Empirical assessments of transgene inheritance and phenotypic expression will assist in the development of efficient breeding strategies for transgenic germplasm, and guide research into the improvement of transformation techniques. The inheritance of a barley yellow dwarf virus (BYDV) coat protein gene and bar, and the expression of bar as measured by resistance to glufosinate‐ammonium damage, was studied in the T1 and T3 generations of barley (Hordeum vulgare L.) populations derived from seven independent transformation events. Most populations deviated from Mendelian inheritance patterns, and several showed evidence of transgene silencing. To further study transgene behavior, several transgenic lines were crossed to a diverse set of nontransgenic cultivars and breeding lines to produce single cross‐ and backcross‐derived populations. In these populations, the inheritance of glufosinate‐ammonium resistance generally fit Mendelian expectations for single, dominant loci. Quantitative measurements of glufosinate‐ammonium resistance showed heritable variability for glufosinate‐ammonium resistance both among and within individual transformation events, but no variability could be attributed to the different genetic backgrounds of the nontransgenic parents. It is concluded that, although transgenic parents such as these can be used in a breeding program, transformation systems that result in greater stability of transgene behavior are desirable.

The effects of postemergence rimsulfuron, metribuzin, and adjuvant combinations on potato crop safety and weed control were evaluated in field studies conducted at the University of Idaho Aberdeen Research and Extension Center in 1999 and 2000. Rimsulfuron at 26 g ai/ha plus metribuzin at 0, 140, or 280 g ai/ha was combined with nonionic surfactant (NIS), crop oil concentrate (COC), or methylated seed oil (MSO) in a 3 by 3 factorial with two controls. Under cool, cloudy conditions in 1999, initial ‘Russet Burbank’ potato injury was greater when metribuzin was included in the tank mixture than when rimsulfuron was applied alone, regardless of adjuvant. Under warmer conditions in 2000, however, adding MSO or COC to the tank mixture caused more injury than adding NIS. Rimsulfuron did not provide acceptable season-long common lambsquarters control in 1999 (76%) or in 2000 (88%), regardless of adjuvant. Rimsulfuron combined with metribuzin at 140 or 280 g/ha provided ≥95% common lambsquarters control both years, regardless of adjuvant. Among adjuvants, using MSO (1999 and 2000) or COC (2000) in the spray mixture improved common lambsquarters control compared with using NIS. Tuber yield and quality were not reduced as a result of metribuzin rate or adjuvant treatments either year compared with the weed-free control.

Field studies were conducted to assess weed control and potato (Solanum tuberosum) tolerance to ethalfluralin. Ethalfluralin applied preemergence (PRE) alone at 1.05 kg ai/ha generally did not control weeds adequately. However, ethalfluralin at 1.05 kg/ha combined with either metribuzin at 0.28 kg ai/ha or rimsulfuron at 0.018 kg ai/ha controlled common lambsquarters (Chenopodium album), redroot pigweed (Amaranthus retroflexus), and green foxtail (Setaria viridis) ≥ 98%, which was similar to control observed with several currently registered herbicide mixtures. Volunteer oat (Avena sativa) control with either ethalfluralin at 1.05 kg/ha plus EPTC at 3.4 kg ai/ha or ethalfluralin plus metribuzin was equal to registered two-way mixtures. Ethalfluralin plus metribuzin did not adequately control hairy nightshade (Solanum sarrachoides), but ethalfluralin mixtures with either rimsulfuron or EPTC controlled hairy nightshade equal to or better than the registered two-way mixtures evaluated. A sequential application of ethalfluralin PRE followed by rimsulfuron or rimsulfuron plus metribuzin postemergence (POST) did not improve hairy nightshade control compared to ethalfluralin plus rimsulfuron applied PRE. Potato tolerance to herbicide treatments applied PRE or POST to potato was evaluated in weed-free studies. Ethalfluralin alone or with metribuzin was compared to mixtures of metribuzin with either pendimethalin or EPTC. Initial visual injury with ethalfluralin PRE was ≤ 4% both years. In 1996, initial injury with ethalfluralin POST was ≤ 4% and U.S. No. 1 and total tuber yields were not affected by herbicide treatment or application timing. However in 1997, initial injury from POST ethalfluralin at 1.05 or 2.1 kg/ha was 2 or 8% and increased to 9 or 17%, respectively, at potato row closure. Averaged over all herbicide treatments, POST applications reduced U.S. No. 1 and total tuber yield 7% relative to PRE applications in 1997.