Influence of developmental stage and time of assessment on hot water weed control

Abstract

Summary The influence of plant developmental stage in hot water weed control was studied on the test weed Sinapis alba in field experiments. The dose was measured as thermal energy in the hot water (kJ m−2) and the response as reduction in plant weight. The energy dose for a 90% reduction in plant weight was 340 kJ m−2 at the two‐leaf stage, which is one‐third of the energy required for the same reduction at the six‐leaf stage. Treatment at an early stage saves energy, increases the driving speed and lowers the costs. Hard surface areas with naturally developed weeds were used to study the required treatment interval and the influence of time of assessment on the reduction in weed cover. The required treatment interval was 25 d on average, which is similar to that of flame weeding. A longer lasting effect requires a higher energy dose. A 50% higher energy dose was needed to obtain a 90% reduction in weed cover that lasted for 15 d instead of 7 d. After 3–4 weeks, hardly any reduction could be recorded because of regrowth of perennial weeds. However, hot water weed control has a potential on urban hard surfaces and railroad embankments, especially where the use of herbicides is restricted.

Effectiveness of Hot Water, Infrared and Open Flame Thermal Units for Controlling Weeds

“…In agreement with other studies (Hansson & Ascard, 2002;Kolberg & Wiles, 2002;Rifai eta/., 2002), this study demonstrated the importance of controlling weeds when they are in their early growth stage. For young weeds, the best treatment combinations were IR at 2.5 km h-1 for all species and OF at 1.5 km h-1 for all species except white mustard.…”

“…These percentages are all lower than those obtained with IR (all speeds) and OF (speeds of 1.5 and 2.5 km h-1 ). Compared with the results reported by Hansson & Ascard (2002), the HW unit performed poorly perhaps because the driving speeds were too fast for HW to be effective, and only one application was used.…”

“…Weeds in advanced stages of growth are more resistant to thermal weed control than are young seedlings. For example, Hansson & Ascard (2002) reported that 2.7 times more energy was required to kill white mustard at the 6-leaf stage than at the 2-leaf stage; with the driving speed required for the 2-leaf stage being 1.26 km h-1 and a slower speed of 0.44 km h-1 being necessary for the 6-leaf stage.…”

Interspecific Differences in Weed Susceptibility to Steam Injury

“…Among these tactics, the use of steaming promises to be useful because it efficiently transfers heat (Rask and Kristoffersen 2007) and reduces fire risk, especially in areas where dry plant residue is present (Hansson and Ascard 2002). However, there is limited information about the factors that determine the effectiveness of steaming as a POST weed control tactic.…”

Precise tillage systems for enhanced non-chemical weed management

“…Pre-emergence thermal weeding using hot water (Kurfess and Kleisinger, 1999;Hansson and Ascard, 2002), steam (Kolberg and Wiles, 2002) or recycling hot air (Bertram, 1996) prevent fire hazards in dry residues but are relatively costly. Hot water applied to narrow strips (20% of the field area) with small weeds would require approximately 1.6 m 3 water ha À1 and 20 kg propane ha À1 (derived from Hansson and Ascard, 2002). Combining strip flaming and punch planting (Rasmussen, 2003) allows for crop establishment without soil disturbance, which reduces and delays weed germination.…”