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    Trap cropping: an innovative biological pest control method

    Farm­ers who have struggled to tame pests are re­cord­ing in­creased yields and re­duced pest in­fest­a­tion on their crops thanks to cer­tain crops like sorghum, napier grass and des­modium among oth­ers which are nat­ur­ally cap­able of con­tain­ing pests at min­imal or no cost.

    The crops known as trap crops have also as­sisted farm­ers cut on the cost of pesti­cides which eats up to 30 per­cent of all farm­ers’ ex­penses. In Mar­im­anti area of Tharaka Nithi farm­ers have re­duced the de­struc­tion of maize by stem borers by plant­ing maize along­side sorghum.

    "With a peri­meter ring of sorghum plants around the maize plots, we have noted less dam­age from birds and the borers. Birds such as weaver birds prefer the sorghum thereby sav­ing our maize from at­tack", ob­serves Kag­wiria Mun­yua, a farmer in Kam­a­tungu vil­lage.

    The farm­ers have also real­ised in­creased yields after sur­round­ing their crops with napier grass as well. Re­search con­duc­ted at the Kenya Ag­ri­cul­tural and Live­stock Re­search Or­gan­isa­tion (KARLO) ) in Kib­wezi has shown that pi­geon peas planted along the bor­der­line of an okra plot sig­ni­fic­antly re­duced aphid in­fest­a­tion-in­creas­ing yield of the okra crop.

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    A sim­ilar study car­ried out in West­ern Kenya also shows that using a trap crop ' of napier grass sur­round­ing maize and an in­ter­crop of the legume des­modium, re­pelled the in­sect pests and sup­pressed a para­sitic weed, Striga her­monthica.

    The re­search­ers say trap crops con­cen­trate the pest in the bor­der area, re­du­cing num­bers of pests and dis­ease spread on the un­sprayed cash crop in the centre and pre­serving nat­ural en­emies. Re­search­ers, however, re­com­mend that trap crops such as sorghum should also be har­ves­ted and their re­mains burned or bur­ied deep into the soil as they may act as a pest reser­voir in the fol­low­ing sea­son. For in­stance, the larva stages of stalk borers bore into the stems of sorghum wait­ing the rainy sea­son for them to trans­form into adults but­ter­fly and lay eggs on the young maize. Burn­ing the crop residues of sorghum and maize stalks at the end of the sea­son breaks the cycle.

    "This tech­nique elim­in­ates the use of broad-spec­trum pesti­cides on the cash crop, which helps pre­serve nat­ural en­emies and helps pre­vent re­sur­gence of the primary pest pop­u­la­tion, sec­ond­ary pest out­breaks and ad­di­tional spray­ing. "It res­ults in im­proved crop qual­ity and dra­matic pesti­cide sav­ings. It re­duces the cost of pro­duc­tion and im­proves qual­ity of pro­duce as the amount of chem­ical residues in the har­vest is lowered. It also delays de­vel­op­ment of pesti­cide res­ist­ance," says the re­port by Kari.

    Bey­ond the primary role of con-trolling pests, trap crops can be be­ne­fi­cial to farm­ers. "While we are not very in­ter­ested in their grain, we still har­vest some sorghum, which we can use as por­ridge flour or use it to feed chicken. The dry sorghum stalks can be used as fod­der or fuel wood es­pe­cially in the cold sea­son in July," noted Mun­yua as she tends her three-and-half acre price of land.

    In the West­ern Kenya study, re-search­ers noted that there was im­prove­ment in soil fer­til­ity lead­ing to in­creased maize yields from 39 per cent to 129 per cent. Cattle were also able to ob­tain fod­der from napier and des­modium legumes. Of fur­ther im­port­ance is the re­por­ted sup­pres­sion of Striga weed by trap crops.

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    Striga re­duces maize and cowpea yields by up to 80 per cent in Sub-Saha­ran Africa, threat­en­ing over 100 mil­lion people. "Striga cur­rently re­mains the biggest threat to maize pro­duc­tion, par­tic­u­larly in the East Africa re­gion where maize is the staple for mil­lions of in­hab­it­ants," said Mel Oluoch, head of the In­teg­rated Striga Man­age­ment in Africa pro­gramme at the In­ter­na­tional In­sti­tute of Re­search in Trop­ical Ag­ri­cul­ture (IITA)

    The weed at­taches it­self on the root suck­ing the sap and starving the crop of vital nu­tri­ents ab­sorbed from the ground. A com­bin­a­tion of a napier grass trap crop and a legume in­ter­crop in a plot of maize has been known to sig­ni­fic­antly de­cline the pop­u­la­tion of Striga weeds ul­ti­mately boost­ing over­all yields. Ag­ri­cul­tural ex­ten­sions work­ers have re­com­men­ded trap crops to limit the dam­age to im­port­ant food crops by pests.

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