• Analysis of Rootstocks and New Fungicides for Control of Phytophthora Root Rot and Gummosis in Arizona Citrus Groves

      Matheron, Michael; Porchas, Martin; Wright, Glenn (College of Agriculture, University of Arizona (Tucson, AZ), 1996-09)
      Experiments were initiated to evaluate potential new citrus rootstocks for their relative tolerance or resistance to root rot and gummosis caused by Phytophthora citrophthora and P. parasitica and to determine the efficacy of potential new fungicides for disease control. In greenhouse trials conducted in 1994 and 1995, the range of root loss due to Phytophthora in the 44 different rootstocks tested ranged from 26-96 %. Rootstocks sustaining 80% or less root loss will be evaluated further to identify those with superior tolerance to Phytophthora. In growth chamber experiments, the same rootstocks were inoculated on the stem to evaluate resistance to gummosis. The length of canker that developed on these test plants ranged from 1-25 mm. Rootstocks with canker development in the range of 1-10 mm in length will be tested further to identify the most resistant selections. Laboratory studies were conducted to determine the comparative activity of Aliette, Ridomil, Dimethomorph, Fluazinam, ICIA-5504, and SM-9 at concentrations of 1, 10, 100, and 1, 000 mg/l on sporulation and growth of P. citrophthora and P. parasitica. Each of the four new molecules was either comparable or superior to Aliette or Ridomil with respect to activity on at least one component of the life cycle of the Phytophthora species tested. The results presented in this report are preliminary in nature and will be validated in future studies.
    • Biology and Control of Coniophora Causing Decay and Decline in Arizona Citrus

      Gilbertson, R. L.; Matheron, M. E.; Bigelow, D. M.; Wright, Glenn (College of Agriculture, University of Arizona (Tucson, AZ), 1996-09)
      A field survey of mature lemon trees showed an average of 30% of trees with symptoms of brown heartwood rot caused by Coniophora sp. In vivo growth of Coniophora inoculated into branches of different types of citrus (Valencia orange, Marsh grapefruit, Orlando tangelo or Lisbon lemon) on rough lemon rootstock was significantly higher in lemon while Coniophora inoculated into Lisbon lemon wood branches on trees established on rough lemon, volkameriana, macrophylla, Cleopatra mandarin, sour orange or Troyer citrange rootstocks showed no significant differences in growth. Vegetative incompatibility trials from one mature orchard demonstrated that isolates from different trees are incompatible. In vitro fungicide trials showed that only NECTEC paste effectively reduced decay on lemon blocks 15 weeks after inoculation with Coniophora. Field fungicide trials showed that NECTEC P paste as well as the blank paste without fungicides, propiconazole at 10,000 μg /ml, imazalil at 20, 000 μg /ml or propiconazole plus imazalil in combination at 10,000 and 20,000 μg/ml, respectively, significantly inhibited the advance of fungus 7 mo. after inoculation. A second fungus isolated from brown rot in branches in younger orchards was identified as Antrodia sinuosa, a native decay fungus on conifers in Arizona.
    • Comparative Control of Phytophthora Root Rot of Citrus with Sodium Tetrathiocarbonate, Metalaxyl, and Dosetyl-Al

      Matheron, M.; Matejka, J.; Butler, Marvin (College of Agriculture, University of Arizona (Tucson, AZ), 1991-01)
      This study was initiated to evaluate and compare the effect of root and soil treatments with sodium tetrathiocarbonate (STTC) (Enzone), metalaxyl (Ridomil), and fosetyl-Al (Aliette) on subsequent development of Phytophthora root rot on citrus. Disease development was significantly reduced on rough lemon seedlings treated with STTC or metalaxyl compared to untreated plants when this citrus rootstock was inoculated with sporangia of P. citrophthora or P. parasitica. Growth of rough lemon seedlings in soil naturally infested with P. parasitica that was treated one week before planting with STTC or metalaxyl was equivalent to that obtained in sterilized orchard soil STTC applied as a soil drench at 2,450 ppm was lethal to P. citrophthora and P. parasitica on colonized leaf disks of lepton buried in soil, whereas a similar treatment with metalaxyl at 10 ppm or fosetyl Al at 3,000 ppm did not appreciably affect pathogen viability. Sporangium production on leaf disks of lemon colonized by P. citrophthora and P. parasitica and buried in soil was reduced at least 90% compared to the untreated control six days after treatment of soil with 2,450 ppm of STTC, 10 ppm of metalaxyl, or 3,000 ppm of fosetyl AL These studies demonstrate the potential usefulness of sodium tetrathiocarbonate as a fungicide for control of Phytophthora root rot of citrus. Only fosetyl-Al (Aliette) and metalaxyl (Ridomil) currently are registered for control of Phytophthora diseases on citrus.
    • Development of Control Measures for Alternaria Fruit Rot on Roanges in Arizona

