The large pine weevil (Hylobius abietis) is the most serious insect threat to young reforested sites in Ireland. Conifers are particularly vulnerable but it also feeds off broadleaves.
Coillte continuously contends with weevil control because of its high annual reforestation programme but, up until recently, weevil damage wasn’t an issue in private reforestation.
However, an increasing number of forests established by private growers – mainly farmers – up until the early 1990s are now either at or approaching final harvest stage so forest owners are faced with the added cost of controlling weevil when replanting these sites.
Insecticide treatment is the only effective control option although promising non-chemical alternatives are being explored by Teagasc.
A recent Teagasc conference on pine weevil integrated pest management (IPM) explored a number of options in controlling damage by the weevil in Irish forests.
“An average of 50% of unprotected young plants are killed by the pine weevil,” Dr Nuala NiFhlatharta, head of the Teagasc Forestry Development Department, told a recent conference on pine weevil IPM. “This increases the re-establishment costs substantially through the cost of insecticide application, replacing plants and additional weeding, she said.
Pine weevils are always present in coniferous crops regardless of age but following clearfelling, the crop produces a large increase in breeding numbers.
Alternative plant material
At this stage, alternative plant material suitable for adult feeding may be reduced so young trees used for restocking are prone to attack by adult pine weevils feeding on the stem from the root collar upwards. Heavy damage can completely girdle stems and cause plant death.
“One-third of reforestation costs could be down to pine weevil control,” said John Casey, forestry adviser, Teagasc. “While cost is high, the potential cost of crop failure and replanting is higher.”
There is currently no single method of weevil control although pesticide treatment is the most effective, so the conference examined a number of IPM options.
IPM is described as “a sustainable pest management approach that takes the ecology of the pest species into consideration and employs a variety of pest management methods which can be used singly or combined”.
Adult pine weevil is approximately 1.5cm long and has a dark brown body with yellow patches.\ ITGA
“High numbers of pine weevils in Ireland make control more challenging, with physical protections often not enough on high-pressure sites, meaning we will still require pesticides in the future,” said Dr Louise McNamara, Teagasc entomology research officer .
Dr Louise McNamara, Teagasc Entomology Research Officer.
She outlined some research already under way including the introduction of Entomopathogenic (insect-killing) nematodes that seek out and kill insects. These tiny worms occur naturally in soil throughout Ireland but can also be mass produced commercially and applied to soil in water, using standard pesticide application techniques.
“In trials by Coillte and Maynooth University, nematodes applied to the stumps of felled trees were able to reach and kill pine weevil larvae developing within the stump and roots, even at soil depths of up to 50cm,” Dr McNamara said.
“The number of adult pine weevils emerging from nematode-treated stumps could be reduced by up to 80%, and so nematodes have potential use in population reduction of this pest,” she added.
“Any decision to use nematodes to suppress pine weevils on a reforestation site would require careful consideration, taking into account both the numbers of weevils developing on the site and the potential for immigration of adults from neighbouring untreated clearfells.”
She said nematodes have been successfully used for pine weevil suppression by Natural Resources Wales “and are a potential component in the IPM toolbox for pine weevil in Ireland”.
The importance of timing in weevil control
Mosstown Wood, near Keenagh, Co Longford, is independently certified by the Forest Stewardship Council (FSC) as being managed according to the principles of sustainable forest management.
Owned by the Irish Forest Unit Trust (IForUT), the forest has to achieve a range of wood and non-wood objectives as part of the certification process, maintained Darryn McDowell of IForUT during a recent field day in Mosstown, organised by the Irish Timber Growers Association (ITGA).
Sitka spruce, reforestation in 2018, in Mosstown Wood without fertiliser, herbicide or onsite pesticide application.\Donal Magner
He said when Mosstown was reforested in 2018 after final harvest, it had to fulfil a number of criteria – wood and non-wood – to ensure it maintained its certification status.
IForUT reforested the 32ha site without resorting to fertilisers, herbicides or onsite pesticides.
