ANY 0W30, 5W30, 10W30, SAE30, 0W40, 5W40, 10W40, 15W40, 25W40, SAE40 oil will work perfectly fine in your engine.
If you don't already have the oil, and have to buy it, considering your climate, I'd look at Rotella 10W30, Delo 10W30, Delvac 10W30, or John Deere 10W30.
If the engine has low hours, a synthetic 5W30 or 10W30 would be a good choice. If it has a ton of hours, I'd skip the synthetic.
Those DR trimmer mowers are usually low hour machines, from what I have seen.