      Matheron, Michael; Maurer, Michael; Bacon, Dean; Truman, James; Lopez, Al; Wright, Glenn; Department of Plant Sciences; Department of Plant Pathology (College of Agriculture, University of Arizona (Tucson, AZ), 1996-09)
      The incidence and severity of Alternaria fruit rot on navel oranges has increased in Maricopa County. The objectives of this study were to test the efficacy of two fungicides, Kocide 101 and Rovral, for disease control and to determine an application schedule that will result in optimum control of disease. In 1994, compared to nontreated trees, a significant reduction in the number of dropped oranges occurred on trees sprayed one to five times with Rovral at monthly intervals from April through August. In the same year, monthly applications of Kocide 101 from April through August were no better than leaving trees untreated. In 1995, Rovral treatments from March through August provided no apparent beneficial effects on control of Alternaria fruit rot, while a single application of Kocide 101 in December, January, or February resulted in significantly less dropped oranges compared to nontreated frees. Because of the inconsistent activity of Kocide 101 and Rovral in these two studies, an additional trial is in progress during 1996. The additional data from 1996 may help identify when and what fungicide(s) could provide significant control ofAlternaria fruit rot of navel oranges in Arizona.
    • Distribution of Two Species of Phytophthora Within the Citrus Acreage in Arizona

      Matheron, M.; Matejka, J.; Bacon, D.; Butler, Marvin (College of Agriculture, University of Arizona (Tucson, AZ), 1988-12)
      Pkvtophthora citrophthora and P. parasitica cause gummosis and root rot of citrus trees in Arizona. A disease survey was initiated to determine the relative distribution of each pathogen within the citrus acreage of Maricopa and Yuma Counties. Both pathogens were recovered at the same time from 75% and 17% of orchards containing Phytophthora in Maricopa and Yuma County, respectively. P. citrophthora alone was found in 15% of the groves containing Phytophthora in Yuma County, while P. parasitica alone was detected in 25% and 68% of the citrus plantings containing Phytophthora in Maricopa and Yuma County, respectively. This survey will be continued for another year. The potential value of this information for improved disease control is discussed.
    • Evaluating the Potential Threat to Citrus Plantings from Phytophthora Parasitica Originating from Noncitrus Hosts

      Matheron, M.; Matejka, J.; Butler, Marvin (College of Agriculture, University of Arizona (Tucson, AZ), 1991-01)
      The relative virulence of Phytophthora parasitica recovered from citrus and other plants to rough lemon was investigated Isolates of Phytophthora parasitica from citrus were highly virulent to rough lemon seedlings, causing crown rot and significant reduction of root weight. Isolates of the pathogen from noncitrus hosts caused slight damage to rough lemon, with no crown rot and only minor reduction of root weight. Evidently, isolates of P. parasitica from several noncitrus hosts do not pose a serious threat to citrus groves.
    • Improving Management and Control of Fungal Diseases Affecting Arizona Citrus

      Matheron, Michael; Maurer, Michael; Porchas, Martin; Wright, Glenn (College of Agriculture, University of Arizona (Tucson, AZ), 1997-11)
      Experiments were initiated to evaluate chemical disease management tools for Alternaria fruit rot on navel orange and Coniophora brown wood rot on lemon trees, examine the possible effect of branch diameter on development of Coniophora wood rot on lemon trees and continue evaluations of relative resistance of rootstocks to root rot and stem canker development when inoculated with P. citrophthora and P. parasitica. Rovral or Kocide did not significantly reduce the amount of Alternaria fruit rot on navel orange trees occurring in late summer and early autumn when applied during the preceding winter or spring months. Of several chemical treatments tested, only Nectec paste inhibited the development of Coniophora brown wood rot on inoculated lemon branches. The size of wood decay columns on branches 10 mm (0.5 inch) in diameter were significantly smaller than those developing on branches 50-70 mm (2.0-2.75 inches) in diameter. In extensive trials evaluating root rot caused by Phytophthora citrophthora and P. parasitica, some relatively tolerant rootstocks were found among the group of new potential rootstocks as well as currently used rootstocks such as rough lemon, C. macrophylla and Troyer citrange. C. volkameriana was relatively tolerant to the development of root rot by P. citrophthora but demonstrated variable tolerance to P. parasitica. Comprehensive evaluation of stem canker development on citrus rootstocks inoculated with P. citrophthora or P. parasitica revealed that rough lemon is usually highly susceptible to both pathogens, while C. volkameriana was at times less susceptible (more tolerant) than rough lemon to both pathogens. Some of the new potential rootstocks were highly tolerant or resistant to infection of stem tissue by P. citrophthora or P. parasitica.
    • Improving Management and Control of Fungal Diseases Affecting Arizona Citrus Trees, 1997

