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Project description

Decision support system for IPM of prune brown rot. (02DS021)
Program UC IPM competitive research grants program
T.J. Michailides, Plant Pathology, UC Davis/Kearney Agricultural Center
Host/habitat Prunes; Stone Fruits; Tree Crops
Pest Monilinia fructicola; Brown Rot Monilinia fructicola
Discipline Plant Pathology
Decision Support
Start year (duration)  2002 (Three Years)
Objectives Obtain information for constructing and completing the uncompleted parts of the Decision Support System for IPM of Prune Brown Rot (DSS-PBR) (http://tjm.uckac.edu/).

Test and improve DSS-PBR by using observed and experimental data from multiple locations.

Final report We have completed construction of the Decision Support System for IPM of Prune Brown Rot (DSS-PBR) located at the University of California, Kearney Agricultural Center. The DSS-PBR is accessible to growers and the general public at http://tjm.uckac.edu. This system provides decision supports relevant to timing of fungicide sprays and other orchard cultural practices to reduce risk of brown rot epidemics in prune orchards. The disease management decisions are based on 15-day periods, starting at bloom until harvest. The system utilizes inputs by users such as the average ambient temperature, the estimated inoculum potential in orchards, weather forecasts relevant to rainfall, and crop growth stages. During the bloom period, the DSS-PBR can help growers make decisions on whether a fungicide spray is needed and when it is needed. In midseason, decision supports take into account fruit thinning and irrigation practices to reduce the risk of disease inoculum accumulation in orchards. In the late season, the system provides decision support on needed fungicide spray(s) to reduce the risk of fruit rot at harvest. Generally, the system is easily accessed and used. Simply, the user, after logging in, needs to answer several easy questions. Based on the answers given, the system will automatically provide three statements: a "Note," a "Warning," and a "Recommendation" to guide growers in their decision to manage brown rot. Multi-year and multi–location field experiments showed that the incidence of latent fruit infection at the pit hardening stage significantly correlated with that at the late stages and with the incidence of fruit rot at harvest. Thus, determination of inoculum potential in early season is important to decide on the timing of fungicide application. Fruit thinning and improper timing of irrigation in an orchard can result in high inoculum potential due to increased sporulation of Monilinia fructicola on thinned fruit, which eventually cause high incidence of latent infection on green fruit. In a normal year, spore trapping, using Burkard spore traps showed spore concentration of M. fructicola in the air to be relatively high during bloom and at very low levels in midseason. Only orchards with high level of latent infection showed an increased spore concentration in the air in late season.

In the third year of the project, we continued conducting experiments in 10 prune orchards with artificial inoculation to confirm our previous conclusions about the seasonal pattern of fruit rot development and about the best time period to determine fruit latent infection. Artificial inoculations were conducted at different growth stages. In each inoculation, 20 branches were selected in each orchard, and each immature fruit was inoculated with 0.1 ml of Monilinia fructicolaconidial suspension by injection. The inoculated branches were checked periodically to determine the percentage of fruit rot, and fruit rot development curves for different inoculation dates were obtained. The linear regressions on inoculation date and fruit rot developmental rate for 2002 and 2004 were compared. In order to confirm the seasonal pattern of fruit susceptibility on peaches and nectarines, we also conducted field experiments at University of California Kearney Agricultural Center (KAC). Inoculations were conducted by spraying M. fructicola conidia suspension on blossoms and immature fruit, followed by maintaining the inoculated branches under high humidity for 16 hours. Inoculations were performed at different blossom and fruit developmental stages. The percentage of fruit rot per inoculated branch was determined at harvest. Seasonal patterns of fruit susceptibility on peaches and nectarines were similar as that on prunes we observed previously.

At midpoint of the project, we have basically completed modification and extension of the existing DSS-PBR system proposed in objective 1. We also have obtained needed information on the best time period to determine the fruit latent infection. This information can be used to help growers in decisions on fungicide application in mid-season to reduce risk of infections on immature fruit. We have tested some already—completed parts of the DSS-PBR system by using field experimental and observation data. We conducted experiments on peach and nectarine susceptibility similar to those on prunes and concluded that seasonal patterns of peach and nectarine susceptibility are similar with the susceptibility on prunes. Thus, the main principles that were used to construct the DSS-PBR system could be also extended on other stone fruits.

In the second year, we conducted experiments in 15 prune orchards with natural infections of brown rot. Blossoms once and fruit periodically were collected in each orchard to determine incidence of latent infection caused by M. fructicola. Incidences of fruit rot were also determined before harvest in each orchard. Incidence of blossom infection did not correlate with incidence of latent infection of immature fruit for any sampling or fruit rot at harvest. However, incidences of latent infection of fruit between any two fruit samplings after mid-season significantly correlated. Incidence of fruit rot at harvest significantly correlated with those of latent infection of immature fruit in the early and late developmental stages, but not in the middle stage. Sprinkler irrigation resulted in significantly longer dew periods than flood irrigation in prune orchards. The best time to determine the incidence of latent infection (ILI) of immature fruit would be from mid-May to mid-June. A chronological decision-support diagram was developed to guide growers as to when to determine latent infection. This diagram has been based on orchard inoculum potential, irrigation type, and timing of fruit thinning. The existing decision support system for IPM of prune brown rot (DSS-PBR) has been updated. The decision models used for the period of April 15 to July 15 have been essentially completed. Focus during this period of disease management is placed on decisions relevant to fungicide application, time of determining latent infection of immature fruit, irrigation, and fruit thinning.

In the first year, we conducted inoculation experiments in 10 orchards. Inoculations were conducted five times from full bloom to the first harvest stages. For each inoculation, 20 branches bearing 30 - 40 fruit were selected, and each fruit was inoculated by injection with the 0.1 ml of suspension of M. fructicola (10,000 conidia/ml). The percentage of fruit rot per branch was determined at different times during the season. The earlier the fruit inoculation, the slower development of fruit rot recorded. A linear regression between rate of development of fruit rot (% fruit rot per day) and the days after full bloom was obtained. A diagram was produced to guide growers when to determine latent infections. Three different recommendations can be given in this diagram relevant to determining latent infection, such as not recommended, recommended, and strongly recommended. These recommendations also take into account low, moderate, and high levels of spore inoculum potential in dried plum (prune) orchards. A new decision support model for timing of fungicide spray(s) to reduce risk of latent infection during mid-season has been added in the existing DSS-PBR system. This addition was based on the experimental data obtained in 2002. In order for the Web site user to obtain a recommendation on fungicide application he needs to input the current date and the corresponding latent infection level in his orchard. Four recommendations can be provided by the system as following: do not spray, wait, check the weather as a reference, and spray immediately. An orchard-based database for dried plum orchards in different counties in California is now under construction by using the Geographic Information Systems (GIS) techniques.
See also http://tjm.uckac.edu/

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