I was not initially alarmed by an unusually prolific infestation of anthracnose among some shamel ash I recently inspected in Fremont. Although the disease is usually present, it is not often so apparent among shamel ash. I then found it among two pair of Modesto ash in Willow Glen that had been nearly defoliated as quickly as the foliage emerged. When I found four more similarly afflicted specimens in Mountain View, I knew that this would be bad. I have since received many telephone calls and emails concerning the health of otherwise healthy ash, primarily Modesto ash, as well as the various species of sycamore.

This is unfortunately a "bad year" for anthracnose because of the alternating rainy and warm weather, with subsequent humidity that allows the proliferation of the fungus. Because the epidemic is so advanced and spores are very abundant, continued infestation is very likely if rain resumes—or even next spring as dormant (secondary) spores become active. Infected Modesto ash should otherwise become foliated as warm and dry weather promotes foliar growth but inhibits fungal proliferation.

Fungal proliferation is inhibited during summer but not eliminated, so foliage of any infected Modesto ash will likely be sufficiently infected by late summer to cause premature defoliation. Because the foliage will be necrotic at that time, it will not exhibit the typical yellow foliar color if it is still present in autumn. Shamel ash that are normally somewhat evergreen may now become unusually defoliated as older foliage is abscised when it would otherwise be replaced with new foliage, but the next phase of new foliage should help.

Sycamores are also affected by anthracnose, particularly the native California sycamores. The related "Yarwood" London plane tree (sycamore) is less susceptible. Removal of foliar litter of any infected tree is recommended because it unquestionably contains viable dormant spores. Black foliar necrosis among rosicious species (of the family rosaceae) is another, completely different epidemic of fireblight, which will be discussed in a future column.


Flower of the Week: Hebe

Does anyone else wonder where some of the Latin botanical names originate? "Hebe" is pronounced with two syllables like the first word of "heebie-jeebie" and is both the common and the Latin name of the genus. Most found in nurseries are known by their cultivar names rather than by their (Latin) species, such as Hebe "Coed." Perhaps the botanist who brought them from New Zealand just thought it was funny at the time. Another botanist who was not amused, assigned it the alternate name "Veronica," which is only occasionally seen.

The bright purple bloom of Hebe "Coed" in the garden of a neighbor reminded me that the other cultivars of Hebe will continue to bloom later through summer, with various shades of pale purple, purplish blue, pink, red or white. Flowers are very small but profuse, suspended by abundant conical trusses. The 1¹/2-inch-long, glossy dark green leaves are typical of Hebe, but some cultivars exhibit smaller leaves or purplish or bronzed foliage. Hebe "Coed" is usually less than 3 feet high and wide, while others are either lower or as large as 5 feet high and wide.

Hebe actually perform better nearer to the coast, where weather is milder. Either frost or heat with minimal humidity may cause damage. Partial shade is beneficial in warmer areas of the garden. Full sun exposure is otherwise preferred. Irrigation should be regular, but adequate drainage is very important because roots rot easily if soil becomes saturated. Pruning or shearing after bloom will enhance foliar density.

Horticulturist Tony Tomeo can be contacted at 408-358-2574 or at LGHORTICULTURE@aol.com.