Corn is one of the world’s major food crops, and with over 90 million acres of corn growing in almost every state, the United States is the world’s largest producer and exporter.
Yet, like so many important crops, corn has its nemesis: the stem borer moth. This pest devastates corn in stages. First stem borer larvae feed on the leaves of the maize plant; then, they bore into the stem.
Using pesticides to control stem borer is usually ineffective, as the chemicals cannot reach deep inside the plant stems where stem borer larvae reside. Another pest, the parasitic invasive species Striga (witchweed), attacks corn and other globally important agricultural crops, including sorghum, sugarcane and rice. Striga is native to Africa and Asia and was first identified in the U.S. in North Carolina in 1956. As with stem borer, use of chemical herbicides against Striga is ineffective.
These pests don’t feed exclusively on U.S. crops. According to reports from International Centre of Insect Physiology & Ecology (ICIPE), preventing crop losses from stem borers and Striga weeds and improving soil fertility in eastern Africa alone could increase cereal harvests enough to feed an additional 27 million people. Now, some U.S. producers are learning about a method developed in Kenya that prevents such losses and may help farmers everywhere protect their crops in the erratic weather created by climate change.
Learning from nature
In Africa, economic barriers to conventional pest resistance-led researchers at ICIPE to work with farmers in Kenya and other partners to look for clues in nature. By examining how native grasses deal with pests and weeds, the researcher/farmer team discovered certain plants that can more effectively and less expensively eradicate certain pests.
In a process scientists call “selective allelopathy,” some plants actually suppress others. Desmodium, commonly known as Ticktrefoil, not only suppresses weeds, but also conserves the soil, exudes antixenotic allomones to repel pests and provides high protein stock feed. Desmodium is a member of the pea family with native roots on every arable continent. In North America, there are 76 varieties of the plant. Ticktrefoils are also useful as living mulch, as green manure and as a climate change mitigator, as they improve soil fertility and reduce greenhouse gasses in the atmosphere via nitrogen fixation. (Most also make good animal fodder.)
Napier grass works well in its native sub-Saharan Africa as a trap for Ht corn borer. The sharp silica hairs and sticky exudates on the Napier grass kill the stem borer larvae when they hatch, breaking the life cycle and reducing pest numbers.
With this information, ICIPE and its partners developed a growing method known as “push-pull,” which relies on Napier grass and Desmodium to protect crops. To date, push-pull has been adopted by over 130,000 smallholder farmers in East Africa where maize yields have increased over 300 percent with minimal inputs. The process and science behind it are described:
“The technology involves intercropping maize with a repellent plant, such as Desmodium, and planting an attractive trap plant, such as Napier grass, as a border crop around this intercrop. Gravid stemborer females are repelled or deterred away from the target crop (push) by stimuli that mask host apparency while they are simultaneously attracted (pull) to the trap crop, leaving the target crop protected.”
Desmodium produces root exudates; some of the exudates stimulate the germination of Striga seeds, while other exudates inhibit their growth after germination. This combination reduces the Striga seed bank in the soil through efficient suicidal germination, even in the presence of graminaceous host plants. A perennial cover crop, Desmodium exerts its Striga control effect even when the host crop is out of season. Desmodium also conserves soil moisture, enhances arthropod abundance and diversity, and improves soil organic matter.
Desmodium and Napier grass protect fragile soils from erosion. These factors enable cereal cropping systems to be more resilient and adaptable to climate change while providing essential environmental services and making farming systems more robust and sustainable.
According to Andre Leu, president of the board of directors of the International Foundation for Organic Agriculture Movements (IFOAM), farmers he met in Kenya and Ethiopia are successfully using push-pull technology on millet, sorghum, pulses, mango, tomato, lettuce, squash, potatoes and other crops. “In the middle of a drought, where the crops of 40 million people have failed, these farmers are thriving,” Leu said.
Adapting push-pull for your farm
Conventional push-pull was developed in 1997 and introduced to a small group of Kenyan farmers in 1998. It uses Silverleaf desmodium (Desmodium uncinatum) and Napier grass (Pennisetum purpureum). In response to sub-Saharan Africa’s increased drought pressures in recent years, ICIPE and its partners developed what they call “climate-smart” push-pull in 2011 and introduced it to farmers in 2012. Climate-smart push-pull uses two drought-tolerant species: Greenleaf desmodium (Desmodium intortum) and Brachiaria grass (Brachiaria cv mulato II).
Push-pull is already used in large-scale commercial systems. Leu, a native of Australia, where the typical farm is thousands of acres and the smallest paddock on his family farm was a square mile, said it’s just as easy to put Napier grass and desmodium around a 1-acre circle of corn as it is to plant it around 1,000 acres of corn if you’ve got the right machine and the right system. “It shouldn’t be an either-or,” he said. “It’s matters of appropriate scale for who you are.”