EFFECTS OF CHEMICAL SEEDHEAD SUPPRESSION ON THE CARBOHYDRATE STATUS, QUALITY, ROOTING AND HEAT STRESS TOLERANCE OF ANNUAL BLUEGRASS (POA ANNUA L.) (ASSIMILATES, PARTITIONING, TURFGRASS)

Studies were conducted from 1981 through 1984 to determine if elimination of Poa annua seedhead production using mefluidide or Aqua-Gro('(REGTM)) would result in increased carbohydrate partitioning to the roots of annual bluegrass. Investigations were also carried out to determine if increased carbohydrate flow to roots would result in a better rooted plant with improved tolerance to summer heat stress.;Under favorable environmental conditions, April mefluidide application at rates as low as 0.07 kg a.i./ha provided excellent seedhead suppression. The wetting agent Aqua-Gro('(REGTM)) did not provide acceptable seedhead suppression.;Seedhead suppression associated with mefluidide application (0.14 or 0.21 kg a.i./ha) resulted in increased fructose and glucose in Poa annua roots compared to untreated turf during the seedhead development period. Mefluidide had little effect on the fructose, glucose, sucrose, or fructan content of leaf and stem tissue.;April mefluidide treatment reduced turfgrass quality for three to four weeks after application due to leaf tip discoloration. Following initial phytotoxicity, treated turf exhibited quality superior to the control for five to six weeks due to improved color, density, and finer texture.;Late fall mefluidide application is not recommended due to extensive shoot dieback during the winter and loss of Poa annua cover the following spring.;Seedhead inhibition in response to mefluidide application (0.14 kg a.i./ha) resulted in root elongation superior to the control for four weeks following late March 1983 application. Mefluidide applied at 0.21 kg a.i./ha during April 1984 enhanced root elongation for four of eight weeks during May and June.;In 1983, the maximum rooting depth of untreated turf decreased significantly during seedhead emergence while the maximum rooting depth of mefluidide treated turf increased during the same time period.;Increased partitioning of fructose and glucose to the roots of Poa annua during April did not confer improved heat tolerance during June, July, or August. The increased carbohydrate content of treated Poa annua roots during early spring was probably depleted during heightened root growth immediately following mefluidide application.;Spring mefluidide treatment is a sound cultural practice for improving the early season quality of fairway Poa annua.