Ok, kinda loaded question but relatively simple.... The ONLY case, in this dry of a year down south, Brassicas will germinate from "dew or moisture somehow in soil" is if you have massive amounts of organic matter OR have a mat on top like crimped Rye for example. I highly doubt, with how dry it is, you have enough organic matter because I have yet to see a situation where someone does with how bad this drought is BUT - it's possible. For every 1% increase in OM, you can hold basically an additional 16k gallons (ballpark) of water per acre. Which is about 1/2 of rain. That's "additional holding" BUT, in reality, when you're in places with "severe drought" we're, talking lack of moisture down several FEET into the ground, or lower. It's a disaster as of now for germinating anything. One the rye.... That's where it'll work. Which, is simply knowledge for the future. 1) Build up your OM & 2) if you think a drought is coming, crimped rye, etc can keep soil moist (it's just like mulch). Drilling through it can be done. residue of the rye moving back over the rows can create a challenge but it will help with moisture. Now, when we are talking about most folks- DISCING & working soil..... That's just further moisture loss. Side notes: brassicas are pretty hardy for "hanging on" so if you do get germination, they can hang on longer than you think. BOTTOM LINES: 1) build up OM with dbltree rotation (more moisture holding capacity and "drought prevention over time") 2) if you can drill, ideal. If need to disc, still can try. 3) Be prepared for replanting or late germination if you seed. Which either isn't end of world. 4) If too much time and back up plans go by...... Your rye mix of choice is going to be your final plan of the year along with leaving any successful crops you can. Good luck.