Farmers Cautioned About Pea Weevil

EDMONTON - Jun 21/10 - SNS -- Dry edible pea fields could be at greater risk of attack from pea weevils than in the past because a high proportion of the crop was seeded late and emergence was delayed by cooler and wetter weather, cautions Alberta Agriculture.

When the temperature reaches 17° C and higher, pea leaf weevil (PLW) begins to fly, seeking field pea or faba bean crops. Generally, early planted field pea plants are at greater risk of damage, but temperatures have been uncharacteristically low this spring except for a few early warm days, and the cool weather could increase the risk for later emerging pea plants.

"The main range of PLW is in southern Alberta, south of highway 1, where the weevil causes more visible damage," says Neil Whatley, crop specialist with Alberta Agriculture and Rural Development.

"Crop damage occurs in both the foliage and root nodules with root nodule damage being the main concern, resulting in partial or complete inhibition of nitrogen fixation by the pea plant. The adults feed on pea leaf margins producing a characteristic scalloped or notched appearance. These adults lay eggs in the soil near to the stem of pea plants and after hatching from the eggs, the larvae proceed downwards to feed on the pea nodules."

To control this weevil, Alberta growers can use Cruiser Maxx Pulses as a seed treatment to reduce weevil damage for up to 28 days from the time of seeding. A foliar insecticide (Matador) is also registered as an option to reduce weevil numbers. One would consider applying Matador if pea seedlings are still small and the seed treatment has worn off, or if the seed treatment was not used.

Since the objective is to control the adult weevils before they lay eggs, it is important to use insecticide control when the pea seedling is quite young. The economic threshold is to spray before the 6th node stage when one or more feeding notches appear on 30% (3 out of 10 plants along a seeded row) of the pea seedlings and as long as these 30% have received feeding damage to the plant's clam or terminal leaf (the most recently emerged leaf). Damage on the clam leaf suggests the weevils are still actively feeding in the field.

"The pea leaf weevil can fly a long distance (a few kilometers). Since the weevil enters the field from the outside, initial damage will occur along the field borders," says Whatley. "Therefore, it may be economically wise for farmers to spray insecticide on the field borders if damage is restricted to this area. When scouting, observe at least 10 plants at each of five spots along the edge of the field. Repeat this at another five spots more than 100 meters into the field. Chemical application should only occur if there is new feeding damage on the clam leaf."

The pea leaf weevil becomes more active when the temperature rises. Whether field pea crops are later emerging due to cold weather, or if seeding is late due to precipitation disruptions, pea producers in the southern regions of the province should be scouting for pea leaf weevil to prevent crop damage. As of late May, it appeared that pea fields at more advanced stages had been damaged more than late planted fields.

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