Occurrence Patterns and Control Methods of Cherry Blossom Pests and Diseases

Cherry blossom belongs to the genus Prunus in the rose family (Rosaceae). It has both the subtle fragrance of plum and the gorgeous beauty of peach, with as many as several hundred cultivars. In recent years, with the demand for landscape gardening, cherry blossoms have been widely used in gardens, adding much beautiful scenery to urban landscapes. However, cherry blossoms suffer from many pests and diseases, mainly the following:

1 Cherry blossom witches' broom disease

The symptom is that many short, thin branches emerge from the affected parts, resembling a bird's nest. On these branches, either no flowers or only a few flowers are produced, and the leaves on the branches are numerous and small. Each year, deformed branches increase at the affected parts. In May to June, the leaves on the affected branches turn dark brown and wither and fall off, while greyish-white spores are produced and spread by wind to surrounding branches. The control method is to prune off the affected branches, burn the diseased branches and leaves, spray lime-sulfur mixture before bud break, and spray once more after bud break in April, which can achieve good results. During the disease period, chemical agents can be chosen such as 50% carbendazim 20x solution or chlorothalonil and other fungicides.

2 Cherry blossom shot-hole brown spot disease

Occurs in May to June. Purple-brown small spots appear on the leaves, then gradually expand into circular shapes. After the diseased spots dry and contract, they become small holes. The control method is to remove diseased leaves and burn them, spray 8:8 Bordeaux mixture before bud break, or spray 45% amobam aqueous solution 40x after leaf emergence.

3 Cherry blossom leaf blight

In summer, yellow-green circular spots appear on the leaves, then turn brown, with scattered small black dots. The diseased leaves wither but do not fall off. The control method is to remove and burn diseased leaves; spray Bordeaux mixture before bud break. After leaf emergence, spray 45% amobam aqueous solution 40x or 0.8% Junlimei No. 2 20x.

4 Cherry blossom sclerotinia disease

This disease occurs on leaves and young fruit. First, irregular brown spots appear on the leaves, then spread to the entire leaf surface, and grey powder is produced. Young fruit becomes diseased shortly after petal fall, with brown spots forming on the surface, which then gradually expand, while the fruit shrinks and dries, and greyish-white small masses form on the surface. Similar to this disease is "ripe fruit sclerotinia disease," which only occurs on mature fruit. The control method is to burn diseased leaves and fruit, spray 6:6 Bordeaux mixture before and after flowering, 45% amobam aqueous solution 40x or 25% peifurong 50x or 50% carbendazim 20x.

5 Cherry blossom crown gall disease

The affected area appears dark brown or blackish-brown, sunken, and often exudes resin. Galls usually form, but depending on tree vigor and the site of infection, galls may not form. The control method is to remove the affected parts and burn them, or after removing the diseased parts, disinfect with 0.05-0.1% mercuric chloride solution and then apply lime milk; or spray 8:8 Bordeaux mixture or 5° Baumé lime-sulfur mixture before bud break; or spray 500x thiophanate-methyl or 50% carbendazim 20x.

6 Lesser clearwing moth

The larvae of the lesser clearwing moth bore into and feed on the inner side of the bark of cherry blossom and peach. The adult body is blue-black, with the 4th and 5th abdominal segments black, and the outer margin of the forewings black. It occurs once a year. The larvae overwinter under the bark and can cause damage in early spring of the following year, emerging as adults in August to September. Eggs are laid in bark crevices or wounds on the bark. The control method is to apply lime coating on branches and trunks to prevent egg-laying; in spring, when holes are seen on branches with gum exuding or insect frass, use a hammer to tap and crush the larvae inside, or use a small knife to cut open the bark to catch and kill the larvae and apply tar to the wound.

7 Plum caterpillar

It occurs once a year, overwinters as eggs, and hatches in March. The larvae spin silk in a canopy-like web and live gregariously in the silk nest. At night they come out to damage buds and leaves, and after growing larger they leave the nest and disperse. Around May they cocoon and pupate, and from late May to mid-June they emerge as adults and lay eggs. The control method is to collect egg masses in winter or burn the insect nests together during the gregarious larval stage. For adults, use 1000x sophora alkaloid or other contact insecticides or stomach poisons for control.

8 Scale insects

Besides cherry blossom, they also damage pear, apple, apricot, plum and other trees. The female scale is circular, slightly raised on the back, white to greyish-white, about 0.2mm in diameter. The male scale is also white, elongated, about 0.1cm long. The control method is to spray mechanical oil emulsion in winter or spray lime-sulfur mixture before bud break in spring. During the adult stage, use 2000x Supujiesha for control.

9 Others

In late April, Japanese beetles, leaf beetles, and mulberry looper moths can be caught and killed, or 1000x sophora alkaloid or other contact insecticides or stomach poisons can be sprayed for control. In early May, capture and kill Mongolian grey weevils. In early June, spray 200x Bt emulsion on small grey weevils; in mid-June, spray 10% imidacloprid 2000-3000x or other systemic insecticides on aphids. In mid-July, for red spider mites, use pyridaben 2000-3000x or Baihongmansha 1500-2000x. In early August, for slug moths, spray 1000x sophora alkaloid or 200x Bt emulsion or other insecticides.