Texas Root Rot in Pecans

What to do about ... Texas Root Rot in Pecans

Item Type Article

Authors Streets, R. B. Sr.

Publisher College of Agriculture, University of Arizona (Tucson, AZ)

Journal Progressive Agriculture in Arizona

Download date 01/10/2021 05:32:03

Link to Item http://hdl.handle.net/10150/300193 monium sulphate solution to the root zone. A small tractor with a border disc may be used around the . drip line What to do about.. . the tree for two or three times to fo a border. Spread the manure two to three inches deep within the basin.It can be fresh and full of straw for that which is needed is the rapidly decay- Texas Root Rot in Pecans ing organic matter. Scatter one pound each of ammonium sulphate and soil sulphur over the manure for each ten square feet of area. by R. B. Streets, Sr.* When theseingredientsarein place, flood the area with three to four inches of water to leach the ammonium sulphate down into the root zone. Pecan trees are amazingly tolerant of heavy applications of ammonium sulphate as well as ammonium phos- phate. If anyone should try to "invent" alook for and map the spots of dead Usually by the time one becomes tCsuper"plantdisease,hecouldplants within the field. Do this at theconcerned about the health of a tree, hardly out -do the destructiveness ofend of the growing season near Octo-it has already lost from 60 to 80 per- Phymatotrichum Texas Root Rot. Nor,ber first.The areas of dead plantscent of the roots to Root Rot. Thus, could he find a disease as difficult toindicate quite accurately the pres-to balance the tree top with its re- treat. ence and extent of Root Rotinfesta-duced root system remove from 50 to The culpritcausingthediseasetion in the field. 75percentofthefoliageand known as Texas Root Rot is a soil - The most accurate way to make abranches. borne fungus ( Phymatotrichum omni-permanent map of the infested areas The tree will quickly grow a new vorum ) .It attacks more than 2,000of a field is the use of aerial photog-top if the treatment is successful. kinds of broad- leafed plants, and itraphy. Color film gives the best re- There is always the problem of de- does its work only in the southernsults. Keep the pictures for recordstecting infected trees before root dam- states along the United Statesandbecause the root rot infection will re-age becomesextensive.We ha Mexico border.It has not been re-main in the same field for many years.found that a slight yellowing is a ported in any other part of the world. Mark off these areas in the fieldearly sign. This symptom is not usu- Two conditions which favor its oc-where Root Rot occurred and plantally recognized by grower as Root Rot currence are (1) analkaline soil lowto monocot plants, which are im-connected. in organic matter, and (2) mild win-mune to Texas Root Rot. Someof A tree with small, or sparse, foliage ters. these include: grain crops and forageusually indicates that it was infected There are three ways to combatsorghums,corn,milletandotherthe previous fall.When in doubt, Texas Root Rotprevention, chemi-grass type plants. treat the tree because the cost is small cal treatment and rotation with crops Root Rot can be greatly reduced incompared to the cost of replacing it. which are not susceptible. subsequent years using this rotation.The material used in the treatment is When a response is obtained, a one -all plant food except for the excess of Avoiding Root Rot year rotation is sufficient.It is wisesulphur. It is far cheaper and more satisfac-to plant immune plants a second year, As one might expect, trees in early tory to prevent root rot infestationparticularly before investing in theor light stages of infection respond than to bear the expense and laborplanting of a long -lived fruit or nutmore promptly and with less loss of of treating it. tree. production.Ideally, a grower should The presence of Root Rot can be Another means of preventing Rootnot let his trees go beyond the early accurately determined only by grow-Rot is to inspect nursery stock beforestage before applying the treatment. ing very susceptible indicator plantsplanting.It would be careless to in- Remember that recovered trees are in soil for two years before you plantroduce the Root Rot fungus into ansurviving on a damaged root system. to plant long -lived tree crops. otherwise clean field. These trees need a followup treat- Alfalfa, or cotton, make the most Treatment of Spot Infestations ment, a booster of ammonium sul- practicalindicatorplants,because A good treatment is the acidifica-phate about the first of May each you need not losethe use of the landtion of alkaline soils. The addition ofyear. This is about the time when an during the test period.There arelarge quantities of organic matter oractive Root Rot season begins. This other good test plants, but who needssome sulphur and ammonium sul-followup rate of application should be a thousand acresof okra? phate will accomplish this. It is neces-one pound of ammonium sulphate for If cotton is used as the test plant,sary to treat the roots to their extremi-each ten square feet of space within °Plant Pathologist, Department of ties.This is known as the drip line.the drip zone. Then, irrigate. Plant Pathology Dig a basintoconfinethe am- (Turn to Next Page) 1 16 New Canker Disease Found in Pecans

