Remember those wildlife documentaries where a pride of lions slowly circle a herd of wildebeest picking off the oldest, youngest or sickest animals to hunt down and devour? Gardening can be a bit like that sometimes. Insects instinctively know when a plant is undernourished or dry, and target their attacks on weakened specimens. Sick plants make easy prey, and the insects are in for the kill.
It’s not always that simple, of course – perfectly healthy people can be struck down by disease, and seemingly strong plants can succumb to insect attack. But keeping your plants well-fed and well-hydrated is the first line of defence against pests and diseases.
Powdery mildew appearing on zucchini plants, for instance, is a sign to me they are on their way out to the compost heap (the average zucchini plant produces twelve fruits, apparently, before dying.) But powdery mildew is also a sign of heat and humidity combined with dry roots. A good feed and a deep soak, with seaweed or comfrey tea, can help a plant recover.
Certain plants also seem to have inbuilt pest resistance. So far this summer we haven’t seen signs of the dreaded psyllid, looking like an aphid-sized cicada, which can cause tomatoes and potatoes to yellow and die almost overnight. But when I got it two years ago, it was the old heirloom peruperu potatoes that withstood attack, while all the others died.
Weather also has an influence; sustained periods of hot, dry weather help insects hatch in droves. As summer settles in, one pest turning up in many gardens is the green vegetable bug (aka shield beetle or stink bug), generally found on beans, sweet corn and tomatoes. They are sap-suckers, and while not fatal, having your sap sucked out is never good. The younger the plant, the softer, juicier and more vulnerable its tissue. Symptoms include deformed tomatoes, curly leaf tips and twisted beans, as well as viral diseases which show up as yellow mottling on leaves. Like needle-sharing junkies, sap-sucking insects spread these diseases between plants.
The good news is that now, when they first hatch out, is the easiest time to catch these critters. Juvenile bugs (nymphs) are black with white spots. They start off looking like tiny ladybirds and slowly change, over a week or so, through orange and black to their eventual well-camouflaged green. So while mature green vegetable bugs can be very hard to see, the juveniles are easily spotted. In my garden they often hatch on calendula seed heads where they like to bask in the sun building up body heat.
If you squash one of these bugs, nymph or adult, they emit an indescribable stench. This is their defence mechanism, warning other bugs that danger is at hand. The bugs’ response is to drop to the ground, and this dropping instinct is the key to catching them. It’s as simple as going out with a cup of hot water, finding some bugs and placing the cup beneath them. Then flick the bugs into the water, or squash one and watch the others drop in. This also works with cold water, though very hot water is possibly more humane. It might not be everyone’s cup of tea, but gardening in general, and pest control in particular, is not for the overly squeamish. Remember, it’s a jungle out there.