Bollworm and the spotted maize beetle are a couple of the pests which aren’t recognised for the damage they can do. It’s worthwhile to be aware of them so you don’t get caught out with unexplained losses.
A couple of pests aren’t recognised for the damage they can do. It’s worthwhile to be aware of them so you don’t get caught out with unexplained losses. The first is the bollworm (Helicoverpa armigera), which most incorrectly call American bollworms – in fact, they’re African. This pest is very widespread but sporadic, often absent for long periods and then suddenly appearing in large numbers. As climatic conditions induce the moths to hatch out all at once, they will often affect whole districts at a time. This is where pheromone traps are useful, as they’ll indicate when this occurs and help farmers prepare for an outbreak of caterpillars a short while later.
In the case of cucurbits, bollworms lay their eggs on the tender, developing new growth, where the larvae start feeding. They later migrate to the crown of the plants and start to feed on flowers. After one such flush of egg laying, at a certain point on the runners, the leaves will appear somewhat tattered or torn, though they’ll appear normal and healthy on either side.
Bollworms usually bore into unopened flowers and feed on the stigma and style, which receive the pollen when the flowers are open. When the developing fruit turns yellow soon afterwards and falls off, the farmer blames it on pollination – in a way this is correct because with the damaged style, the bees’ pollination efforts come to nothing. This whole process is almost 100% unobserved by the farmer.
If you see damaged leaves, it’s worthwhile looking at newly opened flowers early in the morning for bollworms, which are easily seen. If they’re there, the crop should be immediately sprayed. If pumpkin flies are around, a pyrethroid spray will be effective for both pests. Be sure to spray in the late afternoon after bee activity has stopped.
A pest which does similar damage is the spotted maize beetle, sometimes called astylus beetles or even pollination beetles. They’re certainly associated with pollen – they eat it.
They can usually be seen on maize tassels where enough of them can prevent effective pollination. They’re about 1cm long, yellow with small black spots and very attracted to the colour yellow. Sometimes there are so many of them, they completely cover flowers in clusters as they wait for opening time. They’ll tackle the pollen on both male and female flowers. They usually start appearing after Christmas and are controlled in the same way as bollworms.
Bill Kerr ((016) 366 0616 or e-mail [email protected])