Black spot on red tip photinia
I have 5 red tip photinia hedges totally 26 plants. They are around 22 years old and are planted between 4 to 5 feet apart. I have been battling black spot disease for many years. Each hedge gets the disease at a different level. I have been treating the disease by pruning affected leaves and removing leaves from underneath the plants.. I have also spayed with Lily Miller Kop-R-Spray. Generally with good results after a couple of treatments. I have two questions. First, how can I treat the plants for the remainder of this year and going into next year to prevent this problem. Second, I have pruned the hedges down to 10'. I would like to lower them to 8'. Can this be done now, or should I wait until the plants are in a healthier state. Thanks of your reply.
Lane County Oregon photinia
Thank you for your question about your photinia. There is a great 'sister question' from a gardener in Benton County that answers your question about the disease, and has links to some control mechanisms and effective chemicals. Lilly Miller Kop-R-Spray (from copper ammonium complex) is actually not approved for use on photinia, nor is it listed as being effective against the fungus Entomosporium maculatum, which is the source of the black spot.
If the cultural controls listed in the Clemson U. article, above, are not effective, the chemical controls recommended are chlorothalonil, propiconazole and muclobutanil. (The commercial brand names are listed there as well.) As the article suggests, this requires spraying every 2 to 3 weeks.
As to your pruning question, these cultural control suggestions are pertinent:
" Prune red tips in the winter when they are dormant. Pruning during the growing season will encourage new growth, which is highly susceptible to attack by the fungus. Mature leaves are more resistant to leaf spot.
- Rake up and discard fallen leaves, and remove infected plant material. Apply fresh mulch around plants to cover any leaves that were missed. These practices reduce the amount of fungus present in the spring, resulting in less infection.
- Provide excellent air circulation. This often means thinning out a few plants in a hedge.
- Avoid wetting the leaves when watering. Splashing water spreads the fungus.
- Avoid summer fertilization that will promote new growth late in the season.
BTW, here's a link to an article about Lilly Miller Kop-R-Spray that you might find interesting. Six years old, but some information is still relevant.
Hope this is helpful. Good luck!
Thank you for the quick response. I looked at the Benton County Master Gardener post and it says to prune in late winter. Would this mean the time range to prune would be from early February to early March?
Indeed! You want to prune most--but not all--woody perennial shrubs while they are dormant. That is, there are no leaves that are photosynthesizing, so no sugars are going to the roots and above-ground structure. Once you see leaf buds, it can be too late. Having said that, with our wacky weather, it's hard to predict when our plants will break dormancy!