Vol. 54—2000 - NorthEastern Weed Science Society

BIOLOGICALLY BASED WEED CONTROL STRATEGIES FOR Poa annua
MANAGEMENT USING Xanthomonas campestris pv. poannua
S. Mttra and T. E. Vrabel'
ABSTRACT
Annual bluegrass (Poa annua L.) is a widespread serious weed species of
golf turf. Its competitive nature when managed at close mowing heights on golf
course greens and fairways allows annual bluegrass to outcompete desired
species such as creeping bentgrass (Agrostis palustris Huds.) and take over as
the dominant species. The susceptibility of annual bluegrass to environmental
stresses and diseases as well as its undesirable characteristic of prolific seed
head production in early summer make it a major turf management problem for
the golf course superintendent.
Eco Soil Systems, Inc. initiated in 1998 an EUP to evaluate for
comrnerclalizlnq a strain of Xanthomonas campestris pv. poannua that is
formulated as a liquid containing live active bacteria in high concentrations. This
product has the flexibility of bein9 marketed as a packaged material delivered
directly to the end user or, in the near future, increased at the application site in
conjunction with the BioJect on site fermentation system. This report is a
summary of the findings from the applications made in 1999. The objective of
the application program is to cause significant levels of infection in annual
bluegrass plants which would weaken them and make them more susceptible to
mortality caused by cold stress over the winter, and by heat and drought stress in
the earily summer. Applications in 1999 beqan when mid day air temperatures
reached 18 degrees C.
Infection rates were similar to those seen in 1998 with leaf tissue analysis
of Poa annua plants sampled from treated golf courses shows an 80% or better
infection success rate. Initial infection symptoms are seen as an etiolation of
seed stalks and stems that is followed by subsequent chlorosis and epinasty of
affected plants. Infection and symptoms occurred in both the annual (P. annua
ssp. annual and perennial (P. annua ssp. reptans) annual bluegrass subspecies.
Annual bluegrass infection and mortality levels were greater when applications
were made at temperatures between 24 and 31 degrees C and turf was
maintained at lower irrigation levels following treatment. Applications of growth
regulators such as paclobutrazol prior to Xanthomonas application weakened the
Pas annua and increasedeffectiveness.Desirablespeciessuchas creeping
bentgrass (Agrostis palustris Huds.) and velvet bentgrass (Agrostis canina L.) are
not affected by Xanthomonas campestris pv. Poannua regardless of growth
stage.
'Eco Soil Systems, Inc., 10740 Thornmint Road, San Diego, CA 92127
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