“The biggest challenge was to control pine weevil without resorting to on site pesticide use when we replanted the site in 2018,” said John McGarr, forestry manager with Forestry Services Ltd (FSL).
John McGarr, Forestry Services Ltd.
He ordered strong nursery plants with large root collar diameters which offer some resistance to weevil attack, he said.
“I decided to plant in May – close to the end of the spring planting season. The plants were chemically treated in the nursery before delivery to the forest site. The relatively late planting reduced the risk of weevil damage as the chemical lasted throughout the growing season when the plants are vulnerable, especially in late summer.”
Even though the plants – Sitka and Norway spruce, birch and oak – are into the fourth growing season, he still monitors the site as it is not unknown for weevils to attack up to year five.
While Teagasc recommends mounding before planting to help reduce the risk of weevil attack, FSL pit-planted the site and still avoided herbicide and pesticide control.
Agroforestry is likely to be a strong element of the next forestry programme (2013-2017).
The Irish Agroforestry Forum (IAF) is highlighting this initiative as a viable land use that can be integrated with agriculture.
IAF organised an agroforestry farm walk on the holding of Micheál O’Donovan, Ballinspittle, Co Cork, last month to highlight the benefits of agroforestry. The O’Donovan family has a 16.5ha beef and sheep farm and last year they transferred 2.4ha to agroforestry for their lowland sheep flock.
“The ground has a steep slope and Micheál felt that planting it would bring benefits to his sheep and also improve farm safety as a tractor would not be used on the high ground anymore,” said Maureen Kilgore, IAF.
“Trees on pasture can provide shade, shelter, nutrients and worm prevention when animals can browse the tree leaves and also improve nutrient cycling and the overall farm environment,” she added.
“The species planted comprised oak, birch and cherry with 7m between the rows and 3.5m spacing between trees in each row.
“The agroforestry plot is currently being grazed by sheep – mixed lowland ewes with lambs at foot.”
The large pine weevil (Hylobius abietis) is the most serious insect threat to young reforested sites in Ireland. Conifers are particularly vulnerable but it also feeds off broadleaves.
Coillte continuously contends with weevil control because of its high annual reforestation programme but, up until recently, weevil damage wasn’t an issue in private reforestation.
However, an increasing number of forests established by private growers – mainly farmers – up until the early 1990s are now either at or approaching final harvest stage so forest owners are faced with the added cost of controlling weevil when replanting these sites.
Insecticide treatment is the only effective control option although promising non-chemical alternatives are being explored by Teagasc.
A recent Teagasc conference on pine weevil integrated pest management (IPM) explored a number of options in controlling damage by the weevil in Irish forests.
“An average of 50% of unprotected young plants are killed by the pine weevil,” Dr Nuala NiFhlatharta, head of the Teagasc Forestry Development Department, told a recent conference on pine weevil IPM. “This increases the re-establishment costs substantially through the cost of insecticide application, replacing plants and additional weeding, she said.
Pine weevils are always present in coniferous crops regardless of age but following clearfelling, the crop produces a large increase in breeding numbers.
Alternative plant material
At this stage, alternative plant material suitable for adult feeding may be reduced so young trees used for restocking are prone to attack by adult pine weevils feeding on the stem from the root collar upwards. Heavy damage can completely girdle stems and cause plant death.
“One-third of reforestation costs could be down to pine weevil control,” said John Casey, forestry adviser, Teagasc. “While cost is high, the potential cost of crop failure and replanting is higher.”
There is currently no single method of weevil control although pesticide treatment is the most effective, so the conference examined a number of IPM options.
IPM is described as “a sustainable pest management approach that takes the ecology of the pest species into consideration and employs a variety of pest management methods which can be used singly or combined”.
Adult pine weevil is approximately 1.5cm long and has a dark brown body with yellow patches.\ ITGA
“High numbers of pine weevils in Ireland make control more challenging, with physical protections often not enough on high-pressure sites, meaning we will still require pesticides in the future,” said Dr Louise McNamara, Teagasc entomology research officer .
