What is tomato blight?
Tomato blight is a common disease that affects tomato plants. It is caused by fungi-like organisms called oomycetes, specifically the species Phytophthora infestans. The disease causes lesions and rotting on leaves, stems, and fruits of tomato plants. Under humid conditions, a white mold will appear on affected plant parts. Tomato blight thrives in damp, humid environments and can spread quickly through a garden or field.
The fungi-like pathogen enters the plant through natural openings or wounds. Once inside, it spreads rapidly, destroying plant tissues as it travels through the tomato plant’s vascular system. Lower leaves typically show symptoms first, followed by upper leaves, stems, and fruits as the disease progresses. Entire tomato plantings can be destroyed within just a few weeks by tomato blight infection.
Some common symptoms of tomato blight include:
– Water-soaked spots on leaves that turn brown or black
– White fungal growth on affected areas in humid conditions
– Brown/black lesions on stems
– Rotting fruit
– Defoliation
– Plant wilting and death
There are several species of Phytophthora that can cause tomato blight. The most common is Phytophthora infestans, which also causes late blight in potatoes. Other species include P. nicotianae, P. capsici, and P. parasitica. Environmental conditions favorable to tomato blight development include cool, wet weather and prolonged leaf wetness from rain, irrigation, or heavy dews.
Is it safe to eat tomatoes affected by blight?
Tomatoes affected by early stages of tomato blight are generally considered safe to eat, as long as the fruit itself appears healthy. The fungal pathogens typically only affect the plant’s stems, leaves, and outer skin of the fruit. The inner flesh of mildly affected tomatoes is usually not compromised.
However, fruits showing advanced rotting or lesions should not be eaten raw. The decaying areas on severely diseased tomatoes may contain high levels of the fungal pathogens. Consuming this decayed fruit material could potentially cause gastrointestinal upset in some cases, especially for people with sensitivities.
It’s important to check each individual tomato fruit carefully and cut away any damaged or rotten parts before eating. The tomato skins can be removed if they have black or brown lesions. Any fruits with firm, healthy looking flesh can be eaten after peeling off the skin and affected outer layers.
Cooked tomatoes affected by blight are safer, as heat from cooking helps destroy fungal organisms and pathogens. Tomatoes with mild or moderate blight can be cooked into sauces, soups, stews and other dishes. However, fruits with advanced decay should still be discarded and not consumed.
Here are some guidelines for determining if blight-affected tomatoes are safe for consumption:
– Fruits with minor spotting or lesions limited to the skin – Safe to eat if outer layers and skins are removed.
– Firm fruits with healthy looking flesh under the skin – Safe to eat after peeling off skin and any damaged tissue.
– Overly soft or severely damaged fruits – Do not eat raw, cook only if damage is minor.
– Fruits with extensive dark lesions or rotting – Do not consume at all. Discard completely.
– White fungal growth on fruit – Do not consume, even if flesh underneath appears healthy.
– When in doubt, throw it out! Only eat firm, healthy looking tomato flesh.
Proper cleaning and sanitization of knives, surfaces, pots and utensils is also important after handling and preparing affected tomatoes.
Should I discard all tomatoes if some have blight?
If you notice tomato blight symptoms on some fruits or plants, it does not necessarily mean you have to discard all the tomatoes in your garden. Healthy looking, disease-free tomatoes are still fine to eat.
The key is inspecting each fruit individually for any lesions, fungal growth or rot. Pick off and throw away any affected tomatoes showing damage. Only keep the firm, healthy fruits free of spots or mold.
Severely diseased plants that are clearly dying from blight should be pulled up and destroyed. But plants that look vigorous with some good fruits can be kept. Continue monitoring for new symptoms and remove any newly affected tomatoes immediately.
To limit the disease spread:
– Inspect plants frequently, at least daily if blight is detected.
– Remove and destroy all diseased fruits and leaves. Do not compost them.
– Keep foliage dry to limit fungal spore production. Avoid overhead watering.
– Increase air circulation and reduce humidity in covered gardens.
– Sanitize tools, cages and stakes between plants using bleach solution.
