Biological warfare

With a cold wet summer such as we’re experiencing this year it can be a bit of a relief to go down to the polytunnels where it’s nice and dry and we have much greater influence over the growing environment. These warmer conditions can bring problems of their own, however, as what is good for something like a cucumber can also be good for pests such as aphids and red spider mite, which can rip through a crop if nothing is done about it. Aphids have a life cycle of 3-4weeks (depending on climatic conditions) and during that time can give birth to 40-100 live young who emerge with the next generation already inside them!

Some predators will follow these pests through the doors: ladybirds, lacewings and hoverflies are all welcome visitors and we have some plants dotted around to encourage them (lacewings love fennel, for example) but this isn’t always enough and so we boost their numbers by distributing extra pest-specific, insects and bugs through the crop.

These fall into two main categories: predators and parasites. Predators (like phytoseiulus persimilis for red spider mite and aphidoletes aphidimyza for aphids) will attack and eat the pest, then lay eggs which hatch into a new generation to continue the process. Parasites are, if anything, more gruesome: aphidius colemani, for example, will lay an egg inside the aphid itself. This obviously kills the pest as the larva grows and when it hatches, carries on the process. Parasites tend to be much more host-specific than predators, which aren’t too fussy (within reason) what they go for. In both cases, the second generation tend to be more active and vigorous than the parents we introduced as they are more acclimatised to the conditions in the tunnels.

Some battles you win and some you lose: to date there are no signs of red spider mite, but our peppers have a few green aphid and one of our cucumber tunnels is fairly heavily infested with black aphid. We have ordered extra insects to help in the war and I have even been introducing the odd ladybird I have found in the fields! Hopefully this will be enough and we can get on top of the problem.

ImageBack outside, meanwhile, we are beginning to harvest our globe artichokes. These highly architectural plants, a relative of the humble thistle, are one of the many crops to have taken a bit of a battering from the elements: they can suffer from browning leaves if conditions are too humid but are worth persevering with as they’re relatively low maintenance for a perennial crop and have a great and unique flavour. I tend to just steam them and eat as a starter with loads of melted butter, though I’m sure Rob in our Field Kitchen restaurant has far more imaginative uses for them…

4 responses to “Biological warfare

  1. Linda Broadbent

    Where does one order extra insects to help fight the war?

  2. At greengardener.co.uk

  3. sally crockford

    I treat aphids with a sollution I make myself. Take a block of “savon du marsielle” or other castille soap and grate about a teaspoonfull, try not to breath in the dust its not pleasant……….pop this into a jug with about a pint of warm water and whisk till disolved, allow to cool, pour contents into a hand pump spray ( cost very little at garden centers ) and zap the little blighters! It works well, tho you need to keep an eye out for more and spray whenever you see them, my roses look a treat now. I have also used this on tomato plants in the past, since we can no longer buy “soft soap” sadly so this is the next best thing.

  4. sally crockford

    On the subject of ladybirds……. we had so many of them earlier in the year, I put them on my potted parsley in the greenhouse as it was being attacked by aphids………. I think they were rather pleased with the feast!

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