carrot seedlings outside

Planted in March took until april to come up.that's a weed seedling pulled up in the picture,the allotment is very very weedy.I use slug pellets to start of some things because if I didn't they slug would have more to eat then me.I'm trying carrot in a 2 ft high bed and in a lower bed with enviromesh after the last 2 years of carrot fly something has to be done.the first year was great as they did not know the carrots where there but now its early carrot or none. I hoping the two methods will give me late carrots this year.