How to prevent and control the damage of Lijuan spruce tip rust to Meijing?

Meijing tip rust is a newly discovered disease on Qinghai spruce (Picea crassifolia), mainly distributed in spruce forests at altitudes of 2600-2800 m in the eastern section of the northern slope of the Qilian Mountains in western Gansu, harming Qinghai spruce. Its harmfulness is second only to Qinghai spruce needle rust, and its onset period is about one month earlier than Qinghai spruce needle rust.

Symptoms: Diseased buds of spruce sprout 10-15 d earlier than healthy buds. Starting in early June, the diseased buds swell into a conical shape, peach-red in color, with densely dotted small protrusions on the surface, which are the fungal spermogonia. New leaves emerging on the tender tips are deformed, with enlarged leaf shapes slightly curved into a banana shape, and the surface is covered with yellow-brown spermogonia. Subsequently, many orange-yellow elongated, slightly raised aeciospore pustules appear, and the color of the diseased tip turns orange-yellow. The aeciospore pustules form continuous patches on the diseased tip, with bright color and shaped like beautiful flowers, hence the name Qinghai spruce Meijing tip rust. In mid-June, the aeciospore pustules gradually mature, the peridium ruptures, and a large amount of yellow powdery aeciospores is released. In late June, the diseased tips gradually become dark brown and dry up, but they remain on the branch tips year-round without falling off, and the traces of damage from the previous year can still be seen until the following year.

Pathogen Peridermium gansuense Wu sp. nov. is called Gansu peridermium rust fungus, belonging to the Basidiomycotina fungi. Spermogonia are nearly round flask-shaped, almost entirely protruding from the host tissue, 64-205 μm in diameter; aeciospore pustules are elongated along the stomatal lines of the needles, 4-12 mm in length, some almost as long as the diseased leaf, 210-705 μm in diameter, with the largest diameter reaching more than 1 mm; peridial cells are irregularly elongated, 19-45 μm × 17-32 μm, with the inner wall 3-5 μm thick and the outer wall 5-7 μm thick, both inner and outer walls densely covered with fine warts; aeciospores are long-oval, oval, or nearly round, 15-23 μm × 21-37 μm, with a spore membrane 1-3 μm thick, the surface densely covered with fine warts, light yellow-brown.

Disease characteristics: The pathogen overwinters in diseased buds, and begins to cause disease in early June of the following year, forming diseased tips that become the primary infection source. This disease is strongly regional and highly selective in its host, often occurring under alpine, cold, and humid ecological conditions; sparse forest (canopy density<0.7)比密林病情轻。

Control methods

(1) Agricultural control.

Create mixed forests and try to avoid creating pure Qinghai spruce forests in areas where Qinghai spruce Meijing tip rust occurs; carry out reasonable tending and thinning to maintain stand closure, which can effectively reduce disease occurrence; in early June at the initial stage of disease onset, promptly prune diseased tips in young forests and nurseries and burn them in a centralized manner to reduce sources of infection.

(2) Chemical control.

When the disease occurs on a large area, spray conventional concentrations of chlorothalonil, triadimefon, and lime sulfur, with an application rate of 750 kg/hm, to achieve effective control.

Commonly used fungicides: chlorothalonil, triadimefon, and lime sulfur.