– Wash hands thoroughly after contact with affected plants.
– Consider applying fungicide sprays labeled for tomato blight.
With diligent inspection and sanitation practices, healthy tomatoes can continue to be harvested from plants with minor blight, especially if fruit show no symptoms. But severe infection will likely require removing and destroying the entire plant to protect remaining tomatoes. So inspect and control blight carefully.
Can you prevent tomato blight infection?
There are several effective strategies gardeners can use to prevent or reduce the likelihood of tomato blight infection:
– Plant resistant tomato varieties – Some tomato cultivars have resistance or tolerance to blight. Look for labels indicating resistance, or varieties marketed as “blight resistant”.
– Avoid overhead watering – Water at the base of plants instead of sprinklers or hoses overhead. This keeps foliage dry.
– Use drip irrigation under mulch – Drip systems and moisture-retaining mulches help prevent wet plant leaves.
– Stake and prune plants – Improving air circulation through staking and pruning prevents humidity buildup in the canopy.
– Remove lower leaves – Lower leaves most prone to early infection can be removed to reduce initial spore sources.
– Copper sprays – Applying copper fungicide spray to plants can help suppress blight spread.
– Sanitize equipment – Cleaning tools, stakes, pots, etc. between plants with a bleach solution helps destroy spores.
– Remove plants promptly – Pull up and destroy any plants showing advanced blight symptoms to prevent further spread.
– Avoid planting where tomatoes grew last year – Rotate crop locations and avoid planting tomatoes in the same spot as previous years.
– Apply appropriate fungicides – Commercial fungicide products containing chlorothalonil, mancozeb or other active ingredients can prevent blight. Always follow label instructions.
– Ensure proper nutrition and care – Healthy, vigorous tomato plants are less susceptible to infections. Provide adequate water, fertility, sunlight etc. for strong growth.
No single strategy provides complete protection, so utilizing multiple integrated preventive measures is ideal for managing tomato blight. Be especially diligent during cool, wet seasons when blight thrives.
What’s the best way to control tomato blight?
An integrated approach combining proper cultural practices and targeted fungicide applications provides the most effective blight control in tomato plants:
– **Use resistant varieties** – Plant tomato cultivars labeled as blight resistant if available. Varieties with resistance genes offer the best protection.
– **Employ preventive fungicides** – Applying targeted fungicides containing chlorothalonil, mancozeb, copper, or other approved active ingredients helps prevent initial infections.
– **Practice crop rotation** – Don’t plant tomatoes in the same location as last year. Rotate to a different garden spot to prevent buildup of blight inoculum.
– **Stake and prune plants** – Allow adequate airflow and light penetration by staking, training and pruning tomato plants.
– **Sanitize equipment and tools** – Clean and disinfect any garden tools, stakes, ties, pots, etc. with a 10% bleach solution between uses in different plants.
– **Promote foliage dryness** – Use drip irrigation, avoid overhead watering, and improve airflow to keep plant leaves as dry as possible.
– **Remove diseased plants and fruits** – At first sight of blight, remove and destroy affected leaves, stems and fruit. Don’t compost them.
– **Apply copper sprays** – Copper is a natural fungicidal agent. Copper-based sprays suppress sporulation on plant tissues.
– **Disinfect garden debris** – Burn, bury or hot compost all tomato plant material after harvest to destroy overwintering sources of blight.
– **Time plantings appropriately** – Avoid having tomatoes at peak maturity during cool, damp periods favorable to blight development.
Consistently implementing an integrated blight management plan reduces disease impacts. But be prepared to remove badly infected plants when necessary to protect remaining tomatoes.
What are some common tomato blight lookalikes?
Several other tomato problems can resemble blight infection on the surface and are sometimes confused with actual tomato blight. Common tomato blight lookalikes include:
**Septoria Leaf Spot** – Caused by a different fungal pathogen, Septoria lycopersici. Symptoms include small circular leaf spots with dark edges and lighter gray centers. Spots may have tiny black fungal fruiting bodies. Unlike blight, Septoria usually starts on lower leaves.
