Before spraying for two-spotted spider mites, scout the field and confirm that living mites are present. Examine other areas of the field, especially downwind, to identify the extent of the infestation in healthy plants. Because they are small and stay on the undersides of leaves, spider mites can be difficult to see. One way to spot them is to slap leaves against a white piece of paper and look for moving yellow dots on the paper.
Under dry conditions, treatment is recommended when plants in infested areas have substantial stippling or leaf-yellowing and live spider mites. Treatment may be delayed if cooler temperatures and high humidity are expected; however, scattered thunderstorms and rain alone will not reduce mite infestations. Closely monitor infested fields if treatments are delayed, and treat before mites cause leaf browning and leaf drop. Spot treat if the infestation is localized, but check other areas for mites.
Under drought conditions, treatment is recommended if leaves in infested areas are stippled and live mites are present. Before treating, check the entire field (and adjacent fields) for mites. Under very dry conditions, mites usually will occur throughout the field and spot treatments are unlikely to prevent the infestation from spreading. If mites are found throughout the field (even in low numbers) in addition to the more heavily infested areas, treat the entire field. Closely monitor treated fields for reinfestations. Avoid unnecessary sprays, but treat before injury becomes severe and leaves drop.
Late infestations can be difficult to control because mites accelerate soybean maturity and increase shattering. Chemicals labeled for mite control have 21- to 28-day harvest intervals. Consequently, if infested fields still have green pods but seeds are filling, it may be better to accept some yield loss from mites and not treat, rather than treat and have shattering but be unable to harvest.
Spider mite field damage: Prolonged spider mite feeding can cause stippling on the leaves, plant stunting or death. A widespread infestation will make the field look yellow. (Photos by Marlin E. Rice)