I once said that I have never seen an euonymous without scale. The same can be said of arborvitae. I have never seen one without leaf blight. Leaf blight (Pestalotiopsis funeraea) is prevalent on arborvitae and other related species such as Leyland cypress, false cypress (Chamaecyparis spp.) and junipers. It is a fungal disease that attacks foliage that has been injured, weakened by unfavorable weather or growing conditions. The disease may kill the smaller twigs when the infected needles die.
Working in a plant nursery at a young age and noting diseased arborvitaes in home landscapes, I knew that I would encounter this leaf blight when I planted eight (8) Emerald Green Arborvitae (Thuja occidentalis ‘Smaragod’) to serve as a “green” privacy screen around our new patio. There are several steps a homeowner can take to minimize the impact of this unsightly disorder.
First Step Cultural Practices to Reduce Infection:
- Since the existing infected foliage will be a source of new inoculum, remove infected foliage by using hand-held pruners. You may want to sanitize the pruning blade with alcohol or hydrogen peroxide between cuttings to prevent further spread of the fungus by dipping or spraying the pruning shear blade with either one of the solutions. I specifically used Sani-Date® Ready-To- Use an activated form of hydrogen peroxide that is listed by the Organic Materials Review Institute® (O.R.M.I.)
- Discard the trimmings and any needles that may have fallen to the ground.
- Avoid pruning during wet weather as this is the time when the fungus is most actively producing and spreading.
- Avoid overhead watering with sprinklers that leaves moisture for further disease development. Hand-watering newly planted trees is preferable. I personally water all my shrubs, trees, and flowers with a directed drench to the root zone using a garden hose, soaker hose or bucket.
- Use a mulch cover around the shrubs to prevent the spores splashing from the soil onto the lower branches.
- Use caution when mowing or trimming around the plant to prevent pathogens from entering through wounds in the needles and bark.
Preventative vs Curative:
My actual application was curative since I did not realize the shrubs I recently purchased were affected until I saw the first signs of the disease two weeks after they were planted. Once I noted the signs of leaf blight, I took immediate action with copper fungicidal soap a product that is listed for Organic Gardening by the Organic Materials Review Institute (O.M.R.I). Next spring when the environmental conditions are favorable for leaf blight, I will apply 1-2 sprays 10- 14 days apart and then monitor the progress of the disease. The goal is to prevent and/or eradicate the pathogen early in the season to prevent unsightly twig dieback and plant damage.
My experience:
- Product: Bonide® Liquid Copper Fungicide Concentrate (10% copper octanoate)
- Rate: 2 oz/1 gallon of water. Approximately a 2% solution.
- Sprayer: Lesco® 4 gallon back sprayer with a hollow cone nozzle
- Spray technique: Spray for coverage including underside of foliage. Avoid run-off. The one (1) gallon solution was adequate to treat eight (8) shrubs approximately five (5) feet tall.
- Multiple sprays: Fungal pathogens are difficult to control and for best results 2- 3 applications, and possibly more, 10-14 days apart may be required to eradicate the disease.
Observations:
Dry hot conditions persisted for 2-3 weeks shortly after the first application. Most likely the dry conditions and excessive heat prevented further recycling of the disease. I saw no further twig dieback during this period. This dry period was followed by heavy rains and high humidity which are ideal for disease development. Once the threat of rains passed, I again sprayed each shrub with the 2% Bonide Copper Fungicide Concentrate solution.
Additional Resources:
Other brand names of copper soap fungicide that are currently available at the local garden center, hardware store or on-line include:
- Ferti-Lome® Natural Guard Copper Soap Fungicide (Conc/RTU)
- Bonide® Copper Fungicide RTU
- Garden’s Alive® Soap-Shield Flowable Liquid Copper Fungicide (Conc)
- AM Leonard® Disease Shield Copper Soap (Conc)
- Espoma® RTU Copper Soap
- Monterey® Liquid Copper Fungicide RTU
Many of these products are Listed for Organic Gardening by Organic Materials Review Institute® (O.M.R.I). If so, it will be noted on the package label. When using these products and any pesticide, always read and follow the label directions.