How long ago did you plant it. In what kind of soil. Does it have drainage? . How much water has it been getting lately? I am leaning towards root rot. Have you seen any black beetle like bugs with pointed sucker mouths

Here is a link that might be useful: Yucca weevil

I wouldn't do drip irrigation on yuccas, I don't water them at all unless maybe because its had months without rain otherwise it isn't ever necessary. If its rotting, the whole top of the plant will inevitably easily come off by just pulling it or pushing it over, it'll smell like rotten bananas. There will possibly be suckers coming up in the area if its rotted but well established. Looking at the picture with a fence on one side and what looks like a tree on the other makes me wonder how many hours of sun?

That does not appear to be Yucca. I think what you've got is an Agave, which are macrocarpic (live, bloom, die).

I don't know for sure what it is, but I would guess a soft leaf yucca from looking at photos online and what the blooms looked like. The leaves are flat and thin, not succulent like at all. Its been in for two years. Soil is thin over rock so probably quite alkaline (I tested soil from the back yard with vinegar/baking soda and it was totally alkaline), but I assume these are probably used to a more alkaline soil. Have not had the drip on recently because we have had some rain. I did not see any bugs. I am thinking it might be rot, though I had another of these about 10 feet away that died about 18 months ago and it was soft and smelly (so likely root rot on that one), not browning leaves like this. It does not get much sun since that area is fairly shaded. I did see what I know believe to be a sucker (it was quite small) so maybe it is one of those particular types of yuccas that do die.

It looks like Yucca flaccida. I used to have several clumps. They don't die after blooming. I think the only kind that dies after blooming is 'Our Lord's Candle' (Yucca whipplei). Maybe there are others that do too but I only know of that one, most kinds don't.

It doesn't look like an agave to me at all. Dried bloom definitely looks like a yucca, so do the leaves.

Here is a link that might be useful: http://search.aol.com/aol/imageDetails?s_it=imageDetails&q=yucca+flaccida&img=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fc%2Fc0%2FYucca_flaccida.jpg&v_t=nscpsearch&host=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FYucca_flaccida&width=114&height=171&thumbUrl=http%3A%2F%2Ft2.gstatic.com%2Fimages%3Fq%3Dtbn%3AANd9GcQmUKxmsVdAIDnjIURq4c__BMQLAI5jnWGOzQDxwMThwanJ8Rx-5mB4kqD_%3Aupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fc%2Fc0%2FYucca_flaccida.jpg&b=image%3Fq%3Dy%3DimageResultsBack%26v_t%3Dnscpsearch%26oreq%3D2ca971571231486cb72989f1fa754933&imgHeight=1889&imgWidth=1262&imgTitle=Yucca+flaccida&imgSize=2180401&hostName=en.wikipedia.org

I had a soft leaf yucca that I killed with kiindness -- overwatering -- in other words.. The top was as dead as a door nail but, it came back! I was amazed. Now I never water it at all. It's been years and it's still going. I guess it gets what it needs from other plants growing a few ft. from it that I do water.

I hope your's comes back too.