Research was conducted during 1988 and 1989 in Georgia and Florida to determine the densitydependent effects and critical periods of wild poinsettia interference with peanut. Peanut yield loss ranged from 0 to approximately 50% over the wild poinsettia density range from 0 to 32 plants 9 m−1 peanut row. Predicted peanut yield losses across 2 yr in Georgia were 0, 4, 8, 12, 15, 26, 40, and 54% for season-long wild poinsettia interference at densities of 0, 1, 2, 3, 4, 8, 16, and 32 plants 9 m−1 of row, respectively. Across 2 yr in Florida, predicted peanut yield losses were 0, 9, 14, 22, 30, 37, and 41% for wild poinsettia densities of 0, 1, 2, 4, 8, 16, and 32 plants 9 m−1 row, respectively. Peanuts had to be maintained poinsettia free for 10 wk after peanut emergence to prevent yield loss. Wild poinsettia that interfered with peanut for more than 2 wk after peanut emergence reduced peanut yield.

The effect of two dates of initial manual weeding, i.e., before flowering and after flowering, and of no weeding on yield of a local groundnut variety was studied during 1988 and 1989 at Minkoameyos, Yaounde, Cameroon, in comparison with chemical weed control method or control. The use of herbicides ametryn plus promotryn for weed control gave the best mean yield, followed by handweeding after flowering, and handweeding before flowering, in that order. The no weeding treatment had the lowest yield throughout the trial period.

Greenhouse and field studies were conducted to characterize wild poinsettia growth response to imazaquin (140 g ai ha−1), fomesafen and acifluorfen (420 g ai ha−1), and chlorimuron (9 g ai ha−1) applied at 5 to 7 cm (POST1), 8 to 10 cm (POST2), and 15 to 20 cm (POST3). Based on reductions in weed height and lateral branch number 28 DAT, wild poinsettia was controlled more effectively in both greenhouse and field studies for all herbicides applied at POST1 than at POST3. In the greenhouse studies, reduction in wild poinsettia biomass with the herbicides 28 DAT was similar when applied at POST1 and POST2 and, with the exception of chlorimuron, was higher at POST2 than at POST3. In the field study, weed biomass reduction measured approximately 4 mo after herbicide application was higher for imazaquin, acifluorfen, and chlorimuron applied at POST2 than at POST1. Wild poinsettia biomass was reduced more with imazaquin applied at POST3 than at POST1. Increased lateral branch production, indicative of decreased weed control, was often manifested in higher seed production per plant. With application of all herbicides at POST3 seed production was equal to the untreated check.

The potential of several common weed species to produce adventitious shoots when the plants were excised approximately 1.0 cm below the cotyledonary node at the cotyledon growth stage and at the four true-leaf stage is reported. Indian jointvetch (Aeschynomene indica L. ♯3 AESIN), northern jointvetch [Aeschynomene virginica (L.) B.S.P. ♯ AESVI], and wild poinsettia (Euphorbia heterophylla L. ♯ EPHHL) produced adventitious shoots at both growth stages after shoot excision. Adventitious and vegetative regeneration of wild poinsettia damaged by herbicides was similar to that from decapitation.

In field studies conducted over 2 yr, POST applications of chlorimuron, imazaquin, fomesafen, or acifluorfen following PRE applications of clomazone, metribuzin, or metribuzin plus chlorimuron enhanced wild poinsettia control when compared with the PRE herbicides applied alone. Wild poinsettia control was highest for imazaquin compared with other PRE treatments and with the exception of fomesafen, applications of POST herbicides following imazaquin PRE did not improve weed control. With the addition of POST herbicides, soybean yields were generally not increased, but moisture content in one year and foreign material content both years were reduced. In other studies, early POST applications (2 to 8 cm) of fomesafen, imazaquin, acifluorfen, lactofen, and chlorimuron controlled wild poinsettia better than late POST applications (10 to 15 cm) in only one year. Soybean yields both years were generally similar regardless of herbicide application time.

Wild poinsettia germination was at least 95% when exposed to solution pH of 2.5 to 10 or solution osmotic potential of up to −0.8 MPa. No germination was observed at pH 12 or osmotic potential of −1.5 MPa. Light was not required for germination. Seed germinated at temperatures ranging from 20 to 40 C with maximum germination of 97% at 35 C. Wild poinsettia had the highest emergence (80%) from seed placed 2 to 4 cm below the soil surface, while 20% of the seed planted at 14 cm emerged. Wild poinsettia germinated over a wide range of conditions, which explains why it is becoming an increasingly serious problem.

Wild poinsettia is a serious weed in several crops, including peanut, grown in the southeastern United States. A study was conducted over 3 yr at Jay, FL, to characterize the growth and development of wild poinsettia grown from seed collected at Plains, GA; Marianna, FL; and Baton Rouge, LA. Seedlings from each selection were transplanted to the field and were grown either alone or in competition with peanut. Observations made throughout the growing season indicated that the Louisiana selection flowered later, grew to a larger size, produced more leaf area and biomass, and caused greater light attenuation and peanut yield reduction than the other two selections. The Georgia selection produced the smallest plants, least leaf area and biomass, and was least competitive with peanut. The Florida selection was intermediate for these parameters. Wild poinsettia dry biomass production was reduced by 78 to 83% when grown with peanut compared with monoculture wild poinsettia.

Field-studies were conducted over two years to determine the area of influence and duration of interference of wild poinsettia in soybean. Soybean canopy width averaged across years was reduced approximately 10% beginning at 6 wk of interference for both the 0- to 10-and 10-to 20-cm distances from the weed. Soybean dry weights decreased from 14 to 38% within 20 cm of the weed for 12 through 18 wk of interference. In 1990, soybean yield within 10 cm of wild poinsettia was similar to distances of 10 to 20 and 20 to 40 cm, but was less than that for distances greater than 40 cm from the weed. Weed interference resulted in a 9.5% yield reduction in the 0- to 10-cm distance when compared with the 80-to 100-cm distance. In contrast, yield of soybean in 1991 growing within 10 cm of the weed was less than at greater distances, corresponding to an 18% yield reduction when compared with 80 to 100 cm. Differences in wild poinsettia dry weights when growing alone and when growing within the soybean row occurred after 6 and 8 wk of interference in 1990 and 1991, respectively. In 1991 when rainfall during the growing season was twice that of the previous year, canopy width and dry weight of wild poinsettia growing within the soybean row were reduced an average of 57 and 82%, respectively, compared with weeds growing alone.

Wild poinsettia control in peanut was evaluated following various preplant-incorporated and postemergence herbicide applications. The addition of vernolate or alachlor to a preplant-incorporated treatment of benefin improved wild poinsettia control obtained with treatments of lactofen or paraquat plus alachlor applied at the time of peanut emergence. Lactofen applied postemergence following lactofen plus alachlor applied at the time of peanut emergence provided ≥92% wild poinsettia control and peanut yields equivalent to the handweeded control. Treatments of paraquat plus alachlor applied at the time of peanut emergence followed by acifluorfen (applied once or twice) or paraquat followed by acifluorfen provided good (74 to 100%) wild poinsettia control for up to 12 weeks after planting and peanut yields not different from the handweeded plots. Treatments that did not provide at least 92% wild poinsettia control when evaluated 5 weeks after planting resulted in significant peanut yield reduction compared to the handweeded control.