Weekly Update – Small scarab beetle

Small scarab beetle (Coleoptera: Aphodius distinctus) – This is the time of summer that farmers will be seeing larvae of a small scarab beetle (Aphodius distinctus) in their fields.  There have been scattered reports each June of large numbers of beetle grubs in crops associated with crop damage (e.g., canola, corn, dry bean, onion, pea).


Please help researchers compile information related to this species so they might confirm its pest status!  Information is posted about the beetle and the survey.  Here’s how you can help:


1. Please send reports of high white grub densities and associated crop damage to Kevin.Floate@agr.gc.ca (403-317-2242). 


2. Live larvae accompanied by the following field information would be extremely helpful please – contact Dr. Kevin Floate if you have a sample!


3. Include answers to the following so the pest status for this species can be ascertained:  
     – Previous crop?
     – Legal land location or latitude+longitude?
     – Irrigated or not?
     – Was composted manure added this spring?
     – Surface residue in spring?

Pea leaf weevil

Pea leaf weevil (Sitona lineatus) – Be aware that higher densities of pea leaf weevil and higher levels of feeding damage have been observed in 2016 compared to 2015.  The 2015 pea leaf weevil risk map, based on damage observed on peas, is below as reference.

  





Review the updates provided by Carcamo for southern Alberta and Hartley related to southwest Saskatchewan posted last week.  


Reminder – Pea leaf weevils emerge in the spring primarily by flying (at temperatures above 17ºC) or they may walk short distances. Pea leaf weevil movement into peas and faba beans is achieved primarily through flight.  Adults are slender, greyish-brown measuring approximately 5 mm in length (Figure 1).

Figure 1. The pea leaf weevil, Sitona lineatus, measures ~5mm long (Photo: H. Goulet).


The pea leaf weevil resembles the sweet clover weevil (Sitona cylindricollis) yet the former is distinguished by three light-coloured stripes extending length-wise down thorax and sometimes the abdomen (Link here for the Pea leaf weevil monitoring protocol with photos of related weevils).  All species of Sitona, including the pea leaf weevil, have a short snout. 

Adults will feed upon the leaf margins and growing points of legume seedlings (alfalfa, clover, dry beans, faba beans, peas) and produce a characteristic, scalloped (notched) edge (Figure 2).  Females lay 1000 to 1500 eggs in the soil either near or on developing pea or faba bean plants from May to June.

Figure 2. Feeding notches on clam leaf of pea plant resulting from pea leaf weevil (Photo: L. Dosdall).

Weekly Update – Pea leaf weevil update

Pea leaf weevil monitoring is underway in Alberta and Saskatchewan.  Despite the common name, Sitona lineolatus, will feed on several species of legumes including faba beans, seedling alfalfa, dry beans and of course peas!


Thanks to Dr. Hector Carcamo (AAFC-Lethbridge) for the following update (24May2016):
A mild winter and a very warm and early spring have contributed to what looks like the worst outbreak of pea leaf weevil in southern Alberta. Weevil densities appear to be high enough to be threatening stand establishment of peas this year.


Normally, adult feeding damage has little consequence whereas the main concern is related to larval feeding damage to nitrogen fixing nodules.  That’s NOT the case this year – several growers are spraying for PLW in peas because small seedlings are suffering very high defoliation resulting in stand reductions – something seen previously only in seedling alfalfa stands. Additionally, this year some stands treated with a registered neonicotinoid insecticide have required foliar spraying; the insecticide seed treatment may not provide sufficient protection when weevil densities are extremely high.  Growers hoping to prevent yield losses may consider supplementing with nitrogen during the seedling stage but be cautious – the economic returns should be carefully considered, given input prices.  Finally, be mindful that PLW adults emerge from overwintering over several weeks so sprayed fields may be repeatedly invaded – continued monitoring is a necessity!

Weevils have natural enemies such as ground dwelling beetles that feed on their eggs. The best way to protect natural enemies is to avoid foliar applications of insecticide unless damage reaches the economic threshold of 30% of seedlings with damage on the clam leaf (i.e., assess using 10 transects of 10 seedlings, half near the edge and half inside the field).


Thanks to Scott Hartley (Sask Ag) who noted (25May2016) that PLW surveying is underway in the southwestern Saskatchewan (i.e., as far north as Kindersley / Outlook and east to mid-way between Swift Current and Moose Jaw).   Preliminary reports include  high levels of feeding in several areas in the southwest.  Crops were generally seeded earlier this year than in the past few years. Seed treatments are considered the best control for the pea leaf weevil but, if 30% of plants are showing damage, a foliar insecticide could be required but this strategy is not as consistently effective as a seed treatment. Foliar insecticide may be necessary if plants are very young and therefore more vulnerable to heavy feeding pressure. Remember plants can outgrow PLW damage once they are past the 6th node stage.



Also refer to previous PLW posts for additional information!
Weekly Update from May 18, 2016
Insect of the Week from 2015
Pea leaf weevil in Central Alberta in 2015
The PPMN’s Pea leaf weevil monitoring protocol

Weekly Update – Pea leaf weevil

Pea leaf weevil (Sitona lineatus) – Pea leaf weevils emerge in the spring primarily by flying (at temperatures above 17ºC) or they may walk short distances. Pea leaf weevil movement into peas and faba beans is achieved primarily through flight.  Adults are slender, greyish-brown measuring approximately 5 mm in length (Figure 1).

Figure 1. The pea leaf weevil, Sitona lineatus, measures ~5mm long (Photo: H. Goulet).



The pea leaf weevil resembles the sweet clover weevil (Sitona cylindricollis) yet the former is distinguished by three light-coloured stripes extending length-wise down thorax and sometimes the abdomen (Link here for the Pea leaf weevil monitoring protocol with photos of related weevils).  All species of Sitona, including the pea leaf weevil, have a short snout.


Adults will feed upon the leaf margins and growing points of legume seedlings (alfalfa, clover, dry beans, faba beans, peas) and produce a characteristic, scalloped (notched) edge (Figure 2).  Females lay 1000 to 1500 eggs in the soil either near or on developing pea or faba bean plants from May to June.

Figure 2. Feeding notches on clam leaf of pea plant resulting from pea leaf weevil (Photo: L. Dosdall).

Weekly Update – Pea leaf weevil

Reminder – Pea Leaf Weevil (Sitona lineatus– Pea leaf weevils emerge in the spring primarily by flying (at temperatures above 17ºC) or they may walk short distances. Pea leaf weevil movement into peas and faba beans is achieved primarily through flight.  Adults are slender, greyish-brown measuring approximately 5 mm in length.  

The pea leaf weevil resembles the sweet clover weevil (Sitona cylindricollis) yet the former is distinguished by three light-coloured stripes extending length-wise down thorax and sometimes the abdomen (Access the Pea leaf weevil monitoring protocol).  All species of Sitona, including the pea leaf weevil, have a short snout.  


Adults will feed upon the leaf margins and growing points of legume seedlings (alfalfa, clover, dry beans, faba beans, peas) and produce a characteristic, scalloped (notched) edge.  Females lay 1000 to 1500 eggs in the soil either near or on developing pea or faba bean plants from May to June.


Information related to Pea leaf weevil in Alberta and the forecast for 2016 is posted here.