Jointed goatgrass is most commonly described as a winter annual species. However, it has been observed to produce spikes in spring crops, apparently without being exposed to vernalizing conditions. A controlled environment study was conducted to determine the reproductive response of jointed goatgrass plants grown from seeds of fall- and spring-emerging parent plants to various vernalization durations. Winter wheat was included as a control. Winter wheat spikelet production was dependent on vernalization, and the number of spikes per plant was 10-fold greater if the plants were exposed to 4 C for 10 wk. In contrast, jointed goatgrass spike production without vernalization remained as high as 50% of that produced by plants exposed to 10 wk of vernalization conditions. Jointed goatgrass is thus not as dependent on vernalization for reproduction as the comparative winter wheat standard. Apparently, jointed goatgrass is more a facultative rather than an obligate winter annual. Rotating to a spring-seeded crop should not be expected to completely prevent jointed goatgrass seed production. Fields rotated to spring wheat to eliminate jointed goatgrass seed production should be monitored, and jointed goatgrass should be hand pulled or otherwise controlled to ensure zero seed production.

Two DNA molecular marker techniques were used to evaluate genetic diversity in 58 accessions of jointed goatgrass and 6 accessions of the related wild species barb goatgrass. Random amplified polymorphic DNA (RAPD) assays were performed on 8 U.S. and 50 Eurasian jointed goatgrass accessions using 30 random decamer primers. The frequency of scorable polymorphic bands within jointed goatgrass was 6 out of 90 (6.7%). Cluster analysis of RAPD data showed small genetic distances (values of 0.005 or less) among jointed goatgrass accessions. To validate the effectiveness of RAPD techniques to detect genetic diversity in tetraploid Aegilops species, six accessions of barb goatgrass were assayed using a subset of 20 decamer primers (from the original 30). RAPD data for barb goatgrass were pooled with jointed goatgrass data from the same primers. A total of 63 scorable bands were generated, of which 27 (43%) were polymorphic between two or more accessions. RAPD analysis readily distinguished between the two species and detected much greater levels of genetic diversity within barb goatgrass than between the jointed goatgrass accessions. Amplified fragment length polymorphism (AFLP) assays were performed on a subset of the 58 jointed goatgrass accessions, 3 U.S. and 13 Eurasian. These accessions were selected to represent a range in geographic diversity within our collection. Ten primer combinations generated 560 scorable bands of which 28 (5%) were polymorphic. Cluster analysis of AFLP data showed a slightly smaller range in genetic distance (0.0002 to 0.0022) among accessions compared with RAPD results; however, AFLPs distinguished among all but 2 of the 16 accessions surveyed. Although AFLP produced more scorable bands than RAPD did, both methods revealed limited genetic diversity in jointed goatgrass.

Wheat cultivars resistant to imazamox will facilitate selective chemical control of many winter annual grass weeds, including jointed goatgrass, downy brome, and feral rye. These three weed species respond differently to imazamox postemergence treatments with feral rye, demonstrating more tolerance than jointed goatgrass or downy brome; therefore, growth chamber studies were conducted to evaluate imazamox absorption in all three weed species and translocation and metabolism in jointed goatgrass and feral rye. Adding nonionic surfactant (NIS) or methylated seed oil increased absorption in jointed goatgrass and feral rye but not in downy brome, compared to imazamox applied alone. Imazamox applied with NIS and urea ammonium nitrate resulted in the highest absorption in each species: 97, 91, and 92% of applied 14C for jointed goatgrass, downy brome, and feral rye, respectively, 48 h after treatment (HAT). Imazamox translocation from the treated leaf was similar for jointed goatgrass and feral rye across seven harvest intervals between 0 and 96 HAT. Shoot tissues of jointed goatgrass and feral rye accumulated 17 and 14% of applied 14C, respectively, by 96 HAT. Differential translocation of imazamox into root tissue was observed within 12 HAT; by 96 HAT, 20% of applied 14C translocated to jointed goatgrass roots compared to 27% for feral rye. Imazamox was readily metabolized in both weed species. At 96 HAT, 73 and 98% of the applied 14C was metabolized in the treated leaves of jointed goatgrass and feral rye, respectively. Metabolism was consistently higher in feral rye than in jointed goatgrass in all plant parts 96 HAT. On a whole-plant basis, metabolism was 25% greater in feral rye than in jointed goatgrass. The differential response of jointed goatgrass and feral rye to foliar applications of imazamox appears to be related to differences in translocation and metabolism but not in absorption.