Both adults and juveniles feed on plant juices from the underside of the leaves. On heavily infested plants, the foliage will become yellow, curled and bronzed. Untreated, such plants lose vigour, become progressively thinner, and may eventually die. Examination of the underside of the foliage should reveal a fine webbing. Tap leaves against a white piece of paper or cloth and look for moving yellow dots.
Thresholds are four or more mites per leaf or one severely damaged leaf per plant prior to pod-fill.
Therefore, check the short and long term weather forecasts to determine if these conditions will continue. The longer it remains hot and dry the increased likelihood that economic damage will occur from the mites. Re-scout the field a few days after a rain. Heavy dews are often enough moisture for successful infection of the mites by parasitic fungi. If mites are found in field margins only, do not treat the entire field, just the margins.