Tech Notes Issue 4

Ecology and Control of Poa annua in Overseeded and Non-overseeded Bermudagrass: Part I

The major winter weed in overseeded and nonoverseeded couchgrass is Poa annua. It is common throughout   Australia and South Africa.
Although both annual and  perennial biotypes exist of Poa   annua, the predominant biotype that occurs in couchgrass is the annual type. For timing preemergent herbicide treatments  the conditions favorable for Poa annua germination might be valuable.

In a recent paper¹, 8 "annual" Poa annua biotypes were collected from the southeastern United States and the seed harvested. Conducting standard seed germination studies the researchers found that the optimum temperature for Poa annua seed germination was 19 C (day)/10 C (night) (Figure 1). Significant Poa annua germination also occurred at 29 C (day)/19 C (night). I would assume as autumn approaches and temperatures drop below,  germination  will start and increase to reach optimum germination around 19/10 C.

Additionally, the germination studies  were done under different photoperiods (hours of daylength)  across the various temperature regimes. The striking result from  the study is the high percentage of Poa annua seed that germinated under complete darkness  (Figure 2, 0/24 treatment). The  common perception that weeds that produce a small seed need light to germinate does not apply  to Poa annua. The implication is  that Poa annua will germinate in   your couchgrass even under a full undisturbed canopy cover.

In the next issue we will look at controlling Poa annua.

Literature Cited:
1. McElroy, J.S., R.H. Walker, and  G.R. W. Edzard van Santen. 2004. Annual bluegrass (Poa annua) populations  exhibit variation in germination
response to temperature, photoperiod, and fenarimol. Weed Science 52:47-52.

Figure 1. Effect of temperature (day/night)on Poa annua seed germination (average of 8 annual biotypes)¹

 

Figure 2. Effect of photoperiod on Poa annua seed germination (average of 8 annual biotypes)¹

 

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