Gray mold, caused by the fungus Botrytis cinerea, is a common and destructive disease of tomato plants. It can affect leaves, stems, and fruits and spread rapidly under the right conditions. Identifying and treating gray mold early is key to saving your tomato crop.

What Causes Gray Mold on Tomatoes?

Gray mold is caused by the fungus Botrytis cinerea. This fungus thrives in cool, humid conditions and can infect tomato plants in a variety of ways:

Airborne spores – Wind and air currents can spread B. cinerea spores onto tomato plants. The spores can land on leaves, stems, or fruit and start new infections.
Soilborne spores – The fungus can overwinter in plant debris or soil. Spores splash up from the soil onto lower leaves and stems.
Infected seed – Botrytis spores can be transmitted on or in tomato seeds, infecting seedlings as they emerge.
Insect damage – Feeding by insects provides entry points for B. cinerea spores to infect plant tissues.

Once the spores land on susceptible tissue, the fungus germinates and starts to colonize the plant. Cool, wet weather promotes growth and spread of gray mold.

How to Identify Gray Mold on Tomato Plants

Detecting gray mold early is critical to effectively managing this disease. Here are the key symptoms to look for:

Leaves

Small brown/gray lesions that rapidly expand and turn tissues gray and water-soaked.
Fluffy gray fungal growth develops on older lesions.
Leaves eventually wither and die.
Lesions often start at leaf margins or tips.

Stems

Brown discolored lesions that enlarge and girdle stems.
Gray mold on stems stops water and nutrient flow, causing wilting above infected sites.
Stems eventually turn gray and rot.

Fruit

Water-soaked spots that develop into large, firm brown lesions.
Lesions eventually become soft as fruit tissue collapses.
Fluffy gray fungal growth on lesions when humidity is high.
Fruit mummies dry out and become hard. They harbor spores for future infections.

Carefully inspect leaves for small lesions and be alert for any gray fuzzy growth on plant tissues. These are the first signs of Botrytis infection.

How Gray Mold Spreads on Tomato Plants

Botrytis cinerea is an opportunistic pathogen that infects stressed or senescing tissues. It requires high humidity or free moisture on plants to germinate and penetrate. The fungus spreads quickly by:

Producing an abundance of airborne spores that travel on air currents, splashing water, and insects.
Growing long threadlike hyphae through plant tissue – one lesion can expand into healthy tissue.
Forming sclerotia (survival structures) in dead plant debris in soil.
Colonizing dead flowers, leaf litter, and plant wounds.

Once plants are infected, the conidia (spores) and mycelium from the lesions are spread by wind, rain, watering, and physical contact to other plants. The spores germinate and start new infections when free moisture is available on leaves or fruit for 6 or more hours.

Cool, wet weather (60-75°F/15-24°C) accelerates gray mold development. The disease spreads rapidly in crowded plantings with poor air circulation and continues late into the season when nights are cool and days short.

Preventing Gray Mold on Tomato Plants

Preventing gray mold requires integrating cultural, mechanical, and chemical controls throughout the season:

Start with clean transplants – Inspect seedlings carefully and reject any with suspicious lesions.
Avoid excessive nitrogen fertilizer – It promotes soft, dense foliage that stays wet longer.
Use drip irrigation – To avoid wetting foliage and minimize humidity around plants.
Improve airflow – Space plants appropriately, prune selectively, and stake/trellis to open up the canopy.
Remove debris – Discard dead leaves/plants and prune out affected shoots promptly.
Apply preventive fungicides – Use labeled products at bloom and fruit set when conditions favor disease.
Avoid working wet plants – To limit potential spread on hands and tools.
Rotate crops – Don’t plant tomatoes in the same location as previous tomatoes, potatoes, peppers or eggplants.
Control weeds – Eliminate alternate hosts like nightshade weeds.
Pick ripe fruit promptly – Avoid leaving ripe fruit on vines to rot.

By utilizing as many of these preventive measures as possible, you can reduce inoculum and limit infections by this aggressive pathogen. But even with excellent prevention, gray mold sometimes breaks through, so early detection and prompt treatment is key.

