Research – Wiliwili Preservation

1. The Importance of Regular Treatment: Merit Injection is recommended every 6 months to control the Erythrina Gall Wasp. Since the discovery of the wasp January 2006 at the Fleming Arboretum , Arboretum Wiliwili have been injected every 5 months as a preventative. Fleming Arboretum trees show evidence of the wasp but appear healthy. I suspect the lack of success commonly reported on Merit Injection against the Gall Wasp is due to lapse in regular application or possibly the need for early application as a preventative before damage.2. Thorough Cambium Injections: Injection of insecticide into the tree’s cambium layer is advised every 6 inches into the trunk at the base of a tree. From our trees’ only partial positive response to our first treatment in January 2006 and logic, we have revised insecticide injection practice at the Arboretum.

On large trees, the trunk branches into large branches.Treating only at the base of the trunk leaves untreated cambium on the inside of these branches. Arboretum trees have since been injected every 6 inches around the trunk base as well as the cambium on the inside of the large branches branching from the trunk.Tho this treatment may be beneficial for all branches over 6 inches, Arboretum trees have been treated from the ground (without the use of ladders) up to approximately 4 feet.

The Fleming Arboretum has two large Wiliwili – one planted in 1952, the oher in 1976. The following are notes on an every-5-month-treatment of these Wiliwili using the Merti Systemic Insecticide. Jan 1, 2006: First sighting of Gal Wasp stings.

Jan 12, 2006: Merit injections made into large trunks bases every 6 inches.

Feb 2006: Older, larger WiliWili shows less response.

May 25, 2006: Merit injections – 6 inch intervals on all branches up to 5 feet.

June, 2006: Trees show galling but doing okay.

Nov 28, 2006: Trees dormant – Merit injection.

Dec, 2006 – Mar, 2007: Trees still dormanat – question of dormancy or Gall Wasp effects.

Apr, 2007: New growth

May 15, 07: Merit injections

End of May, 07: Trees go into dormancy

End of August, 07: New healthy leaves

September, 07: Merit inject early… concerned that chemical would not have thoroughly traveled throughout tree during dormancy.

October, 07: All new leaves attached by galls. This may be evidence that the Merit injection in May at beginning of dormancy did not travel thru tree so new leaves in October were vulnerable.

October 24, 07: Chemical has taken effect in 6 ½ weeks. New leaves are not attached.

November thru January 08: Trees look good

February 28, 08: Merit inject

March to April, 08: Dormant

May 15, 08: Out of dormancy. New growth no damage

September 11, 08: Merit injection done late-6weeks and 11 days. We previously were averaging injections every 5 weeks tho recommended every 6 weeks on label.

October 23, 08: Gall damage

November 1, 08: Galls dead, which means it took 7 weeks for chemical injections to take effect.

Field Test Notes:

• Chemical into the cambium during dormancy does not travel throughout the tree.
• Wiliwil dormancy is approximately 3 months.
• It takes 6 weeks for merit to travel throughout the Fleming Arboretum’s 20-25 foot tall Wiliwili trees.
• 5 month preventative Merit injection most successful, not 6 months as instructed on label.