This article was originally published in The Macadamia. Click here to read the original.
An unwelcome new pest, the macadamia felted coccid, has made its way from Australia to the macadamia orchards of Mpumalanga, where it is causing tree die-back and reduced yields. The macadamia felted coccid has had a major detrimental effect on orchards in Australia where it originated, and on macadamia plantations in Hawaii.
Dense infestations cause leaf die-back and flower drop, with subsequent reductions in nut set. In extreme cases trees will die-off completely. The coccid has recently been discovered and identified on several farms in the lowveld.
Although the infestation was first thought to have been contained in Barberton, where it was first found, it spread to White River within a month, presumably through infected plant material.
Dr Schalk Schoeman, senior researcher at the Agricultural Research Council, said little was known about how the coccid had reached South Africa or how it was dispersing.
“My suspicion is that it was somehow brought over in Australian plant material. I would advise anyone that has recently bought trees in the Barberton area to inspect the tree carefully for the coccid,” Schoeman said.
Felted coccids can be identified by their elongated shape. They are covered with a felt-like sac, are whitish in colour and form thick encrustations on leaves, twigs and even on the main stem.
The adult female is about 1,5mm long, dirty white or pale yellow, with a raised circular opening at the posterior end. The male, with white scale cover, is smaller than the female at about 1mm long. In some cases infested trees can be detected by a dull bronze colour in the foliage.
“The literature states that once the coccids are in the orchard, they tend to stay in the same tree and spread is relatively slow. But observations in White River contradict this as there was considerable spread to adjoining trees. These trees were young and although the planting density was high, the trees were not touching which makes me think they are probably dispersed by wind,” said Schoeman.
He said the focus should now be on awareness so that everyone becomes informed about the presence of the pest in the country.
“Following on from that, we should focus on containment. I have noticed branch die back in White River and from photos in Hawaii it looks like this can get quite bad affecting nearly the entire tree, with obvious detrimental effects on yields. On bearing trees, nut yields are reduced and there is a delay in the fall of mature nuts,” Schoeman said.
Currently there are no registered chemicals to combat the coccid. A sprayable oil mixed with Movento and an insect growth regulator such as Buprofezin can be used. The felted coccid is treated differently to stinkbugs. The oil and Movento is directed at adults and Buprofezin is directed, as a second spray, against the crawlers.
Schoeman said stink bug spraying programmes should offer some form of protection but would not give adequate control and could increase the development of resistance by the coccid in the future.
He pointed out that there seemed to be an increase in the prevalence of insects attacking macadamias in the last two years.
“We have picked up that bark borers have become an issue. Our initial thoughts were that they were secondary (pests) but I no longer think this is the case. Thrips and mites have also increased during the last few years. There is a possible link with climate change, but it is difficult to prove at this stage. Farmers need to remain vigilant and report any unusual insect activity in their orchards,” he said.