Mould on soil from slug pellets

Slugs dont like tomato plants , i've never used pellets with toms 

To be honest i've never had a snail or slug on my Toms Mr Murphy , maybe other people can add to this  

Gently scrape away the mouldy pellets without disturbing your tomatoes and throw them in your rubbish bin. Like Dave Mack I have never had problems with slugs and tomato plants but if you want to use pellets just take care not to get them too wet or they will go mouldy and do not get them too near to your plants.

Just another thought - could the mould be a slime trail from a slug.

They've never bothered my tomatoes, but they do like the marigold and basil that I also plant in there 

Slugs may not bother the plants but they lurve ripe tomatoes.  And the french marigolds I grow at the base to repel the white fly.  They can eat a french marigold plant to a stump if they are so minded overnight.