This article is a follow-up to ‘Problems with Light-My Geodesic dome Greenhouse Part 2’.
Although I’ve been harvesting lovely vegetables from my geodesic dome and grow tunnel daily, a new problem appeared in February, just after the wet season had started. POWDERY MILDEW!!
I really want to make the dome work, as it’s such an efficient use of space. The downside is, I’m finding that its unusual shape creates a unique set of problems. The spherical dome deflects the wind around it, so I’m finding that there is minimal air movement within it. Air flow is also proving a problem in the grow tunnel, albeit to a lesser extent. Another issue unique to the dome is water movement. It effectively rains less in the dome, because water trickles down the mesh at the sides, rather than running through it. Every time it rains, the plants in the centre of the dome (where the mesh is flat) receive rain. Yet the plants in the bathtubs around the edges have empty drainage buckets. So they are obviously getting far less water.
The main issue has been powdery mildew on the plants. I noticed a temperature difference between the two structures when I initially built them, but at first I put it down to location. The dome got more sun, as the tunnel is sited next to trees which shade it at each end. I have now pruned those trees, so both structures get the same amount of sun and access to breeze.
However as I mentioned above, the shape of the dome itself is what prevents air movement. (You can read here in part 1, how the dome just lifted up like an umbrella when we had a huge storm with strong winds). Unfortunately this poor air circulation results in an increase in both temperature & humidity inside the dome. This is the ideal environment for fungal diseases to breed and spread, and this is exactly what has happened.
Grey and sooty mould or powdery mildew has spread throughout the plants in the dome and the grow tunnel. This type of fungal disease looks like white powder sprinkled over a plants leaves- see the pic above. Despite this being the drier part of the year, and even with this 2021 spring season (September-November) shaping up to be very dry, the powdery mildew is rife inside both my self-built structures. Powdery mildew can never really be eliminated, so it is something I need to manage.
Fungal diseases like these thrive in warm dry climates, and love the cool nights and warm days that occur in spring. If left unchecked, it will spread over all susceptible plants, and it particularly loves curcurbits. While fungal diseases won’t kill plants outright, issues like powdery mildew need to be managed carefully to maintain plant vigour and fruiting. Powdery mildew spreads very rapidly in the right conditions, so I check my plants every day, as I know the yield and fruit quality can quickly worsen. Quick action is the key to effective management.
I find that milk spray (a commonly-touted remedy) is ineffective, so I use semi-organic sulphur and copper spray instead. For me it works marginally on zucchini and reasonably well on tomatoes and beans. It works for 7 to 9 days, then needs reapplying. Naturally, sprays can only work on the areas they come into contact with, so you do need to be thorough when applying, and remember to coat both the top and underside of every leaf. Rain may wash away sprays, too, so be sure to re-coat after rain as well.
I remove leaves as soon as they become badly infected. Pruning always encourages healthy new growth, and zucchini are no exception. Throw away infected prunings, as they can spread the fungal spores to other plants via compost. Fungal diseases also spread with the wind carrying spores throughout the rest of your garden. Disinfect your secateurs, too, as they can be one of the easiest ways to spread disease to other plants.
Stay tuned for part 4! Will I solve my issues with powdery mildew? Can I make the geodesic dome greenhouse a workable part of my garden??