992 in the Tambo River valley in southern Peru with excellent results. Participating growers reduced sprays from six to zero in two years. Pilot projects were established in the Cañete Valley two years later under more severe fly infestation.

A balanced attack

Yellow cards and banners, first tested at CIP by Gaby Chávez and K.V. Raman in 1982, are just one component of the leafminer management program. The traps are designed to lure and kill adult flies active in the early phases of the potato plant's growth, when they do the most damage.

Meanwhile, the potato plant is contributing to its own defense by killing fly eggs deposited on its leaves. This occurs as rapidly expanding plant tissue surrounds and squeezes the eggs from their nests. This ejection process, which was first described in CIP's 1985 Annual Report, tapers off as the potato plant reaches maturity, and the eggs deposited late in the growing cycle hatch into larvae.

Parasitic wasps (reintroduced as part of the IPM program) and one or two carefully timed sprays of insect growth regulators now team up to minimize damage. As added insurance, CIP field-tested potato clones with some resistance to the leafminer fly. In addition, a new fly-resistant potato, María Tambeña, was released and is gaining favor with producers.

Farmer participation

Once a center for large-scale sugar cane and cotton production, the Cañete Valley is now the most intensively cultivated region in Peru, producing potatoes, maize, asparagus, fruit, cut flowers, cotton, and other crops for the Lima market and for export. With 23,000 hectares of mostly small- to medium-sized family farms under canal irrigation, it is also the most technologically advanced of the river valleys in Peru's coastal desert.

Four agricultural organizations in Cañete are currently running pilot leafminer IPM projects in coordination with CIP. They are the Instituto Rural Valle Grande, a nongovernmental organization; the Central de Cooperativas Agrarias-Cañete y Mala, a group of farmer cooperatives; the Estación Experimental de la Asociación de Agricultores de Cañete, an association of farmers; and the Instituto Superior Tecnológico Público de Cañete.

CIP has presented guidelines for the deployment of the various IPM components, but nearly all the participating farmers are adapting the recommendations to suit their needs. Whereas adhesive cards and banners were originally designed as alternatives to one another, some farmers are using both. While CIP prototypes use imported plastic and chemicals, many growers are experimenting with local materials, such as inexpensive yellow plastic sheets coated with motor oil or fish oil, to reduce costs.

Catching on

Daniel Flores and José Asato are each growing two hectares of the popular Tomasa potato variety. Both are enrolled in an innovative work-study program run by the Instituto Rural Valle Grande. In 1995, they sprayed four times to control adult leafminers at a cost of $200. In 1996, they devised a trap using two 12-meter by 1-meter yellow plastic sheets, coated with motor oil and mounted on the arms of a field spraying machine. At the height of the adult fly season, Flores and Asato were netting about 90,000 flies with each pass of the sheets over the field.

"We've already been able to cut the cost of production and the number of insecticide applications," says Flores. Asato says that the potato plants are much healthier than they were at the same stage a year before. "With selective sprays to control leafminer larvae, we should be able to top the 40 tons per hectare we produced last year," he says.

"In-the-field, evidence has a powerful psychological effect on farmers," says CIP Director General Hubert Zandstra. "It can spell the difference between the success or failure of an IPM program."

José Cose, who farms potatoes with his father Celso, agrees. "I think the traps are becoming more accepted by farmers because they can see immediate results," he says. "Farmers are very curious, and will quickly copy each other if they see proof that something is working."

Cañete's IPM pedigree

CIP's effort to combat the leafminer fly isn't the first time Cañete Valley farmers have tried IPM to counteract the effects of excessive pesticide use.

From the 1920s to the 1950s, most of the irrigated farmland in the valley was devoted to large cotton plantations. Beginning in 1949, the valley was repeatedly blanketed by DDT and other broad-spectrum insecticides to control cotton insect pests. But despite stronger and more frequent doses, the pest problems persisted.

It became clear that the insecticides had wiped out the natural predators of the cotton pests while the pests themselves had grown resistant to the chemicals. Meanwhile, a number of previously harmless insects had begun to take their toll on the crop.

Growers, working in partnership with private-sector researchers and Peru's Ministry of Agriculture, decided to ban all synthetic organic insecticides and to repopulate the valley with beneficial insects. The results were dramatic. The pest problem abated, cotton yields soared, and production costs fell. The experience became a classic study in the success of integrated pest management.

Today, implementing IPM in Cañete is more complex. There are more landowners and more crops, and decision-making is more decentralized. But growers are still receptive. Potato farmer Mario Ortiz says that he used to watch with curiosity as a neighbor carried an oil-coated banner through his field. Now he has his own banner, to go with 140 standing traps.

"The plants are looking good, the flies have decreased, and we are saving money on insecticides," he says. "It is a good experience not only for us, but for farmers in general."