Tag: Dry bean

Lygus bug monitoring

On the Canadian prairies, lygus bugs (Heteroptera: Miridae) are normally a complex of several native species usually including Lygus lineolaris, L. keltoni, L. borealis, L. elisus although several more species are distributed throughout Canada. The species of Lygus forming the “complex” can vary by host plant, by region or even seasonally.

Lygus bugs are polyphagous (i.e., feed on plants belonging to several Families of plants) and multivoltine (i.e., capable of producing multiple generations per year). Both the adult (Fig. 1) and five nymphal instar stages (Fig. 2) are a sucking insect that focuses feeding activities on developing buds, pods and seeds. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.

Recent research in Alberta has resulted in a revision to the thresholds recommended for the management of Lygus in canola. Under ideal growing conditions (i.e., ample moisture) a threshold of 20-30 lygus per 10 sweeps is recommended. Under dry conditions, a lower threshold may be used, however, because drought limits yield potential in canola, growers should be cautious if considering the use of foliar-applied insecticide at lygus densities below the established threshold of 20-30 per 10 sweeps. In drought-affected fields that still support near-average yield potential, a lower threshold of ~20 lygus per 10 sweeps may be appropriate for stressed canola. Even if the current value of canola remains high (e.g., >$19.00 per bu), control at densities of <10 lygus per 10 sweeps is not likely to be economical. Research indicates that lygus numbers below 10 per 10 sweeps (one per sweep) can on occasion increase yield in good growing conditions – likely through plant compensation for a small amount of feeding stress.

**Figure 1**. Adult *Lygus lineolaris* (5-6 mm long) (photo: AAFC-Saskatoon).

**Figure 2**. Fifth instar lygus bug nymph (3-4 mm long) (photo: AAFC-Saskatoon).

Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. In canola, lygus bugs feed on buds and blossoms and cause them to drop. They also puncture seed pods and feed on the developing seeds causing them to turn brown and shrivel.

Scouting tips to keep in mind: Begin monitoring canola when it bolts and continues until seeds within the pods are firm. Since adults can move into canola from alfalfa, check lygus bug numbers in canola when nearby alfalfa crops are cut.

Sample the crop for lygus bugs on a sunny day when the temperature is above 20 °C and the crop canopy is dry. With a standard insect net (38 cm diameter), take ten 180 ° sweeps. Count the number of lygus bugs in the net. Sampling becomes more representative IF repeated at multiple spots within a field so sweep in at least 10 locations within a field to estimate the density of lygus bugs.

How to tell them apart: The 2019 Insect of the Week’s doppelganger for Wk 15 was lygus bug versus the alfalfa plant bug while Wk 16 featured lygus bug nymphs vs. aphids! Both posts include tips to discern the difference between when doing in-field scouting!

Biological and monitoring information related to Lygus in field crops is posted by the provinces of Manitoba or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol. Also refer to the Lygus pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page. The Canola Council of Canada’s “Canola Encyclopedia” also summarizes Lygus bugs. The Flax Council of Canada includes Lygus bugs in their Insect Pest downloadable PDF chapter plus the Saskatchewan Pulse Growers summarize Lygus bugs in faba beans.

Lygus bug monitoring

WESTERN BEAN CUTWORM – WILL THE RANGE EXPANSION REACH THE PRAIRIES?

Western bean cutworm (Striacosta albicosta) is a native North American insect that, at high levels, can be a pest of corn and dry beans. However, the way they feed is different than some of the other cutworms many may be familiar with. Western bean cutworm feeds on the reproductive parts of plants (corn tassel, silks, and kernels, or dry bean pods and seeds). This can result in yield loss, and spread ear mold. In Ontario, injury by western bean cutworm has been shown to increase mycotoxin production in grain corn.

Range Expansion: The historical geographic range of the western bean cutworm covered the western Great Plains states including Colorado, Nebraska, and Wyoming but, over the past two decades, its distribution has been more easterly rather than north to the prairies. A report from the 1950s of western bean cutworm in Alberta has instead been confirmed as a misidentification of another species. Currently, it has not been detected in the Canadian prairie provinces. Since 1999, the geographic range of the western bean cutworm has rapidly expanded eastward across the U.S. Corn Belt and eastern Canada. Western bean cutworm adults have been collected in 22 additional states and provinces since 1999, spreading from western Iowa to the east coast of the United States and Canada. It was first found in Canada in Ontario in 2008. Keep an eye open for this insect when scouting for crop pests in corn or dry beans this summer.

Figure 1. Detailed expansion of western bean cutworm distribution into the eastern Corn Belt between 2000 and 2017. From: Smith et al. 2019. Journal of Integrated Pest Management. Volume 10, Issue 1, pg. 1-19.

Appearance and monitoring tips:
Larvae:
• There are six stages (instars) of the larvae, and appearances vary.
• Older larvae are a light tan colour, with an orange head. The pronotum (the shield-like structure just behind the head) has two broad dark brown stripes.
• You may find young larvae on the silks of corn. Older larvae may be on the ears of corn, but you may have to peel back the husks to find them (Fig. 2).

Figure 2. Western bean cutworm feeding on corn. Photo: Jocelyn Smith, University of Guelph.

Adults:
• Each forewing has a white or tan band running along the edge or margin of the wing (Fig. 3). Inside this band are 2 distinctive markings: a brown circle and a brown kidney bean shape, both surrounded by a tan border.
Note – Other moths across the Canadian prairies, such as redbacked cutworm, have similar markings.

Figure 3. Western bean cutworm adult. Photo: Jocelyn Smith, University of Guelph.

Please help – When monitoring in the Canadian prairies, adults or larvae suspected to be western bean cutworm can be directed to your provincial entomologist for species verification. New and confirmed sightings of this species are important and will help mobilize research and pest management strategies.

Additional information on western bean cutworm can be found in the publication “Western Bean Cutworm” by the Canadian Corn Pest Coalition: https://cornpest.ca/corn-pests/western-bean-cutworm/

Did you know? Bt corn with the Vip3A protein effectively controls western bean cutworm, but some of the Bt corn products for European corn borer will not.

Reference:
Ecology and Management of the Western Bean Cutworm (Lepidoptera: Noctuidae) in Corn and Dry Beans—Revision With Focus on the Great Lakes Region. 2019. J. L. Smith, C. D. Difonzo, T. S. Baute, A. P. Michel, and C. H. Krupke, Journal of Integrated Pest Management, Volume 10, Issue 1: 1-19.

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).

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.