We have been getting many questions lately about late-season annual morningglory control in peanut. In most cases, it is too late in the year to legally apply herbicides. Pre-harvest intervals (PHI) of peanut herbicides with POST activity on annual morningglory are as follows: Cadre = 90 days; Cobra = 45 days; Ultra Blazer = 75 days; 2,4-DB = 30-45 days.
In the opinion of Dr. Prostko, UGA Weed Scientist, the best thing a grower can do for annual morningglory this late in the season is to apply a pre-harvest application of either Aim or ET (i.e. 7 days before digging). Both herbicides will provide sufficient dessication of annual morningglory plants (except smallflower) to improve peanut vine flow through a digger with minimal effect on the peanuts (Figures 1 and 2). It is very important that the peanuts be dug in 7 days after treatment (or as soon as possible after that time). If digging is delayed, the morningglory vines could start to recover/regrow especially after a rainfall event. Specific recommendations for these herbicides can be found on page 502 of the 2015 UGA Pest Control Handbook.
Figure 1. Annual morningglory response to Aim (5 DAT).
Figure 2. Peanut injury caused by a pre-harvest application of Aim (5 DAT).