Fertilization Effects On Resistance of Captiva St. Augustinegrass to Southern Chinch Bugs and Gray Leaf Spot.

Captiva is a recently released variety of St. Augustinegrass which is resistant to the southern chinch bug, Blissus insularis Barber.  Soil nutrient levels can affect the level of insect damage as well as modifying the expression of resistance.  We evaluated the influence of variable-rate N and P fertilization on the resistance of Captiva to insects and disease.  Fertilization enhanced the growth and establishment of sprigs, and growth rates were proportional to fertility level.  Tissue N and P content increased with increasing fertilization rate.  Fertilization did not have a significant effect on host-plant resistance to southern chinch bug. There were no significant differences in female survival, male survival, or reproduction between fertilization rates.  However, incidence and severity of gray leaf spot disease (Pyricularia grisea (Cooke) Sacc.) increased with fertility level. Gray leaf spot development was highly correlated with tissue nutrient content, with r=0.84 and r=0.92 for the relationships between tissue-N and GLS incidence and severity, respectively.  Delineation of the association between GLS and plant nutrition indicates that sod managers and homeowners should be advised to avoid excessive fertility in the establishment and management of Captiva.