Those cacti can reach out and touch you like you can't believe. Four years ago, we were racing a National in southern US territory, and my son got just a little too close to a cactus, and snagged a section with needles. Didn't crash, just got too close. At the half way pit stop, he complained about his nose hurting really bad, but nothing was apparent in the 15 seconds it took to pit, so off he went on the second half of the race.
At the end of the race, I took a close look at his nose, and found that when he snagged the cactus, one needle has pocked through on side of his nose, through the middle part of his nose, and about 1/2 way into the other nostril.

Fortunately, there was still about 1/4 inch protruding at the nose entry point, so ol' Doc Rick grabbed a pair of needle nose pliers (how ironic to remove a cactus needle with needle nose pliers

), grabbed the needle, and pulled it out from his nose the same way it went in. I didn't feel a thing, but the boy was none too happy.
The moral of the story...you don't have to crash into a cactus to get stuck. Give 'em a wide berth. Also, Manny is 100% correct. Don't try and win this event, just enjoy the experience, and you will do well, as too many folks ride over their head. In fact, when I won the Open Expert class in 2002 in the region series, it wasn't because I was the fastest guy in the class, but rather the most consistent. There were a couple of riders who were a lot faster than I am, but they kept crashing. The result...the old guy wins the class for the year, and only finished first in one race.
Good luck
Rick