Issues of the week

Sclerotinia stem rot risk may still be there even if it hasn’t rained. Humidities of 85% or more, combined with morning dews and thick crop canopies can produce microclimates much more favourable for infection and lesion growth than we might expect based on the general  weather pattern. Disease spread and fungal growth may take a break during afternoon heat, but can resume again as the evening cools off and humidity rises.

When spraying in high temperatures (> 25 C), check product labels or consult retailers or fungicide companies about results in hot weather. Efficacy of some products may be reduced when applied during the heat of the day. In some cases, fungicide can have strong adjuvant systems that can, under hot weather and ample moisture, cause some contact injury to leaf tissues. Applying during cooler periods of the day and at high water volumes can reduce the risk of this contact injury.

Late flower and podding stages are when lygus feeding causes the most damage. While sweeping for lygus, look at what other insects are present, including beneficials such as lacewing, diamondback or bertha larvae that may be feeding up in the canopy, as well as blister beetles and leafhoppers. Leafhoppers reached higher than usual numbers this year, and while sprays are rarely effective, high levels of leafhoppers can mean high levels of aster yellows.

Missing pods are a sign of lygus damage, but missing pods can have many causes, including other insects, heat, excess moisture, and herbicide damage. Sweep netting to make sure lygus is the cause could save the cost of an insecticide spray.