Because environmental factors facilitating the breaking of dormancy of seed of catclaw mimosa (Mimosa pigra L. ♯ MIMPI) under field conditions were unknown, the effect of constant temperatures (2 to 44 C) on germination of scarified and unscarified seeds, and the effect of diurnally fluctuating temperatures on unscarified seeds were examined. Temperatures fluctuated diurnally by 10 and 20 C in these latter experiments. Germination was less than 10% at all constant temperatures except 44 C, which had 40% germination. Scarification increased germination to 100% at constant temperatures greater than 12 C. Germination of unscarified seed was significantly lower (0 to 23%) when day/night temperature ranges fluctuated by 10 C than when they fluctuated by 20 C. Optimum temperature for germination was 40/20 C, where 93% germination occurred within 4 days.

The timing of weed seedling emergence relative to the crop is important in planning and optimizing the time of weed control, but very little work has been done to predict seedling emergence of tropical weed species, especially in low-input and small-scale farms. We developed a simple model based on hydrothermal time to predict seedling emergence of tropic ageratum. Hydrothermal time at 2-cm soil depth was calculated from soil moisture and soil temperature simulated from several micrometeorological and soil physical variables. The model was developed using 5 yr of field emergence data from a continuous corn–cassava production system in southwestern Nigeria. Percentage of cumulative seedling emergence from the 5-yr data set was fitted to cumulative soil hydrothermal time using a Weibull function. The predicted cumulative emergence curve significantly matched observed field emergence (r 2 = 0.83). Model predictions were evaluated with root mean square error (RMSE) using four field emergence data sets from southeastern Nigeria (RMSE ≤ 10.1) and Los Banos, Philippines (RMSE = 8.9). RMSE values ≤ 10 indicated that predictions represented observations well. With such models, extension personnel working on tropical soils, especially in West Africa, may be able to provide additional advice to farmers on the appropriate time for the management of tropic ageratum.

Cogongrass is a noxious perennial grass that has invaded many countries in the tropical and subtropical regions of the world. Its management has been a significant challenge because of large rhizome and bud reserves in the soil. The emergence pattern of this weed under field conditions has received little attention. Field trials were conducted in 2002 and 2003 in the humid forest zone of southeastern Nigeria to model shoot emergence. The experiment had four treatments: (1) count and tag crop-free cogongrass shoots, (2) count and suppress crop-free cogongrass shoots with paraquat, (3) count and cut crop-free cogongrass shoots, and (4) count and cut cogongrass shoots in cultivated corn. The rationale for these treatments was to determine the effect of different monitoring techniques on shoot emergence of cogongrass. The development of the model was based on hydrothermal time, which was calculated from soil moisture and soil temperature at a 2-cm depth. A Weibull function was fitted to cumulative percent shoot emergence values of Treatment 4 and hydrothermal time. The model closely fit the observed pattern of cogongrass shoot emergence (r 2 = 0.95, n = 36). It also predicted shoot emergence satisfactorily in six treatments (r 2 > 0.85, P < 0.001, n = 7 in each treatment) that simulated farmers' practices in southwestern Nigeria. This is the first model developed for cogongrass shoot emergence based on hydrothermal time under field observations. The model should facilitate further analyses of cogongrass emergence patterns and the timing of its management.