|Bermuda grass competes with young tree|
|Light green leaves indicates low nitrogen|
The third reason Bermuda grass is so competitive with trees is that it secretes allelopathic chemicals from its roots which suppresses the growth of other plants including pecan trees. Once Bermuda grass is established in a pecan orchard it it very difficult to control. Only orchard wide and repeated applications of gylphosate seems to do the trick.
I a twist of nature's irony, pecan trees will eventually win the war against Bermuda grass. Given enough time, pecan trees will grow so large as to completely shade out the low-light intolerant Bermuda grass.