How to Treat Gray Mold on Tomato Plants

If you find gray mold lesions on your tomato plants, take action promptly to stop the disease from spreading:

Cultural Controls

Improve air circulation further – remove young suckers, excess foliage, etc.
Eliminate any infected plant debris – remove blighted leaves/shoots, prune out affected branches.
Avoid overhead watering or working plants when they are wet.
Increase plant spacing if possible – thin crowded plants.

Organic Fungicides

Several OMRI-listed organic fungicides can help suppress gray mold on tomatoes when applied preventively:

Copper fungicides (copper octanoate, copper hydroxide, etc.) – Broad spectrum protection.
Bacillus subtilis – Controls fungal diseases and boosts plant defenses.
Potassium bicarbonate – Fungicidal soap that disrupts cell membranes.
Hydrogen peroxide/peroxyacetic acid – Oxidizing agent that kills fungi on contact.
Neem, rosemary, clove or thyme oil – Antifungal essential oils.

Apply these as soon as botrytis lesions are detected, repeating every 7-10 days if conditions are favorable for disease. Complete coverage of all plant parts is essential. Combine with cultural tactics above for best control.

Conventional Fungicides

Several synthetic fungicides are also very effective against Botrytis on tomatoes:

Chlorothalonil – Broad spectrum, protectant fungicide.
Pyraclostrobin – Systemic fungicide, stops spore germination.
Boscalid – Targeted mode of action against Botrytis species.
Fluopyram – Xylem systemic fungicide, redistributes after rainfast.
Penthiopyrad – Targeted fungicide that stops spore germination.

Rotate between chemical modes of action to avoid resistance developing in the Botrytis population. Always follow label directions for rates, intervals, and safety precautions.

Biological Controls

Bacillus amyloliquefaciens – Colonizes leaf surfaces and inhibits Botrytis.
Trichoderma harzianum – Competes with Botrytis fungus for resources.

These biofungicides can help suppress gray mold but are most effective when integrated with some of the cultural or chemical controls listed above.

How to Identify and Treat Gray Mold (Botrytis) on Tomatoes: FAQs

Here are answers to some frequently asked questions about identifying and managing gray mold on tomato plants:

What causes gray fuzzy mold on my tomato leaves and stems?

The fungus Botrytis cinerea causes gray mold disease on tomatoes. It produces grayish spores and fuzzy fungal growth on infected tissues. Cool, wet weather promotes growth and sporulation of this pathogen.

How do I know if my tomato plant has gray mold?

Inspect leaves, stems, and fruits closely for small brown/gray lesions that expand rapidly. Fluffy gray fungal growth on lesions is a sure sign of Botrytis infection. Wilting foliage or rotting fruit are other symptoms.

Can gray mold on tomatoes spread to my other garden plants?

Yes, Botrytis spores are easily spread by wind, water, insects, and hands/tools to many common garden crops. Other susceptible plants include peppers, potatoes, lettuce, peas, roses, and more.

Should blighted tomato leaves and stems be removed?

Absolutely. Prune out any infected leaves, shoots, or branches well below affected areas. Remove this debris from the garden to lower spore levels.

What is the best treatment for early blight in tomato plants?

At the first sign of disease, improve air circulation, prune out infections, avoid wetting foliage, and apply an organic or conventional fungicide labeled for gray mold. Repeat applications may be needed.

Is gray mold on tomatoes treatable or should affected plants be pulled up?

Early infections can often be controlled through prompt treatment. But badly infected plants or those defoliated by gray mold are unlikely to recover and should be discarded.

Can you eat tomatoes with gray mold?

Do not consume tomatoes with any gray fuzzy mold growth. Discard or destroy infected tomatoes to prevent spread of the pathogen. Cherry tomatoes with slight lesions can be eaten if you cut away all diseased tissue first.

Conclusion

Left unchecked, gray mold can quickly defoliate and destroy a tomato crop. But by recognizing the early symptoms and immediately implementing cultural controls and targeted fungicide applications, you can contain infections before they get out of hand. Consistent prevention measures like drip irrigation, removing debris, and pruning for airflow are also key to avoiding gray mold issues in the first place. Catch this aggressive fungus early and take a multi-pronged approach to treat and manage it for healthy, productive tomato plants.

