Detailed Guide to Symptom Identification and Control Methods for Apple Moldy Core

Apple moldy core is also called core rot, moldy rot, red rot, fruit rot, etc. The symptoms mainly damage the fruit, especially an important fruit disease of Delicious strain varieties and Fujin, Luxiang, etc. bred using Delicious strain varieties as parents. Its symptoms appear in 2 types. (1) Moldy core type: gray-green, gray-white, gray-black and other colored moldy substances are produced in the core cavity, and these moldy substances are confined only to the core cavity. (2) Core rot type: the flesh in the core area rots from the core cavity outward, and in severe cases the flesh can rot through to the fruit surface. The rotten flesh tastes bitter; severely affected young fruit will drop early; lightly affected fruit can mature normally, but from the ripening stage to after harvest the core cavity can still develop the disease.

The pathogen is caused by mixed infection of various fungi, mainly Alternaria sp., which produces black mold layers, Trichothecium roseum, which produces pink or pinkish mold layers, Cephalothecium sp., which produces gray mold layers, Fusarium moniliforme, Penicillium sp., and Phomopsis sp., all belonging to the Deuteromycotina fungi. The dominant species differ slightly among regions; in some places Alternaria fungi are dominant, while Fusarium is rare. In Golden Delicious fruit during late storage, Trichothecium roseum is often dominant.

Transmission route: The pathogen overwinters as mycelium in diseased mummified fruit or necrotic tissue, and as spores hidden among the scales of buds. The following year it produces various types of spores, which spread by wind and rain; the spores enter the core cavity from the calyx tube. The pathogen mainly invades during the flowering period, after which the spores lie dormant in the fruit core. As the fruit develops, the mold begins to proliferate; diseased fruit can be seen dropping in June, but most cases occur in the later stage of fruit growth. Some diseased fruit only shows symptoms during storage, causing moldy rot.

Disease conditions: The occurrence of this disease is closely related to climate and variety. Early rainfall, abundant rainfall, humid climate, low-lying orchards, dense canopy, and poor ventilation favor the disease. Among apple varieties, those with a large calyx opening and a long calyx tube connected to the core are susceptible; those with a small calyx opening and a short calyx tube are more resistant. Delicious strain varieties such as Starking, Huanong No. 1, Delicious, Fujin, Luxiang, and Red Chief have long, wide calyx tubes and suffer severe disease; Golden Delicious and others with half-open calyxes suffer relatively mild disease; Zhuguang with a closed calyx and short calyx tube shows resistance.

Control methods:

(1) In orchards with severe disease, choose and plant resistant varieties. Such as Red Fuji apple from Feng County, China.

(2) Strengthen cultivation management, prune reasonably, keep the tree canopy ventilated and light-permeable, pay attention to drainage, and reasonably increase the application of organic fertilizer.

(3) Remove the primary infection source. In late autumn and early winter, remove diseased fruit, mummified fruit, and diseased branches, and burn them in a centralized manner.

(4) Strengthen storage period management. Develop simple controlled-atmosphere storage or cold storage; during storage, the fruit storage temperature should be maintained at 0.5-1°C and the relative humidity at about 90%.

(5) Chemical control. Spray once every half month before flowering, after flowering, and during the young fruit stage. Use 1:2:200 Bordeaux mixture, or 10% polyoxin wettable powder 1200-1500 times liquid, or 50% iprodione wettable powder 1500 times liquid spray.