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The Science Behind Fall Trunk Injection

The fall is an opportunity to treat trees successfully by tree injection with micro-nutrients and systemic insecticides.

Absorbing and storing minerals

With cooler temperatures and fall precipitation (and moist soils), trees naturally absorb and store minerals in preparation for the next year’s growth.  This is an ideal time to inject micro-nutrients (e.g., MIN-jet Iron) into trees. In the Midwest, oaks, maples and birches suffering from Iron chlorosis (expressed as leaf yellowing) will benefit from fall treatment without the concerns of foliar burning that may occur to tender leaves, or slow uptake in hot weather or in droughty conditions.  Likewise in the south and west, injections in palms with PALM-jet to alleviate symptoms of Manganese deficiency ought to be made in the relatively cool, moist conditions that often occur in the fall.  This is also an ideal time to apply ROOT-jet Iron to the soil for trees to absorb and store.

Evapo-transpiration in the fall

Evapo-transpiration continues in trees in cool, moist conditions, resulting in improved uptake in the fall. Trees transpire through leaf stomates and lenticels in the bark.  These pores are essential for gas (H2O, CO2 and O2) exchange. It has been estimated that 90% of the water absorbed by roots is lost to evapo-transpiration.  Stomatal opening and closure is under circadian and environmental control.  Generally, stomates open in the day and close at night.  Guard cells surround the stomata and their function is to open and close the pore.  When ambient temperatures increase and Trunk injection using Arborjet's TREE IVhumidity drops, the guard cells loose turgor (water), become flaccid and close the pore. This behavior has survival value, conserving water in the tree.  This event occurs most frequently in hot, dry weather and in dry soils.

When soil moisture is adequate, root uptake keeps up with moisture lost to evapo-transpiration, the guard cells remain turgid and water moves easily from roots to shoots.  This event most often occurs in the fall and spring in most areas of the country. Tree injection relies on this upward movement into the canopy, therefore is most efficient when trees are actively transpiring. A liquid injected into the tree’s sapwood (the transport tissue) moves up the stem from the point of injection into the branches and leaves.  The rate of movement of the liquid depends on the physical chemistry of the formulation placed into the vascular tissues.

Hemlock Woolly Adelgid

Hemlock Woolly Adelgid -  Image from ca.uky.edu

Early fall is a key time to treat hemlock trees infested with Hemlock Woolly Adelgid (HWA). HWA resumes feeding in the fall following summer aestivation (dormancy). Fall injection exposes the piercing sucking insect to the insecticide when it is most vulnerable. Hemlock retains its foliage from 3 to 6 years, so injected chemistries, such as Imidacloprid (e.g., IMA-jet) accumulate into the extant and newly developing foliage for multiple year of efficacy (Doccola et al., 2007). Currently IMA-jet has a label approved for up to 2 years of HWA control from a single application. Although not yet approved on the label, new research has demonstrated 3 years and suggests up to 4 years of control from a single treatment with IMA-jet.

Spiraling Whitefly

Spiraling Whitefly - Image from monroe.ifas.ufl.edu

In southern Florida, the spiraling whitefly feeds on a broad range of ornamental and shade trees. It feeds on the undersides of leaves on plant sap, rich in carbohydrates.   The whiteflies produce copious amounts of honey dew, which sticks to surfaces and supports the growth of sooty mold. It completes its life cycle in ~35 days.  We havereceived reports of injections with IMA-jet controlling the spiraling whiteflies in gumbo limbo trees (Bursera simaruba) in as little as 4-days. It has also been reported on Calophyllum species, black olive (Bucida buceras), Brazilian pepper (Schinus terebinthifolius), live oak (Quercus virginiana), and on several species of palms including, Veitchia species and coconut (Cocos nucifera) (Mannion, 2010).  Spiraling whitefly remains active in the cooler weather, and therefore susceptible to fall applications.

Emerald Ash Borer

Fall applications for the treatment of Emerald ash borer in ash (Fraxinus species) trees can be made in ash when leaves senesce (start to turn color), with specific systemic insecticides that have demonstrated efficacy and residual activity in trees (Smitley et al., 2010).

References

Doccola, J., E. Bristol, S. Sifleet, J. Loyjko and P. Wild. 2007. Efficacy and duration of trunk-injected imidacloprid in the management of hemlock woolly adelgid (Adelges tsugae). Arboriculture & Urban Forestry 33(1): 12-21.

Smitley, D., J. Doccola and D. Cox. 2010. Multiple-year protection of ash trees from emerald ash borer with a single trunk injection of emamectin benzoate, and single-year protection with an imidacloprid drench. Arboriculture & Urban Forestry 36(5): 206-211.

Mannion, C. 2010. Gumbo Limbo Spiraling whitefly, a new whitefly in south Florida. University of Florida, IFAS, Tropical Research and Education Center, Homestead, FL. 6 pp.

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