To be fair, at least around these parts a field left fallow for a year and a half will have 20 foot tall saplings covering everything. I have to break out the bushhog just to get to my pond. Bit more than "weeds and shrubs", some of those trees need a chainsaw to remove. And the grass is six or seven feet tall in places.
Given how fertile Ukraine's farms are (fuckers actually sell bags of their dirt as fertilizer at Walmart, "Chernozem-something or other"), they're probably dealing with a forest thick enough to hide a line of T-72s by now.