VEGETATIVE REPRODUCTION IN RUSSIAN OLIVE: IMPLICATIONS FOR CONTROL Dennis Worwood Ron Patterson Utah State University Extension
Russian olives regrow vigorously from crowns and/or roots after trees are removed. In our trials, an average of 44 new shoots emerged when a Russian olive was uprooted or cut down.
Four month old regrowth from Russian olive stumps.
Root suckers from a tree that was uprooted twelve months earlier.
Russian olive control would be simplified if regrowth could be prevented or minimized. This presentation will discuss: Sources of vegetative regrowth in Russian olive. Environmental factors that favor or inhibit regrowth. How these factors influence control strategies.
Background: In a three-year study, Worwood and Patterson found that cut stump herbicide treatment provided nearly 100% control of Russian olive regrowth, regardless of time of year. Nearly 100% of untreated stumps re-sprouted vigorously. No suckers were produced by roots of treated or untreated stumps.
Soils and Vegetation Change Following Russian olive Removal Erin Espeland, USDA-ARS NPARL Sidney, MT https://www.youtube.com/watch?v=lkn4e9r0nkk 2500 Russian olives were cut down, and stumps treated with herbicide. 3.9% Re-sprouted 10% of sprouts came from stumps 90% of sprouts originated from roots exposed by flooding
Questions: Do cut stump herbicide treatments kill roots? Why are root suckers produced in some situations but not in others?
From Jan to June, 2016 Russian olives were cut down and stumps treated with herbicide. The dead stumps were uprooted in August, 2016. 40% of the stumps produced suckers from the exposed root ends. Dead Stumps, Live Roots
On a site with shallow and exposed roots, suckers appeared after Russian olives were cut down. Right: no herbicide applied to stump. Far right: herbicide was applied to the stump.
Regrowth in Russian olive originates from two types of buds: Adventitious Buds Epicormic Buds
Adventitious buds are: buds that emerge in areas where buds do not usually develop [they] tend to develop from the plant s meristem or secondary tissues Definitions, Modern Maximum Yield Growing https://www.maximumyield.com/definition/2266/adventitious-bud
All root suckers and some crown shoots originate from Adventitious buds. New cells from the vascular cambium of this Russian olive root produced callus tissue, which morphed into Adventitious buds, which grew into suckers. This process takes 3 months or more and is controlled by Auxin and Cytokinin. New Tissue Original Root
EPICORMIC BUDS Dormant, or latent buds that are common on the base and trunk of Russian olive trees. Epicormic buds sprout and grow rapidly if the top of the tree is weakened or removed.
Buds form at nodes such as leaf axils. Adventitious buds form in other areas. Auxin produced by buds and expanding leaves suppresses growth of lower buds, which remain alive, but dormant.
Buds Bud Trace Trees maintain a vascular connection to Epicormic buds as the trunk expands. This connection is visible as a Bud Trace. Epicormic buds may survive for decades, and sometimes divide to form clusters of dormant buds.
Single Epicormic Bud Cluster of Epicormic Buds Epicormic buds are easily seen if the bark is removed. Buds protrude outward and are nearly flush with the bark surface.
Russian olives don t sucker in the same way as some other species. This Silver Poplar root sucker emerged from a root that was nine inches deep. In digging up hundreds of Russian olive root suckers, we never found a sucker that originated from a root more than one inch deep.
Root suckering is possible only when Russian olive roots are shallow or exposed. This includes sites where: root depth is limited by shallow soil; root depth is limited by a high water table; roots have been exposed by erosion, soil disturbance or tree removal activities.
Suckers on broken Russian olive roots that were exposed by erosion.
Russian olive suckers on an intact root that was exposed by erosion. No suckers emerged from this tree s buried roots.
Typical suckering pattern when Russian olives are uprooted. X marks the location of the original tree in both photos. Above, right: A halo of suckers formed on exposed root ends. No suckers emerged from buried roots.
Questions: Does burial physically prevent Russian olive regrowth from emerging? How does root depth and exposure affect suckering ability? How does the potential for regrowth influence control strategy?
Can regrowth be prevented by burying stumps?
Stumps do not need to be exposed to produce regrowth. These shoots originated from Epicormic buds.
Can burial prevent regrowth from Adventitious buds on crowns of shredded Russian olive trees?
Burial did not stop shredded Russian olive crowns from producing Adventitious buds, and new shoots. Buried crowns can produce new shoots from both Epicormic and Adventitious buds.
Question: Will burying exposed roots of uprooted trees prevent or minimize sucker formation? Roots of Russian olives were exposed by uprooting trees or by trenching around trees. Some roots were left exposed while others were buried. Sucker production on buried and exposed roots was compared.
Sixteen Russian olives were uprooted in August, 2016. Broken root ends of eight trees were left exposed. Twelve months later, numerous root suckers had emerged from exposed roots. The eight trees with exposed roots produced an average of 38 root suckers/tree.
Broken roots of eight of the trees uprooted in August, 2016 were immediately buried. Twelve months later, no root suckers had emerged from this tree s buried roots. The eight trees with buried roots produced a total of one root sucker, from a root that remained exposed.
Left: Buried roots excavated one year after the tree was uprooted were still alive but showed no callus or bud development. Below: Suckers on an exposed root of a tree uprooted the same day.
Trenches 16 inches deep were dug completely around nine Russian olive trees. All roots encountered were severed. Half of each trench was backfilled to ground level. Root sucker production in open and backfilled trench segments was compared.
Roots in open trenches produced a total of 460 suckers.
A total of two suckers emerged from roots in buried trench segments. One of the root suckers that emerged from a backfilled segment of trench. This sucker did not appear until the second growing season after the trench was dug. The originating root was exposed in a cow s hoof print.
Uprooted Trees: Exposed roots produced 300 times more suckers than roots that were buried after trees were uprooted. Open vs. Backfilled Trench: Roots in open trench segments produced 230 times more suckers than roots in backfilled trench segments.
Burial as a method of reducing root sucker formation: larger [Russian olive] trees can be removed using a bulldozer or a tractor with an attached chain. Any remaining exposed roots should be cut off below ground level and buried. DiTomaso, J.M., G.B. Kyser et al. 2013. Weed Control in Natural Areas in the Western United States. Weed Research and Information Center, University of California. 544 pp.
Conclusions Russian olive crown tissue can produce new shoots from Epicormic and Adventitious buds, whether buried or exposed. Regrowth from crown tissue can be minimized or prevented by herbicide treatment, or by completely removing crown tissue.
Conclusions Russian olive roots must be shallow or exposed to produce root suckers. Burying exposed roots after trees (or stumps) are uprooted minimizes sucker production. It is not known why roots must be shallow or exposed to sucker. In tissue culture, callus produces roots when treated with high Auxin/low Cytokinin, and shoots when treated with high Cytokinin/low Auxin. Exposure might allow Russian olive roots to produce or accumulate enough Cytokinin to stimulate shoot production.
Base Russian olive control strategies on regrowth potential: On sites where roots are NOT shallow or exposed, root suckering is unlikely unless roots are disturbed. Crown regrowth can be prevented or minimized by removing crown tissue or by treating remaining crown tissue with herbicide. On sites where roots ARE shallow or exposed, root suckering is likely even when measures are taken to prevent crown regrowth. Suckers can be controlled by repeated removal of new growth, or by herbicide treatments.
QUESTIONS OR COMMENTS? dennis.worwood@usu.edu ron.patterson@usu.edu