CMG GardenNotes #113 Diagnosing Root and Soil Disorders On Landscape Trees

Transcription

1 CMG GardenNtes #113 Diagnsing Rt and Sil Disrders On Landscape Trees Outline: Rt functin and symptms f rt/sil disrders, page 1 Diagnsing rt and sil disrders, page 2 1. Define the rt system, page 2 Types f rts, page 2 Depth and spread, page 4 Tree Prtectin Zne, page 5 2. Evaluate rt spread ptential, page 6 3. Evaluate sil cmpactin, page 7 Evaluating sil cmpactin, page 8 Methds t deal with cmpactin arund trees, page 8 4. Evaluate planting depth, page Evaluate rt/sht hrmne balance, page 12 Symptms f rt and sil disrders n landscape trees are ften nn-specific, making diagnsis difficult. This CMG GardenNtes expands n Step 3, Evaluate Rts and Sil, in the Systematic Evaluatin f Trees, (CMG GardenNtes #112). Rt Functin and Symptms f Rt/Sil Disrders Rts accunt fr apprximately 1/3 f the ttal bimass f a tree. The functins f tree rts include the fllwing: Water and nutrient uptake Anchring the plant Prductin f gibberellins, a hrmne that prmtes canpy grwth Strage f phtsynthates (alng with the wdy tissues) Symptms f rt/sil disrders are nn-specific in nature, including the fllwing: Reductin in phtsynthesis Reductin in rt grwth Reductin in canpy grwth Reductin in winter survival Reduced tlerance t ther stress factrs (insects, diseases, drught, etc.) Pr anchring f the plant resulting in tree failure 103-1

2 Rt, sil and water issues cntribute t a large prtin f landscape plant prblems, fr example: Sil cmpactin and/r drught are the inciting factr fr many cntributing insects (brers) and diseases (Cytspra and ther cankers). Sil cmpactin and/r hardscape features ften limit rt spread, which is expressed as reduced grwth and leaf scrch. Sil cmpactin reduces a trees tlerance t cmmn stress factrs, including drught, heat and wind, aphids, mites, and ther insects. Overwatering and drainage prblems (sil cmpactin) are ften expressed as irn chlrsis, rt rts, leaf scrch and limited grwth. Trunk girdling rts, caused by planting t deep, is the mst cmmn cause f tree decline and death in the landscape. Diagnsing Rt and Sil Disrders Unifrm stress thrugh canpy r stress frm the tp dwn suggests rt, sil, and water related prblems. Diagnsis cannt be frm these symptms alne, but requires a mre cmplete evaluatin f the tree, its rting system and grwth. The fllwing is a systematic apprach t diagnsing rt and sil disrders, based n cmmn prblems. 1. Define the Rt System Types f Rts Rt Plate Zne f Rapid Taper The rt plate r zne f rapid taper is the primary structural rts extending utward frm the trunk. Rts branch readily, tapering in diameter. It is a cntinuatin f the pipeline carrying water and nutrients frm the absrbing and transprt rts int the tree trunk. [Figure 1] The rt plate is the tree s primary supprt in winds up t 40 mph. Avid disturbing the sil and rts in the rt plate area. Cnstructin and hardscape features shuld nt encrach int the rt plate! When the tree fails by tipping ver, ften expsing the rt plate, it is failure at the edge f the rt plate. As a rule f thumb, the radius f the rt plate is three t six times the trunk DBH (diameter at breast height, 4.5 feet). Figure 1. The rting system f a tree is shallw and wide spreading. The Zne f Rapid Taper (Rt Plate) area is highlighted in yellw