by R. B. Hine, J. E. Wheeler and E. L. Clark

During the spring of 1969 a cankeryear -oldtrees were common. The The variety, Riverside, used as a root- disease of pecans that occurred inmost likely injury- factors for fungalstock, appeared to be disease free. commercial plantings in the Sahuaritainfections were either winter -low tem- CONTROL Sunburn damage to and Continental areas of Pima Countyperature damage, a late spring frostyoung trees prior to adequate canopy was identified and shown to be causedduring 1968, summer -sun burn, ordevelopment may be reduced by ap- by a species of the fungus, Cytospora.pruning injuries. The extent of cankerplication of reflective materials to re- Approximately 150 -200 trees failed todevelopment was determined by su-duce trunk temperatures. Various di- leaf out during April and May andperficially removing the bark fromlutions of latex paint ( white, indoor) were shown to be killed by fungal in-suspected diseased areas and notingwith water have been recently used fections that girdled the main trunk.the sharp delineation between healthyin other states to reduce the incidence Cankers were also numerous on scaf-and diseased tissue( light and darkof Cytospora canker in stone fruits. fold and other branches. The diseasecolored wood, respectively ). Orang-The material may be sprayedor wasscatteredthroughoutafourish spore masses in long chains werepainted on the trunk and scaffold thousand acre planting but occurredmicroscopically visible in the cankeredbranches. Winter injury may be re- primarily on 2 and 3 year -old trees.areas. The spores are extruded fromduced by preventing excessive tree Although the disease is common onsmall,black,pinhead -sizedfungalgrowth late in the fall caused by late a large number of other trees includ-structures, partially imbedded in thefertilization and irrigation.Pruning, ,ingapple,apricot,cherry,peach,diseased bark, called pycnidia. Theseif possible, should be done in early ;Sim, walnuts, and a number of na-air -borne spores, which are producedspring so that active growth and sub- e Arizona trees including cotton-during periods of moisture, are thesequent callus formation may reduce wood, it has never previously been re-primary sources of infection. Originalthe period of susceptibility to fungus ported on pecan.To the authors'inoculum probably came from dis-infection. Diseased wood, because it knowledge, this is the first publishedeased native trees in the area as exami-is a source of inoculum, should be re- report of the disease on pecans in thenations of a large number of newlymoved. Pruning wounds should be United States. planted trees were disease -free, indi-treated with a wound dressing.Al- The fungus pathogen needs injuriescating healthy planting stock.Thethough the efficacy of fungicide ap- to gain entry into host tissue.Infec-disease occurred on the varieties Bar-plications to pruning wounds in pe- tions on the main trunk of 2 and 3 ton,Bradley, and Western Schley.cans has not been determined, it is reasonable to believe from studies in (Root Rot in Pecans) ammonium sulphate. other trees that this would be a valu- Unfortunately, there are no known Step two: place two inches of theable control measure.Tools used in pecan varieties found to be resistantsoil on top of the manure. the pruning operationsshould be to Root Rot. Step three: repeat step one.Stepdipped in a disinfectant such as alco- Planting Replacement Trees four: repeat step two. Continue build-hol, formaldehyde, or sodium hypo - When a tree is lost from Root Roting alternating layers until the hole ischlorite.Mechanical, herbicidal, or infestation, the soil can be preparedfilled to four inches from the top.other types of injury should be avoid- prior to the planting of a replacementFlood the depression to settle theed. tree. Dig the tree hole 8 by 8 by 2.5soil and make sure it is thoroughly Because the fungus is inactive dur- feet, a hole which will yield 80 cubicsoaked. ing the summer, inoculation studies feet of soil.Twenty pounds of soil Wait one month, then apply waterwill be initiated in the fall to deter- sulphur, ten pounds of ammonium sul-before placing the replacement treemine if differences in disease toler- phate, and eight cubic feet of manureinto the hole.If you are impatient,ance exist in pecan varieties adapted should be distributed through theplant the new tree in the treated holeto Arizona growing conditions. soil. making sure that the roots do not Fill the hole in the following man-come in contact with the treated soil.R. B. Hine is Extension Plant Pathologist, ner alternating the layers: Use untreated soil around taproot. University of Arizona, Tucson; J. E. Wheeler This method has been used success-is a Research Associate, Dept. of Plant Pa- Step one: put one inch of manure thology, University of Arizona, Tucson; and on the bottom of the hole uponwhichfully for 25 years in planting replace-E. L. Clark is associated with Farmers In- 6u scatter some ofthe sulphur andment trees. vestment Company, Sahuarita, Arizona.