Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 18, 1997
Publication Date: March 1, 1998
Citation: Gealy, D.R. 1998. Differential Response of Palmleaf Morningglory (Ipomoea wrightii) and Pitted Morningglory(Ipomoea lacunosa) to Flooding. Weed Science. 46(2):217-224. Interpretive Summary: Palmleaf morningglory (IPOWR) occurs on levees or in shallow areas of rice fields. In rice, it is a worse weed than pitted morningglory (IPOLA), a common weed in soybean fields in the South. In simulated rice field tests, IPOWR proved to be much more flood-tolerant than IPOLA. IPOWR survived deeper floods at younger growth stages than did IPOLA. Flooding reduced growth and photosynthesis more in IPOLA than in IPOWR. Seedlings of both species emerged through a flood better than did germinating seeds, and neither species emerged from shallow soil covered by a shallow layer of water. IPOWR germinated much better than IPOLA at low oxygen levels that are common in flooded soil. Thus, IPOWR probably is more tolerant to flooding than IPOLA because of its ability to germinate and grow at low oxygen levels. These differences appear to explain why IPOWR is a greater weed problem than IPOLA in rice fields. The fact that neither species was capable of emerging from soil even under shallow flood depths helps explai why morningglories are prevalent only in shallow or water-saturated areas near levees in rice fields. These results suggest that cultural practices, such as deep-flooding in drill-seeded systems, or water seeding, may reduce IPOWR infestations in rice, whereas reduced tillage systems, which leave weed seeds on or near the soil surface, may increase infestations of IPOWR.
Technical Abstract: Palmleaf morningglory, Ipomoea wrightii Gray (IPOWR) can be a troublesome weed on levees or in shallow areas of rice fields. IPOWR and pitted morningglory, Ipomoea lacunosa L. (IPOLA) were compared in simulated rice field conditions to determine their flood tolerance characteristics. IPOWR survived a 13-cm flood in the field as early as 12 days after planting (DAP), whereas IPOLA did not survive the flood until 19 DAP. In the greenhouse, neither species emerged from under 1 cm of soil when covered by a flood of greater than 1 cm deep. In water-saturated soil, IPOWR emerged earlier and produced more dry weight than did IPOLA. Water emergence of two-cm-tall IPOWR was better than IPOLA from water depths up to 7 cm, and total dry weight was 2 to 4 times greater for IPOWR. A 5-cm flood, which reduced leaf area, height and dry weight of IPOLA more than that of IPOWR, did not affect leaf photosynthesis of IPOWR, but reduced that of IPOLA by 20%. At 20 C and low oxygen (1%), germination of IPOWR was about 4 times greater than for IPOLA. These results indicate that germination and growth if IPOWR are significantly more tolerant than IPOLA to a moderate flood. These differences appear to explain the observations that IPOWR is a greater weed problem than IPOLA in rice fields. The fact that neither species was capable of emerging from soil under even shallow flood depths helps explain why morningglories are prevalent only in shallow or water-saturated areas near levees in rice fields.