HEMP DOGBANE (APOCYNUM CANNABINUM) SEED GERMINATION AND VEGETATIVE SHOOT EMERGENCE.

Authors: Webster, Theodore; CARDINA, J - OHIO STATE UNIVERSITY

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Hemp dogbane is a perennial weed that has become more common in reduced tillage fields throughout the Midwestern United States and is among the most troublesome perennial weeds in Ohio corn-soybean rotations. Due to the perennial nature of this weed, postemergence herbicide applications that take advantage of transgenic cropping system technology (e.g. glyphosate tolerant crops) will provide an effective alternative weed management option. However, many perennial weeds emerge later in the season than most annual weeds and most herbicide applications are aimed at controlling annual weeds. Field studies were conducted in Wooster, OH in 1997 and 1998 to quantify the time of emergence of hemp dogbane in an effort to provide growers and extension specialists with the knowledge of the emergence patterns of this weed. Results of these studies indicate that hemp dogbane seeds germinate optimally at alternating temperatures averaging about 34 C and with water potentials above 0.2 Mpa. Thus, germination appears to be restricted more by water potential than by temperature. Emergence of vegetative shoots begins after an accumulation of about 90 growing degree units (GDU) and is complete after about 700 GDU. Greater than 50% of the hemp dogbane shoots emerged between May 30 and June 19, 1997 and between May 16 and May 30, 1998. In spite of the large variation in temperatures between growing seasons, hemp dogbane vegetative shoot emergence was accurately described by GDU. Postemergence weed management programs will be more effective if they are applied when the majority of the hemp dogbane shoots have emerged.

Technical Abstract: Hemp dogbane is a native creeping perennial distributed throughout the United States, with increasing importance in reduced tillage systems throughout the Midwest. We studied the relationship between temperature, moisture, and seed germination as well as the relationship between vegetative shoot emergence and growing degree days. At constant temperatures, seed germination was described as a sigmoidal function of temperature (r2 = 0.83), with maximum germination (41%) from 26 to 34 C. Under alternating temperatures, seed germination increased in a near linear relationship between mean temperatures of 15 and 34 C (r2 = 0.85). Maximum seed germination (94%) occurred at mean temperature of 34 C under alternating temperatures. The relationship between seed germination and osmotic potential between - 1.0 and 0 MPa was described by a gompertz function (r2 = 0.98). Vegetative shoot emergence in 1997 and 1998 had a sigmoidal relationship to growing degree units (GDU) using a base temperature of 6 C (r2 = 0.96). However, initial shoot appearance was not consistent over years, with first emergence recorded on May 21, 1997 (132 GDU) and May 5, 1998 (73 GDU). Approximately 50% of the shoots emerged before June 7, 1997 (282 GDU) and May 21, 1998 (285 GDU). Greater than 50% of the hemp dogbane shoots emerged May 30 and June 19, 1997 and May 16 and May 30, 1998.