Farmer's Weekly (South Africa)

Potential Swiss chard pests


It is important to remember that cutworms might be present in the soil before you plant. The caterpilla­rs are extremely hardy, and in the absence of green plants will eat a variety of organic matter.

For safety’s sake, always assume they are present and apply suitable measures before planting Swiss chard. A pyrethroid spray is a good option.

Two other potential Swiss chard pests are the following:

• Hawaiian beet webworm ( Spoladea recurvalis)

This is a sporadic but potentiall­y harmful pest. Fortunatel­y, when a pest is sporadic, its natural enemy is often also present. In this case, a parasitic wasp is able to control S. recurvalis.

The problem is that the wasp is so effective it eliminates the pest on which it breeds, causing its own population to plummet. This allows the webworm to flare up again. The ideal is to have a small number of each to maintain a balance.


To keep a lookout for this pest, walk through the crop regularly. Should you flush out the moths, identified by their brown-andwhite colour and delta-wings, an outbreak may be imminent. Look for damaged leaves with holes in them. If you see any, turn the leaf over; a green caterpilla­r up to 25mm in length means the pest is present.

Next, look for the parasitoid that keeps it under control. You might find small black wasps, each a few millimetre­s in length, resting on leaves or examining the leaves while in flight looking for their host, the webworm caterpilla­r.

Small, blocky, white cocoons are a sure sign that the wasps are present.

Your response will depend on the number of wasps in proportion to the number of caterpilla­rs, and whether the damage to the crop is serious.

Often, only a few moth larvae and wasps are present, in which case you can leave the parasitoid­s to do their work unhindered.

If the damage is bad enough to affect yield, you will need to spray, even if wasps are present.

It’s extremely important to use a product that will control the caterpilla­rs without harming the wasps; products containing Bacillus thuringien­sis are a good option.

• Leaf miner ( Liriomysa huidobrens­is)

This is another sporadic and potentiall­y highly destructiv­e pest that is particular­ly fond of Swiss chard. Well-informed farmers usually have no problem with this pest, however, as, once again, effective parasitoid­s take care of it.

L. huidobrens­is generally becomes a problem when harsh insecticid­es that kill the parasitoid­s are used on the crop. The leaf miner will also be killed, of course, but will flare up again in the absence of parasitoid­s, making it necessary to keep on spraying.

As their common name suggests, leaf miners make serpentine tunnels in the leaf. They also have a very wide host range. But this can work to your advantage, as this allows parasitoid­s to build up in weeds.

In the unlikely event of spraying being necessary, ensure that the product you use is guaranteed not to harm the wasps.

• Bill Kerr is a vegetable specialist and breeder. Email him at farmerswee­ Subject line: Vegetable Production.

 ?? BILL KERR ?? ABOVE:The larva of a Hawaiian beet webworm with a parasitoid cocoon from which a wasp has already hatched.
BILL KERR ABOVE:The larva of a Hawaiian beet webworm with a parasitoid cocoon from which a wasp has already hatched.
 ??  ?? BILL KERR

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