Canola Watch: aster yellows risk? | sclerotinia fungicide at 50% flower | insect update

This 39-minute podcast features host Jay Whetter speaking to three aster yellows researchers about aster leafhoppers and the aster-yellows-causing phytoplasma the leafhoppers inject into canola plants. Let’s hope aster yellows won’t be a concern this year, but this podcast explains all one needs to know if it does appear in Canadian canola fields. 

Is there value to a sclerotinia fungicide at 50% flower? 

The recommended window to spray for sclerotinia is between 20-50% bloom. As early infection tends to cause greater yield loss, a late fungicide application is generally not as effective as earlier spraying. Still, spraying at the late end of the window can offer benefit in a crop with high yield potential in some cases, particularly if flowering is extended and/or conditions suddenly become more conducive to disease (ie: precipitation falls late in flowering). It typically takes two to three weeks for sclerotia to grow and produce spores, so a single precipitation event during very late flowering won’t necessarily impact yield. Avoid applying sclerotinia fungicide after 50% flower, both because sclerotinia’s major economic damage will already be done and because there may not be an adequate pre-harvest interval for that fungicide. (Sclerotinia: does fungicide at 50% flower make sense?) (Factors in the sclerotinia spray decision)

In a variably staged crop with high yield potential, a split application – the first applied when earlier (or the majority of) plants reach 20% flowering and the second applied seven to 14 days later – may provide return on investment. Note: a split application must still be applied at full label rate. Not all products are registered for two applications. Sclerotinia risk assessment tools: Precipitation forecasting / Prairie soil moisture maps / Alberta sclerotinia risk map / Manitoba Agriculture’s Canola sclerotinia treatment decision calculator)
 

Could aster yellows be a major concern this year? 

There is a higher risk for aster yellows infection this year. Leafhopper infection rates are higher than they have been in the past 10 years and higher even than in 2012, the last time aster yellows was a major concern. That said, aster yellows remains only a possible risk at this point, as this year’s agronomic and climatic conditions differ from the wetter, colder conditions of 2012. 

Growers and agronomists should sweep for leafhoppers if they are concerned. Leafhoppers prefer cereals over canola, so sweeping wheat is a better place to start. Leafhoppers also love brome grass and other ditch weeds; if canola is being infected, it is likely via leafhoppers moving in from ditches. To access information on potential testing of samples for aster yellows, email AAFC Field Crop Entomologist Tyler Wist. 

If aster yellows symptoms occur, they are likely to appear by early August. Little can be done to tackle the disease as infection likely occurs early in the crop year, and there are no control options available once plants are infected. While at least one insecticide is registered for control of aster leafhoppers, a positive return on investment is not yet possible to predict. When thresholds are developed from ongoing research, they will likely include the number of aster leafhoppers, percentage of population infected, and amount of time spent feeding on canola.
 

What is this week’s pest management priority?

Most canola crops are approximately two weeks away from the most critical and costly period for insect damage. Bring sweep nets to the field now. Scouting through the early pod stage to assess insect presence, estimate populations and calculate spray threshold enables timely and appropriate pest management. Check canola leaves for feeding damage: an early, easily visible (and non-mobile) indication of insects that are feeding down in the canopy. (Thresholds for major canola insects) (Insect scouting how to)

Diamondback moths are being reported across the Prairies, though not in large numbers. Bertha armyworm reports are likewise still low. Lygus bugs are getting close to threshold in some regions. Grasshopper numbers remain very high, including in some regions that haven’t needed to spray for grasshoppers in nearly 20 years. Patchy wilting (especially at early flowering) may indicate cabbage root maggots. Also keep an eye out for canola flower midge (which do not appear to occur at densities that cause economic damage) and take note of any beneficials. (PPMN Week 10 Update)
 

How to get an early idea of yield?

Accurately predicting yield early, mid and even late in the season is nearly impossible. However, NDVI satellite imagery can provide an estimate as to what portions of a field offer more or less vegetative cover and are, therefore, likely to yield in low, medium and high ranges. An excellent time to consider satellite imagery is as canola comes out of flower, as the crop is progressed enough to show variation and biomass will not be hidden by flowers. Satellite imagery is most effective when used in combination with ground truthing, as it allows producers and agronomists to target their scouting and crop analysis to determine yield limiting growth challenges. Producers may also leverage early yield prediction to help inform grain marketing decisions. Most crop input suppliers, grain buyers and agronomists can direct producers to an imagery provider. Results are inexpensive, simple, user-friendly and accessible, with imagery uploaded to any smart device. (How to use technology to manage yield) (Grain yield forecast on the smart farm) (Why is this canola crop greener on one side of the field?) (Statscan using satellite data to estimate crop yield/production)