Date of this Version
Plant Dis. 98:1248-1252.
Aphanomyces cochlioides and Rhizoctonia solani are important soilborne
pathogens causing root diseases that are primary constraints to
sugar beet production in Nebraska, Colorado, and Wyoming. These
types of diseases are difficult to control because they are often not
noticed until substantial damage has already occurred. Efforts to manage
them would be more effective if techniques were available that
were more predictive than reactive. Therefore, a preplant soil test was
developed to estimate the relative pathogen populations in the soil and
to predict potential root disease problems later in the growing season.
Preplant soil samples collected from fields to be sown with sugar beet
were planted with a susceptible cultivar and tests were conducted for 1
month in the greenhouse. A preplant disease index was developed
based on the time period during the test that seedlings became infected
and was calculated on a 0-to-100 scale. Disease index values were
compared with yields obtained from the same fields after harvest.
Analysis of data collected for 5 years (2003 to 2007) with analysis of
covariance revealed a strong relationship between the preplant disease
index values and recoverable sucrose and root yields but not sucrose
concentration. Results indicated that, for each unit increase in the
preplant disease index, root yield decreased by 0.27 metric tons (270
kg) per hectare (P < 0.05, R2 = 0.44) and recoverable sucrose decreased
by 49 kg/ha (P < 0.05, R2 = 0.45). We concluded that this
preplant soil test can accurately predict root disease potential due to R.
solani and A. cochlioides, and has the potential to help producers make
effective management decisions in production fields using the index
procedure. This soil assay has additionally provided new information
on the biology, incidence, and distribution of root pathogens in production
fields throughout the Central High Plains.