Angular leaf spot is caused by the bacterium Pseudomonas syringae and attacks most of the cucurbit plants, for instance, squash, pumpkin, watermelon, cucumber, etc. The disease spreads very fast when conditions are moist and temperatures range between 25-28 degrees centigrade.
It is thus highly favored by prolonged leaf wetness.
DISEASE CYCLE
When an infected seed germinates, the bacterium multiplies.
The pathogen is thus introduced into the field majorly through contaminated seed. However, it can also be spread by tools, insects, or splashing water.
Pseudomonas syringae can survive in plant debris and infected plant tissues for over 2 years.
IDENTIFICATION & SYMPTOMS
The disease infects all above ground parts of the plant, that is, leaves, fruit and vines.
Initially, symptoms appear as small, angular, brown or straw-colored, water-soaked spots on leaves. These spots expand, eventually covering the entire area between leaf veins. Older spots may dry out and tear, leaving holes behind.
On fruits, this disease manifests as circular, water-soaked spots, which are smaller than those on the leaves. As the disease progresses, the spots develop a whitish appearance and may eventually crack open. Cracking creates avenues for entry of other pathogens like bacterial soft rot. In severe cases of infection, the pathogen moves deep into the fruit and infects the seed as well.
Clear to white sticky bacterial oozes develop on the infected tissues, especially on the fruits.
Infected regions are surrounded by chlorotic halos.
MANAGEMENT & CONTROL
- Chemical control
To effectively control this bacterial infection, the use of copper based fungicides is recommended.
The following fungicides are thus fit for use against Angular leaf spot;
- GREEN COP 500WP 50g/20l
- TRINITY GOLD 425WP 50g/20l
- COLONIZER 440WP 50g/20l
NB; -OPTIMIZER 10ml/20l improves the immune system of the crop.
Spraying PYRAMID 700WP 50g/20l helps in suppressing the activity of the pathogen within the crop.
Always mix the fungicide with INTEGRA 3ml/20l. This is a sticker, spreader and penetrant which improves the efficacy of the chemical.
Other methods
- Proper drainage
- Crop rotation with non-host crops
- Field sanitation
- Proper weed control
- Use of resistant cultivars
- Avoid overhead irrigation