**Early Blight** – Caused by Alternaria fungi. Produces dark leathery target-shaped lesions on leaves and black rotten spots on fruits. Spreads upwards from older leaves.
**Bacterial Speck** – Bacterial disease resulting in small black spotting and speckling on leaves, stems, and fruits. Spots are not typically wilted or water-soaked like blight lesions.
**Blossom End Rot** – A non-infectious physiological disorder triggered by calcium deficiency and water stress. Causes sunken brown lesions on tomato fruit bottoms.
**Herbicide Injury** – Herbicides drifting onto tomato plants can sometimes mimic blight symptoms by causing blackened, dead leaf spots and lesions.
**Sunscald** – Sunscald from excessive heat exposure results in whitish-gray patches on fruits. These dry, papery lesions are not soft and rotten like blight.
**Insect feeding** – Tomato hornworms and some other pests can damage foliage and create holes/lesions mistaken for blight. Look for insect larvae or fecal droppings.
Accurate diagnosis requires examining plants closely and identifying the specific symptoms. Send diseased plant samples to diagnostic labs if the cause is unclear. Proper diagnosis allows selection of appropriate treatments for the specific problem at hand.
Should I pull out tomato plants with early blight symptoms?
It depends on the severity of the infection and overall health of the plants. For mild cases of early blight detection:
– Remove and destroy only visibly affected leaves and stems showing lesions or rot.
– Closely monitor for new symptoms and continuously remove any diseased tissue.
– Improve airflow through pruning and applying fungicides.
– Harvest any healthy fruits promptly before they also become infected.
– At the end of season, discard all plant debris to remove inoculum sources.
For severe, spreading infections:
– Pull out entire plants well ahead of fungus to prevent further spread.
– Uproot nearby plants showing early major symptoms as well.
– Destroy the infected tomato plants – do not compost.
– Focus efforts on any still-healthy plants worth trying to save.
– Replant in a new location next year; avoid planting tomatoes in same spot.
The decision between trying to save plants versus removing them depends on:
– How early the blight was detected
– Rate of disease progression
– Overall vigor of plants
– Amount of fruits set on plants
– Time left in growing season
So for mild cases found early, foliar fungicides and removal of affected tissue may suffice. But severe widespread infection warrants destroying whole plants immediately to contain the epidemic.
Can tomato blight affect the whole garden?
Yes, tomato blight can potentially spread rapidly from your tomato plants to other vegetables and crops in your garden under conducive conditions. The fungal-like blight pathogens produce enormous numbers of microscopic spores that move easily on air currents and contact between plants.
Some tips for reducing garden-wide blight impacts:
– Inspect all plants frequently and remove/destroy any diseased tissue immediately.
– Increase spacing between plants to encourage airflow.
– Avoid working in the garden when plants are wet.
– Apply protective fungicides to unaffected plants.
– Remove weed species like nightshades that can also host blight.
– Disinfect tools, stakes, pots, etc. between uses in different plants.
– Pull out and discard any plants showing severe infection.
– Remove and destroy all garden plant debris after harvest.
– Carefully dispose of diseased material away from gardens in sealed bags.
– Rotate plant families in different beds/plots annually.
While blight can certainly spread throughout the garden, diligent preventive actions can check its progress. Targeting just tomatoes for control measures is not sufficient. Implementing integrated blight management garden-wide provides the best protection.
Conclusion
Tomato blight is a very common and destructive disease of tomato plants. It can spread rapidly under cool, wet conditions and cause complete crop failure. While blight-infected tomatoes may not be edible raw, fruits with minor symptoms at early stages are often still usable if cooked thoroughly after peeling. Checking each tomato individually is necessary, rather than discarding all fruits from affected plants.
Gardeners can reduce impacts through an integrated program of preventive fungicide sprays, cultural practices to promote plant and foliage dryness, and removal of any diseased material immediately upon observation. Blight management should be implemented garden-wide, not just on tomatoes. While blight remains difficult to control once established, following consistent preventive strategies reduces its destructive potential and allows continued tomato harvests.