Science: Little Red Flower

Farmers in 16 counties of North and South Carolina were anxiously watching their fields last week for a delicate, bright green plant that grows to be nine or ten inches high. It is a pretty plant, with gay red and orange flowers shaped something like violets. In South Africa, where it abounds, Boer farmers call it rooibloemetjie (little red flower) and vuurbossie (firebrand). In the U.S. it is witchweed (Striga asiatica), a parasitic plant that sucks the life sap of corn, sorghum, sugar cane and many other crops, leaving the plants as rustling ghosts while the little red flowers bloom over their roots.

In 1951 a few Carolina farmers complained that their corn had a mysterious disease. It looked as if it were dying of drought, but when rain fell, the corn did not recover. The disease spread, and last year sample plants were sent to North Carolina State College, where plant pathologists could find no bacterium, virus, fungus or other malefactor to account for the trouble. Then a graduate student from India took a careful look at the sick corn and recognized among its roots the underground stems of witchweed, which had never before invaded the Western Hemisphere.

No one knows how the little red flower came to the Carolinas, but when the U.S. Department of Agriculture heard the news, it went into action, sending a task force of scientists to help the local authorities. A quick look at the literature told the scientists that Striga asiatica is one of the world’s worst pests. Serious infestation can reduce corn yield to zero. Eradication is almost impossible.

Patient Seeds. Witchweed’s way of life is one of the strangest in nature. The plants produce vast numbers of barely visible seeds, sometimes as many as half a million from a single plant. The seeds fall to the ground and mix with the soil, where they can lie for 20 years without losing vitality. A seed does not normally germinate until the rootlet of a suitable plant creeps close to it through the soil. Influenced by a mysterious substance that the root secretes, the seed wakes up. Out of it pokes a root that snakes through the soil, attaches itself to the host, and thrusts sucking tubes into its juicy tissues. Then life begins for the parasite; it quickly generates a network of roots and underground stems. Sometimes hundreds of witchweeds compete to strangle a single host plant.

After a month of underground parasitic life, the witchweed makes a partial reform, like a successful mobster who buys a legitimate business and joins the church. It sends a shoot above the ground, unfolds green leaves in the sunlight, and manufactures its food by photosynthesis like any respectable plant, while still getting its water and minerals from the host’s roots. Soon its little red flowers bloom and its myriad dustlike seeds poison the soil around it.

Trap Plants. The witchweed-infested area is now quarantined, and strict measures are taken to keep the pest from spreading. The scientists are none too hopeful. Witchweed seeds are invisible when mixed with soil, and they can be carried by farmers’ boots, auto tires, shipments of farm products or almost anything else that moves. Experts shudder to think what would happen if a hurricane were to pick up the seeds and scatter them like smoke. The parasite can probably thrive throughout the South, from Virginia to eastern Texas. It can live on wild grasses, including the common crabgrass, and the 20-year life of its seeds makes it a stubborn enemy.

But witchweed has a weakness: its lurking seeds can be fooled by planting certain crops (e.g., peanuts, soybeans, cowpeas) that induce them to germinate but do not provide the kind of roots that they can live on. In Africa a favorite control measure is planting such trap plants to reduce witchweed infestation, but the U.S. Department of Agriculture has a bolder hope. If it can identify the root secretion that makes the seeds germinate, it may find a cheap chemical that will do the same. Then a field can be treated before planting, and the seeds of the little red flower will wake up only to die.