Location: Subtropical Plant Pathology Research2011 Annual Report
1a. Objectives (from AD-416)
1. Confirm the value of using windbreaks to reduce incidence and severity of citrus canker, and identify optimal ways to deploy them that are applicable in Florida. 2. Identify the contribution of leafminer to the canker epidemic, and demonstrate the effect of good leafminer control in reducing the canker epidemic. 3. Provide useful information on the efficacy of available bactericides, particularly copper compounds, under various weather conditions to help develop optimal spraying protocols sensitive to the crop development and weather in the field. Determine the efficacy of standard grove sanitation procedures. 4. Complete development of a computer controlled system (PLWC)by which the leaf wetness and other environmental factors can be measured, recorded, and controlled. 5. Use the PLWC system to test the effect of leaf wetness duration, on Xcc survival, as well as the interaction of Xcc with other bacteria on the leaf surface. 6. Augment/improve best management practices (BMPs) for citrus canker by determining combinations of wind breaks, insecticide treatments, copper sprays and grove management that will be available for testing in the field in Florida.
1b. Approach (from AD-416)
1. Assess the individual and combined effects of windbreaks, copper sprays and leafminer control in reducing infection of citrus trees with citrus canker. 2. Analyze and investigate the leafminer control treatments to determine effects in reducing the incidence and severity of citrus canker in commercial citrus groves in Brazil, and assess the applicability of this strategy to the US commercial citrus industry in Florida. 3. Analyze data to identify the quantitative relationship between infestation densities of citrus leafminer and incidence and severity of citrus canker. Determine what thresholds exist for treatment. 4. Analyze data to determine the value of copper sprays in protecting plants under various weather conditions. 5. Test how bactericide (particularly copper) treatments stand up to different weather conditions (different wind/rain inoculum conditions). 6. Analyze data to determine if polymer delivery system can improve the efficacy and longevity of Cu++ and other metal ions for control of citrus canker under extreme conditions. 7. Analyze data to determine the efficacy of standard grove sanitation procedures. 8. Finalize the development and testing of the PWLC and use it to determine how bacterial survival relates to leaf surface conditions in a grove situation. Use the PLWC to determine how leaf wetness duration affects the survival of Xcc on the leaf surface. 9. Analyze data to determine if lengthening or shortening leaf wetness duration or amount will allow competitive bacteria to grow on the leaf surface and prevent the growth of Xcc. 10. Investigate the effects of other environmental conditions (temperature, RE, light) in combination with leaf wetness on the survivability and growth of Xcc. 11. Analyze data to identify ways of using available crop management techniques to minimize the survival of bacteria on plant surfaces.
3. Progress Report
This project is related to Objective 3: Develop or improve comprehensive integrated disease management strategies. The intent of this study is to examine the effect of windbreaks, copper sprays to reduce infection, and leafminer treatments to determine there individual and combined effects on control of citrus canker in Brazilian commercial citrus and the applicability of this strategy to the US commercial citrus industry. A preliminary study was published in Crop Protection 27:807-813, that indicated that copper and insecticide applications significantly reduced canker infection but windbreaks did not have any effect. It is believed this is the case because the windbreaks were not tall enough. Thus a new series of plots with much more extensive windbreaks were established. This was accomplished via a USDA/ARS specific cooperative agreement with the University of Sao Paulo, and the Brazilian cooperator, funds were transferred for collaboration, plot maintainence and experimental conduct. Permission was obtained to use a farm, in Xambrê, Parana state, located 350 km west from Londrina and 250 km west from Maringá where replicated field plots were established. The cultivar used is Pêra on Rangpur lime, two years of age at the beginning of the experiment. Windbreaks were completed and plants were be established in Mid April 2010, but severe winds damaged the initial windbreaks which have now been rebuilt. The following treatments are being applied: 1) no sprays (control); 2) Cu++ sprays to reduce citrus canker incidence; and 3) insecticide sprays to inhibit infestations of Asian leafminer (secondary effects). Main effects are windbreak versus no windbreaks. Citrus canker incidence is being estimated on multiple branches on each tree treated as the number of leaves per branch infected. Data collection is underway and continuing. We anticipate running these plots for 2-3 more years to collect all necessary data. The development of the Programmable leaf wetness controller (PLWC) software was written, debugged, is complete, and the control program is working well. New leaf wetness sensors were designed and constructed and calibrated. An electronic glitch was determined in the leaf wetness sensors and an new control circuitry was designed and constructed to overcome. The new design is currently under examination.