Abstract:

The larch needle brown rust (Triphragmiopsis laricinum(Chou)Tai) is a common larch fungal disease in the east of Jilin Province, China. The Larch (Larix olgensis) stands infected in the first year generaly grow normally, but in the second year they are affected seriously, the growth loss increases greatly in the stand infected lasting 2 years or over 2 years. Regresion equation was developed to predict disease index (X) and volume losses of growth/hm²(Y):Y=1.94/1+e^{5.49337-0.06893X}. The injury index was defined as 35. The equation of the economic threshold was developed to describe the relations among standing volume price(C), the efficiency of control (Q) and the cost of control (E):1.94C[1/1+e^{5.49337-0.06893X}-1/1+e^{5.49337-0.06893(1-Q)X}]-E=0.The equation of forecasting the mean disease index was:Y=5.185+3.2596X₁-0.42105X₂+0.08627X₃±6.9(Y:mean disease index, X₁:mean temperature in May of the current year, X₂:mean relative humidity of the current year, X₃:mean precipitation in September of the last year).

Key words: Larch needle brown rust, Injury index, Control threshold, Forecast