How to identify and control black spot on roses

This disease occurs commonly and causes severe damage, leading to massive leaf drop in roses and huge losses. The pathogen is a fungus of the genus Actinonema in the subphylum Deuteromycotina.

1. Symptom identification

In the early stage of the disease, brown radial spots appear on the leaf surface, which then gradually expand into circular or nearly circular spots with a diameter of 4-12 mm; in severe cases, the lower leaves drop early, and the disease gradually spreads upward until the upper leaves also fall off completely. Rainy and humid conditions are the main requirements for spore production; when there are water droplets on the leaf surface and the temperature is suitable, infection can occur in 6-10 hours, and symptoms appear in 3-6 days. Yellow-flowered rose varieties have relatively poor disease resistance.

2. Control techniques

1. For field cultivation, select disease-resistant varieties.

2. In winter, prune out diseased branches, and routinely clear fallen leaves from the field or pots and burn them in a centralized manner.

3. Pay attention to protective spraying. Starting from April, spray Bordeaux mixture at 1:1:160 once a week; from June to August, Bordeaux mixture is still needed, or 50% carbendazim wettable powder at 500-800 times dilution; or 75% chlorothalonil wettable powder at 500 times dilution; or 70% mancozeb wettable powder at 500-600 times dilution.