Weather synopsis – This week, weather data is unavailable due to technical difficulties so we are unable to generate several maps. Please check webpages posted by Environment Canada for weather-related information.
Reminder – Pre-Harvest Interval (PHI) – Growers with late-season insect pest problems must factor in the PHI which is the minimum number of days between a pesticide application and swathing or straight combining of a crop.
The PHI recommends sufficient time for a pesticide to break down and a PHI-value is both crop- and pesticide-specific. Adhering to the PHI is important for a number of health-related reasons but also because Canada’s export customers strictly regulate and test for the presence of trace residues of pesticides.
An excellent summary of PHI for various pesticides in their various crops was posted by Saskatchewan Agriculture’s Danielle Stephens in 2016 within their Crop Production News.
In 2013, the Canola Council of Canada created and circulated their “Spray to Swath Interval Calculator” to help canola growers accurately estimate their PHI. Other PHI are described in your provincial crop protection guides and remember that specific crop x pesticide combinations will mean different PHIs.
Finally, work towards “Keeping It Clean” so your grain is ready for export! More information about PHI and Maximum Residue Limits (MRL) is available on the Keeping It Clean site.
Bertha armyworm (Lepidoptera: Mamestra configurata) – Pheromone trapping across the prairies is almost complete for the 2018 growing season but now it is important to scout for larvae feeding on leaves and developing pods!
Review your province’s 2018 bertha armyworm pheromone trapping results towards the end of this Post.
Larval sampling should commence once the adult moths are noted.
Sample at least three locations, a minimum of 50 m apart.
At each location, mark an area of 1 m2 and beat the plants growing within that area to dislodge the larvae.
Count them and compare the average against the values in the economic threshold table below:
Some bertha armyworm larvae remain green or pale brown throughout their larval life.
Large larvae may drop off the plants and curl up when disturbed, a defensive behavior typical of cutworms and armyworms.
Young larvae chew irregular holes in leaves, but normally cause little damage. The fifth and sixth instar stages cause the most damage by defoliation and seed pod consumption. Crop losses due to pod feeding will be most severe if there are few leaves.
Larvae eat the outer green layer of the stems and pods exposing the white tissue.
At maturity, in late summer or early fall, larvae burrow into the ground and form pupae.
Lygus bugs (Lygus spp.) – The economic threshold for Lygus in canola is applied at late flower and early pod stages.
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. They 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 continue 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. For lygus bug monitoring, sampling is most accurate when repeated at a total of 15 spots within the field. Samples can be taken along or near the field margins. Calculate the cumulative total number of lygus bugs and then consult the sequential sampling chart (Figure C).
If the total number is below the lower threshold line, no treatment is needed. If the total is below the upper threshold line, take more samples. If the total is on or above the upper threshold line, calculate the average number of lygus bugs per 10-sweep sample and consult the economic threshold table.
The economic threshold for lygus bugs in canola covers the end of the flowering (Table 1) and the early pod ripening stages (Table 2). Once the seeds have ripened to yellow or brown, the cost of controlling lygus bugs may exceed the damage they will cause prior to harvest, so insecticide application is not warranted.
Consider the estimated cost of spraying and expected return prior to making a decision to treat a crop.
Remember that insecticide applications at bud stage in canola have not been proven to result in an economic benefit in production. The exception to this is in the Peace River region where early, dry springs and unusually high densities of lygus bug adults can occasionally occur at bud stage. In this situation, high numbers of lygus bugs feeding on moisture-stressed canola at bud stage is suspected to result in delay of flowering so producers in that region must monitor in fields that fail to flower as expected.
Table 1. Economic thresholds for lygus bugs in canola at late flowering and early pod stages (Wise and Lamb 1998).
Table 2. Economic thresholds for lygus bugs in canola at pod stage (Wise and Lamb 1998).
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 new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” – both English-enhanced or French-enhanced versions are available.
Thrips in canola (Thynsanoptera) – While scouting at this time of year, curled canola pods may be encountered. The culprits are quite possibly thrips.
Damage: Flower thrips (Thysanoptera) are pests of a broad range of plants including cereals and broadleaved crops such as canola. Thrips are minute, slender-bodied insects with rasping-sucking mouthparts and feed by rasping the surface of canola buds and sucking up plant fluids.
Biology: Thrips have six life stages: egg, two larval stages, a prepupal and pupal stage and an adult. Both adults and nymphs cause damage by feeding on the flower and buds. Limited surveys in 1999 in Saskatchewan and Alberta indicated that the predominant species were Frankliniella tritici (flower thrip) followed by Thrips tabaci (onion thrip) and T. vulgatissimus (no common name).
