TechNotes Jan. 15 - EAB, Rhododendron Winter Injury

EAB Parasite Could Be Future Biocontrol 

Chinese researchers identified an undescribed parasitoid of emerald ash borer, according to North American Plant Protection Organization. Several parasitoids were found in China, including a new Tetrastichus wasp species. T. planipennisi Yang parasitizes EAB larvae. It produces 56-92 offspring from a single EAB host.

The parasitoids develop from eggs to larvae within an EAB larva, which remains alive until its last instar. Wasp larvae emerge from the dead EAB larva and chew exit holes through the bark of the tree. These wasps may have four generations per year in northeastern China.

The discovery may provide biocontrol measures for North America, where the EAB has destroyed millions of ash trees. 

Rhododendrons: Winter Injury 
  
Rhododendrons susceptibility to winter injury is always a concern to homeowners. Winter injury is caused by a combination of moisture stress and cold temperatures. Interestingly, Injury to rhododendrons is most common during warm winters. 

Under relatively warm temperatures and windy conditions, moisture loss is greater from the plant than can be replenished by water absorption from the roots. The most common damage symptom is bud kill. Visual observation of the bud will not detect damage. 

However, if the bud is cut open and appears brown or black the bud has been killed. A noticeable leaf symptom that appears later in the winter is leaf scorch.

For more information, visit www.greencastonline.com.