Pea leaf Wee­vil in­fes­ta­tion area grows

Southwest Booster - - OPINION - JOHN IPPOLITO RE­GIONAL CROP SPE­CIAL­IST, SASKATCHEWAN MIN­ISTRY OF AGRI­CUL­TURE, KIN­DER­S­LEY

Pea leaf wee­vil were first iden­ti­fied as be­ing present in Saskatchewan in 2007. Since that time there has been an an­nual sur­vey con­ducted to de­ter­mine the geo­graphic area that has the pea leaf wee­vil present.

The map ac­com­pa­ny­ing this ar­ti­cle shows the dis­tri­bu­tion in Saskatchewan based on sur­veys con­ducted in June of 2016.

In the past few years the area of in­fes­ta­tion in Saskatchewan has in­creased in size as they have moved fur­ther east and also north across the South Saskatchewan River.

Pea leaf wee­vil adults emerge in mid to late May and feed on the leaves of field peas. Adults are noc­tur­nal and are in cracks in the soil dur­ing the day so may not be no­ticed. Their pres­ence can be iden­ti­fied by the notches in the leaf mar­gins as a re­sult of feed­ing. Af­ter feed­ing for a pe­riod, eggs are laid at the base of the plants and lar­vae emerge within a few weeks. Eco­nomic losses are most of­ten associated with the lar­vae feed­ing. The lar­vae feed on the ni­tro­gen fix­ing nod­ules and roots of the plant and re­duce yield through re­duced ni­tro­gen fix­a­tion and up­take. This feed­ing can oc­cur for as long as six weeks.

Scout­ing for in­jury from the pea leaf wee­vil should oc­cur from the two to five node stage. The clam leaves should be ex­am­ined for dam­age in the form of notches. Dam­age will be most preva­lent along field edges but at least five lo­ca­tions at least 100 me­tres into the field should be in­spected. In­sec­ti­cide con­trol may be war­ranted if there is feed­ing dam­age to 30 per cent of the clam leaves in­spected. Dam­age to ear­lier leaves is an in­di­ca­tor that the feed­ing may have al­ready stopped and the in­sec­ti­cide will not be ef­fec­tive.

The most ef­fec­tive con­trol for pea leaf wee­vil is to use a seed treat­ment with an in­sec­ti­cide com­po­nent at the time of seed­ing. This will con­trol lar­vae feed­ing which has the largest im­pact. Scout­ing this year for above ground feed­ing may pro­vide valu­able in­for­ma­tion re­gard­ing the pres­ence of pea leaf wee­vil and as­sist in de­ci­sion mak­ing re­gard­ing the use of seed treat­ment when plant­ing field peas in the fu­ture.

More in­for­ma­tion on the pea leaf wee­vil can be found on the Prairie Pest Mon­i­tor­ing Net­work blog.

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