The influence of salinity on the productivity of four plant species occurring or potentially occurring in Suisun Marsh was investigated with laboratory measurements of growth, photosynthetic responses and competitive interacti~ns, and field measurements of water relations, growth and carbohydrate reserves. Special emphasis was placed on the responses of Scirpus robustus and its competitors because of its importance as a waterfowl food source. The results showed that photosynthesis and. growth were much more reduced by increased salinity in Scirpus than in Spartina fo1iosa, Salicornia virginica or ~Cotula cornup i f oLia . However, at low salinities .Scirpus had the highest growth rates. Competition studies showed a strong shift in competitive advantage from Scirpus at low salinities to Salicornia at high salinities. Field studies showed that at most sites where Scirpus occurs, there is a strong seasonal change in salinity from nearly fresh water in the spring to high sun~er salinity levels. The rapid growth of Scirpus at the low salinities present during the spring may give it a competitive advantage over Salicornia. Scirpus also exhibited considerable tolerance to high salinities--defined here as an ability to survive even though growth was completely stopped. This tolerance may be important, since high summer salinities could prevent encroachment of less salt tolerant but highly competitive and less desirable species such as Scirpus acutus or Typha latifolia. We conclude that management plans designed to enhance Scirpus productivity should put as much weight on maintaining an annual cycle of salinity as reducing the yearly average salinity. VIATER RESOURCES CENfER ARCHIVES \ UNIVERSITY OF. CALifORNIA I ~KEJ:EY __ ._f

The segregating F2 population from the hybrid between grain sorghum (Sorghum bicolor), chromosome number doubled, and Johnsongrass (S. halepense) was examined for expression of rhizomes. A rhizome to non-rhizome segregation ratio of 3:1 was observed suggesting a single dominant gene regulation in the rhizome phenotype of S. bicolor and S. halepense. Approximately 72% of the F2 population overwintered and regrew from the rhizomes the following spring. When comparing these data with data in the literature, the rhizome regulating gene in the Sorghum genus may be an incomplete dominant gene requiring a few genes to be expressed additively that result in different degrees of rhizome development in the Sorghum genus.

Copper content and growth of excised hydrilla [DioeciousHydrilla verticillata(L.f.) Royle # HYLLI] apical shoot segments were determined following exposure to copper sulfate (CuSO4), copper-triethanolamine (Cu-TEA), and copper-ethylenediamine (Cu-EDA). For all copper formulations, inhibition of growth was related to the amount of copper associated with the excised shoots. At equal copper exposure, the Cu-EDA formulation produced the greatest inhibition of growth and generally the highest copper levels in the plants. The Cu-EDA formulation inhibited dry weight gain by more than 80% 3 weeks after a 2-h exposure to 2.0 or 4.0 ppmw copper. Under similar conditions, CuSO4or Cu-TEA produced 60% inhibition. The presence or absence of light during a 2-h exposure had no effect on the efficacy of uptake of copper from any of the formulations. Formulation-dependent differences in the mechanism of copper uptake is suggested because rinsing of exposed shoots with dilute acid (0.01N HNO3) removed copper from shoots treated with CuSO4or Cu-TEA but not from those treated with Cu-EDA.

Diurnal and seasonal patterns of plant water potential (ψ) were measured for three common salt marsh species, Spartina foliosa, Scirpus robustus, and Salicornia virginica, that co-occur in the San Pablo Bay marshes of northern California. For all three species, dawn maximum and midday minimum plant ψ declined over the growing season in parallel with decreasing soil osmotic potentials. Maximum leaf conductances for Spartina and Scirpus also exhibited large seasonal decreases as salinities increased. Scirpus, which is more abundant in brackish marshes than in true salt marshes, occurs in a narrow zone between the other two species at the study site. Salinities in this zone were intermediate between those in the Spartina and Salicornia zones, and Scirpus experienced intermediate plant ψ. Therefore, the persistence of the less halophytic Scirpus in a zone between two more halophytic species cannot be explained by lower salinities in this zone. The occurrence of Scirpus in this marsh may be due to its capacity for rapid growth during spring when salinities are low, plus a tolerance for high salinity later in the year after vegetative growth has ceased.

Early watergrass (Echinochloa oryzoides) and late watergrass (E. phyllopogon) have become the most serious weeds in California rice since continuous flooding was used to suppress barnyardgrass (E. crus-galli). Continuous use of a limited number of available graminicides and an increasing number of control failures led to the investigation of herbicide resistance in early watergrass and late watergrass. Greenhouse dose-response studies with POST applications of molinate (Ordram), thiobencarb (Bolero), fenoxaprop-ethyl (Whip), and bispyribac-sodium (Regiment) estimating GR50 (herbicide dose to inhibit growth by 50%) values suggested resistance to all herbicides in two late watergrass accessions, and to Ordram and Bolero in one early watergrass accession, when compared to susceptible late watergrass and early watergrass control accessions, respectively. No resistance was detected in dose-response studies with propanil. Minimum and maximum ratios (R/S) of the GR50 values of resistant to susceptible late watergrass plants (in two experiments involving two resistant accessions) were 7.8 and > 13.3 for Bolero, 2.2 and 4.3 for Ordram, 16.5 and 428.7 for Whip, and 2.0 and 12.0 for Regiment. Minimum and maximum early watergrass R/S ratios (average of two experiments) were 21.9 and 4.6 for Bolero and Ordram, respectively. Thus, early and late watergrass populations may have developed cross and/or multiple resistance. Cross-resistance occurs when a given weed biotype is resistant to different herbicides through a common mechanism, and usually refers to herbicides that share a common mechanism of action. Multiple resistance involves different herbicides and more than one resistance mechanism; this is usually the case of resistance to chemically unrelated herbicides with different mechanisms of action on the weed. A resistant late watergrass (one accession tested) and the susceptible control were killed by POST applications of glyphosate, glufosinate, and clomazone, and by a PRE application of pendimethalin. Thus, the repeated herbicide use patterns resulting from the restricted availability of grass herbicides, and the prevailing practice of continuous rice culture have led to the selection of early watergrass and late watergrass biotypes, with the capacity to survive treatment by different herbicides. Therefore, it is important that the control of these grasses be diversified by the full use of preventive, mechanical, and cultural practices aimed at eliminating the survival, seed production, and dispersal of plants that escape herbicide treatment. Herbicides will continue to be the key resource for weed control in rice, and the importance of avoiding the repeated use of herbicides with the same mode of action cannot be overemphasized. Alternating or mixing herbicides with different modes of action that are equally effective on the target weed should help delay the buildup of resistance. Decisions on alternative herbicides can become more difficult when resistance has already developed to more than one herbicide. In such cases non-chemical means of weed control, such as water management, must be optimized. Some of the fields with resistant watergrass appear in relative proximity, suggesting that dispersal of resistant seed may occur. It is important to prevent transporting resistant seed across fields with agricultural implements, particularly when equipment is shared among growers. It is advisable that the areas infested with herbicide resistant watergrass be harvested last, and the equipment cleaned before