As cotton farmers, we know all too well the challenges that come with nurturing this crop from seedling to boll. But have you noticed any strange markings popping up on leaves lately? It could signal an attack from a pesky disease called angular leaf spot.
Caused by the fungus Pseudocercospora gossypii, angular leaf spot is one of the most widespread and damaging cotton diseases worldwide. Native to Africa, it's since spread globally via contaminated seed and plant material. Where conditions are suitable, it can slash yields by defoliating plants if left unchecked.
To protect our livelihoods, we've got to get well-acquainted with this fungus and how to thwart its spread. So let's start by learning more about the culprit behind angular leaf spot.
What is Angular Leaf Spot of Cotton Plant?
Some key facts about P. gossypii:
- It survives in infected plant debris and as dormant mycelium in the soil between seasons.
- Spores are rain-splashed or wind-dispersed to infect new foliage during humid conditions.
- Prefers temperatures between 77-86°F but can infect at lower temperatures as well.
- Attacks all commercial cotton varieties, causing defoliation that reduces photosynthesis and yields.
- Also infects okra, hibiscus and other Malvaceous plants, potentially moving between crop hosts.
So in summary, we're dealing with a soilborne and airborne fungus that thrives under warm, wet conditions. Its ability to overwinter means angular leaf spot is an constant threat.
Spotting the Signature Symptoms
To catch infections early, it's important to regularly inspect leaves for these telltale signs:
- Angular to elliptical lesions on leaves, stems and bolls that are light brown with dark borders.
- Lesions have a target-board appearance with concentric circles as they enlarge over time.
- Leaf spots coalesce and cause entire leaves to drop prematurely during severe outbreaks.
- Defoliation stresses plants, reducing fruit retention and fiber quality/yields significantly.
Take note - symptoms can vary depending on variety, plant age and environment conditions. But these classic angular leaf spots are a clear sign trouble's brewing. Early detection is key.
Controls and Prevention to Fix Angular Leaf Spot of Cotton
1. Cultural Tactics for a Healthier Crop
Some cultural practices can help suppress angular leaf spot naturally:
- Use disease-free seed from reputable suppliers and remove volunteer cotton plants near fields.
- Rotate cotton with non-host crops like corn, soybean or small grains for at least two years.
- Improve drainage so fields don't flood and create humid conditions favorable to the fungus.
- Control weeds that can serve as alternate hosts like pigweed and lamb's quarters.
- Maintain balanced soil fertility to promote plant vigor and natural defenses against disease.
- Destroy crop residues thoroughly after harvest to eliminate overwintering inoculum.
Combined with other controls, cultural practices are a foundational part of any integrated disease management plan. A little TLC goes a long way!
2. Fungicide Options When Needed
For commercial growers, protective fungicides are an important tool against angular leaf spot:
- Dithiocarbamates (mancozeb, maneb): Low-cost multi-site contact fungicides, though resistance has emerged.
- Strobilurins (azoxystrobin, trifloxystrobin): Systemic fungicides effective at low use rates but high resistance risk.
- Triazoles (propiconazole, tebuconazole): Broad-spectrum group with good preventative and curative properties.
- Carboximides (flutriafol): Contact and locally systemic protectant fungicide for resistance management.
Always rotate between fungicide classes, mixing products or using premix combinations per label instructions. This delays resistance development in the pathogen population.
3. Biological Controls Worth Exploring
For organic growers, some biopesticides may provide eco-friendly alternatives:
- Bacillus subtilis: Soil bacterium with antifungal properties that may suppress P. gossypii.
- Trichoderma spp.: Free-living fungi antagonistic to soilborne plant pathogens like the angular leaf spot fungus.
- Plant extracts: Essential oils from neem, rosemary or other plants show fungistatic effects in greenhouse trials.
While still being optimized, biologicals offer a low-risk approach - especially as part of an integrated program with other controls.
4. Integrated Tactics for Long-Term Success
The most durable angular leaf spot management combines cultural, chemical and biological tactics:
- Start with disease-free seed/transplants and maintain prevention-focused cultural practices.
- Scout regularly and apply protectant fungicides preventatively before symptoms appear.
- Consider biological products that induce resistance or compete with the pathogen.
- Rotate fungicide classes/modes of action per label and include premix combinations.
- Remove volunteer cotton plants and thoroughly destroy crop residues after harvest.
- Consult experts regularly to adapt your strategies based on changing conditions.
With diligent scouting, sanitation and an integrated multifaceted approach, I'm confident we can significantly curb this sneaky fungus's impact on our cotton crops. Our livelihoods depend on it.
Conclusion
Thank you for taking the time to learn more about angular leaf spot. Please feel free to reach out if you have any other questions down the road. Also continue networking with other growers and agricultural advisors - together, with consistent vigilance and adaptation, we can safeguard cotton from this ever-present threat. Wishing you bountiful harvests for many seasons to come!
Post a Comment