plants, pests & the search for balance

The first basil and cucumbers were harvested from our polytunnels last week, and very fine they were too. We grow mainly mini cucumbers as they taste better, are easier to grow and avoid you having that soggy-ended cucumber half lurking in the back of the fridge, so I can’t really understand why anyone grows anything else.

Outside we are in the hands of the Gods with a difficult start to the season, but the protection of our flimsy tunnels can give dangerous delusions of omnipotence. We can manipulate the temperature, humidity and ventilation to promote growth and avoid fungal disease and our team of pickers, pruners and tomato trainers are experts at identifying and monitoring aphids and spider mites. Rather than turning to chemicals as a means of pest control, a dynamic balance of pests and predators is our aim, but when an aphid gets its proboscis plugged into a good stream of plant sap they can squeeze out babies at an alarming rate. If life is good they give up on sex and egg production altogether; why bother with the complications, wasted energy and variable offspring when you can just replicate more like mamma via parthenogenesis. The trick is to introduce enough of the right predators and parasites before the explosion happens and to get the balance at an acceptable level where crops do not suffer significantly.

We are struggling to find that balance out in the fields too. Aphids in the lettuce and flea beetle on rocket, mustard and spinach have forced us to abandon a number of crops, just when we need them most for your boxes. It could be that low temperatures are disproportionately slowing predator activity, but I feel more inclined to attribute our problems to stressed crops emerging from a miserable winter. Just as with humans, stress leads to vulnerability. Later cropsare looking happier however, and past experience would suggest that predator appetites rise with temperature faster than pest fecundity does. So, as we enter summer proper, we expect the balance to come outside in our fields as it has in the tunnels, and all will be well on the farm (for the time being at least).

Guy Watson