Effectivity of reduced dosages of herbicides to weed constitution of spring barley i

The barley variety 'Ansis' was cultivated in the field at the State Stende Plant Breeding station, 2001-2004, in sod podzolic and sod-gleysolic sand loamy soil with neutral soil response. Average annual dicotyledonous weed infestation level in trial years differed: 106.9 weed plants per m 2 in the year 2001; 213 in 2002; 22.7 in 2003, and 216 in 2004. Thlaspi arvense (L.) was the most widespread weed in 2001, 2002 and 2004 trial years, but Chenopodium spp. was dominant in 2003-2004, and Polygonum convolvulus (L) in 2004. Lamium spp. was also widespread in all-trial years, Viola arvensis (Murray) in 2001, 2002 and 2004; Stellaria media (L.) in 2002 and 2003, and Capsella bursa-pastoris (L.) in 2002 and 2004. The effect of herbicides is usually calculated as decrease in weed number and as decrease of fresh weight of weeds (% to control or % to initial amount). In this article the ratio of one weed's weight after herbicide use to one weed's weight in control is recommended for comparing effectiveness of the doses of herbicides to weeds. The effectiveness of herbicides is estimated as a special factor EfKo. The reduction of herbicide doses to one half or one fourth of recommended dosage usually had no significant effects on weed control.