Wednesday, 10 July 2013

Hygiene (Week 14, Wednesday)

Quite a few plants grow in a restricted space in greenhouses, so hygiene is particularly important to prevent and control the spread of pests and diseases.

In terms of prevention, clean tools and surfaces are very important. So pots are dipped into a sterilising solution and tools are cleaned with Hortisept, a persistent germicide active against bacteria, viruses and fungi.

The greenhouse is hoovered clean of plant debris, including the benches, which I did today.

Bench after hoovering
Bench before hoovering

The pots in which the plants grow are also kept clean, by removing plant debris and any weeds, liverworts, mosses or algae that decide to take residence. In fact, although these last three groups do not have roots and do not strictly compete for nutrients with the plant, they are in the way of good maintenance. Availing myself of the latest technology, I used a kitchen fork to help me with the task.

We have quite a lot of Merchantia polymorpha on our pots... I find bryophytes really interesting! 

Unlike the spermatophites (conifers and flowering plants), more familiar to us, where reproduction happens in the cones or in the flowers' ovaries respectively, resulting in the production of seed from which the next generation will be born, bryophytes have a two-generation reproduction process. The gametophyte generation produces sperm and ovules that meet outside the plant in any moisture film that might be present (i.e. after rain) and give birth to the sporophyte generation, growing on top of it (like the umbrellas of Merchantia) and producing spores, starting the process all over again. If you want to know more about Merchantia's lifecycle the University of Miami dept. of Biology has a nice graph and some information about them.

In terms of pests and diseases, scouting for their appearance and monitoring spread is the best way to prevent them reaching unsustainable levels.

For this purpose, in the greenhouses we have plenty of butterwort (Pinguicola sp.), a carnivorous plant with sticky leaves, which is used to monitor the appearance of aphids, so as to release bio control at the right moment.

Today, when clearing debris from under the weaning pots outside, I found some vine weevils (Otiorhynchus sulcatus), so I alerted the greenhouse manager who is going to spread some more nematodes.

Inside, I encountered three pests so far:
  • soft scales (Coccus hesperidum), which I was familiar with as they infected my Citrus at home a while ago, and which I was instructed to spray with insecticidal soap
  • cushion scales (Pulvinaria floccifera), which were new to me, look like soft scale except when they lay eggs in sacs that appear on plants - holly in my case - as white cottony stripes (in fact they are also known as camellia cottony scales); they are most susceptible to insecticidal soap in the crawling stage
  • mealybugs (Pseudococcus sp.). They nest in crevices in plants and are rather difficult to get rid of. They look like tiny, white woodlice with three tails, and cluster in masses, protected by waxy threads.
Individual mealybugs
Cluster of mealybugs

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