PREDICTION OF FLOWERING IN COMMON CRUPINA (CRUPINA-VULGARIS)

Exotic annual weeds on western U.S. rangelands owe at least part of th eir invasion success to prolific seed production. Reproductive output is determined largely by timing of flowering in relation to soil moist ure, light, and competing vegetation. This study investigated the infl uence of temperature (including vernalization), photoperiod, and intra specific competition on reproductive phenology in three populations (t wo varieties, typica and brachypappa) of common crupina. Monthly plant ings at four densities were grown in field plots through two consecuti ve cycles, and the dare each plant reached bud and flowering stage was recorded. Development of greenhouse-grown plants from the same popula tions was compared with those grown outside for 4, 6, 8, and 10 wk of cold induction. Reproductive development in common crupina was influen ced by all factors investigated: temperature, photoperiod, density, an d vernalization. Conditions fostering the shortest thermal time from e mergence to floral induction were a period of cold temperatures/short photoperiod as seedlings followed by warming temperatures and lengthen ing photoperiod. Both varieties of common crupina responded quantitati vely to vernalization, but lack of vernalization caused a greater dela y of flowering in var. brachypappa than in var. typica. Vernalization contributed to convergence of spring flowering among the August to Dec ember plantings, but earlier emergence and lower plant density greatly increased final plant size and fecundity. Lack of vernalization, high temperatures, and shortening day length delayed flowering of spring/s ummer emergents, increasing the probability of succumbing to drought b efore producing seed.