Articles
A TWELVE YEAR SUMMARY OF THE MARYBLYT PREDICTION SYSTEM ON JONATHAN APPLE IN MARYLAND AND WEST VIRGINIA
By 1985, this cooperation resulted in the development of the MARYBLYT prediction system by Steiner and Lightner (1990, 1992).
At AFRS, all weather and research data were collected in blocks of the susceptible apple cultivar Jonathan.
Temperature and rainfall data were collected with a remote weather station (Automata, Grass Valley, CA), and a hygrothermograph for backup.
At the Western Maryland Research and Education Center (WMREC) fire blight observations were made in a block of 8-year-old Gala apple trees in 1990, and on 9- to 10-year-old Rome trees during 1984-85. The remaining observations (1986–89, 1991–95) were collected in grower orchards on 11- to 18-year-Old Rome and Jonathan trees near Smithburg, Maryland.
Between 1984 and 1995, among the 14 primary infection events predicted by the model at 2 sites (Maryland and West Virginia) in 9 of the 12 years, blossom blight symptoms appeared 11 times on or within 1 day, twice within 2 days, and only once within 3 days of the predictive date (Table 1). In four instances (1991, 1992), blossom blight was predicted, but none occurred, whereas in 1995 not a single infection (1) period was recorded.
All these were due to unfavorable weather conditions between infection and symptom appearance.
No spurious symptoms were ever observed, i.e. no blossom blight symptoms ever appeared without the MARYBLYT system predicting such symptoms.
Similar results were reported by Jones (1992) for apple in Michigan.
A summary and comparison of the epiphytic inoculum potential (EIP) for all 12 years is presented in Table 2. The number of I periods varied from none in 1985 to 5 in 1994. The general occurrence and severity of blossom blight correlated positively with the EIP at first or second I dates, e.e.
EIP below 300 resulted in light to no blossom blight, whereas EIP above 300 resulted in moderate to severe blossom blight (1985, 1993, 1994). This correlation agrees with the observation by Zoller and Sisevich (1979) that 40% of pear blossoms contained Erwinia amylovora bacteria at 336 cumulative degree hours above 18.3 C (65.0 F).
The MARYBLYT prediction model proved to be quite accurate in predicting the appearance of natural blossom blight symptoms in Maryland and West Virginia.
The most important aspect of the program is the ability to predict outbreaks of fire blight based on tree phenology, pathogen status, and weather conditions.
This should improve the timing of antibiotic applications and surely eliminating unnecessary sprays and reducing selection pressure on the bacterium to develop resistance to streptomycin.