Early sea­son scout­ing of Cut­worms is important


Cut­worms are early sea­son pests that can af­fect a va­ri­ety of crops in Western Canada. There are around 20 dif­fer­ent species of cut­worm pests in Canada, but, for­tu­nately, only a few of them are ca­pa­ble of caus­ing eco­nomic dam­age in Saskatchew­an.

Cut­worm is the com­mon name given to the lar­vae stage of nu­mer­ous moth species. Only the lar­vae stage of these species cause dam­age to crops, with ei­ther sub­ter­ranean (un­der­ground), above-ground, or climb­ing feed­ing be­hav­iours.

Signs of cut­worms in the field can in­clude notches or holes in fo­liage; plants that are wilt­ing, falling over, or com­pletely clipped off; and, thin or bare patches. It is important to con­firm that the symp­toms are caused by cut­worms and not by poor emer­gence or other pest is­sues such as damp­ing-off dis­ease, which may cause bare patches or wilt­ing.

When scout­ing, it is important to be able to iden­tify which species of cut­worm is in your crop. The dif­fer­ent cut­worms have diverse habi­tats and feed­ing be­hav­iours, and there­fore can af­fect your crop in a va­ri­ety of ways. The lifecy­cle tim­ing and length also varies between species with some lar­vae feed­ing ear­lier or later in the grow­ing sea­son than oth­ers.

Scout­ing for cut­worms should be done reg­u­larly start­ing early in the spring after plant emer­gence un­til ap­prox­i­mately mid-july. Dingy and army cut­worms both over­win­ter as lar­vae and cause most of their dam­age ear­lier in the sea­son, whereas pale western and red-backed cut­worms over­win­ter as eggs and need to be­come lar­vae to cause crop dam­age. Cut­worms tend to cause dam­age at hill­tops, south­fac­ing slopes, and drier parts of the field, but they may be found in other ar­eas as well.

To scout, care­fully search the top one to two inches of soil around the base of dam­aged plants. Cut­worms will move from dam­aged plants to healthy plants to con­tinue feed­ing; so, also search for them at the base of healthy plants within or around the out­side of the af­fected patches. The lar­vae tend to feed dur­ing the night and stay un­der­ground dur­ing the day­time. Even if the pest is not found on plants that show above-ground feed­ing symp­toms, they may be found on or be­neath the soil sur­face. There are var­i­ous man­age­ment prac­tices that can be used to control cut­worms. Nat­u­ral en­e­mies of cut­worms, in­clud­ing par­a­sitoids and preda­tory in­sects, are par­tic­u­larly important for ending mul­ti­ple year out­breaks. Re­fer to the Agri­cul­ture and Agri-food Canada’s Cut­worm Pests of Crops on the Cana­dian Prairies for more in­for­ma­tion on nat­u­ral en­e­mies.

Cul­tural control options vary de­pend­ing on the species of cut­worm present. Weed-free un­cul­ti­vated fields in late sum­mer are less at­trac­tive for egg lay­ing for over­win­ter­ing. Seed­ing later in the spring or cul­ti­vat­ing the soil and keep­ing it black be­fore seed­ing can starve cut­worms that over­win­ter; how­ever, the risk of soil ero­sion has to be taken into ac­count when con­sid­er­ing this control op­tion.

If the level of cut­worms is above the eco­nomic thresh­old for a specific crop, there are fo­liar in­sec­ti­cides avail­able to control the pest. It is rec­om­mended that pes­ti­cides are ap­plied in the late evening when lar­vae be­gin feed­ing so that they come in contact with the spray. For more in­for­ma­tion on in­sec­ti­cides avail­able for specific crops please re­fer to the Saskatchew­an Agri­cul­ture Guide to Crop Pro­tec­tion.

For more in­for­ma­tion on gen­eral and specific cut­worm iden­ti­fi­ca­tion and man­age­ment re­fer to:

- Agri­cul­ture and Agri­food Canada’s Cut­worm Pests of Crops on the Cana­dian Prairies

- Agri­cul­ture and Agri­food Canada’s Field Crop and For­age Pests and their Nat­u­ral En­e­mies in Western Canada

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