3 Transprt Rts Transprt rts serve as a cntinuatin f the pipeline carrying water and nutrients frm the absrbing (feeder) rts t the rt plate rt and trunk. These are the majr spreading rts f the tree and fllw sil xygen gradients acrss the rting area. In cmpacted areas (with lwer sil xygen), they will cme t the surface. In sils with gd structure (higher xygen), they will be deeper. They als prvide additinal supprt t the tree in winds abve 40 mph. [Figure 2] Figure 2. Transprt and absrbing rts are fund thrugh the entire rting area beynd the Zne f Rapid Taper Transprt rts are typically thumb-size in diameter, lng, meandering, and with limited branching. Transprt rts d nt unifrmly spread arund the tree. Sme areas may be vid f rts, ther heavily cncentrated. In a hle dug in the rting area, transprt rts are readily bserved sticking ut the side [Figure 3]. Figure 3. Transprt rt are lng and meandering. They are NOT unifrmly distributed arund the trunk. Absrbing Rts Absrbing (feeder) rts serve the functin f water and nutrient uptake. These tiny rts are fund near the sil surface thrughut the entire transprt rting area. As a rule f thumb, they are fund in the tp 12 inches n sils with gd tilth, and in the tp fur inches r less in cmpacted, clayey sils. [Figure 2] Absrbing rts have a shrt life, being replaced in fur t five flushes f grwth thrugh Clrad s grwing seasn. A shrt-term drught stress (defined as 10 days) can shut dwn grwth fr 1-5 weeks. Lng-term drught stress (defined as 22 days), can shut dwn grwth fr 1-2 years! Refer t CMG GardenNtes #635, Care f Newly Planted Trees

4 Sinker Rts Sinker rts fllw natural penings int deeper sil as sil xygen levels allw. It is unknwn t what extent trees actually have sinker rts in the cmpacted sils f a landscape setting. Sinker rts have the ability t extract water frm deeper sil depths when the surface sil is dry. This helps explain hw trees have gd shrt-term drught resistance. It als helps explain the severe drught stress bserved n trees when there are dry seasns with dry subsil. Sinker rts als prvide additinal supprt in strng winds. [Figure 4] Figure 4. Sinker rts fllw cracks in the sil t deeper depths as xygen levels allw. They extract water when the absrbing rts near the surface have dry sil. Tap Rt The tap rt develps frm the seed radicle, being the primary rt emerging frm the germinating seed. Gardeners are very much aware f the tap rt as they try t pull seeding maples r elms as weeds in the garden. Hwever, beynd the seedling stage, the tap rt is nnexistent n mst trees. As the rt system develps beynd the seedling stage, the rts grw int the rt plate system due t lw sil xygen. Studies fund less than 2% f landscape trees actually have a tap rt. In nursery prductin, the tap rt is cut while tiny, frcing a mre branching rt system that is tlerant f transplanting. [Figure 5] Figure 5. The tap rt develps frm the seed radicle. In the seedling stage, the tree develps the rt plate system due t lw sil xygen. Tap rts are rare in landscape trees. Depth and Spread The typical tree rting system is shallw and wide spreading because rts nly grw with adequate levels f sil xygen. Rting depth and spread is a factr f 1) the tree s genetic tlerance t sil xygen levels and 2) sil texture and structure (actual sil xygen levels). It is difficult t estimate the actual depth and spread f a tree s rt system. Table 1 gives a rule f thumb n rt spread. Rts will be mre sparse and spreading in dry sils, and mre cncentrated in mist sils. [Table 1] 103-4

5 Table 1. Estimated Depth and Spread f a Tree s Rt System With gd sil tilth 90-95% in tp 36 inches 50% in tp 12 inches (absrbing rts) Spread 2-3 times tree height and/r canpy spread Mdified t by actual sil cnditins With cmpacted/clayey sils 90-95% in tp 12 inches r less 50% in tp 4 inches r less (absrbing rts) Spread five r mre times tree height and/r canpy spread Tree Prtectin Zne / Prtected Rt Zne Obviusly, nt every rt is essential fr tree health. The Tree Prtectin Zne, TPZ (Prtected Rt Zne, PRZ) defines the rting area with direct influence n tree health and vigr. The TPZ is the area f fcus in tree care activities and evaluating rt/sil related disrders. T prtect trees in a cnstructin area, there shuld be NO grading, trenching, parking, r stck piling f materials in the TPZ. Several methds have been used t estimate the TPZ. Dripline Methd The drip line (uter reach f branches) is ften used in cnstructin activities and by sme city rdinances t define the TPZ. It may be suitable fr a yung tree with a brad canpy in an pen lawn area. But it critically underestimates the critical rting area fr mst landscape trees. [Figure 6] Figure 6. The dip line is the rting area defined by the uter reach f the branches. It is a pr methd fr estimating a tree prtectin zne. Trunk Diameter Methd The trunk diameter is prbably the better methd frl use n landscape trees. Size f the TPZ is based n the diameter f the trunk, increasing as the tree ages. It may be calculated by measuring the trunk circumference r diameter at DBH (diameter at breast height, 4.5 feet). Fr trees with a brad canpy in an pen lawn, it is apprximately 40% larger in area than the dripline methd. [Figure 7] 103-5

