From e-mails I’ve received, it appears that some gardeners are having problems with their tomato plants. When tomato plants become water-stressed in prolonged hot, dry conditions that are affecting some parts of the country, they are prone to attack by fruit fly, heliothis moth caterpillars (corn earworm) and blossom end rot.
Blossom end rot can be caused by water stress because the plants are not able to absorb calcium from the soil when it is needed. For other causes of blossom end rot and remedies see: this post.
Tomatoes will benefit from being protected by a thick layer of mulch to reduce fluctuations in soil moisture, and a thorough soaking (under mulch) two or three times a week, rather than a light daily watering. Avoid overhead watering of tomatoes.
Hot days increase transpiration (water loss) from plants in the same way we perspire to keep cool. Setting up a light shade cloth canopy over the tomato bed will reduce water loss from plants and help prevent water stress and sun scald on fruit. Tomatoes will ripen under light shadecloth in hot weather. A soil feeding of seaweed extract ‘tea’ can also help plants build resistance to adverse conditions, including drought.
Mosquito netting over plants will serve two purposes. It will prevent attack by Heliothis moth and fruit fly, and provide a light shade for the plants. Modern tomato varieties do not require insects for pollination. If older varieties cease to set fruit, flowers can be hand pollinated with a dry watercolour paint brush.
In some areas, the netting may be enough to slow transpiration, without the shade cloth. All fruit affected by grubs or caterpillars should be collected and fed to the chooks, or placed in a sealed black plastic bag and left in the hot sun. This will kill the larvae and break the breeding cycle. Never compost fruit that contains grubs.