02 Feb 2017

After receiving numerous reports of pests, diseases and plant health issues over the past seasons in Kgalagadi District, the entomology section of Department of Agricultural Research (DAR), recently released a warning about crop pests that have been detected in the district.

In an interview recently, principal agricultural research officer in the Kgalagadi District, Mr Ofentse Sithole said some of these pests, diseases and nutrient deficiencies of vegetables recently detected, were cabbage looper, imported cabbageworm, diamondback moth, bacterial soft rot, early blight, anthracnose, nitrogen and phosphorus deficiencies in plants, among others.

The pests’ most preferred hosts include cabbage, rape and kale, but Mr Sithole said they also attack field crops.

“If you see an extremely mobile caterpillar with prolegs only in the anterior and posterior segments move rapidly from plant to plant, skeletonising the leaf, you probably have cabbage loopers,” he said. 

Mr Sithole said the easiest, most accessible and safest way to get rid of cabbage looper pests was by manual removal by checking in the morning and late evening when temperatures were cool.

He also warned the farmers that the most destructive insect pest of many crops detected was the diamondback moth. Mr Sithole said caterpillars moth catterpillars bore many small holes in the leaves of the host plants, often leaving the leaf epidermis (outermost layer of cells) intact, making a ‘feeding window’. 

“Most damage is caused by the caterpillars tunnelling into the heads of plants such as cabbage and brussels sprouts. They also cause contamination of produce by pupating inside broccoli florets and cauliflower curds,” he said. 

He explained that management of diamondback moth required an integrated approach like understanding the life cycle of the moth and recognising the caterpillar stages, using the bacterial insecticide, bacillus thuringiensis on young plants and on mature plants when pest pressure is low on an area-wide scale. 

Other management of these pest include; ploughing in crop residues or on heavily infested crops promptly.

Mr Sithole said plants also show nutrient deficiency symptoms, especially on their foliage and some deficiencies of potassium, sulphur, boron, chloride, copper, iron, manganese and zinc were observed. 

For example, he said phosphorus deficiency symptoms on foliage were detected when older leaves under very severe deficiency conditions exhibit development of a brown netted veining of the leaves. 

 “The practice of foliar feeding is a common exercise of supplying lacking nutrients to plants through their foliage (leaves)”.

 He further said foliar feeding involved spraying water-dissolved fertilisers directly on the leaves through the openings on the leaves called stomata adding that generally, foliar application of particular nutrients could be useful in crop production situations where soil conditions limit nutrient availability.

Meanwhile, in an effort to prevent accumulation of pesticide residues in the agricultural produce across Kgalagadi District, DAR has taught farmers how to make and use ginger plus garlic as the most effective and easiest way applied on foliage where there are signs of pest infestation on crops, particularly when crops are near harvest. 

Mr Sithole said ginger-garlic extract was good natural antibiotic/preventative medicine for plants.BOPA