6 Figure 7. The Tree Prtectin Zne defined by the trunk frmula methd is a gd estimate f the rting area with direct influence in tree health and vigr. It is apprximately 40% larger than the area defined by the drip line. Trunk Diameter Methd by Circumference TPZ radius = 1 feet per 2 inches f trunk circumference 1. Measure the tree s circumference at DBH (4.5 feet) in inches. 2. Divide the number f inches by This is the radius, in feet, f the TPZ. Fr example 1. Circumference = 24 inches / 2 = TPZ radius = 12 feet Area f the TPZ The area f the TPZ can be calculated by the frmula: [TPZ radius] 2 π Fr example - 12 ft radius: 12 feet 12 feet 3.14 = 452 square feet 2. Evaluate Rt Spread Ptential The ptential fr the rts t spread is a primary cnsideratin in evaluating a tree s rt system. The mature size, grwth rate and lngevity f a tree are directly related t the available rting space. Many trees in the landscape are predispsed at planting t a shrt life and limited grwth ptential due t pr sil cnditins and limited rting space. [Figure 8] Figure 8 shws the relatinship between rt space and ultimate tree size. Fr example, a tree with a 16 inch diameter requires 1000 cubic feet f sil. In a cmpacted clayey sil, rting depth may be restricted t 1 ft r less, requiring an 18-ft r greater radius rt spread. Anything less will reduce tree size, grwth rates, vigr and lngevity. Tree rts can generally crss under a sidewalk t pen lawn areas beynd. The ability f rts t crss under a street depends n the rad base prperties. A gd rad base des nt typically supprt rt grwth due t cmpactin and lw sil xygen levels. The rting area des nt need t be runded, but can be abut any shape. Trees can share rting space

7 When rts fill the available rt vault area and cannt spread beynd, 1) rt grwth slws, 2) canpy grwth slws, and 3) trees reach an early maturity and g int decline. Rutine replacement may be necessary. Figure 8. Tree size, grwth rate, and lngevity are directly related t the size f the available rting area. Fr tree in Clrad s clayey sils, effective rting depth is prbably less than ne ft deep. 3. Evaluating Sil Cmpactin Surface rts f trees are an indicatin f lw sil xygen caused by sil cmpactin and/r verly wet sil. Sil cmpactin is ften expressed as lw vigr and dieback symptms. Sil cmpactin is the mst cmmn inciting factr leading t cntributing factrs in the decline prcess. (Refer t CMG GardenNtes #101, Plant Health Care, fr a discussin f the PIC Cycle.) Sil cmpactin is a reductin in large pre space, reducing sil xygen levels and decreasing sil drainage. As a result, rting depth is reduced. Fr additinal details, refer t CMG GardenNtes #213, Managing Sil Tilth, and #214, Sil Cmpactin. Primary causes f sil cmpactin include cnstructin activities, ft traffic, and the impact f rain n bare sil. Sils are extremely prne t cmpactin when wet as the water serves as a lubricant allwing sil particles t slide clser tgether. Evaluating Sil Cmpactin Sil cmpactin is smewhat difficult t evaluate. Evaluatin tls include the fllwing: Lk at the lawn - It shares the same sil cnditins as the tree and may be easier t evaluate. Is the lawn thick r thin? Screwdriver test Hw easy can a screwdriver be pushed int the sil? Fr this test, the sil needs t have been watered the day befre. Sil prbe With a sil prbe, evaluate sil type, texture interfaces, and rting. It s best if the sil was watered the day befre perfrming this test

