Extension

Prepare for Leaf Spot of Red Tip Photinia

Courtney DeKalb-Myers, Assistant Extension Specialist for Consumer Horticulture

A full, dense photinia hedge can thin out quickly when leaf spot takes hold. Cause by the fungus Entomosporium mespili, this disease is one of the most damaging issues affecting red tip photinias. Cool, wet weather encourages this disease. If May stays rainy and overcast, expect to see leaf spot develop.

The infection starts with circular, bright red spots that eventually coalesce into large purple blotches. In severe infections, the plants will defoliate. This can be especially frustrating when plants are used for sound barriers or privacy hedges.

When managing garden diseases, prevention is the best strategy. There are no truly curative options once infection begins. To slow the spread, prune out infected areas. This improves airflow within the shrub and reduces the humid conditions the fungus thrives in. Leaf spot spores overwinter in fallen leaves, so rake and remove leaf litter from around the plant. Also avoid overhead irrigation to minimize leaf wetness. If planting new photinias, do not plant them too close. Increasing airflow is key to slowing the spread.

Fungicides can be an effective preventative tool. Apply fungicides early in the season, before the flush of new growth. Keep in mind that fungicides are preventive, not curative. Applications need to be made before symptoms appear and before conditions favor disease development.

Oklahoma’s weather is unpredictable, but proper preparation is key to keeping red tip photinias healthy. If plants are severely affected or ongoing management isn’t practical, consider replacing them with alternatives such as cherry laurel, juniper, or viburnum.

Controlling Caterpillar Pests

David Hillock, Senior Extension Specialist and Statewide Master Gardener Coordinator

Caterpillar pests are common on many landscape plants and can cause mild to severe damage depending on plant species and number of caterpillars present. Control of caterpillars may not be necessary in some instances because their numbers are kept in check by numerous natural enemies such as parasitic flies and wasps, disease, predator insects and birds.

On shade trees, even if the caterpillars become numerous, a healthy tree can withstand a complete defoliation early in the growing season. New transplants or trees weakened by weather or other factors may require control.

Hand-picking caterpillars from flowering plants and vegetables is also an effective method. Most caterpillars are very susceptible to products containing Bacillus thuringiensis, such as Javelin®, Dipel® or Thuricide®. This product is less effective on older larvae because they must consume it for effective control. Young and older caterpillars can also be controlled with the naturalyte ingredient spinosad that is found in Conserve® and some retail insecticide products as well as other insecticides that are labeled for these pests in ornamentals. Control is best achieved before caterpillars become full-grown, and it is essential to get thorough coverage, since they are often slightly protected within their "nest". Of course, it is important to select the right product for the given situation and to always read and follow product labels directions...

**Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.