Lead tree (Leucaena leucocephala): Biology and Management How do you kill a zombie tree? Photo credit: The Walking Dead
Lead Tree Leucaena leucocephala Fabaceae (bean family), subfamily/clade Mimosoideae Double pinnately compound leaves up to 12in long, alternate on stem Small white puff ball flowers Long (~15cm) papery bean pods (green when immature, darkening to brown or reddish brown) Tony Pernas, National Park Service, Bugwood.org Dan Clark, National Park Service, Bugwood.org
Lead tree on Dredge Material Management Area (DMMA) 3D in Tampa Bay Lead tree scattered over approximately 400 acres Recent construction activity has spread the seed bank We have had difficulty with control
Initial treatment was in December 2014 Tampa 3D Basal bark application of 20% triclopyr and 2-5% imazapyr Revisited site in January, February and May and noticed that lead trees were not dying. Revisited site in June with contractor to determine possible issues 30 lead trees were flagged for monitoring Lead trees during June, 16, 2015 site visit
Of the 30 lead trees that were flagged Robust resprouts on a tree with several smaller, dead branches Feathery appearance of new foliage Tree producing numerous seed pods after treatment 20 were flagged with orange flagging Although some herbicide effects were evident (e.g. some dead branches, feathery appearance of leaves), the trees appeared as though they would grow out of it Many had already produced large numbers of flowers and fruits Resprouts seemed more robust (greener, dense and >50% of the main branches resprouting)
Of the 30 lead trees that were flagged 10 were flagged with red flagging Herbicide effects were significant, but the trees were still resprouting. Resprouts appeared weak (yellowish color, smaller and more limited along the stems)
Monitoring of Lead Tree Treatment Initial treatment was in December of 2014 Site was revisited several times in January, February and May of 2015 to document efficacy of treatment In June of 2015, 30 lead trees were flagged for monitoring They were all alive at the time with 20 trees (flagged with orange tape) appearing healthier than the other 10 trees (flagged with red tape) that seemed to be struggling to stay alive. Since Imazapyr was used in the initial treatment, there was a possibility that it would have residual activity and eventually kill the trees. The flagged trees were revisited in November of 2015 (prior to follow-up treatment) to determine if any of them had succumbed to the herbicide treatment.
20 Orange Flagged Trees All 20 of the orange flagged trees survived through November 2015. Some of them suffered damage from the herbicide treatment in December 2014, but even if some of the branches were killed, there were still remaining stems that were alive and reproducing. Top row: pictures of orange flagged trees from 6-16-15 Bottom row: pictures of the same trees from 11-12-15
10 Red Flagged Trees When the trees were revisited in November 2015, 6 of the 10 red flagged trees were dead, but 4 of them were still alive. Top row: Pictures of red flagged trees from site visit on 6-16-15 Bottom row: Pictures of red flagged trees from site visit on 11-12-15 (from L to R: alive, dead, alive, dead, alive, alive)
2016 Treatment Treated some areas with Garlon 4 basal bark treatment and some with foliar Milestone treatment at 7oz/acre in December 2016 All treated trees dropped their leaves and appeared to be dead Visited site in February 2017 and treatment appeared to have killed the trees
Zombie Trees Came Back to Life the Following Year Revisited site in December 2017 to find the majority of lead trees had resprouted Appeared that most resprouts were from the Milestone foliar treatment
Failed Lead Tree Treatment
No Logical Explanation Majority of lead trees resprouted No consistency with sizes, treatment areas, site conditions Most resprouts in 2017 appeared to be in the Milestone treated areas Was the concentration too low? Other possible factors Fog/rain Salt spray Soil conditions The only way to kill a zombie tree is to cut off it s head (aka cut stump)!
Need for Additional Research Lead tree is tough to kill Is there some factor in its biology that makes it less susceptible to foliar and basal bark treatments? Is there a treatment method that will provide consistent results on our DMMA, or are the site conditions the main factor? There has been limited research, which is what past treatments were based upon. We need more answers.
Beach Vitex Alert!!! An isolated population of beach vitex (Vitex rotundifolia) in Ponte Vedra Beach, FL was washed out during Hurricane Irma. There were thousands of seeds present and it is unknown where these seeds were deposited after the storm. Anyone with property along the Atlantic Coast should be on the lookout for this species and eliminate it as quickly as you find it. This invasive plant can have serious negative impacts on dune vegetation and sea turtle nesting.
Vitex rotundifolia beach vitex Widespread in Carolinas, established in panhandle near Pensacola, small populations on east coast of FL Opposite leaves with small hairs giving a silvery appearance to the leaves Woody stems and runners that root at nodes Purple flowers Small round fruits that mature from pink to yellow to black Deciduous, losing its leaves in the winter
Beach vitex infestation in Ponte Vedra Beach Homeowner contacted First Coast Invasive Working Group (FCIWG), requesting assistance with control Volunteer work days were held in December 2015 and July 2016 Thousands of mature fruits were present Since then, Hurricanes Matthew and Irma have eroded the dune area and spread seeds along the Atlantic coast
IF YOU ARE AT THE BEACH KEEP AN EYE OUT! Report any sightings in EDDMAPS (www.eddmaps.org) Randy Westbrooks, U.S. Geological Survey, Bugwood.org Forest & Kim Starr, Starr Environmental, Bugwood.org
QUESTIONS? Jessica Spencer Jessica.e.spencer@usace.army.mil 904-318-9110