Using sugar to kill weeds is the subject of study by several university horticultural and agronomic professionals.
Weeds are the stuff of horror to those of us who want a green lush lawn and the effects of sugar on plants seem to point to the white powder as a safe herbicide to deter unwanted weeds. Read the entire article.
Here's a few other ideas:
Using Salt to Kill Weeds
Gardening With Vinegar
Using Sugar to Kill Weeds in Lawn
Using Cornmeal to Kill Weeds and Ants
I have used table salt purchases in 25 lb. bags for areas where we
don't want things to grow (under the gravel in the driveway mainly), and
it works! If there's not nearby vegetation to creep in, it's lasted
for three years. Down by the street in the easement area, the weeds are
quicker to grow into the graveled driveway, so it only lasts a year
We have also used vinegar in a garden sprayer which
was much quicker than sprinkling salt and then adding water to it. You
could enjoy a nice time in the rain if you put the salt down while the
rain could water it in, but my husband likes the idea of putting it in a
"tool" and spraying. He adds a few drops of Sunshine Concentrate since
soap was recommended in one recipe to help the vinegar stick to the
plants and roots until it dies off in a few days.