What are the control methods for Cercospora leaf spot on cantaloupe?
Brown spot is a common disease of cantaloupe, widely distributed, mostly occurring sporadically, with mild symptoms and no impact on production. In severe cases, the diseased plant rate can reach over 80%, causing some leaves to become diseased and necrotic, affecting yield and quality to a certain extent.
Symptoms: This disease mostly occurs in the mid-to-late growth stage of cantaloupe and only infects leaves. Initially, small brown spots appear on the leaves, which later develop into nearly circular to irregular brown necrotic spots of varying sizes, with distinct margins, often surrounded by a yellow-green to pale yellow halo. Generally, no mold layer is seen on the lesions; only under continuous rainy or high-humidity conditions does a dark gray mold layer form, which consists of the pathogen's conidiophores and conidia.
Pathogen: Cercospora citrullina Cke., called cucurbit Cercospora, belonging to the Deuteromycotina fungi. The pathogen's conidiophores are borne in bundles, brown, straight or curved, without geniculate nodes, unbranched, with 0-4 septa, flat-topped at the apex, with prominent conidial scars, measuring 27.5-90μm×4.3-5μm. Conidia are colorless, needle-shaped or whip-shaped, straight or curved, with 4-21 septa, measuring 22.5-175μm×2.8-5μm.
Disease characteristics: The pathogen overwinters in the soil as conidial clusters or mycelium; it can also overwinter as chlamydospores and sclerotia. When conditions are suitable, conidia are produced and spread by airflow or rain splashes for primary infection; after disease onset, new conidia form for repeated infection. Warm, high-humidity conditions favor disease development. The disease develops at temperatures of 20-30°C and relative humidity above 90%; when the temperature is 25-27°C and humidity is saturated, the disease occurs more severely. High temperature and high humidity in the mid-to-late growth stage, or more rainy days, or prolonged closed greenhouse conditions, or large day-night temperature differences all favor disease development.
Control methods
(1) Agricultural control.
① In severely affected plots, implement crop rotation with non-cucurbit and non-legume crops for more than 2-3 years to control the disease.
② Strengthen cultivation management, pay attention to ventilation and air permeability, apply fertilizer scientifically, irrigate timely, cultivate strong seedlings, promptly remove diseased plants, and thoroughly clear diseased plant residues after harvest to reduce field inoculum sources.
(2) Chemical control.
Begin chemical control at the early stage of disease onset. Options include spraying 50% anilazine wettable powder at 500 times dilution, or 50% vinclozolin wettable powder at 1000 times dilution, or 40% flusilazole emulsifiable concentrate at 8000 times dilution, or 6% fenarimol wettable powder at 1500 times dilution, or 70% thiophanate-methyl wettable powder at 600 times dilution, or 80% mancozeb wettable powder at 600 times dilution. In protected cultivation, use 6.5% dimethirimol dust at 15 kg/hm2 for dusting control.
Commonly used agents: anilazine, vinclozolin, flusilazole, fenarimol, thiophanate-methyl, mancozeb, dimethirimol.