Rhododendron leaf swelling disease

Symptoms:

Rhododendron leaf swelling disease is also called cake disease. The young tissues of rhododendron can be damaged, mainly for flower buds, tender leaves and new shoots. The front of the leaf is a light yellow translucent round spot at first, then yellow, sunken; the back of the leaf is reddish, hypertrophic and swollen, followed by a gall tumor, and there is a thick gray-white powder layer on the surface of the gall tumor, such as biscuit-like, withered, yellow and early fallen leaves. In severe cases, the petiole disease is patchy and deformed and hypertrophy. When the tender shoot is sick, the top produces a fleshy lotus-shaped leaf, or a tumor-like leaf, and then shrinks into a sac. After the petals are susceptible, they are abnormally hypertrophic and show irregular gall tumors. The flower buds become fleshy and thicker and harden. These young leaves and flower buds show abnormal fleshy thickening after infection, producing buds of different sizes. Flower farmers call them "rhododendron apples" with a diameter of 3-12 mm, some up to 8-18 mm, and the surface is covered with gray-white powder. this is the basidium and basidiospore of the pathogen. Finally, the disease turned dark brown and dried up and fell off.

Pathogen and regularity of disease:

Fungus. Japanese ecobasidium (ExobasidiumjaponicumShirai.) or rhododendron ecobasidium (E.RhododendriCram.). Basidiomycetes subphylum, stromatomycetes, exobasidiomycetes, ecobasidiaceae, exobasidiomycetes.

The peak period of the disease is late spring and early summer and early summer and early autumn. The basidium of the pathogen is formed under the epidermis of the rhododendron host. After maturation, it breaks through the exposed epidermis and produces cylindrical basidiospores, which infects and spreads. Diseases of low temperature and high humidity are easy to occur. The monthly average temperature is 15 mi 20 degrees Celsius, and the relative humidity above 80% is conducive to the occurrence of the disease. Rhododendron leaf swelling pathogen overwintered by mycelium in plant tissue. Basidiospores are produced in the following spring, which are spread by wind and rain splashing and infect young tissues. The incubation period is 7-17 days. The disease occurs twice a year, late spring and early summer, autumn and early winter, the most common in late spring and early summer, and more serious from March to May. The temperature is low, when the monthly average temperature is 15-20 degrees Celsius, the relative humidity is more than 80%, it is overcast and rainy, the sun is insufficient, the plant grows tender, and the disease is easy to spread. Alpine rhododendron has the most serious disease.

Prevention and control measures:

(1) when the disease first appears and no white powdery substance is formed in the disease, the susceptible tissue is removed immediately and burned. Do not introduce diseased seedlings into disease-free areas.

(2) spray 2-Mel-5-pomethyl sulphur mixture before germination.

(3) 0.5-1% Bordeaux solution or 80% Dysen zinc 500-fold solution can be sprayed before the disease, especially when drawing tips and spreading leaves. During the onset of the disease, 65% of Dyson zinc 500 times solution, or 0.3 won 0.5 Baumetu stone sulfur mixture 3Mel 5 times.