      Matheron, Michael; Maurer, Michael; Porchas, Martin; Wright, Glenn; Kilby, Mike (College of Agriculture, University of Arizona (Tucson, AZ), 1998-09)
      Studies were conducted to evaluate potential chemical disease management tools for Alternaria fruit rot on navel oranges and Coniophora brown wood rot on lemon trees, to investigate the possible effect of branch diameter on development of Coniophora wood rot on lemon trees and to summarize our evaluations of citrus rootstocks with respect to relative resistance to root rot and stem canker development when challenged with Phytophthora citrophthora and P. parasitica. We were unable to reduce the level of Alternaria fruit rot on navel oranges with single applications of Abound or copper hydroxide following significant rainfall events. Wood decay in lemon branches inoculated with Coniophora eremophila was significantly suppressed by Abound and a thick formulation of sodium tetrathiocarbonate. The degree of Coniophora brown wood rot in lemon branches of different diameters was variable, although the level of disease in 10 mm diameter branches was significantly smaller than the amount of wood decay in 30 mm diameter branches. Root loss due to Phytophthora citrophthora and P. parasitica in Citrus macrophylla, rough lemon, C. volkameriana and Troyer citrange was lower than most of the 36 different rootstocks tested. On the other hand, root loss on Carrizo citrange, C-35 citrange and sour orange was among the higher values of disease recorded. Stem canker development due to both species of Phytophthora on Troyer citrange, Carrizo citrange, sour orange and Citrus macrophylla was lower than most of the 36 rootstocks tested. Stem cankers on rough lemon and Citrus volkameriana were among the higher values of disease recorded.
    • Mycoplasma-like Organisms as the Causal Agent for Macrophylla Decline

      Taylor, Kathryn; Ellis, Danielle; Wright, Glenn (College of Agriculture, University of Arizona (Tucson, AZ), 1996-09)
      Previous literature concerning citrus and other tree crops led us to ask if there was molecular evidence for mycoplasma -like organisms (MLOs) as the causal agent of Macrophylla decline and two other decline diseases, citrus blight and lemon sieve tube necrosis. We had molecular probes available to us that were either specific for MLOs of tree diseases and others that were universal for all known types of MLOs. We used a polymerase chain reaction (MLO) to determine if MLOs were present in the vascular tissues of decline and healthy citrus. I all trials performed, the trees were negative for MLO-PCR products. In addition, we attempted to transmit putative MLO 's from decline affected trees to Vinca rosea MLO-nurse plants. We were unable to affect this type of transfer. In addition, our attempts to identify MLO's in phloem tissue gave us negative results. We have since revised our hypothesis. We are currently pursuing the hypothesis that these decline disorders are the result of a rootstock scion incompatibility, that we may be able to avoid culturally, while maintaining these valuable combinations.
    • Phytophthora Gummosis and Root Rot of Citrus-Effect of Temperature on Disease Development

      Matheron, M.; Matejka, J.; Butler, Marvin (College of Agriculture, University of Arizona (Tucson, AZ), 1991-01)
      Experiments were conducted to examine the effect of temperature on development of Phytophthora gummosis and root rot of citrus as well as the influence of temperature on sporulation of Phytophthora citrophthora and P. parasitica. Maximum production of sporangia by each fungus occurred at 25 C, while slight or no sporangia production occurred at 10, 15, and 35 C. Minimal growth of lesions was observed when stems of rough lemon were inoculated with P. citrophthora or P. parasitica and incubated at 5 and 30 C or 10 and 30 C, respectively. The inhibitory and stimulating effect of certain temperatures on sporulation and disease development could be useful for determination of optimum times for application of fungicides or other disease control measures.
    • Relationship of Viroids to Macrophylla Decline

      Taylor, Kathryn; Langham, Richard; Xiong, Zhongguo; Wright, Glenn (College of Agriculture, University of Arizona (Tucson, AZ), 1996-09)
      A physiological characterization has established that vascular changes in Macrophylla decline affected trees are not similar in character to xyloporosis affected trees. In addition, a survey of Macrophylla decline affected citrus did not establish any genetic similarity between Macrophylla decline and xyloporosis. We report diagnosis of either CCV or CEV by reverse transcription-polymerase chain reaction (RT-PCR), as well as diagnosis of Macrophylla decline or xyloporosis by Zn-distribution, water conductivity, accumulation of decline- specific proteins and examination of phloem morphology in lemon trees on the Macrophylla rootstock.
    • Seasonal Changes in Extent of Colonization of Citrus Root Tissue by Phytophthora citrophthora and P. parasitica