How to Identify and Treat Gray Mold (Botrytis) on Tomatoes

Gray mold, caused by the fungus Botrytis cinerea, is a common disease that impacts tomato plants worldwide. Timely identification and aggressive treatment measures are required to protect tomato crops from devastation. This article outlines how to accurately spot gray mold infections and provides integrated management recommendations for effective control in both commercial and home tomato plantings.

Recognizing Initial Symptoms

The first step in managing any plant disease is proper identification. These are the key symptoms that indicate gray mold on tomatoes:

Leaves

Irregular brown or gray spots that rapidly expand into large lesions.
Distinctive fuzzy gray fungal growth forms on lesions in humid conditions.
Leaves eventually wither, die and drop off.
Lesions often begin on leaf tips, edges or areas damaged by insects.

Stems

Elongated brown cankers that girdle and damage stems.
Gray mold on main stems blocks water movement, causing vine wilting.
Cankers eventually rot stems, causing foliage to collapse.

Fruit

Firm brown spots that enlarge into soft, watery decay.
Fluffy gray mold forms on rotting fruit when humidity is high.
Infected tomatoes decompose into dry, shriveled mummies.

Carefully scout plants after rainfall or heavy morning dew for any initial gray mold spots. Check fruits resting on soil for signs of infection. Early detection provides the best chance to arrest spread of this aggressive pathogen.

Conditions Promoting Gray Mold Outbreaks

The spores and mycelium of Botrytis cinerea thrive under the following conditions:

Prolonged humidity – Fungal growth explodes when leaf wetness exceeds 6 hours.
Moderate temperatures – 65-77°F is optimal, but can tolerate 50-86°F.
Dense foliage/poor air movement – High humidity levels persist within the plant canopy.
Senescing or stressed tissue – Provides ready nutrition source for the pathogen.
Wounds on leaves, stems or fruit – Entry points for infection.
Overripe fruit on the vine – Decaying tomatoes are highly vulnerable.

Botrytis spores spread easily via wind, water, and physical contact. The fungus can overwinter in crop debris and weeds, providing primary inoculum for new infections each season.

Integrated Gray Mold Management

Prevention is most effective when multiple cultural, biological and chemical tactics are integrated together:

Cultural Controls

Promote air circulation via wider plant/row spacing, pruning, and trellising.
Avoid excessive nitrogen fertilization.
Promptly remove lower leaves that touch the ground.
Eliminate infected plant debris and fruit mummies.
Rotate out of tomatoes and related crops for 2-3 years.

Biological Options

Weekly applications of Bacillus subtilis inhibit spore germination.
Regular releases of beneficial insects limit insect damage/wounds.

Conventional Fungicides

Chlorothalonil (Bravo) provides broad-spectrum protection.
Fluxapyroxad inhibits spore germination and attachment.
Penthiopyrad stops lesion expansion on leaves and fruit.
Rotate between targeted fungicides to prevent resistance.

OMRI-Listed Organic Fungicides

Copper octanoate coats foliage to suppress spore germination.
Potassium bicarbonate disrupts cellular membranes of fungus.
Bacillus amyloliquefaciens competes with pathogen on leaf surfaces.
Neem, clove or rosemary oil have antifungal properties.

For optimal gray mold control, integrate preventive cultural practices with applications of biological and chemical fungicides timed to protect emerging foliage, flowers and fruit. Scout regularly and be prepared to implement additional measures if weather favors this aggressive disease. Rapid action against initial infections is key to averting significant crop losses.

Conclusion

Gray mold can spread quickly across susceptible tomato varieties under cool, humid conditions. Learn to accurately identify initial leaf spots, stem cankers and fruit lesions caused by Botrytis cinerea. Routinely monitor plants for any symptoms, especially when weather has been overcast and wet. At the first sign of infections, aggressively prune out affected tissues and implement a multifaceted treatment plan. Continue preventive measures like improving airflow and applying targeted spore-inhibiting fungicides on a 7-10 day schedule as long as conditions favor disease development. By integrating cultural, biological and chemical controls, gray mold can be effectively managed for bountiful tomato harvests.