30 | 09 | 2014

 

Insect Control PDF Print E-mail
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Insect Control
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Lucerne is attacked by insects throughout the year. They feed on the stems, leaves, roots and seeds of the plant and can have a serious effect on production.

Which insects occur in a stand of lucerne varies greatly between years, depending on climatic conditions and the occurrence of their natural enemies.

Lucerne should be inspected regularly for the presence of harmful insects, which can do serious damage to the stand before any control measures can be implemented.

It is important that insecticides are correctly and responsibly applied. Apart from being expensive, unnecessary use can lead to the development of resistance to that insecticide, it may build up to toxic levels in the lucerne, pollinators may be killed and game, domestic animals and human health may be affected.

A prerequisite for successful insect control is correct identification of the insect. It is also important to understand what problems it may cause.

The goal of successful control is to suppress the unwanted insect population before it can cause damage, while not affecting desirable insects.

Beetles

White fringed beetle (Graphognathus leucoloma Boh.)

DESCRIPTION
The white-fringed beetle is a serious problem in South Africa. The larvae are white, broad, banana-shaped grubs that remain in the soil.

The adult is a flightless beetle, about 12 mm long, grey with fine whitish lines along the length of the wings, and a characteristic broad white stripe down the length of each side.


The eggs are laid in clusters on plant parts or on other objects on or near the soil surface.

The adult beetles are very common in the summer, but may still be encountered in the winter.

 

They can live for up to 5 months and lay 1000 eggs each. The eggs need contact with free water to hatch. If they do not get this they may still remain viable for some months.

Larvae develop during the winter, usually 10-20 mm under the soil surface, but occasionally up to 160 mm deep.

Larval development is usually complete by spring, but can be extended through the following summer and winter until the pupae hatch and the adult beetles appear.

Although they cannot fly, these are spread in feed, equipment and implements to other areas where they start new infestations. There are no males and new colonies can arise from a single beetle.

DAMAGE TO LUCERNE
The larvae attack the roots of the plant and can cause considerable damage.

They have a serious effect on the longevity of the stand, as the plants are weakened, become wilted and eventually die off .

The adults feed above ground but seldom cause serious damage.

White fringed beetles, even at a low infestation rate, can cause considerable loss of yield. At a high rate of infestation, root losses can run to over 80%.

Because lucerne is a perennial crop, and because of the succession of generations of the insect, there is a possibility that lucerne may already be heavily infested by its second season. Die-off may then reduce plant numbers to such an extent that the stand becomes uneconomical.

RECOMMENDED CONTROL MEASURES
Populations can be limited by rotating with other grains or grasses, or a fallow summer before planting with lucerne may be applied. The insect can only be combated by certain soil-applied insecticides, for instance, those with gamma-BHC’s, methyl bromide and chlorpicrin as active ingredients.

Flea beetles (Podagrica spp. and Nisotra spp.)

DESCRIPTION
The beetles are oval, about 4 mm long, brown or black in color, and have well-developed rearmost "thighs" (femora) with which they can jump if disturbed

DAMAGE TO LUCERNE
The beetles feed on the leaves and chew several small holes through part of the thickness of the leaf, which look like whitish "windows".



 

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