|Our tomatoes always get to about tennis ball size, then split open. Why does this happen? The only pest we've identified is whiteflies, which we've been hosing off.|
|They most common cause of splitting fruit is water stress. Tomatoes are moisture sensitive and need a regular supply of water to thrive and produce fruit, especially in hot, dry conditions. Alternating wet and dry conditions can cause all sorts of problems on the fruit, including the splitting you describe. Be diligent in your watering, keeping the soil evenly moist. Water plants deeply, making sure that water is reaching down 12 inches deep, and add a layer of mulch on top of the soil to help maintain moisture.
Sometimes small cracks will heal over, sometimes not. Others times the cracks serve as an entry point for infection, so you may wish to harvest the cracked tomatoes. Some varieties are more resistant to cracking than others. If you continue to have problems, you might choose smaller size tomatoes, rather than the large beefsteak varieties, and look for those described as "crack-resistant."