Keeping trees healthy in a changing world

October 22, 2019

Jolanda Roux (right) with Dr. Irene Barnes (centre) and MSc student Granny Hlongwane from TPCP, studying the roots of a eucalypt affected by the new wilt disease caused by a Ceratocystis species.

Keeping trees healthy in the shifting world of climate change and the constant adaptation of insect pests and pathogens to changing conditions is a massive challenge that keeps the Sappi forestry team on their toes.

The number of pests and diseases affecting trees around the world is increasing rapidly, driven by an increase in the movement of plant material around the world, as well as changing weather patterns and other factors. Compounding this problem is the ability of insect pests and pathogens to constantly change and adapt, and to come back to attack your trees with renewed vigour just when you thought the problem was under control.

Heading up Sappi’s Pest and Diseases Programme is award-winning forest pathologist, Jolanda Roux, well known for her work with the TPCP, one of the top tree protection research units in the world. Jolanda is assisted by specialist entomologist, Kayla Noeth.

Sappi has some 250 000 hectares planted to Eucalyptus and pine, so that is a lot of trees for just two people to monitor and keep healthy. But Jolanda points out that they are part of a team. The scientific community is like a brotherhood (or should I say sisterhood) that is open to sharing ideas and expertise, and there is extensive collaboration between different research institutes in South Africa and globally, as well as collaboration with other forest owners at home and abroad.

Kayla Noeth and Jolanda Roux with Marcel Verleur and the contracting team doing Cossid moth surveys in field.

A number of forums have been set up in South Africa to promote collaboration in finding solutions for common problems, like the Sirex and Eucalyptus pest and pathogen working groups, which provide a platform for collective action. Leading research programmes, supported by government, Sappi and other forestry companies, are feeding in ground-breaking technology and research that improve the sector’s ability to manage the impact of pests and diseases.

Jolanda says Sappi has adopted an integrated approach to managing pests and diseases and so there is a lot of in-house collaboration within the Sappi team among tree breeders, soil scientists, nursery staff, foresters and contractors. Maintaining tree health is a complex business, and sharing expertise and experience is essential. You also need a lot of eyes and ears in the field, points out Jolanda, as Sappi’s plantations stretch over a vast area from southern KwaZulu-Natal to Zululand in the north, and inland to the Mpumalanga lowveld.

The Sappi team is increasingly looking to technology to help them monitor the health and status of trees across their landholdings, including the use of remote sensing satellite imagery and drones with multi-spectral cameras. This will provide the Sappi team with early warning of pest and disease problems.

“We can’t be reactive – we need to know what is happening out there as early as possible so we can develop strategies to counter new emerging issues,” said Jolanda.

Good tree breeding is one of Sappi’s key pest and disease management strategies. This involves breeding trees that meet Sappi’s fibre requirements but which are also resistant to problem pests and pathogens. But, says Jolanda, pests and diseases change and adapt, so do growing conditions, and so trees that were once resistant may become susceptible later on. The tree selection, breeding, testing, production and planting cycle for eucalypts is currently around 15 years, so careful long term planning and site-species matching is essential.

The work of the Forest Molecular Genetics Programme, a joint research venture between Sappi, Mondi and the University of Pretoria, will speed up this cycle considerably by making it possible to identify trees with the best genes for stem form, fibre characteristics, yield and resistance to pests and diseases.

Good silviculture and site matching is another key strategy, because stressed trees are far more susceptible to problem pests and diseases than strong, healthy trees.

Sappi entomologist Kayla Noeth discussing pest symptoms with contractors. They are the Sappi team’s eyes and ears in the field.

Climate change
Jolanda explains that climate change is a massive concern for her team. Insects especially are very sensitive to even small changes in temperature and moisture, and so they move, adapt and flourish where they couldn’t survive before. The goalposts are constantly shifting.

The Gonipterus snout beetle is a case in point. Introduced into South Africa in the 1920s, it was a problem pest that was largely managed through the introduction of a biological control agent, Anaphes nitens. However in the last few years Gonipterus has come back with a vengeance, defoliating Eucalyptus trees and doing extensive damage.

Gonipterus snout beetle adults on a GU – they have eaten the leaves.

Another shifting goal post – Fusarium circinatum - initially only a nursery problem, moved into plantations in the Western and Southern Cape, and more recently into mature P. patula in the eastern parts of the country, and is also now hitting P. greggii in the Karkloof area of KZN. Jolanda says new strains of Fusarium are emerging all the time and research at Sappi and the TPCP has shown that there are now more virulent strains of the fungus, also causing disease on pine hybrids.

Sappi and other companies continue to monitor and manage the Sirex wood wasp, despite good results with the introduction of two biocontrol agents. This is done through the South African Sirex Control Programme (funded by DAFF). Annual monitoring of the pest and biological control levels as well as inoculation of trees with the nematode biological control agent is ongoing.

Sappi is supporting two post-doctoral researchers at the Tree Protection Co-operative Programme (TPCP), focused on the development of capacity and expertise in chemical ecology and soil health. The field of chemical ecology includes investigation into pheromones (scents) in the management of insect pests. This is more environmentally friendly than synthetic pesticides and can help reduce the use of such chemicals in future.

Dr. Marc Bouwer, one of the Sappi funded post-docs at the TPCP, and collaborators have recently had good success in the testing of a pheromone for the Pine Emperor moth. This is an indigenous insect, related to the mopani worm, that host jumped onto pine. Jolanda says there have been random defoliation events in plantations around Bulwer, Warburton and southern KZN for years, but now these events are happening annually and it is spreading to other areas. Currently the only control strategy is the spraying of a pesticide. The development of a mating disruption strategy using a pheromone will be a much more environmentally friendly management option.

Emperor moths attracted to a trap using a pheromone developed by Dr Marc Bouwer of TPCP.

Another troublesome native is the Brown Tail moth, Euproctis terminalis, which has been responsible for sporadic defoliation events in the past, but in the last 10 years is spreading and the damage is increasing. Marc and Sappi will be testing a recently developed pheromone for this insect later in the year.

Soil health
Jolanda says a lot of work is being done at Sappi to better understand soil health, due to concerns about long term sustainability as well as a number of pathogens affecting the roots of trees.

“We have a lot of questions about soil health, and how this is impacted by our silvicultural regimes. We need to understand this better,” she said. Sappi and other forestry companies have over the past few years invested in several research projects to gain information towards better management of this resource.

New pest and disease problems continue to appear globally, and in South Africa. Ceratocystis wilt disease of eucalypts is another concern that is keeping Jolanda and Kayla up at night. Ceratocystis species include deadly pathogens of agricultural crops as well as plantation trees, and is now affecting at least two Eucalyptus clones in Zululand. Ceratocystis manginecans, for example, was responsible for wiping out Acacia mangium plantations in South East Asia.

Ceratocystis wilt
“Ceratocystis wilt is a big problem internationally. We have to find out how it spreads and what it is doing in our soil. Importantly, we need to make sure we have eucalypt varieties that are tolerant/resistant to this disease.”

She said it is already affecting one Sappi clone, but more may be susceptible.

“We are looking at opportunities to build collaboration across companies and into academia, in order to manage our pest and disease problems. They are not restricted to a single company, or country, and with limited resources it makes sense to collaborate. At the same time we have to prioritise the transfer of information from academia to industry and streamline adaptation and implementation of management strategies,” said Jolanda.

“Communication remains key to successful pest and disease management, particularly in ensuring that commercial application of new knowledge is improved and that academia and industry goals are aligned.”

*First published in SA Forestry magazine, September 2019

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