Four categories of billbug (Sphenophorus parvulus Gyllenhal) resistance were identified and contrasted in terms of anatomical, morphological, and physiological characteristics of 12 Kentucky bluegrass (Poa pratensis L.) cultivars. Discriminant analysis was used as a separatory procedure to determine the relative importance of these plant characteristics to observed billbug resistance and to construct a prediction procedure for potential billbug resistance classes. Variables measured from field-, controlled environment-, and greenhouse-grown plants were analyzed for the most biologically revealing characteristics of potential billbug resistance. Separatory discrimination indicated that cultivars exhibiting moderate and high billbug resistance had tougher tissue than tolerant or susceptible cultivars. Tolerant and highly resistant cultivars differed from those susceptible and moderately resistant by concealing billbug injury. Development of a predictive classification procedure was promising, with percent correct classification ranging from 67% to 94%, depending on number and type of discriminating variables analyzed.
A cultivar and blend trial of Kentucky bluegrass (Poa pratensis L.) demonstrated differential cultivar responses to larval infestation and injury by bluegrass billbug (Sphenophorus parvulus Gyllenhal). Correlation between billbug injury ratings and billbug larval density was r = 0.92. Injury ratings and larval density for blends approximated mean response for cultivars in pure stands. These results suggested that blending could be beneficial in reducing injury symptoms, if appropriate cultivars were selected.
A trial of 38 cultivare of Kentucky bluegrass (Poa pratensis L.) demonstrated genetic differences to an infestation of bluegrass billbug. The correlation coefficient between injury ratings and billbug larval density in sod samples was r = 0.73. Thatch accumulation was not significantly correlated (r = 0.31) with billbug density.
Sixty Kentucky bluegrass (Poa pratensis L.) cultivars and experimental lines and 24 bluegrass blends were investigated for thatching tendency. Cultivars and experimental lines differed in thatch accumulation during the course of this 5-year study. Increasing N level from 10 to 20 g N m-2 season -1 had no effect on thatch accumulation. Thatch accumulation in cultivars and experimental lines was correlated (r = 0.87) to verdure, indicating vigorous cultivars had greater thatching tendency. Thatching tendency of cultivars was correlated (r = 0.74) to their total cell-wall content expressed on a mg dm-2 basis. Accumulation of thatch in blends approximated the mean accumulation for cultivars growing in pure stands. These results indicate a potential for reducing thatch accumulation in Kentucky bluegrass lawns through blending of appropriate cultivars.