Field biology of Cleome gynandra L.: A difficult to manage weed of cultivated vegetable crops

Spider plant (Cleome gynandra L.) has been identified as an emerging significant weed of cultivated vegetable crops in southeast Queensland (SEQ). In Australia, the importance of spider plant relates to its biological characteristics and the difficulty land managers are facing with its management. It’s a prolific seed producer, can accumulate biomass rapidly at high temperatures and soil moisture levels and can tolerate extended drought. Two separate studies were carried out: the first controlled environment study investigated root-shoot growth, biomass accumulation and raceme growth under four substrate moisture (viz., 90 to 100%, 70 to 80%, 50 to 60% or 30 to 40% of the FC) and two temperature levels (25/35℃, 15/25℃) which represent average Summer and Winter temperatures in SEQ. The second study investigated seed production and seed-pod morphology during the Summer and Winter periods. Results demonstrated that both soil moisture, temperature and their interaction can profoundly impact root-shoot growth, biomass accumulation, and raceme growth. Adequate soil moisture and Summer temperatures (25/35℃) contributed to taller stature (17%), more shoot dry wt (25%) and greater raceme growth (20%) compared to plants under Winter temperatures (15/25℃). However, moisture stress increased root depth by 66% and advanced flowering time by 5 days. The interaction of temperature and moisture increased dry weight by 330 to 510% and raceme growth by 223 to 265%. The Summer plants produced over 70,000 seeds plant-1 with significantly higher pod length, width, and seeds pod-1 than the Winter plants. Since cultivated vegetable crops are irrigated, knowledge of the combined effects of temperature and soil moisture will provide better understanding on the field biology of spider plant under fixed crop management practices. The outcome of this research will contribute to better management of the persistent spider plants in cultivated crops.