Inconsistent watering. Tomatoes like even watering which can be hard when it is hot and dry then a cool change comes through with a huge down pour of rain. When tomatoes are grown in Melbournes hot 30+ days, the fruit will develope a tough thick skin to protect itself. After heavy rain or if you decide to give the plant a good drenching, the flesh inside will grow rapidly and swell causing the fruit to split. So the trick is to give your plant a good drenching everyday when it is fruiting. But remember not to wet the foliage as tomatoes suffer from Black spot, a fungal infection encouraged by humidity
Most people realise it’s dry, but how dry? The 3 months leading up to Black Saturday in 2009 we had around 91mm of rain. The 3 months leading up to February 2013 we had around 45mm of rain. So if some of your trees and plants are dying now you can see why. The best thing you can do for your plants while we go through this dry spell is to add a soil wetting agent to the soil and water as needed then water with a seaweed extract once a fortnight.
The rainfall during 2008 for the months from May to October we averaged 253.6 mm of rain for the north-east outskirts of Melbourne, unfortunately for the same time in 2014 we only had 254.6 mm. Its going to be a hot dry Summer so water, seasol, apply a soil wetting agent and mulch plants to limit damage.