This plant disease is caused by soil-inhabiting bacteria (Agrobacterium tumefaciens) that infect many ornamentals, fruits, and vegetables in the garden. The bacteria are often brought to a garden initially on the roots of an infected plant and are spread with the soil and by contaminated pruning tools. The bacteria enter the shrub through wounds in the roots or at the base of the stem (the crown). They produce a substance that stimulates rapid cell growth in the plant, causing gall formation on the roots, crown, and sometimes branches. The galls disrupt the flow of water and nutrients up the roots and stems, weakening and stunting the top of the plant. Galls do not usually cause the shrub to die.
Crown gall can''t be eliminated from the shrub. Infected plants may survive many years, however. To improve the appearance of the plant, prune out and destroy affected stems below the galled area. Disinfect pruning shears after each cut. Destroy severely infected shrubs. The bacteria will remain in the soil for two to three years. Plant only resistant species.
Yponomenta cagnagella This insect is a major pest of euonymus. First discovered on this continent in Ontario in 1968, it is now widespread. It originated in Europe, where it is a common pest of the native spindlebush tree (Euonymus europaeus). The adult, a small whitish moth, lays eggs in July. Larvae remain inactive until spring, when they construct copious webbing and begin feeding. The webs are dirty with their droppings, cast-off skins and cocoons. The caterpillars appear in May and reach full size by June, when they spin cocoons within the webbing and pupate. The adult moths emerge in late June or early July. Because there is only one generation a year and feeding halts in June, the damage is less than that done by similar tent caterpillars and fall webworms. Plants usually recover with little lasting damage, but the webs are unsightly and can persist until winter. Besides European spindlebush, the caterpillar feeds on spreading euonymus (E. kiautschovicus), winged euonymus or burning bush (E. alatus), and Japanese euonymus (E. japonicus).
Control euonymus caterpillar with an insecticide labeled for this pest. Break up webbing with a garden hose, then spray it with as much pressure as possible.
Unaspis euonymi Many species of scales infest euonymus, but the most common and destructive is euonymus scale. It is especially damaging to evergreen euonymus. The narrow white scales are males, and the larger brown scales are females. The females spend the winter on the plant and lay their eggs in the spring. In late spring to early summer the young scales, called crawlers, settle on the leaves and twigs or are blown by the wind to other susceptible plants. The small (1/10 inch), soft-bodied young suck sap from the plant. The legs atrophy, and a shell develops, brown over the female or white over the male. Females lay eggs underneath their shells.
Euonymus scales may be hard to detect until after they have caused serious damage. Check the plant periodically for yellow spotting and scales. During the winter, check the base of the plant for hidden overwintering females. Apply a horticultural oil, following directions on the label. For very heavy infestations, cut plants to the ground.
This plant disease is caused by two species of fungi (Oidium euonymi japonici and Microsphaera alni) that thrive in both humid and dry weather. Fungal strands and spores make up powdery patches or a thin powdery layer. The spores are spread by wind to healthy plants. The fungus saps plant nutrients, causing leaf yellowing and sometimes death of the leaf. In late summer and fall, the fungus forms small, black, spore-producing bodies that are dormant during the winter but produce spores to reinfect new plants the following spring. The fungus is especially devastating in low-light situations and is generally most severe in late summer and fall. Since Microsphaera alni attacks many different kinds of plants, the fungus from a diseased plant may infect other types of plants in the garden.
When mildew is first noticed, apply a fungicide labeled for powdery mildew, following label instructions. . Clean up plant debris in late summer.
Leaf scorch is caused by excessive evaporation of moisture from the leaves. In hot weather, water evaporates rapidly from the leaves. If the roots can''t absorb and convey water fast enough to replenish this loss, the leaves turn brown and wither. This usually occurs in dry soil, but leaves can also scorch when the soil is moist. Drying winds, severed roots, or limited soil area can also cause scorch.
To prevent further scorch, water plants deeply during periods of hot weather. Water recently transplanted shrubs more often than established plants. If possible, shade the shrub during very hot weather. Hosing down the leaves may help cool the shrub and slow evaporation. Plant shrubs adapted to your climate.