8 Penetrmeter This instrument measures the amunt f pressure it takes t push the prbe int the sil. The clred dial sectins indicate when rt grwth may be slwed r inhibited. The sil must be watered the day befre perfrming this test. Figure 9. Sil penetrmeter measures the pressure it takes t push the prbe int the sil. It is a great tl t evaluate sil cmpactin. Shvel Smetimes the nly way t evaluate the sil is with a shvel and sme hard wrk. Methds t Deal with Cmpactin Arund Trees Standard methds f dealing with cmpactin in a garden setting (adding rganic matter, cultivating the sil nly when dry, and aviding excessive tilling) d nt apply t tree situatins, as we d nt cultivate the rting zne. Practices Wrth Cnsidering Aeratin, with plugs at tw-inch intervals Lawn r sil aeratin is helpful fr tree rt xygen levels if enugh passes are made ver the area t have plugs at tw-inch intervals. Figure 10. Cre aeratin helps reduce sil cmpactin arund trees. T make a difference, plugs needs t be at tw-inch intervals. Managing traffic flw Established walks help minimize the cmpactin t ther areas. The first time a cultivated sil is stepped n, it can return t 75% maximum cmpactin. The furth time a newly cultivated sil is stepped n it culd return t 90% maximum cmpactin. Ft traffic n a cmpacted sil causes little additinal cmpactin. Sils are much mre prne t cmpactin when wet, as the sil water acts as a lubricant allwing the sil particles t slide clser tgether. Organic mulch A wd/bark chip mulch prevents sil cmpactin frm ft traffic if maintained at adequate depths. When using medium sized chips, the ideal depth is 3-4 inches. Less des nt give the prtectin frm cmpactin; mre reduces sil xygen levels

9 Sil renvatin with an air spade This methd is used by arbrists n high value trees (due t the expense). Steps include the fllwing: 1. Sd in the TPZ is remved with a sd cutter 2. Organic matter is spread and mixed int the sil with an air spade. The air spade is a high pressure stream f air that cultivates the sil withut cutting the rts. 3. The area is cvered with rganic wd/bark chip mulch. Practices f Questinable Value Vertical mulching with an augur The TPZ is drilled with 2 hles, typically at inch intervals. Hle may be filled with carse sand r rganic matter. Lng-term research finds that is des nt aerate enugh sil area fr a significant increase in tree vigr. [Figure 11] Figure 11. Vertical mulching with hle drilled thrughut the tree prtectin zne. Trenching Trenches (dug between primary rting paths) are backfilled with imprved sil. Lng-term research finds that while it imprves rt grwth in the backfilled trenches, it des nt supprt a lng-term significant increase in verall tree vigr. [Figure 12] Figure 12. Trenches dug between primary rt paths des nt result in significant imprvements in tree vigr. Punching hles with a pipe, pick, r bar This practice cmpacts the sil arund the punch site and des nt increase sil xygen levels. It des nt aerate enugh sil area fr a significant increase in tree vigr. T be effective, the sil cres must be remved. Fracturing The sil is subjected t a high-pressure release f air r water, fracturing the sil prfile. It has limited effectiveness in sandy sils. It may actually increase the cmpactin arund the fracture lines in clay sils. In summary, there is NO quick, easy fix fr cmpacted sils in tree rting areas

10 4. Evaluate Planting Depth Trunk girdling rts are the mst cmmn cause f tree decline and death f landscape trees. Trunk girdling rts are caused by planting the tree t deep. It may shw up sme twelve t twenty plus years after planting, causing decline and death f trees after they have significant grwth. Thus in evaluating the rting system f a tree, it makes sense t evaluate the tree planting depth. [Figure 13] Figure 13. Trunk Girdling Rts Circling/girdling rts may als develp as trees are planted up frm pt size t pt size in nursery prductin. They may be hidden inside the rt ball. Fr additinal infrmatin n tree planting, refer t CMG GardenNtes #633, The Science f Planting Trees. Recently Planted Trees Tw cnsideratins are imprtant in evaluating the planting depth f trees: 1) the depth f tree in the rt ball, and 2) the depth f rt ball in the planting hle. [Figure 14] Depth f tree in the rt ball Industry standards include the fllwing: Generally, at least tw structural rts shuld be within the tp 1-3 inches f the sil surface, measured 3-4 inches frm the trunk. On species prne t girdling rts (crabapples, green ash, hackberry, littleleaf linden, red maple, pplars, and pssibly thers), the tp structural rt shuld be within the tp ne inch f the sil surface. Depth f rt ball in planting hle T deal with the texture interface between the rt ball sil and the back fill sil, the rt ball must cme t the surface with NO backfill sil ver the rt ball. The tp f the rt ball n newly planted trees shuld rise 1-2 inches abve grade (depending n rt ball size). When the rt ball settles, it will be at grund level. On recently planted trees, the height f the rt ball shuld be slightly abve grade r at grade level after the rt ball settles. The rt ball sil shuld be visible n the surface with the site sil t the sides. With a small trwel, evaluate the planting depth f the rt ball in the planting hle. With a small trwel r screwdriver, evaluate the planting depth f the tree in the rt ball

