ORGANIZACION DE LA ESCUELA PRIMARIA

Powdery mildew is a common category of foliage disease on many ornamentals and shade trees. This fungal disease appears as a white powdery growth on the surface of leaves, flow- ers and stems. The fungus absorbs nutrients from the leaf, resulting in a weakened plant. The unsightly lesions can greatly reduce the aesthetic quality of the plant.

Powdery mildews are important on flowers including zinnia and phlox, as well as shrubs such as lilac and rose. Although powdery mildews may also be common on trees such as oak, they normally develop late in the season and seldom cause significant damage. The fungi that cause powdery mildew are host specific; the mildew fungus that infects one species of plant will usually not infect another.

Powdery mildew often thrives on plants that are located in partially shaded areas with poor air movement. Therefore, avoid planting susceptible plants in these locations. If avail- able, select plant varieties with resistance to powdery mildew. For example, many crabapple cultivars have good resistance to this disease. Certain fungicides will provide protection against mildew. These fungicides need to be ap- plied at routine intervals. Though the fungicide will prevent further disease development, the unsightly lesions may remain on the leaves even though the fungus has been killed.

Powdery mildew on lilac

Rusts

Rust is another type of fungal foliage disease that affects a wide variety of ornamental plants. Rusts are common on junipers, hawthorns and flowering crabapples, ash, rose, holly hock, and many other ornamental plants. Rust pathogens, such as the powdery mildews, are host specific. For example, the rust fungus that infects ash is different from the rust fungus that infects rose.

Rust diseases often result in the forma- tion of small, orange to brick-red pustules or blisters on the leaves. The blisters are filled with powdery spores of the rust fungus. Excessive rust on leaves may result in early defoliation. On certain plants such as junipers, pines, ash and hawthorns, rusts can cause swellings or galls on twigs and branches.

Cedar-apple rust and the related cedar- quince and cedar hawthorn rusts are common in Kansas. These rust fungi spend part of their life cycle on eastern redcedar and other juni- pers, and the other part on certain species of apple (including crabapple) and hawthorn. In the spring, the cedar-apple rust fungus pro- duces bright orange, gelatinous galls on juniper. Although these galls are are visually strik- ing, they rarely cause significant injury to the juniper. Fungal spores produced by these galls are dispersed by wind and infect developing leaves of apple and flowering crab in April and May. The first symptom of the disease on apple is the formation of bright yellow-orange spots on the upper surface of the leaves in late June. Eventually, an orange, cup-like fungal structure is formed on the lower leaf surface and pro- duces spores that infect junipers. Apple leaves

with numerous spots drop prematurely during the summer. This weakens the tree and reduces winter hardiness and fruit set the following year. The cedar-quince rust infects hawthorn twigs, resulting in small galls and twig dieback.

Cedar apple rust on eastern red cedar

Cedar apple rust on apple

The best means of controlling cedar-apple rust is use of resistant varieties of apple, flower- ing crabapple, and junipers. Avoid planting susceptible junipers and flowering crabapples close to each other. If susceptible varieties are used, fungicide can be applied to protect the trees. This is usually done in April and May when galls are active on the junipers. Several applications may be needed.

Anthracnose

Anthracnose is a general term used to describe a group of fungal diseases whose symptoms include foliar and/or twig blight- ing. In Kansas, anthracnose is most common in spring and early summer on deciduous trees such as ash, elm, maple, sycamore, and black walnut. The fungal pathogens differ for each tree species.

Anthracnose causes a range of symptoms, depending on the tree species and weather conditions. Symptoms may include leaf spots and twig blight.These diseases may occasion- ally result in premature defoliation, but often damage is minimal. In fact, most shade trees in vigorous condition recover rapidly from anthracnose infections.

Sycamore anthracnose is the most serious of the anthracnose diseases in Kansas. Dur- ing wet, cool springs, the fungus may kill leaf buds and expanding shoots. Repeated killing of young twigs can result in abnormal branch- ing, giving the tree a ragged appearance. Later fully expanded leaves develop elongated tan to brown lesions along the veins.

Anthracnose rarely causes significant dam- age to shade trees in Kansas. Consequently, specific control measures generally are not required. Nevertheless, the disease may be unacceptable in high visibility landscape set- tings, particularly on sycamore. Several cultural practices, including proper tree spacing, fertil- ization, and irrigation will decrease severity of anthracnose. Fungicide sprays normally are not necessary, but fungicides can be applied at bud swell to control the disease on ash, elm, maple, oak, and sycamore. One to two additional ap- plications may be necessary. Certain fungicides are labeled for systemic injection into sycamore trees for the control of anthracnose. Read the label for accurate information on timing.