While nurturing the growth of tomatoes, two significant adversaries that can jeopardize their health are early and late blight. Although these terms may seem ambiguous at first, they actually refer to specific fungal diseases that afflict tomato plants in humid environments. Early blight strikes during the initial stages of the growing season, while late blight targets plants later on.
While both forms of blight have the potential to decimate your tomato harvest, early blight is generally less severe and more manageable than its counterpart. To safeguard your tomatoes against these deadly pathogens, it’s essential to understand the characteristics of each blight and take preventative measures accordingly.
What are the Differences Between Early & Late Blight?
While both early and late tomato blights can have devastating effects, they differ significantly in terms of their causative agents, timing of onset, and impact on plant growth. The two fungi responsible for these diseases attack at distinct stages of a tomato’s life cycle, resulting in unique symptoms and management strategies.
Early blight typically strikes when the fruit is still developing, causing visible damage to leaves and stems.
In contrast, late blight tends to emerge later in the season, targeting mature fruit that has already begun to ripen.
As we delve deeper into the characteristics of each disease, it’s essential to consider their respective effects on tomato plants and the best approaches for mitigating their impact.
Early Blight
Tomato early blight is a prevalent fungal disease caused by two closely related pathogens: Alternaria tomaphilia and A. solani. This highly contagious disease is one of the most common afflictions affecting tomatoes, with most seasons experiencing at least some signs of infection. The impact doesn’t stop at tomatoes; both fungi can also target other members of the nightshade family, including potatoes, peppers, and eggplants.
If you’ve planted multiple nightshade vegetables in close proximity, early blight can spread rapidly from plant to plant.
The Right Environment for Early Blight
While both diseases affect tomatoes in humid conditions, early blight tends to flourish in scorching heat and high humidity. When temperatures soar above 80°F and the air becomes saturated with moisture, this fungal disease makes its presence known. This is particularly true during the early stages of tomato growth, when young plants are still developing their strength and resilience. As they focus on rapid expansion, they’re more susceptible to infection.
In most summer seasons, a stretch of hot and humid weather will inevitably arrive. Whether it’s an intense heatwave or just a muggy spell, as long as the relative humidity exceeds 31%, early blight can start to take hold.
Signs of Early Blight
At the onset of early blight, subtle symptoms emerge at the base of the plant. Take a closer look at the lower stem and leaves of your tomatoes. In affected plants, you’ll notice roundish, brown spots that gradually expand into lesions with yellowish edges and darker interior rings. If left unchecked, these lesions will spread across the leaf, rendering it useless, or creep up the stem, killing the plant.
When fruit is infected, the rot typically begins at the stem base before spreading to the tomato itself. The resulting spots are often dark brown or black, sunken, and pock-marked on the surface. Early blight tends to ravage leaves more severely than other parts of the plant, potentially leaving you with leafless plants and scorched fruit. While not necessarily fatal, early blight can still ruin your tomato season by reducing yields and quality as plants focus on repair rather than production.
Late Blight
Tomato growers know all too well the terror that is Late blight. This fungal menace has no qualms about decimating nightshade plants, including prized tomato crops. The infamous Phytophthora infestans, a type of oomycete or water mold, is responsible for the devastating potato famine that ravaged Ireland in the 1850s. When Late blight strikes, it’s a swift and merciless attack. In ideal conditions, an entire crop of tomatoes can be obliterated in mere days.
The impact can be crushing, leaving growers feeling powerless against this formidable foe.
The Right Environment for Late Blight
While early blight may be more widespread, late blight is a significant threat to tomatoes. Its environment is highly specific, with optimal conditions found between 60-80°F, with the highest levels of proliferation occurring at around 70°F. Late blight also requires humidity to thrive, but unlike its early counterpart, it demands total saturation. A humid morning with dew-kissed plants or a prolonged period of rain-soaked leaves are ideal for late blight growth.
The perfect storm includes cloudy skies and temperatures hovering around 65°F, signaling the onset of this destructive disease in tomato gardens.
