This week participants visited the 100 year-old allotments in St Johns Close to search for pests and predators.
Discussion focussed on the need to grow a healthy plant. This is done by selecting seed that is resistant to local pests and diseases, ensuring that essential nutrients are available and manipulating the environment to promote natural predation:
Late blight is a common problem in potatoes and tomatoes, however there are a number of new varieties, such as potato 'Orla' and tomato 'Ferline F1' that are said to have high levels of resistance to this disease.
Plants lacking in essential nutrients are more vulnerable to pests and diseases. Symptoms of nutrient deficiences can be clearly seen in plant leaves. Those in the picture are lacking in potassium (leaf margins dying), magnesium (yellowing between green veins) and phosphorus (green leaf turns reddish).
The use of barriers was recommended to exclude pigeons, carrot fly, codling moth, leaf miner and onion fly.
The need to increase diversity by planting fruit trees and insect-friendly flowers was stressed to encourge beneficial insects such as honey bees and bumble bees as well as predatory insects such as hover flies, lacewings and parasitoid wasps. The parasitoid wasp pictured here is shown next to a human hair and is just 0.3mm long. I collected several that were hovering around a flowering kale plant in my garden. These essential creatures feed on nectar and have larvae that parasitise aphids, leaf miners, white fly and many different caterpillars.
The allotment holders in St Johns Close said that slugs and snails are their biggest enemies. The main predators for these molluscs are chickens, song thrushes and hedgehogs. Unfortunately, song thrushes are in decline because of a shortage of nesting places - they need tall, thick hedges, while hedgehogs need safe places to hibernate and gaps in the fence so that they can travel easily between gardens.