Kettle sour the wort for 1-2 days (to your taste or PH) with what ever you prefered (active yogurt starter, kefir grain, proper lacto culture, acidulated malt innoculation). Then proceed as usual with boil and ferment, adding cucumber and lemongrass to secondary 3 days before bottling or kegging.
Acidulated malt is being used to lower the PH of the wort, and is also used to create the lacto starter.
No need to include the Acidulated malt if you are not using it to lower ph or innoculate and sour.