Citrus Research Report 1991
ABOUT THE COLLECTION
The Citrus Report, first published in 1978, is one of several commodity-based agricultural research reports published by the University of Arizona. The purpose of the report is to provide an annual research update to farmers, researchers, and those in the agricultural industry. The research is conducted by University of Arizona and USDA-ARS scientists.
Both historical and current Citrus Reports have been made available via the UA Campus Repository, as part of a collaboration between the College of Agriculture and Life Sciences and the University Libraries.
Contents for Citrus Research Report 1991
- Comparative Control of Phytophthora Root Rot of Citrus with Sodium Tetrathiocarbonate, Metalaxyl, and Dosetyl-Al
- Seasonal Changes in Extent of Colonization of Citrus Root Tissue by Phytophthora citrophthora and P. parasitica
- Phytophthora Gummosis and Root Rot of Citrus-Effect of Temperature on Disease Development
- Evaluating the Potential Threat to Citrus Plantings from Phytophthora Parasitica Originating from Noncitrus Hosts
- California Red Scale Again Eradicated from Yuma County
- The Ash Whitefly as a Pest of Citrus
- Chemical Freeze Protection of Citrus 1988/1989
- Chemical Freeze Protection of Citrus 1989/1990
- Arizona Cooperative Citrus Registration-Certification Program Celebrates Silver Anniversary
- Report on the Salt River Valley Citrus Experiment Station
Arizona Cooperative Citrus Registration-Certification Program Celebrates Silver AnniversaryNew methods of determining the content of virus and virus-like disorders in citrus trees are heralding a new era of the Arizona Cooperative Citrus Registration-Certification Program (ACCRCP). It has been 25 years since the first budwood was released to participating nurseries. During that time, the program has relied on indexing using various indicator plants. Last year, indexing was begun in the laboratory using the ELISA unit for tristeza tests. Efforts are now being made to obtain antiserum for stubborn disease which currently has no reliable indexing method using indicator plants.
Chemical Freeze Protection of Citrus 1989/1990Three chemical frost protectants were applied to Lisbon lemons using a hand gun operated from a John Bean sprayer. Leaf samples were placed in test tubes with 10 ml of distilled water to determine the temperature at which they froze using a constant temperature bath. Although the sample size was increased by 50 percent over the previous year, the treatments were not significantly different from the untreated.
Chemical Freeze Protection of Citrus 1988/1989Five chemical frost protectants and a water treatment were applied to Lisbon lemons by dipping branches to insure complete coverage. A constant temperature bath was used to determine the effect of chemical frost protectants on the freezing temperature for leaf samples placed in test tubes with 10 ml of distilled water. Although the relative temperature at which the different treatments froze remained fairly constant, the differences were not significant.
California Red Scale Again Eradicated from Yuma CountySince 1973, Yuma County has had three apparently unrelated infestations of California Red Scale (CRS). The Yuma County citrus Pest Control District (YCCPCD) was successful in eradicating the first two in 1980 and 1984, respectively. We are continuing our spray program on the third, but our detection methods indicate that this infestation has now also been eradicated.
Evaluating the Potential Threat to Citrus Plantings from Phytophthora Parasitica Originating from Noncitrus HostsThe 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.
Phytophthora Gummosis and Root Rot of Citrus-Effect of Temperature on Disease DevelopmentExperiments 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.
Seasonal Changes in Extent of Colonization of Citrus Root Tissue by Phytophthora citrophthora and P. parasiticaFor 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.
Comparative Control of Phytophthora Root Rot of Citrus with Sodium Tetrathiocarbonate, Metalaxyl, and Dosetyl-AlThis 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.