The critical period of weed control (CPWC) for ‘Pardina’ and ‘Brewer’ lentil
was determined in field experiments near Pullman, WA, in 2008 and 2009.
Trial treatments were kept either weed free for periods of 0, 14, 25, 35,
45, 60, 75, or ∼90 d after emergence (DAE), or weeds were allowed to grow
before removal for periods of 0, 14, 25, 35, 45, 60, 75, or ∼90 DAE.
Averaged across varieties, lentil with season-long weed interference had
29.5 and 32% seed yield reduction compared to weed-free lentils in 2008 and
2009, respectively. When measured at crop maturity, a 1% loss in lentil seed
yield resulted from each 5.68 g m−2 of dry weed biomass. Based on
a 5% yield loss threshold, the CPWC for lentil was estimated to be from 270
to 999 growing degree days (GDD), 22 to 57 DAE, or crop growth stage (CGS) 7
to the early pod stage during 2008. In 2009, the CPWC was 624 to 650 GDD,
with no occurrence of a CPWC when estimated using DAE and CGS. Spiny
sowthistle emerged and competed with the lentil crop later in the growing
season than mayweed chamomile, indicating that mayweed chamomile may be an
earlier and stronger competitor than spiny sowthistle.