This would take a bit more coding, but depending on how you place your wheat you can add a nav generation pre-process to gather all wheat and create nav modifiers for them (you’d need to use UNavModifierComponent since you won’t be able to procedurally create volumes). Or better yet, just have your wheat implement INavRelevantInterface (or simply have UNavModifierComponent, depending on how you do it).
Hope it helps. I’ll have a look at your game in a spare moment.
Cheers,
–mieszko