By Tanisha Heiberg
LIMPOPO, South Africa (Reuters) - Inspecting the damage on his 4,000 hectare farm, Petri van der Walt breaks open the stem of a sorghum plant to reveal the crop-eating pest that has for the first time been detected in Africa's biggest grain producer.
Bearing four dark spots on its abdomen and a white Y-shaped marking on its head, the fall armyworm has invaded South Africa's northern province of Limpopo -- just months after farmers struggled though the worst drought in a quarter century.
"It eats through the stem of the plant and damages the whole plant and then there will be no production," van der Walt told Reuters on his farm where he also grows sunflower and maize.
White maize is the main source of calories for many South Africans while sorghum is used in animal feed and alcohol.
The army worm was confirmed for the first time in South Africa along the maize belt of Limpopo and the North West province last week.
Pointing out the tell-tale signs of tears in the leaves, van der Walt said it was still too early to estimate the impact on output, and that so far the armyworms had attacked his sorghum plants at a higher rate than his maize crop.
"The drought is still with us and financially everyone is still struggling, so this is an enormous amount of money that has to be taken out to spray the pesticides," said van der Walt, whose family has farmed the 4,000 hectare (10,000 acre) holding for 67 years.
The agriculture ministry has so far registered two pesticides for use against the fall armyworm. Van der Walt says it is difficult and costly to eradicate, with pesticide prices ranging from 200 rand ($15) to 600 rand per hectare.
The thumb-sized adult worm - which can cause extensive crop damage and has a preference for maize - can breed a new generation within a month, senior research entomologist at the Agricultural Research Council's Grain Crops Institute, Annemie Erasmus said.
Armyworm is classified as a quarantine pest, so countries with confirmed outbreaks can lose access to export markets. It is an invasive Central American species that is harder to detect and eradicate than its African counterpart.
Suspected outbreaks have been noted in Zambia, Zimbabwe and Malawi, which also suffered drought last year.
It is unclear what impact the pest will have on farm output, the department of agriculture has said, and crops such as maize, sorghum, soybeans, groundnuts and potatoes are under threat.
But the cost of spraying pesticides is a big concern.
"It's going to be a financial problem for us because if the seed is destroyed or damaged it gets taken off the price of our commodity," said farmer George Rhodes, who is battling the fall armyworm on his farm where he grows seed to supply other farms.
($1 = 13.4200 rand)
(Editing by James Macharia/Ruth Pitchford)