Pest Profile: Pea Leaf Weevil
Sitona lineatus
Photo Credit: Manitoba Pulse Soybean Growers
Description:
- Chewing mouth part
- Leaves V shaped notch in leaves
- Adults are long, slender and greyish-brown.
- Key distinguishing feature: young Pea Leaf Weevil are distinguished by alternating dark and light brown stripes.
- Adult Pea Leaf Weevil are 3.6-5.4mm long.
- Eggs are 0.5mm
- Eggs are yellowish-white initially but darken over time
- Larvae hatch at about 0.5mm and grow to about 5.5mm
- There are 5 larval instars
- Larvae are milky-white to yellowish, legless, cylindrical, soft and fleshy with a coppery-brown head capsule; reddish bristles extend from each segment.
Damage: (caused by both Larvae and adults)
- Adults chew on leaves and potentially stems if there is not enough leaf material
- Larvae bore into root nodules and eat the nodules
Lifecyle:
- Single Generation per year in Saskatchewan
- Adults overwinter in Shelterbelts, field margins, alfalfa or other perennial legumes
- Become Active when temperatures exceed 4.50c
- Adults emerge from early to mid may in warm years
- Adults feed on any legume foliage they can find immediately after emergence
- Pea leaf weevil migrate to host crops that support larvae (Peas & Faba Bean)
- Adults mostly walk but are capable of flight once temperatures reach12.50c
- Mating occurs once primary host is found
- Females can lay eggs within one week of mating
- Females can lay 1-24 eggs per day & 254-1655 eggs over ovulation period
- Eggs are laid on soil surface near host seedlings
- Eggs hatch after 14 days
- Larvae enter and feed on nodules
- Larvae grow for 30-60 days
- Larvae enter soil to pupate
- Pupal stage last around 15 days
- Adults then feed on foliage until there is none left and its time to move to overwinter
Economic Thresholds and Control Options
Pulse Crop Pea Leaf Weevil Thresholds:
- Damage of 30% of seedlings showing terminal leaf damage during 2nd-5th node stages (this is to determine larvae pressure)
- Seedlings can survive all but the heaviest adult pressure
Control Options:
Contact products can be effective, but timing is difficult to get adults before eggs are laid. Systemic products can be used but are not ideal due to the harm they can have on beneficials. A seed treatment with thiamethoxam is the most effective option however only if the eggs are laid before 2nd node
Practical Tips:
- Having enough available Nitrogen for the plant will reduce impact of Pea Leaf Weevil as the plant will not be relying on its own nodulation
- The active ingredient in SILENCER® 120 EC targets the nervous system of insects, specifically the sodium channel. Insect biology is such that the sodium channel is not active when temperatures are high. To achieve optimal efficacy, applications should be made when temperatures are at or below 25ºC.
References
Pea Leaf Weevil | Insects | Government of Saskatchewan
Pea leaf weevil – Overview | Alberta.ca
Pea Leaf WeeviI | Saskatchewan Pulse Growers
