Poplar leaf rust

Control of species of type Disease Latin: Melampsora larici-populina Kleb.
English: Poplar leaf rust
French: Rouille foliaire du peuplier
Order/Class: Pucciniales

Prevention

When establishing a poplar plantation, it is important to select sites with no larch species or to eliminate any larch trees that are present. Poplars should be planted on sites that are favourable for their development (Bernier et al. 2003; Ménétrier 2005; van Oosten 2006). Weeding of plantations promotes the growth and health of young poplar trees.

The plantations should be monitored to ensure early detection of poplar leaf rust.

Control

1. Mechanical and silvicultural

Melampsora larici-populina requires an alternate host (i.e., larch species) to complete its life cycle. The rust has little effect on larches but can severely defoliate certain poplar clones, reducing their growth and possibly killing them. The incidence of poplar leaf rust can be reduced by eliminating all larches (alternate host) in the area around plantations and nurseries, since this keeps M. larici-populina from completing its life cycle. Monocultures, often established by poplar growers, create conditions conducive to rust outbreaks since amplification of Melampsora is facilitated by the presence of an abundant supply of susceptible leaves (Bernier et al. 2003). In addition, the resistance barriers created by the development of hybrid poplars could be breached, creating new M. larici-populina virulences.

2. Chemical

Application of a registered fungicide in a plantation can be helpful at the onset of a rust infection, especially during hot, humid weather (Spiers 1976). Most fungicides will prevent or reduce sporulation of M. larici-populina.
Fungicides registered for use in Canada: chlorothalonil and myclobutanil.

Caution
There are many different chemical pest control products available. They may be toxic to plants, animals, humans or the environment in general. A number of these products pose potentially lethal risks to humans. To protect human health and the environment from pesticide-related risks, Canada adopted the Pest Control Products Act (PCPA). The Pest Management Regulatory Agency (PMRA; http://www.hc-sc.gc.ca/ahc-asc/branch-dirgen/pmra-arla/index-eng.php) is responsible for administering the Act. A pesticide product label indicates the class designation (domestic, commercial, agricultural), the potential risks to human health and the environment, and the conditions and restrictions pertaining to product use. Compliance with the label directions and restrictions is mandatory. The provinces may also regulate the use of pesticides within their respective territory. For more information, consult the PMRA database at the following address: http://pr-rp.pmra-arla.gc.ca/portal/page?_pageid=34,17551&_dad=portal&_schema=PORTAL

3. Biological

Developing a biological control agent is always a challenge, because even if the in vitro testing and greenhouse stages are successful, the candidate organism often does not do well in field testing (Moricca et al. 2005). Cladosporium tenuissimum Cooke has been extensively studied because it is a parasite of rust spores (Moricca et al. 2005). This potential biocontrol agent has several requisite properties such as the ability to reduce the number of rust spores produced and their viability, and thereby impede the spread of poplar leaf rust. However, this biocontrol agent should be incorporated into an integrated disease management framework (Moricca et al. 2005).

4. Genetic resistance

Over a number of decades, many crosses were carried out to obtain poplar clones with complete resistance to the rust caused by Melampsora. The crosses made in North America were aimed primarily at making poplar immune to M. medusae and Septoria canker. However, since M. larici-populina became introduced, some previously rust-free poplars no longer have resistance. In addition, since it was first reported in 1991 (Newcombe and Chastagner 1993), M. larici-populina has become established in North America and is able to complete its life cycle and reproduce (Grondin et al. 2005). Some researchers still believe that the only way to obtain rust-free poplar plantations is to develop resistant species (Newcombe et al. 2001). However, the poplars developed in Europe that were completely resistant to the disease caused M. larici-populina to mutate and adopt new virulences (Bernier et al. 2003). This occurrence is often attributable to resistance controlled by a single dominant gene, which the fungus is able to circumvent more easily. It is therefore better to develop crosses of poplars that have several resistance genes. Although this may not give them complete resistance to M. larici-populina, it will enable them to grow well despite the presence of the fungus at a low level.

5. Stages in an integrated disease management program

  1. Eliminate the alternate host of the causal fungus when establishing a new plantation.
  2. Select an appropriate site that meets the needs of the poplars.
  3. Select poplars that are not very susceptible to rust.
  4. Plant a wide diversity of poplar species.
  5. Limit the size of the plantations.
  6. Maintain the general health status of the plantation by limiting all competition between young poplar and by carrying out weeding.
  7. Check the trees often to ensure early detection of the presence of disease, including rust. Carefully diagnose nuisance factors. Treat based on the types of disease found.
  8. Protect the poplar trees against rust by applying a fungicide in accordance with the manufacturer's directions.
  9. Develop new rust-resistant hybrid poplars.

References

  1. Bernier, L., Gagné, P., Feau, N., Mottet, M.-J., Périnet, P., and Hamelin, R.C. 2003. L'établissement et la protection des plantations. In Actes des Colloques du Carrefour de la recherche forestière. Réseau ligniculture, Québec
  2. Grondin, J., Bourassa, M., and Hamelin, R.C. 2005. First report of the aecial state of Melampsora larici-populina on Larix spp. in North America. Plant disease; 2005 Nov; 89(11): 1242 89(11): 1242.
  3. Ménétrier, J., Perron, M., Daoust, G. et Sirois, G. 2005.Le boisement des friches - Programme de Forêt 2020 pour l'évaluation et la plantation de démonstration au Québec. Notice d'information 2005, Ministère des ressources Naturelles et de la Faune du Québec et Ministère des Ressources Naturelles du Canada, 23 pp.
  4. Moricca, S., Ragazzi, A., and Assante, G. 2005. Ttile. In Rust diseases of willow and poplar. Edited by M. H. P. A. A. R. McCracken. CABi publishing. p. 213.
  5. Newcombe, G., and Chastagner, G.-A. 1993. First report of the Eurasian popular leaf rust fungus, Melampsora larici populina, in North America. Plant Disease 77(5): 532-535.
  6. Newcombe, G., Ostry, M.E., Hubbes, M., Périnet, P., and Mottet, M.-J. 2001. Title. In Poplar Culture in North America. Edited by J. G. I. D.I. Dickmann, J.E. Eckenwalder, J. Richardson. NRC Research Press, National Research Council of Canada, Ottawa. pp. 249-276.
  7. Spiers, A.G. 1976. Fungicides for control of poplar leaf rust and effects of control on growth of Populus nigra cv. 'Sempervirens' and Populus X euramericana cv. 'I-214'. New Zealand journal of experimental agriculture; June 1976, 4 (2); 249 254 4(2): 249-254.
  8. van Oosten, C. 2006. Hybrid Poplar Crop Manual for the Prairie Provinces. Saskatchewan Forest Centre, pp. 17-32.

Authors

Josée Grondin et Pierre DesRochers

Auditors

Jacques Tremblay