      Matheron, M.; Matejka, J.; Butler, Marvin (College of Agriculture, University of Arizona (Tucson, AZ), 1991-01)
      For 24 consecutive months, root pieces were collected from field -grown Lisbon lemon trees established on Citrus aurantium (sour orange), C. jambhiri (rough lemon), and C. volkameriana rootstocks. Root segments were wounded, inoculated with Phytophthora citrophthora or P. parasitica, and incubated for 96 hr in moist chambers. Smaller lesions developed during Jan -Feb than during Jul-Oct on root pieces of all tested rootstocks inoculated with P. citrophthora as well as root pieces of C aurantium inoculated with P. parasitica. Apparently there is a seasonal variation in the susceptibility of citrus rootstocks to colonization by Phytophthora. This information could be useful for more effective timing of fungicide applications.
    • Seasonal Variation in Susceptibility of Citrus Rootstocks to Phytophthora

      Matheron, Mike; Matejka, Joe (College of Agriculture, University of Arizona (Tucson, AZ), 1986-12)
      Phytophthora parasitica and P. citrophthora are routinely recovered from diseased citrus groves in Arizona. Stem sections were collected monthly from Citrus macrophylla, rough lemon, .sour orange, Cleopatra mandarin, Troyer citrange and Citrus volkameriana. Stem pieces were wounded, inoculated with mycelium of P. parasitica or P. citrophthora, then incubated for 7 days at 21° C in moist chambers. For all tested rootstocks, the smallest cankers were produced on tissue collected in December, January and February, the winter dormancy period for citrus in Arizona. The period of higher susceptibility ranged between March through November, depending on the rootstock tested. Apparently, these six citrus rootstocks possess seasonal differences in their susceptibility to P. parasitica and P. citrophthora.
    • Sodium Tetrathiocarbonate - Potential New Fungicide for Control of Phytophthora in Citrus Groves

      Matheron, M.; Matejka, J.; Butler, Marvin (College of Agriculture, University of Arizona (Tucson, AZ), 1988-12)
      Sodium tetrathiocarbonate (STTC) releases carbon disulfide when added to water and applied to soil. Laboratory tests were conducted to determine the effect of this chemical on growth and sporulation of Phytophthora citrophthora and P. parasitica, which cause Phytophthora gummosis and mot rot of citrus in Arizona Zoospore motility, zoospore cyst viability, sporangia production, and mycelia' growth were significantly reduced in the presence of STTC Results of laboratory tests suggest that application of S7TC as a soil drench could reduce inoculum production and subsequent new infections by P. citrophthora and P. parasitica.
    • Studies on Stubborn Disease and its Vector in Arizona Citrus Groves and Nurseries

      Oldfield, George N.; Creamer, Rebecca; Wright, Glenn C.; Wright, Glenn (College of Agriculture, University of Arizona (Tucson, AZ), 1997-11)
      Seasonal flight of beet leafhopper vectors of stubborn disease was monitored at wholesale nurseries in Yuma County, and at young citrus groves in Maricopa County using yellow sticky traps exposed at successive two-week intervals. Trapped leafhoppers were removed and assayed for presence of the citrus stubborn agent by PCR. Leafhoppers were collected live from weed plants in groves and nurseries using an insect vacuum and both leafhoppers and tissue from weed plants were assayed by PCR for the stubborn agent. Selected trees in groves in Yuma and Maricopa Counties were visually inspected for stubborn symptoms.
    • Trunk Application of Phosphorous Acid and Two Other Fungicides for Control of Phytophtora Gummosis of Citrus

      Matheron, Mike; Matejka, Joe (College of Agriculture, University of Arizona (Tucson, AZ), 1986-12)
      Gummosis caused by Phytophthora parasitica and P. citrophthora is a serious problem in Arizona citrus groves. In a 15-year-old Orlando tangelo planting at the Yuma Mesa Agricultural Center, a 20 cm section of trunk on each tree was painted with phosphorous acid, metalaxyl or fosetyl-Al. After treatment, pieces of bark were periodically removed from within, as well as below, the treated area and inoculated with P. parasitica and P. citrophthora. After 117 days, both Phytophthora species were inhibited on bark treated with phosphorous acid, metalaxyl or fosetyl-Al. Canker development was also reduced on bark tissue sampled 10 cm below the site of treatment. The results suggest that trunk application of phosphorous acid, metalaxyl or fosetyl-Al can provide effective protection against Phytophthora gummosis of citrus.