The effects of common cocklebur (Xanthium pensylvanicum Wallr.) on soybean [Glycine max (L.) Merr. ‘Wells′] development and seed yield were investigated at Urbana, Illinois, from 1974 through 1977. Increased densities of common cocklebur reduced soybean seed yield, total dry weight, and number of pods per plant. Under full-season competition, one common cocklebur/3 m of row reduced soybean seed yield by 3 to 12%. Soybean seed yield, total dry weight, and number of pods per plant increased as the length of time from soybean emergence to common cocklebur emergence increased. Common cocklebur emerging 4 weeks after soybean emergence reduced soybean seed yield by 7%. As duration of competition with common cocklebur increased, soybean seed yield, total dry weight, and number of pods per plant decreased. The reduction in soybean seed yield was less than 10% when common cocklebur was removed 6 weeks after soybean emergence. Effects of common cocklebur competition with soybeans in Illinois were similar to those observed in the southern United States.

Absorption and translocation characteristics of both root- and shoot-applied mefluidide N-[2,4-dimethyl-5-[[(trifluoromethyl) sulfonyl] amino] phenyl] acetamide were determined in soybean [Glycine max (L.) Merr. ‘Wells’], common cocklebur (Xanthium pensylvanicum Wallr.), and giant foxtail (Setaria faberi Herrm.). Absorption of 14C-mefluidide was greater through the foliage than the roots of all plant species. Rate of leaf absorption and translocation of 14C initially was greater in giant foxtail than in either soybean or common cocklebur, but these processes failed to increase greatly with time in giant foxtail. Absorption and translocation increased over time in soybean and common cocklebur. Soybean absorbed slightly greater quantities of 14C-mefluidide than common cocklebur, but by 8 days after labeling, common cocklebur translocated approximately 47% more radio-label out of the treated leaf than soybean. The foliar-applied 14C-label appeared to move in the phloem along with the assimilate stream in all species, mainly to areas of high metabolic activity. 14C was associated with the root systems and/or nutrient solutions of soybean and giant foxtail, but not of common cocklebur. Exuded material chromatographed as mefluidide. Movement of 14C-label in all root-treated plants appeared to be confined within the xylem with older tissue containing greater amounts of 14C than the younger tissue. Differences in selectivity between crop and weed species may be partially due to differential mefluidide absorption, translocation, and subsequent concentration in certain plant tissues.

The objective of this study was to fit a hydrothermal germination model to germination data for a seedlot of radiata pine (Pinus radiata D. Don). Seeds were incubated for 50 d at constant temperatures and water potentials (T = 12.5–32.5°C, Ψ = 0 to − 1.2 MPa). Most seeds completed germination within 50 d, but for low Ψ and/or non-optimal temperatures (T < 17.5°C, T>25°C) many seeds did not complete germination. In general, germination data conformed to the hydrothermal model. Departures from the model were encountered for slow-germinating seeds at suboptimal temperatures (T ≤ 20°C). To account for these departures, two alternative hydrothermal models were fitted with an additional term for an upwards shift in seed base water potential with increasing time to germination. The alternative models more correctly predicted germination time than the original model. Similarly, reduced percentage germination at supra-optimal temperatures (T>20°C) was explained by including a term in the hydrothermal model which shifted the base water potential of seeds upwards towards zero, which in turn reduced the predicted rate that hydrothermal time would be accumulated by seeds. The rate of this upwards shift in base water potential was dependent on time to complete germination and ambient water potential as well as supra-optimal temperature.