A member of the rose family, pyracantha (Pyracantha coccinea) is commonly known as scarlet firethorn. Because pyracantha is a thorny plant, it is generally grown as a barrier hedge, although the white spring flowers and red berries in fall provide lots of ornamental interest. Pyracantha does best when grown within zones 6 through 9 on the U.S. Department of Agriculture hardiness zone map.The most common causes of yellowing foliage on the pyracantha are spider mites and firethorn scab, caused by a fungus.
Check the foliage for webbing. You may need to use a magnifying glass to see the actual mites. Look on both sides of the leaves. Pest management experts with the University of Florida suggest holding a piece of white paper under the leaf, rapping the leaf sharply and examine what falls from it.
Spray the pyracantha with insecticidal soap or horticultural oil. The product needs to be sprayed directly onto the pests to smother them, so ensure that you provide complete coverage of both the upper sides of the leaves and the undersides.
Apply a miticide to the pyracantha, according to package directions. Because miticides do not penetrate the eggs, reapply the product in five days in the summer. For winter infestations, reapply every seven days.
Inspect the pyracantha's foliage for dark splotches. Also look for shrivelling of the berries. These are both symptoms of scab.
Cut out all diseased wood in fall or winter. Disinfect your pruning shears after each cut by dipping them in a solution of 1 part household disinfectant and 5 parts water.
Bag the pruning debris immediately. Rake the bed to remove fallen leaves and twigs and bag those as well. Remove the infected material from the garden.
Spray fungicide on the pyracantha, completely covering all parts of it until the product drips from the plant. Make the first application in the spring and reapply, per label instructions, until two weeks after flowering.
Water the pyracantha at the soil and not overhead to avoid splashing soil, which may contain fungal spores, onto the foliage.
There are few fungicides listed for treatment of pyracantha scab. Consult with your county cooperative extension agent to determine which control works in your region.