Watch for signs of drought stress

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

The “dog days”of summer have come early to mid-Michigan this year. As warm and dry conditions continue, it’s important to keep an eye on trees and shrubs in the landscape and look for signs of stress. This is especially critical for plants that have recently (within the past year) been planted. Homeowners and landscapers should plan to water newly established trees and shrubs once a week in the absence of rainfall. In addition to recently established plants, trees and shrubs in high-stress areas, such as parking lot planters, may become water stressed as temperatures soar.

Common signs of drought stress include:

  • Grayish cast to leaves.
  • Leaf curling or rolling.
  • Drooping leaders on conifers.
  • Leaf drop.

Leaf curling or drooping leaders will first be evident around mid-day when the leaf-to-air vapor pressure deficit is highest. Trees may recover during the overnight hours in the early stages of drought, but as soil moisture continues to decline, they may start the day in a low water status. This is the point where growth will be severely impacted and depending on the species, the tree may begin to drop leaves.

Watering tips

  • One good soaking a week is better than light, frequent irrigation.
  • Make sure irrigation is infiltrating the soil and not running off the surface. “Gator-bags” or similar devices that reduce the irrigation rate are useful in this regard, especially on heavy soils that tend to become impermeable when they dry
  • Use mulch to cover the soil surface and reduce water loss to evaporation. In our mulch research, all of the mulches we’ve tested (ground pine bark, ground hardwood bark, ground recycled pallets and cypress mulch) work equally well in conserving soil moisture

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