Time and Temperature Requirements for Weed Seed Thermal Death

Abstract

Mortality of weed seeds at temperatures of 39, 42, 46, 50, 60, and 70 C was recorded through time under controlled laboratory conditions similar to those of soil solarization for six weed species: annual sowthistle, barnyardgrass, black nightshade, common purslane, London rocket, and tumble pigweed. Time and temperature requirements for thermal death varied considerably among the species studied. Barnyardgrass, London rocket, and annual sowthistle were more susceptible to heat treatment than black nightshade, common purslane, and tumble pigweed. Temperatures of 50 C and above were lethal for seeds of all species. Common purslane seeds were unaffected at 46 C and below, tumble pigweed and barnyardgrass seeds were unaffected at 42 C and below, and black nightshade seeds were unaffected at 39 C. Nonlinear models for mortality as a function of duration of heat treatment were developed for each species at each temperature at which mortality occurred. These models provide an empirical relationship for the construction of field-applicable decision models that could predict the accumulation of time and temperature combinations for effective solarization of weed seeds.

Effect of different solarizing materials on weed suppression and lettuce response

“…The high SS sensitivity of annual weeds such as speedwell, henbit, corn poppy and common sowthistle seems to agree with literature reports, whereas previous statements contrast with strong suppression of common purslane and resistance of amaranth species observed in this study (Candido et al 2008;Dahlquist et al 2007;Stapleton and DeVay 1995). The lesser presence of amaranth species in nonsolarized soil could be explained by the strong competition of Canada thistle; also, the increased amaranth infestation in the plots solarized with the BDF mulch may be attributed to the lower thermal effect of this material.…”

“…The time and temperature needed for thermal death of weeds vary considerably among different species, but temperatures above 50°C are generally lethal to some weed seeds (Dahlquist et al 2007). Under appropriate climate conditions, SS can provide an effective and environmentally safe suppression of weeds under field and greenhouse conditions (Elmore 1991;Yaduraju and Mishra 2004).…”

Effect of desiccation temperature on viability of immature dandelion (Taraxacum agg.) seeds dried in mowed inflorescences

“…Water content of seeds decreases with maturation (Bewley and Black 1983) and ripening dandelion seed is presumably sensitive to high temperatures because its water content is higher than in ripe seed. This would be consistent with the studies of imbibed seeds (Egley 1990, Dahlquist et al 2007 which showed that temperatures above 50°C are fatal for seeds of twelve weed species, some of which (Echinochloa crus-galli L. Beauv., Sisymbrium irio L., Sonchus oleraceus L.) are killed within few hours even at temperatures between 40-50°C.…”

‘Formiguers’, a historical system of soil fertilization (and biochar production?)

“…The latter values would be lethal for most seeds and propagules (Dahlquist et al, 2007) and would therefore be an important tool for farmers when clearing a piece of forest for agriculture, as recognised in old documents (de Roxas, 1808). Similar temperatures may be reached in the soil under the 'formiguer' down to a depth of 1-2 cm (Giardina et al, 2000b).…”