A glasshouse creates brilliant conditions for fungal growth.
as the lucky and loving husband of the proud owner of a brand new glasshouse, I am perfectly eligible to write this column about the top pests of such a habitat. This glasshouse, I’ll have you know, is not just a metal-and-plastic contraption, but a fair dinkum, old-fashioned wood and glass building.
As I write these words, I am still painting and glazing the multi-year birthday and Christmas present – a great project that allows me to study the entomology of this brilliant little hothouse, whilst comparing it to my trusty and productive plastic tunnelhouse, one level down in the garden.
Watch the mercury
It truly is astonishing how quickly the temperatures can rise inside a glasshouse or tunnelhouse. There were days, last summer, that my tomatoes were screaming blue murder (or was that orange-red murder?) at 49˚C in the middle of the day. The plants simply shut down, show signs of wilting and leaves don’t last that long in such conditions.
Watering needs to be carried out a few times a day, as the roots suck up all the moisture they can find to compensate for transpiration from the leaves that still function. You can open all the doors and windows, but if there isn’t much wind, air movement is negligible.
Shade is absolutely crucial to avoid mass casualties. Be sure to have an internal system that allows shade cloth to be installed inside the house: our relentless nor’westers rip anything to pieces that is draped over the outside of the structure!
Fungal attacks
Remember if you are gardening undercover you are creating some brilliant conditions for fungal growth. Temperatures, shelter, warmer nights, higher relative humidity often stimulate fungal development in soil, on stems and on leaves.
If you install a watering system, use the micro-pipes and aim them at the soil, not the stems or leaves of the plants. Because of the year-round higher temperatures, powdery mildew can hang on to the plants for approximately 12 months of the year.
Ironically, keeping the glasshouse dry only makes mildew matters worse but making the plants wet to control the mildew will provide benefits for the blight on stems of tomatoes. Sometimes, you just can’t win.
Biological control agents for New Zealand glasshouses can be sourced from local companies bioforce.co.nz/ and zonda.net.nz/. These folk are helpful, communicative and – best of all – entomo-literate!