Signs of Tomato Late Blight
Late blight can strike your tomatoes with devastating speed. The first signs are often subtle – small, water-soaked patches on the lower leaves that resemble pale green or translucent spots. These lesions begin at the leaf’s edges and rapidly spread inward, taking on a velvety black or purple hue as they progress. Before you can even wonder what’s causing these unsightly marks, the affected leaf will wither away, turn brown, and ultimately die.
Stems are also susceptible to infection, resulting in lesions that weaken their structural integrity. In many cases, these stem lesions serve as the primary indicator of late blight’s presence. As the disease advances, the lesions spread quickly, often developing a white, fungal growth that accelerates the decay process. The entire plant can collapse under the weight of rot and fungus, leaving behind a mushy mess of decaying plant material.
When late blight targets tomato fruit, it produces reddish-brown spots beneath the skin, which rapidly become leathery, hard, and wrinkled before eventually softening as the plant succumbs to rot.
Preventing Blights
By implementing a few simple strategies, you can significantly reduce the risk of fungal and water mold diseases in your garden. One effective approach is to maintain a clean and open environment by removing debris and ensuring good air circulation between plants. This makes it more challenging for fungal spores to survive and spread. Additionally, avoid using overhead watering systems, which can lead to over-saturating leaves and stems.
Instead, water at the base of your plants to prevent moisture from accumulating on foliage. In humid conditions, wet leaves can quickly become a breeding ground for pathogens. Another key tactic is crop rotation, particularly when it comes to nightshade crops like tomatoes, peppers, and eggplants. To minimize the risk of blight, avoid growing these in the same bed year after year and consider rotating their locations every season.
By doing so, you’ll create a more diverse and resilient ecosystem that’s better equipped to resist disease.
Treating Blight
While early blight is more contained and treatable, it’s still crucial to address the issue promptly. A simple yet effective approach is to remove affected leaves as they emerge, taking care to dispose of them by burning or throwing them away – never composting blighted leaves. This will help prevent the disease from spreading. For a more targeted solution, copper-based fungicides can be used to contain early blight.
Consistent applications every week or two will keep the disease in check while symptoms are present. By taking swift action, you’ll be able to minimize the impact of early blight on your tomato plants. On the other hand, late blight is a different story altogether. Unfortunately, there isn’t a reliable treatment for this disease once it takes hold. Its rapid progression means that by the time symptoms appear, it’s often too late to stop or reverse the damage.
Given the unique nature of late blight, which isn’t caused by a fungus, you’ll need to adopt a different strategy to manage its spread. As soon as you notice signs of late blight developing or spot the conditions that foster its growth, treat your tomatoes with copper fungicides or products containing beneficial bacteria like Bacillus subtilis. Timing is critical when it comes to preventing late blight from gaining traction on your tomato plants.
A strong pretreatment can help keep this disease at bay long enough for you to harvest your fruits.
Blight Resistant Tomato Varieties
When it comes to minimizing the ravaging effects of blight on your garden, cultivating resistant tomato varieties is a tried-and-true approach. As growers have been battling tomato diseases for generations, they’ve developed plant breeds that are less susceptible to the fungi causing early and late blights.
While no variety can guarantee complete immunity from disease, planting blight-resistant cultivars significantly reduces the risk of infection.
For instance, ‘Mountain Magic,’ ‘Jasper,’ and ‘Defiant PhR’ have both early and late blight resistance, making them an excellent choice for low-risk tomato gardens. If you’re primarily concerned about early blight, consider planting ‘Mountain Supreme’ or ‘Juliet.’ On the other hand, if you’re focused on warding off late blight, opt for ‘Iron Lady’ or ‘Matt’s Wild Cherry.
‘ These cultivars have demonstrated their resilience in humid conditions, remaining resistant to pathogens that cause early and late blight.
Before planting, it’s essential to determine which type of blight is prevalent in your area. Check with your local extension office to confirm whether you’re more likely to encounter early or late blight. This knowledge will help you make informed decisions when selecting the best tomato varieties for your garden.