Dr Louise McNamara, Teagasc Entomology Research Officer.
She outlined some research already under way including the introduction of Entomopathogenic (insect-killing) nematodes that seek out and kill insects. These tiny worms occur naturally in soil throughout Ireland but can also be mass produced commercially and applied to soil in water, using standard pesticide application techniques.
“In trials by Coillte and Maynooth University, nematodes applied to the stumps of felled trees were able to reach and kill pine weevil larvae developing within the stump and roots, even at soil depths of up to 50cm,” Dr McNamara said.
“The number of adult pine weevils emerging from nematode-treated stumps could be reduced by up to 80%, and so nematodes have potential use in population reduction of this pest,” she added.
“Any decision to use nematodes to suppress pine weevils on a reforestation site would require careful consideration, taking into account both the numbers of weevils developing on the site and the potential for immigration of adults from neighbouring untreated clearfells.”
She said nematodes have been successfully used for pine weevil suppression by Natural Resources Wales “and are a potential component in the IPM toolbox for pine weevil in Ireland”.
The importance of timing in weevil control
Mosstown Wood, near Keenagh, Co Longford, is independently certified by the Forest Stewardship Council (FSC) as being managed according to the principles of sustainable forest management.
Owned by the Irish Forest Unit Trust (IForUT), the forest has to achieve a range of wood and non-wood objectives as part of the certification process, maintained Darryn McDowell of IForUT during a recent field day in Mosstown, organised by the Irish Timber Growers Association (ITGA).
Sitka spruce, reforestation in 2018, in Mosstown Wood without fertiliser, herbicide or onsite pesticide application.\Donal Magner
He said when Mosstown was reforested in 2018 after final harvest, it had to fulfil a number of criteria – wood and non-wood – to ensure it maintained its certification status.
IForUT reforested the 32ha site without resorting to fertilisers, herbicides or onsite pesticides.
“The biggest challenge was to control pine weevil without resorting to on site pesticide use when we replanted the site in 2018,” said John McGarr, forestry manager with Forestry Services Ltd (FSL).
John McGarr, Forestry Services Ltd.
He ordered strong nursery plants with large root collar diameters which offer some resistance to weevil attack, he said.
“I decided to plant in May – close to the end of the spring planting season. The plants were chemically treated in the nursery before delivery to the forest site. The relatively late planting reduced the risk of weevil damage as the chemical lasted throughout the growing season when the plants are vulnerable, especially in late summer.”
Even though the plants – Sitka and Norway spruce, birch and oak – are into the fourth growing season, he still monitors the site as it is not unknown for weevils to attack up to year five.
While Teagasc recommends mounding before planting to help reduce the risk of weevil attack, FSL pit-planted the site and still avoided herbicide and pesticide control.
Agroforestry is likely to be a strong element of the next forestry programme (2013-2017).
The Irish Agroforestry Forum (IAF) is highlighting this initiative as a viable land use that can be integrated with agriculture.
IAF organised an agroforestry farm walk on the holding of Micheál O’Donovan, Ballinspittle, Co Cork, last month to highlight the benefits of agroforestry. The O’Donovan family has a 16.5ha beef and sheep farm and last year they transferred 2.4ha to agroforestry for their lowland sheep flock.
“The ground has a steep slope and Micheál felt that planting it would bring benefits to his sheep and also improve farm safety as a tractor would not be used on the high ground anymore,” said Maureen Kilgore, IAF.
“Trees on pasture can provide shade, shelter, nutrients and worm prevention when animals can browse the tree leaves and also improve nutrient cycling and the overall farm environment,” she added.
“The species planted comprised oak, birch and cherry with 7m between the rows and 3.5m spacing between trees in each row.
“The agroforestry plot is currently being grazed by sheep – mixed lowland ewes with lambs at foot.”
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