Herbicide Performance Under Cool/Moist vs Hot/Dry Conditions

Cool, moist conditions are generally considered ideal for good herbicide performance. Herbicide absorption and translocation are high and all metabolic processes that might be necessary for bio-activation or herbicide activity are functioning. Occasionally, crop injury can occur under these conditions. Under these conditions several factors work together to maximize weed control and potentially to increase crop injury.

  1. Leaves are oriented for maximum light capture and thus maximum herbicide interception.
  2. Herbicide absorption is high due to slow droplet drying and hydrated plant cuticles.
  3. Plant metabolism is high so herbicide bio-activation or translocation are not limited.

Hot, dry conditions can reduce the performance of any herbicide. Auxinic, post-applied grass and amino acid-inhibiting herbicides are less effective when weeds are moisture stressed (Rossi et al. 1994). There are a number of factors that can contribute to this lack of herbicide performance.

  1. Leaf orientation that reduces light interception would also reduce herbicide spray retention by orienting leaves perpendicular to the ground.
  2. Dehydrated plant cuticles can result in less herbicide absorption.
  3. Herbicides that depend on active plant metabolism for bio-activation or translocation will have reduced activity.