Thursday, November 19, 2015

Pea Leaf Weevil Update

Typically a Southern Alberta pest, reports of pea leaf weevil damage were recorded as far north as the Camrose area and spreading. Learn more about the pea leaf weevil and how to protect your pulses.

Background

The pea leaf weevil has been a predominant problem in southern Alberta for over a decade now. Its range has expanded from British Columbia and the northwestern U.S. into the southern Prairies of Alberta and Saskatchewan.  With the increase of pulse acres in the south, we are only giving the pea leaf weevil more to feed on.  However, the pea leaf weevil is no longer just a “southern Alberta” problem.  In spring 2015, reports of pea leaf weevil damage were recorded as far north as the Camrose area and spreading.  Growers were seeing the characteristic scalloped or notched edge bites on their pulse crops.  However, when it comes to pea leaf weevil damage, the scalloped or notched edges are the least of our concerns.

Life cycle

Under Alberta conditions, the pea leaf weevil can produce one generation per year.  The pea leaf weevil will go through four stages in its ten-week life cycle. The pea leaf weevil will seek out a pea or faba bean field in early May, or as temperatures reach 17 degrees Celsius, to lay eggs on the surface of the soil near the plant stem.  The next stage of the pea leaf weevil life cycle, the larva stage, is crucial and this is where the most economic damage to your crops can occur.   At this stage, the larvae will burrow down into the soil and start feeding on the nitrogen-fixing nodules of the pea or faba bean roots for up to six weeks.  After the immobile pupae stage, adults will emerge in mid-August to September and start to feed on any legume crop they can find. Typically, no economic damage is done by the adults chewing.  Pea leaf weevils can also lay eggs anytime throughout May, June and July, so it isn’t uncommon to be able to see all four generations at one time.

Preventative measures

Even though the pea leaf weevil can lay eggs continuously from May-July, there are some preventative measures that can be put in place to protect your yields.  We know that the most crucial time for the growing pea plant is from the second to the sixth node stage.  We also know that pea leaf weevil larva can chew for up to six weeks.  Stress Shield® by Bayer CropScience is a registered insecticide that can be added into your pulse seed treatments.  Stress Shield has the highest rate available on the market in Canada for an insecticide with a rate of 62.5 gai/100 kg of seed.  As such, it can last on the seed in the soil for two to three weeks and up into the plant for another two to three weeks.  This is giving you protection for four to six weeks under ideal conditions for your pea and faba bean crops.  Stress Shield will put the pea leaf weevil larva into a haze-like state, and prevent it from feeding on the nodules.  Another additional benefit of Stress Shield is that it can prevent the pea leaf weevil adult from laying her eggs in the first place, as long as she takes a bite out of the leaf as well.  Timing is very important here.  If Stress Shield can protect the plant until it is past the sixth node stage, any chewing and sucking occurring after that the plant should outgrow. 

By Beth Markert, Bayer SeedGrowth Specialist

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