Gliricidia sepium for Rat Control: A Recipe

We have written in the past about the use of Gliricidia sepium for rat control (see Amaranth to Zai Holes p. 214), but were not able to give a specific recipe. Recently we heard from a network member who has had success using gliricidia. Below we give details.

First, a bit of background. Gliricidia is Latin for ‘killer.’ The common name for the tree in Cuba is ‘mata raton,’ meaning ‘rat killer.’ This versatile Central American tree is used widely around the world for animal fodder, to shade coffee and cocoa trees (it is sometimes called ‘mother of cacao’), as a living fence, as a green manure, in barriers for erosion control, and for firewood. The young shoots are nontoxic to humans and are considered to be a delicacy in some parts of Central America. Gliricidia can also be used in animal feed.

We learned from the Nitrogen Fixing Tree Association that rodent poison has been made from ground or chopped leaves mixed with either corn or rice. The mixture was then fermented. Other oral reports said that the poison has been made directly from the seeds or by boiling bark with corn.

Roland Bunch told us years ago that, in Honduras, he had seen a few good-sized pieces of gliricidia bark stripped from the tree and boiled in water with about 20 pounds of corn. The corn was then tossed into the fields. Both rats and mice were killed by the treated corn. Roland shared that it worked, but was not as effective as regular commercial rat poison; it took a day or two before they started finding dead rats and mice in the fields. [This kind of delay is normal in commercial rat poisons that act by destroying the ability of the animals’ blood to clot.]

Fermentation seems to be necessary for the rat poison to work, according to a 1966 technical report by Harry Hockman titled “Mechanism of Rodenticidal Activity of Gliricidia sepium.” The report detailed use of gliricidia in Central America as both a rodenticide and an insecticide.

Dr. Hockman isolated a substance called coumarin from the leaves of gliricidia. This compound is itself not especially toxic. But it is converted by bacteria into dicoumarol, which is chemically so similar to vitamin K that it interferes with the normal role of vitamin K in permitting the blood to clot. This was shown in 1948 to be effective in killing rodents. It is not a rapidly acting substance, but repeated doses result in fatal hemorrhages within a few days. Rats fed baits containing dicoumarol feed freely and do not develop the bait shyness that is so common with other rodenticides.

The article detailed how Central Americans have used gliricidia. “In southern Mexico the bark or leaves are ground and mixed with damp corn flour or spread on bananas. In Panama the leaves are ground or mashed and then mixed with grain. At this point, however, there are two versions of the proper procedure. One method requires that the bait be cooked or steeped and dried before use, and the other that the uncooked mixture be used. At either locality it is worthy of note that the ground leaves are mixed with grain and allowed to ferment under the conditions of high humidity and temperature that exist in these areas.” Others observed that “when rats eat it, their hair stands straight up and they bloat up and die in four to five days. This is the type of clinical picture one would expect from a hemorrhagic poison.”

Dr. Hockman quoted research in which rats “fed a normal diet of unincubated gliricidia leaves in amount of 1.5 grams three times a day for six days showed no pathological changes. Those fed on incubated leaves in amounts of 1.5 grams three times a day for six days showed clear signs of hemorrhage in the gut, lung, and spleen.”

New Information

The discovery that dicoumarol can be made from gliricidia is promising for small-scale farmers. But we did not have a specific recipe to share, until recently.

After a conversation with ECHO staff member Larry Yarger at ECHO’s conference in December 2009, network member Jake Hoogland shared some information about his efforts to make a rat poison from gliricidia in Boliva where he works. “Reading in EDN that [rat and mouse] poison can be made with gliricidia, but not finding a good recipe led me to experiment. This is what I came up with and [it] has worked very well for me for over a year now. Take one branch of gliricidia about 5 to 6 feet long and about 1 to 2 inches in diameter (it is usually a new shoot less than a year old), cut off the bark with a knife in small pieces (about 1 by 2 inches in size), and mix with about 3 gallons of shelled corn in a large pan. Add water to the top of the corn (no more, a little less is better), bring to a boil, and boil for about 10 to 15 minutes. Turn off the heat and let set. The next day I like to pour this into a 5 gallon pail (to mix it up a bit) and let it ferment for two or three days. If I don't need to use it all immediately, I dry the extra in the sun to use later.”

About its use, he commented, “I use it almost all the time when I seed, because I don't burn [my fields] and there is a lot more straw and other organic matter on the ground for the mice to hide in….On the days that I seed I spread the poison in the seeded area at the end of the day, spreading it thicker where I suspect that there could be a higher [rodent] population. We've had several neighbors that have walked through my corn this year commenting on how uniform the stand was. Rats and mice eat so many seeds in their corn when it first sprouts. If I don't use it when I seed sunflowers, I lose over 90% when they are sprouting.”

Jake Hoogland also shared, “We just had a friend visit…and he told me about his experience with the gliricidia poison. He said that he has no rats or mice in his house now, and before it smelled of rodents because there were so many. What he did was to remove the other food sources and put the poisoned corn all around his house. He said that after a month he had no more rats and mice in his house. He was quite excited when he told me because I think that he was skeptical about it.”