11 Figure 14. Summary: Planting Hle Specificatins Generally, at least tw structural rts shuld be fund in the tp 1-3 inches f sil, 3-4 inches ut frm the trunk. On species prne t trunk circling rts (such as Crabapples, Green Ash, Hackberry, Littleleaf Linden, Pplar, and Red Maple) the tp structural rt shuld be within the tp ne inch f the rt ball. Tp f rt ball rises 1-2" abve grade. N backfill sil cvers tp f rt ball. Backfill sil cvers rt ball "knees" and tapers dwn t riginal sil Saucer-shaped planting hle, three times rt ball diameter. Tree sits n undisturbed sil. Recently planted tree, planted t deep If the tree is stressed with pr vigr, replace the tree. If the tree is currently in gd health: Live with pssible cnsequences f slwer grwth and trunk girdling rts. Check fr circling/girdling rts. Replant the tree 1) Dig arund the tree expsing the rt ball. 2) Wrap the rt ball in burlap and twine t hld it tgether. 3) Lift the rt ball frm the hle. 4) Replant at crrect depth. This wuld be difficult t d! Established Trees Planted T Deep The lack f a visible rt flare is an indicatin f planting t deep (r that sil has been added ver the rt system). If the rt flare is nt visible, check fr trunk circling/girdling rts. Circling/girdling rts may be several inches belw grund. Circling rts nt embedded int the trunk shuld be cut and remved. Fr girdling rts putting pressure n the trunk, cut and remve the rt withut causing injury t the trunk. The tree will likely recver withut any lng-term effects. When girdling rts embedded int the trunk, cut the rt withut causing injury t the trunk, if pssible. Hwever, d nt remve the girdling rt sectin if it is

12 embedded int the trunk, as this pens the trunk t decay and the trunk will be structurally weak. The tree may r may nt survive; nly time will tell. 5. Evaluate Rt/Sht Hrmne Balance Auxins (plant hrmnes) prduced in the twig s terminal buds stimulate rt grwth. Gibberellins (plant hrmnes) prduced in the rt tip stimulate canpy grwth. The tree balances rt grwth versus canpy grwth by these hrmnes. [Figure 14] Figure 14. Trees balance sht and rt grwth based n the cncentratin f auxins and gibberellins. Sil factrs that limit rt grwth will influence canpy grwth. Strm damage r excessive pruning may reduce auxins, slwing rt grwth. Fllwing strm damage, trees ften develp a large amunt f water sprut grwth due t a lw auxin/high gibberellin rati (cupled with unbserved, limited rt grwth). This is fllwed by a decline in the canpy caused by the reduced rt grwth. Authr: David Whiting, Extensin Cnsumer Hrticulture Specialist (retired), Department f Hrticulture & LA, Clrad State University. Artwrk by David Whiting; used by permissin. Revised by Mary Small, CSU Extensin Clrad Master Gardener GardenNtes are available nline at Clrad Master Gardener training is made pssible, in part, by a grant frm the Clrad Garden Shw, Inc. Clrad State University, U.S. Department f Agriculture and Clrad cunties cperating. Extensin prgrams are available t all withut discriminatin. N endrsement f prducts mentined is intended nr is criticism implied f prducts nt mentined. Cpyright Clrad State University Extensin. All Rights Reserved. CMG GardenNtes may be reprduced, withut change r additins, fr nnprfit educatinal use. Revised June