In canola, pods damaged by thrips are often curled and tend to drop prematurely. Some species, such as T. vulgatissimus have been credited with contributing to pollination.
Flea Beetles (Chrysomelidae: Phyllotreta species) – By early pod stages in canola, newly eclosed adult flea beetles begin to emerge from the soil. These individuals typically feed then move away from canola fields to locate overwintering habitats.
Normally, it can be difficult to locate these newly emerged adults but every few years they are easily observed among canola pods. These adults can feed on upper leaves and nip at the exterior of canola pods but are typically observed in low densities – too low to cause economic damage. Even so, be watchful – areas with high numbers of flea beetles late in the growing season are worthwhile to scout early in 2019.
Remember – the Action Threshold for flea beetles on canola is 25% of COTYLEDON LEAF AREA consumed.
Normally, it is NOT recommended to apply foliar insecticides for flea beetles in canola during the pod stages for the following reasons:
Flea beetles are very mobile at this point in the season,
Canola canopy is very thick,
Growers must be cautious about pre-harvest intervals,
PLUS, little is understood about overwintering survival of this pest!
Reminder – While scouting, you may encounter these fascinating organisms…..
Ladybird beetle larvae (Fig. 1-2), pupae (Fig. 2-3), and adults (Fig. 4) can all be found in fields at this time of year. Take a look at the various stages and the many patterns of native and introduced species to recognize these as Field Heroes! Ladybird beetles are categorized as general predators and will feed on several species of arthropods but are partial to aphids (Fig. 5).
The Canadian Grain Commission is ready and willing to grade grain samples harvested in 2018. Samples are accepted up to November but send samples as soon a harvest is complete.
This is a FREE opportunity for growers to gain unofficial insight into the quality of their grain and to obtain valuable dockage information and details associated with damage or quality issues. The data collected also helps Canada market its grain to the world!
More information on the Harvest Sample Program is available at the Canadian Grain Commission’s website where growers can register online to receive a kit to submit their grain.
In exchange for your samples, the CGC assesses and provides the following unofficial results FOR FREE:
dockage assessment on canola
protein content on barley, beans, chick peas, lentils, oats, peas and wheat
oil, protein and chlorophyll content for canola
oil and protein content and iodine value for flaxseed
oil and protein for mustard seed and soybean
NEW for 2018-19: Participants will receive Falling Number and deoxynivalenol (DON) results for their wheat samples at no cost. This enhancement to the Harvest Sample Program is the first initiative to be funded by the Canadian Grain Commission’s accumulated surplus.
Many producers find having both grade and quality information on their samples before delivering their grain to be helpful.
Provincial entomologists provide insect pest updates throughout the growing season so we link to their most recent information:
Manitoba‘s Insect and Disease Updates for 2018 can be accessed here. Issue #11 (posted August 8, 2018) includes initial reports of very low levels of soybean aphids and reports of bertha armyworm in canola fields in western Manitoba yet few fields exceeding economic levels. Agronomists in southwest Manitoba reported “melting” bertha armyworm larvae-read more to learn how insect-specific viruses are at work in fields! Finally, a reminder that the annual grasshopper survey is underway in August.
Alberta Agriculture and Forestry’s Call of the Land regularly includes insect pest updates from Scott Meers. The most recent Call of the Land (posted August 9, 2018) includes reports of the bertha armyworm in Birch Hills county, the expected appearance of red turnip beetles which feed, mate and lay eggs at this point in the growing season, relatively low numbers of diamondback moths but a reminder to scout in canola at early pod stages, and peculiar behaviours of parasitized ladybird beetles and grasshoppers.
This week’s Insect of the Week is the twospotted spider mite. This tiny mite is 0.5 mm long and has eight legs. It has a greenish, yellowish to orange oval body with two dark spots on its abdomen. To the unaided eye, it looks like a small speck. they feed on corn, soybean, dry beans, alfalfa, vegetables and fruit.
These mites overwinter in protected sites as eggs, immatures or adults depending on food hosts and habitat. Immatures and adults move to emerging plant hosts in the spring. They create webbing on the underside of leaves where they puncture cells to feed on cell contents. This feeding causes stippling, yellowing or browning of the leaves. Leaves may dry and drop which can further reduce crop yields.
Infestations start at the field edge and move inwards. Extended hot, dry conditions favour rapid population build up and exacerbate feeding injury.
For more information on the twospotted spider mite, check out our Insect of the Week page!