A forgotten farming technique is making a big comeback – here’s why » Yale Climate Connections

Farmer Rafik Danwade had been pumping more pesticides on his acre-long field in Jambhali village in India’s Maharashtra state, but the chemicals were getting less effective at protecting his 3,200 chili plants from nematodes and other bugs. So Danwade, 56, turned to a practice his grandfather taught him in the 1970s: He planted 1,000 marigolds on the border and alternating rows of the field.

“Sometimes you must look into the past to find solutions for the present and future problems,” Danwade said.

He and other farmers around the world are relearning the ancient wisdom of sowing plants known as trap crops to protect their harvests from pests. The lessons must be relearned now because climate change has raised temperatures and humidity, leading to increased pest attacks in many regions of the globe.

Marigolds produce compounds that suppress the root-knot nematodes, killing the pests that enter their root systems or contact soil containing a marigold’s bioactive compounds. The bright yellow and orange flowers also release compounds that deter aphids and whiteflies. For Danwade, marigolds also act as a natural barrier, confusing pests looking for his chili plants. Experiments conducted between 1990 and 1993 in India found that African marigolds also effectively managed the cotton bollworm pest on tomatoes.

The eco-friendly method vastly reduces the need for pesticide use at a time when several parts of India and the world have reported increased pest attacks. This method is much healthier for farmers working the fields, people consuming the crops, and soil quality. 

Global warming could expand the geographic range of pests, increase the number of generations, and make it easier for invasive insect species to survive the winter season. Pests already destroy 20% to 40% of crop production worldwide every year. According to the U.N.’s Food and Agriculture Organization, insect attacks cause a loss of $70 billion annually, while plant diseases cause a staggering loss of $220 billion. Trap crops could lower these losses while reducing the need to use excess chemical pesticides, which in addition to harming health, also contribute to climate change.

A global trend

Trap crops are helping farmers all over the world. In Italy, a two-year study found that Brassicaceae (mustard family) trap crops helped reduce the damage caused to sugar beets by flea beetles. Another paper found that broccoli yield was high when cultivated with diverse trap crops. A Chinese study found that using maize as a trap crop helped reduce the intensity of whiteflies on cotton.

“Trap cropping offers an environmentally friendly alternative to chemical controls by manipulating pest behavior and reducing reliance on pesticides,” said Shovon Chandra Sarkar, a research fellow at Australia’s Murdoch University who coauthored a paper on trap crops published in the Journal Insects in 2018.

Many trap crops protect the main crop by creating “hot spots” where pests are attracted to specific areas, making it easier for helpful insects to find and attack them, he explained. The paper contrasted the effectiveness of trap cropping to insecticides, which are more harmful, more expensive, and often ineffective due to growing pest resistance.

Sorghum is an effective trap crop in cotton fields, and black mustard in sweet corn farms reduced kernel injury by 22%. The authors also suggest that a trap crop should ideally attract at least twice as many pests as the main crop during the vulnerability stage and shouldn’t cover more than 2%-10% of the crop area. 

Over the last decade, Danwade said he has witnessed severe changes in climate patterns.

“Rains have become infrequent, followed by a rise in humidity and heat, a perfect breeding ground for pests,” he said. He recalled learning about trap crops from his grandfather, the late Muhammad Danwade, when he roamed the fields as a child, and the traditional knowledge has served him well.

In recent decades, farmers turned to the convenience of chemical pesticides. Globally, pesticide use has doubled since 1990, reaching a staggering 3.69 million metric tons in 2022. Yet rising pesticide use has increased production costs for farmers while hurting their health. Some 385 million cases of pesticide poisoning occur every year, leading to 11,000 mortalities. Of this, 44% of farmers are poisoned by pesticides yearly, with the highest number of cases in South Asia. 

Trap cropping has given Danwade a sustainable way to protect his chilies and boost his profits. Marigolds not only deter pests; they also attract bees and other pollinators that aid chili production.

He also sells marigolds, which are essential for daily prayers and decorative garlands in India. 

“Because of marigolds, I have seen an increase in chili harvest … adding to the profits,” he said.

Among Danwade’s neighbors in Jambhali village, farmer Shailaja Gaikwad, 45, battled pest attacks on sorghum in 2022 by following her father-in-law’s advice of cultivating hyacinth bean or Indian bean as a trap crop.

“I thought I would end up losing all the sorghum, but to my surprise, everything remained safe,” she said.

This success reduced her cost of production as she did not spray pesticides even once. Before this, Gaikwad lost a considerable part of her soybean, peanut, and leafy vegetables to pest attacks.

“Even if the pests eat all the hyacinth beans, we can still earn money as the entire sorghum remains safe,” she said.

Timing is crucial

A government report pointed out that 23 states in India witnessed pest attacks between 2015-2016 and 2021-2022, and trap crops are an important part of the response to these challenges.

Farmers typically use green and black gram or hyacinth beans as trap crops for sorghum, while pigeon peas and hyacinth beans are favored for peanuts. Trap crops such as finger millet or moth bean are commonly used for rice.

“There are several such combinations which farmers used earlier,” Gaikwad said. 

A review study published in Applied Soil Ecology in 2019 looked at potential trap crops for reducing the risk from a species of plant-parasitic nematode that causes significant damage to a variety of crops globally. In Northern Europe, yield losses are as high as 40-80% for vegetables like carrots, lettuce, onion, and sugar beet. The study said that trap crops like fodder radish can reduce the nematode populations when mulched early, a process in which the trap crops are cut before the pests trapped in the roots start reproducing. 

Timing plays a crucial role in trap cropping. Field trials have shown that if legume-grass cover crops are planted in autumn and mulched in late spring or early summer, they help reduce the nematode population by up to 90%. However, a delay in planting or mulching can increase the nematode numbers as they reach the temperature threshold and proliferate. Moreover, legumes also provide additional benefits by enriching the soil with nitrogen, which helps boost soil fertility. 

“The main challenges in designing knowledge-intensive trap cropping systems include understanding pest behavior, optimizing plant species selection, and integrating these systems into existing farming practices,” Sarkar said.

Effective trap cropping, he said, requires a deep knowledge of pest-host interactions, the chemical ecology of attractant compounds, and habitat manipulation techniques. To address this, he suggested identifying supplementary food, the color of trap crops, and attractant chemicals to develop reliable attractants for pests and their natural enemies. What’s also essential is “establishing partnerships with government and research organizations can ensure adequate support for farmers to integrate these strategies,” he added. 

Many farmers in Jambhali and several other villages, especially the younger ones, are reluctant to use trap crops and are sticking to pesticides, hoping to maximize yields of a single crop without having to devote space to the trap crop. But Danwade said his sons Yunus, 35, and Shahid, 30, trust trap cropping.

“I am not sure for how long they will continue this practice, but as of now, they are convinced of its results,” he said with a smile.