Management Options to Control Beech Leaf Disease
By Nicholas J . Brazee , UMass Extension Plant Pathologist
Beech leaf disease ( BLD ) is caused by the foliar nematode Litylenchus crenatae ssp . mccanii . The BLD nematode is strongly believed to be non-native in North America and can readily infest American ( Fagus grandifolia ) and European beech ( F . sylvatica ). Nematodes are microscopic , rounded , non-segmented worms in kingdom Animalia . Historically , they have been studied by plant pathologists and are important pests of turfgrasses and vegetable crops . The current situation with beech leaf disease is unprecedented ; there has never been a documented case of a foliar nematode causing widespread tree mortality . Therefore , identifying successful management strategies has been a major challenge without any frame of reference . The disease is spreading rapidly across Massachusetts and many infected trees are quickly declining .
Beech Leaf Disease
Presently , phosphites ( Agri-Fos™ , Reliant™ , Polyphosphite 30 £) have been shown to reduce populations of the BLD nematode in infested trees . However , it may take several years of treatment to see a notable improvement in tree vigor . Phosphites can be applied by drenching the soil around the base of the tree or by spraying the lower trunk of infested beech . This systemic fungicide moves readily in the tree ’ s vascular system . Currently , it ’ s not understood how phosphites reduce nematode populations , but trials are continuing . Phosphites have two modes of action , with one acting as a weak fungicide and the second working to stimulate the tree ’ s natural defense response . Phosphites are not a fertilizer and do not provide plants with a usable source of phosphorous .
Recent research has suggested that fluopyram is effective in controlling the BLD nematode . Fluopyram is a relatively new chemical that was approved for use by the EPA in 2012 . It has efficacy as both a fungicide and nematicide in woody and non-woody plants . Several studies have shown fluopyram provides effective control over an array of plant pathogenic nematodes . This chemical is locally systemic and can be applied as a foliar spray . Currently , there are no products that contain only fluopyram that are labeled for use on trees in landscape settings . There are two combination products labeled for use on trees ( Broadform™ and Luna Experience™ ). Broadform ( fluopyram + trifloxystrobin ) is the only one labeled for use in commercial landscape settings and could be used to treat BLD . However , in accordance with good IPM practices , this product must be rotated with alternate chemicals to reduce the risk of resistance development . Indemnify™ is a product that contains fluopyram only but is labeled for turfgrasses .
Early laboratory trials showed that the insecticide emamectin benzoate kills the BLD nematode . However , injections of this chemical into infested beech has produced limited to no control . Uptake in trees has been an issue and further use is not recommended .
The BLD nematode has proven very adept at traveling long distances into seemingly remote areas . While the specific vectors remain unknown , insects and birds are strongly suspected . Some movement has occurred on nursery stock , but this does not represent the primary means of dispersal . Regardless , carefully examine any beech nursery stock for symptoms of the disease . BLD symptoms are present when leaves emerge , so the disease can be diagnosed very early in the growing season .
Hort Notes 2022 Vol . 33:8
8 MAA NEWS WINTER 2022