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Plantwise Technical Factsheet

short-spiked canarygrass (Phalaris brachystachys)

Description

Annual Phalaris species have leaves with an open leaf-sheath, membranous ligule and flat blade with auricle; upper leaves have a swollen leaf-sheath which envelopes the inflorescence before flowering; the inflorescence is a compact panicle; the spikelets are composed of three flowers; the upper one fertile or sterile, the two lower ones sterile, reduced to two lemmas; the two glumes are the same size, longer than the flowers, coriaceous, with a winged keel (Jauzein and Montegut, 1982; Talavera, 1987).

The leaves of Phalaris seedlings are glabrous, pale green, with a reddish pigmentation at the base (Jiménez et al. 1997). To distinguish between the Phalaris species in the seedling stage it is necessary to observe the caryopsis from which they emerge. In P. brachystachys and P. minor the spikelets disperse separately, while P. paradoxa several spikelets remain together (as a group), with the fertile one in the middle. The lemma of the caryopsis of P. paradoxa is glabrous, which it is not in the other species (Jiménez et. al. 1997).

In the flowering stage, P. brachystachys has a short panicle 3 to 3.5 cm long, 1.5 cm wide, the spikelets densely crowded and overlapping. The glumes are 7-8 mm long, acute, flattened, the upper part with narrow papery wings and a dark-green stripe on each side at the base of the wings. Fertile lemma about 5 mm long. The sterile spikelets are 4-6 mm long.

Prevention and control

Cultural Control

Date of crop sowing
Delaying crop sowing enables the main flush of Phalaris seedlings, which emerge after the first autumn rains, to be controlled before planting. Additionally, in late winter or early spring-sown crops, temperatures are higher, crops grow more quickly, and are more effective at suppressing weed growth. However, crop yields are generally reduced by late spring-sowing.

Crop density
Increased crop seed sowing rates result in higher crop densities which are able to suppress weed growth. For example, in winter cereals where infestation by Phalaris spp. is often a problem, high seed sowing rates (>170 kg/ha) effectively reduce the density of these weeds. Conversely, low seed rates of wheat or barley (60-80 kg/ha) contribute to a rapid increase in populations of Phalaris spp..

Crop rotation
This involves replacing crops in which Phalaris control is difficult or expensive (winter cereal), with other crops with a different growth cycle (sunflower), thus avoiding Phalaris infestations, or in which a high degree of control can be achieved (rapeseed). In the Mediterranean region, Phalaris infestations in winter cereal were greatly reduced by introducing spring-sown sunflower into the rotation.

Roguing
Mature Phalaris plants at the flowering and seed setting stage are taller than wheat and barley crop plants. Thus, roguing may be practised to reduce or prevent seed return to the soil seed bank. Normally this practice is only feasible when the weed density is low <1500 plants/ha, which may take 3-4 h to hand-rogue). Herbicide-roguing involves the application of a chemical (often glyphosate) to the top of the Phalaris plants with special gloves moistened by a herbicide solution. Chemical roguing is much faster than hand roguing as it does not involve the removal of the plant from the field.

Chemical Control

Several herbicides applied pre-emergence or early post-emergence have been used to control Phalaris spp. in winter wheat and other crops. These include isoproturon, methabenzthiazuron, terbutryn and pendimethalin. More recently specialized post-emergence graminicides have been developed and used to control Phalaris spp. (Mirkamali, 1993). Tralkoxydim is effective, fenoxaprop-p-ethyl may be applied in many dicotyledenous crops and in wheat, clodanifop-propargyl is effective in triticale and durum wheat (Welsh and Popay, 1994). Cycloxydim, haloxyfop, fluazifop and sethoxydim are highly selective graminicides that can be used in many broad-leaved crops. The use of herbicides to control P. brachystachys in cereals in Spain is described by Gonzalez-Diaz et al. (2009) and Zambrano-Navea et al. (2012).

Resistance to herbicides has developed in some populations. Avci and Uygur (2008) report resistance to several herbicides used in wheat in Turkey.

Hosts / species affected

Annual Phalaris spp. (P. paradoxa, P. brachystachys and P. minor) are actual, or potential weed problems in most annual winter (autumn-sown) crops of temperate regions and annual summer (spring-sown) crop in colder, subtemperate regions within the geographical range of these species. 

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