The southern chinch bug, Blissus insularis (Image 1.) is the most destructive sucking pest of St. Augustinegrass. Nymphs and adults feed on plant sap, leading to wilting, chlorosis, stunting and ultimately plant death. The initial feeding injury results in small patches of dead grass which eventually will become larger dead patches in lawns that are difficult to repair (Image 2). This damage can mimic other lawn problems so it is always important to identify the pest before starting a management plan. This pest remains active from March to October in northern Florida where it can complete 3 to 4 generations, while 7 to 10 generations occur in southern Florida where it may remain active throughout the year.
Thatch (Image 3.) is the layer of dead and living grass tissues, stolons intermingled with organic matter to provide a suitable habitat for chinch bugs. This is a problem in the chinch bug control because of the tendency of binding of the chemicals applied for controlling chinch bugs to the thatch layer. Removal of thatch by vertical mowing (verticutting and topdressing) can alleviate thatch and related chinch bug problem as turfgrass has the ability to minimize compaction recover the wearing losses during thatch management. We are trying to artificially induced thatch in a field plot experiment by applying excessive fertilizer and overwatering so we can compare the differences in chinch bug densities in the plots where thatch is being induced compared to plots that are managed like a well maintained home lawn. Our first year of research indicates that higher numbers of chinch bugs were present in the plots where thatch was being induced by using higher N rates. Once we get a layer of thatch in these experimental plots, thatch management will be done by doing vertical mowing and its effect on turf health and insect densities will be noted and reported in a future article.
We conducted a lawn survey in summer of 2011 to study the association of chinch bug densities with various abiotic and biotic factors present in St. Augustinegrass lawns. We found a relationship between chinch bug density, turf color and grass density this supports the commonly held belief that healthy turf can withstand the insect pressure better. The number of common predators like big eyed bugs and ants increased with chinch bug densities indicating their increased predation efficiency on chinch bugs. Big eyed bugs are very important predator of chinch bugs and can be easily mistaken for chinch bugs. Big eyed bugs are shiny black colored insects with large prominent eyes; nymphs also resemble the adults except absence of wings. Chinch bugs have black body with grayish white wings with a conspicuous black triangular spot on the outer margins of fore wings; nymphs are reddish brown to black in color with a conspicuous transverse white colored band on the dorsal side of their abdomen. So to answer our question- proper identification tools are necessary for making biological control successful by conserving natural enemies.
We are currently testing the effect of different mowing height on chinch bug densities. We hypothesize that lower than recommended heights will cause plant stress and make the turf susceptible to insect damage. The results of this study will be reported in future articles. We are also comparing the differences in infestation levels among the plots where clippings were recycled on the lawn or not recycled by bagging and removing. We have not seen any chinch bugs being transferred by clippings from the infested to non-infested plots. Grass clippings do not contribute to thatch induction as these are low in lignin content and can breakdown easily, this helps return nutrients to the lawn.
We studied the interactions of nitrogen fertilizers (rates and sources) on chinch bug survival and population dynamics in a laboratory feeding trial. The insects were fed on grass plugs receiving different rates of N for one generation. Our results indicated that higher survival and faster development rates were observed on treatments having higher N rates (6 lbs. N/1000 sq. ft/year). The effect of fertilizer source was not significantly different. Responsible use of N fertilizer using current UF/IFAS recommended rates (2-4 lbs N/1000 sq. ft/year) will make plants less susceptible to insect damage. Be sure to follow all local ordinances and Best Management Practices (BMPs) involving fertilizer applications.
If you need assistance identifying insects you find in your landscape please contact your local county extension office for assistance. Special thanks to the USDA/NIFA PMAP (00076304-00085594-2010), for funding the project “Developing, demonstrating and disseminating cultural control recommendations for chinch bugs.”
Authors: Navneet Kaur, Eileen A. Buss, and Jennifer L. Gillett-Kaufman
Entomology and Nematology Department, University of Florida, Gainesville, FL 32611