FARMER'S NOTEBOOK
Woolly aphid menace in sugarcane plantations
M.J. PRABU
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Weekly monitoring of the crop is the ideal way to locate the pests
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SEVERE INFESTATION: Spot spraying of insecticide is better to control aphid (white patches) infestation.
SUGARCANE IS affected by about 90 species of sucking pests, of which the sugarcane woolly aphid (SWA) is the most serious. The infestation is capable of spreading very fast because of its high reproductive potential.
The invasive phase (entry phase) of the pest should be tackled by periodically locating the inoculum (first batch of colonies of SWA that had reached the location) colonies and destroying them, according to Dr. N. Mukunthan, Principal Scientist and Head of Entomology, Sugarcane Research Institute (SRI), Coimbatore.
"Weekly monitoring is the ideal way to locate the inoculum colonies," he said.
Planting methods
It is advisable to plant the sugarcane in pits or in wider rows in areas prone to SWA infestation. This would give adequate moving space for monitoring the crop and for taking up plant protection measures.
Besides, the increased spacing allows more sunlight which in turn deters new SWA colonies from settling.
The second step is detrashing the field during the 5th and 7th month after planting.
"This improves aeration and light penetration into the field which helps in monitoring and plant protection operations," said Dr. Mukunthan.
Fertilizer application
The third step is timely application of nitrogenous fertilizers. "Avoid excess application of urea and excess irrigation," he said. Once an inoculum colony is located during the weekly inspections, the infested clumps should be sprayed with 2 gm of acephate diluted in one litre of water.
This method of spraying is called spot spraying. In the absence of acephate, about 20 gm of detergent soap diluted in one litre of water may be sprayed.
The spraying should be done on the lower side of leaves covering the entire surface.
The aphids get stuck to the leaves sprayed with the soap solution. Spot application has some advantages.
The quantity of insecticide used, and the time and labour spent on spraying is greatly reduced.
It also prevents contamination of healthy plants, thereby retaining the fodder value of the crop.
Blanket spraying
Another method called blanket spraying, where the insecticide is sprayed all over the field to control the inoculum colonies, will be of little use as the protection offered by the insecticide is only for a limited span of time in uninfested plants; it will curb the spread of the infestation from the infected plants.
Blanket application is not advised for farmers because of wastage of insecticide, labour and time in addition to destruction of beneficial organisms in the soil.
"In severely infested crops, acephate should be sprayed on the entire crop. Before spraying the insecticide, predators such as Dipha aphidivora (known as Pachai valai puzhu in Tamil) present in the field should be conserved," he said.
The leaves on which the predators are present may be manually collected and placed in four or five spots in the sugarcane field.
"These spots are called refugia. While spraying the insecticide, farmers should take care to see that it is sprayed on the entire crop and not on the refugia," he said.
New technique
According to Dr. Mukunthan, this type of spraying saves the crop from SWA damage. The Sugarcane Breeding Institute has developed a technique called `simple tray method' by which the predator Dipha aphidivora can be reared in plastic trays.
Farmers can adopt this method to produce about 350 Dipha cocoons in 18 days from a single tray.
When the SWA population reappears 18 to 20 days after the insecticide spraying, the tray reared Dipha cocoons may be released at the rate of 1000 larvae/cocoons per hectare at different spots in the field to control the infestation, according to him.
Dr. N. Mukunthan, Principal Scientist and Head of Entomology, can be contacted at Sugarcane Breeding Institute, Coimbatore, Phone: 0422 2472621and 265, email: krishnammukunda@yahoo.com
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