Symptom Identification and Control Methods of Red Pine Needle Cast

Red pine needle cast is a common disease worldwide. The disease can infect trees from young saplings to large trees, causing premature needle drop, affecting growth, and can lead to the decline and death of diseased plants.

Symptoms: The disease usually affects 2-year-old needles, and some 1-year-old needles can also be affected. In the early stage of the disease, very small yellow spots or segmental spots appear on infected needles, and by late autumn the entire needle turns yellow and falls off. In the spring of the following year, larger, black or gray, long oval or oval raised granular dots appear on infected needles, with a paint-like luster and a longitudinal crack in the center, which are the ascocarps of the pathogen. Some diseased needles wither but do not fall off, and fruiting bodies form on them; other needles are only infected and killed in the upper part, also producing fruiting bodies, while the lower part remains green.

Pathogen: The pathogen is Lophodermium maximum B.Z. He et Yang, belonging to the Ascomycota, Discomycetes, Rhytismatales, Lophodermium genus of fungi.

Disease cycle: The pathogen overwinters as mycelium or immature ascocarps on fallen needles. In the spring of the following year, when conditions are suitable, the ascocarps mature and successively produce ascospores. On rainy days or under humid conditions, the ascocarps absorb water, swell, and open, and the ascospores are discharged from the asci and spread by air currents. The ascospores land on needles, germinate to form germ tubes, and invade through the host's stomata to cause infection. Ascospores can be released from early June to late August, with the highest numbers in July, so multiple infections can occur from spring to summer. The pathogen mainly infects needles more than 2 years old, and current-year needles are sometimes also infected. Disease occurrence is closely related to climatic factors. When the daily average temperature is 25°C and the relative humidity is above 90%, ascospore dispersal and germination and invasion are most favorable. During the period of ascospore dispersal, if there is continuous rainy weather with relatively high rainfall, spore dispersal is inhibited. In addition, the occurrence of this disease is closely related to tree growth conditions; any factor that causes tree growth decline can aggravate the disease. There are many causes of tree vigor decline, such as drought at the planting site, excessive rain, poor soil, tree damage by pests and diseases, and poor tending and management. According to foreign reports, the occurrence of pine needle cast is related to air pollution; at present, it is believed that air pollutants affect the soil and climate, thereby causing tree growth decline and leading to disease occurrence.

Control: 1) Reduce sources of infection: cut down severely diseased trees, properly prune the lower branches of diseased trees, and remove and burn diseased needles to reduce disease spread. 2) Strengthen cultivation management, increase soil fertility, and promote tree growth. 3) Chemical control: in the early stage of the disease, spray 1:1:100 Bordeaux mixture, or 65% zineb 500x solution, or 45% amobam 200-300x solution.