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Analysis of the Relationship Between Rusty Patches on Pear Fruit Surfaces and Pesticide Use

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Irregular rust-colored patches often appear on pear fruit surfaces, affecting the appearance quality of the fruit. Fruit surface rust is generally called fruit russeting, which is formed by the gradual thickening and suberization of cell walls, with epidermal cells and the cuticle rupturing and exposing the surface, forming brown rust-colored patches. Another type of rusty patch is actually "pesticide russeting," caused by improper pesticide use or excessive pressure when spraying pesticides. There is also a type called "water russeting," mainly caused by poor environmental conditions, damp and rainy weather, insufficient light, and mold parasitizing the fruit surface. The occurrence of fruit russeting is related to many factors in cultivation. Such as variety, strain differences

Irregular rust-colored patches often appear on pear fruit surfaces, affecting the appearance quality of the fruit. Fruit surface rust is generally called fruit russeting, which is formed by the gradual thickening and suberization of cell walls, with epidermal cells and the cuticle rupturing and exposing the surface, forming brown rust-colored patches. Another type of rusty patch is actually "pesticide russeting," caused by improper pesticide use or excessive pressure when spraying pesticides. There is also a type called "water russeting," mainly caused by poor environmental conditions, damp and rainy weather, insufficient light, and mold parasitizing the fruit surface.

The occurrence of fruit russeting is related to many factors in cultivation. For example, different varieties and strains show differences in rusty patches. The "large-fruit self-pollinating strain" Yali pear in Wei County, Hebei Province, and the "large Yali pear" in Jin County have larger rusty patch areas than ordinary Yali pears. Fruit russeting is also related to the position of the inflorescence and fruit. Within the same inflorescence, the higher the position of the inflorescence, the smaller the rusty patch area; for fruits at the same inflorescence position, those borne on the outer part of the canopy have larger rusty patches than those in the inner canopy. Frost during the flowering period or young fruit stage produces ring-shaped rusty patches, commonly known as "frost rings." Fruit russeting is directly related to pesticide spraying. Young pear fruits are very sensitive to copper ions. For example, spraying Bordeaux mixture on them in mid-June easily irritates the tender fruit skin, triggering "pesticide russeting" and "fruit russeting," and at the same time enlarges the fruit dots and roughens the fruit surface.

During the young fruit stage of pear trees, carbendazim and thiophanate-methyl should be used instead of Bordeaux mixture. Experiments have shown that spraying 25% carbendazim at 400 times dilution during the young fruit stage of Cili pear reduces rusty patches by 1/3 compared with spraying Bordeaux mixture, and the rate of fruit without rust reaches 68.7%. When spraying, do not use a high-pressure spray gun; instead, switch to a fine-mist nozzle with low pressure. If Bordeaux mixture must be used, the proportion of lime can be increased to lower the copper ion concentration, using a 3-fold or double-strength 240-times Bordeaux mixture (weight ratio of copper sulfate, lime and water is 1:3 to 2:240).

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