Grey Mold on Tomatoes: Symptoms, Causes, Treatment & Prevention

Botrytis cinerea, a fungus, is the primary cause of the grey mould of tomato, but can infect the leaves, stems, flowers and fruits, especially during cool, wet, humid weather. Since the disease is more than manageable, commercial farmers need to have more control over it. A combination of sanitation, humidity control, irrigation management, good air circulation, proper crop management and judicious biological or fungicidal measures can help minimize the disease pressure. Raising plants free of infected plant material and field or greenhouse cleanliness are also essential in reducing the sources of infection.

Why take early action?

The disease is systemic and attacks various plant parts and it can be very fast to spread under moist conditions when water is on the surface of the plants. For commercial production, early recognition is important because flower and fruit infections can decrease yield of marketable fruit.

Once growers see gray mold on plants, the first step is to find where it is occurring and cut down on disease favoring conditions. Any infected leaves, stems, flowers and fruit should be removed to help minimise the quantity of potential sources of spore in the crop. The other key points involve reducing humidity, encouraging better air flow and watering appropriately, as well as avoiding unnecessary wet foliage in the farmer's field. This is particularly important in greenhouses, and even more important in high tunnels where the humidity can be high around the dense tomato canopy.

Some may have heard of the grey mold on tomatoes or want to know how to get rid of white fungus on tomato plants or the very best tomato leaf mold remedy. But simply the sight of fungus growth does not necessarily indicate the disease condition. Before making a decision on tomato leaf mold treatment, ensure proper identification as a number of diseases caused by fungus and bacteria may have similar symptoms.

How will gray mold appear on tomato plants?

Grey mold on tomatoes are usually recognized on a farm by brown/gray lesions, grey moldy patches, wilting of flowers, lesions on stems, and soft rot in fruits. However appearance may differ depending on the affected plant tissue and environmental factors.

Gray Mold: Tomato leaves that have gray mould

In tomato plants, gray mold can start from brown to greyish spots which will grow over time. Affected tissue may be sprinkled with typical molds and mildews under moist conditions. As lesions increase in size, infected areas of the leaf may die.

Leaves that are left wet for extended periods of time should be especially monitored by farmers, particularly those in dense foliage. Lack of ventilation and high humidity can favour disease. Crops can be inspected for signs of infection regularly to reduce the availability of spores from an infection source.

How to Identify Gray Mold on Tomato Stems?

Gray mold may cause brown oval growths to appear on stems. Lesions can enlarge around the stem, and eventually encircle it. If the area is being affected, leaves and other above ground parts of the plant may start to wilt if water has become limited.

Don't immediately conclude that a dark lesion on the tomato stem is due to gray mold. There are several diseases which may cause brown or black stem, so farmers should check the full pattern of the tomato grey mould symptoms, environmental conditions and the presence or absence of gray fungal growth.

What does the grey mould look like on tomato fruit?

Fruit rotting may be recognised as pale soft watery rot, or gray mold. Certain varieties of green tomatoes will develop the characteristic white rings, known as “ghost spots.” During the course of the infection, a fuzzy gray mottling of the fungus may be seen.

With high humidity and wet plant surfaces, symptoms of fruit may develop quickly. It is important for commercial growers to harvest affected fruit as soon as possible as affected fruit may also help to spread the disease and cause post harvest losses.

Black spots tomato stems, Brown Stems or Mold – What is the problem?

It is important for farmers to not automatically determine that all dark lesions on tomato stems are due to Botrytis cinerea when they first observe tomato plant stem turning brown spots on the stems of tomato plants. Symptoms in tomato stems, leaves or fruit may not be caused by gray mold.

Other diseases may cause variations of the lesions, which are usually brown or gray, often covered with fuzzy gray spores produced by gray mold. Plum curculio and early seasonal diseases such as tomato leaf mold, early blight and late blight can cause citrus declines, as well as other fungal issues. Some of them can be distinguished by the location of symptoms, the appearance of the lesions, rate of symptom development, environmental conditions, and presence of characteristic spores.

When diseases begin to be a problem in a crop, as in greenhouse and high tunnel crops, diagnosis becomes critical. Before choosing a disease treatment program, farmers should decide upon the type of disease based on their needs.

Causes of grey mold on tomatoes

Free moisture on plant surfaces can exist in the form of rain, dew, fog or overhead irrigation and provide a condition for infection. Fungal development can also occur on dead flowers or on plant debris, wounded stems and damaged leaves.

It's advisable to pay special attention to growers who grow in greenhouses or high tunnels especially if they are experiencing gray mold on plants. A high humidity may persist for a longer time when ventilation is inadequate and thick greenery can delay the air drying. Farmers should be able to manage disease, achieve good ventilation, manage canopy density, try not to brush infected material against plants with care and ensure that infected plant material is removed.

The first step at the appearance of grey mold on tomatoes

For tomato grey mould symptoms, the initial step is to thoroughly examine the crop for typical gray mold infection on leaves, stems, flowers and fruit. When infected tissue is detected, all affected leaves, stems, flowers and fruit should be destroyed and disposed of safely.

Hence by using proper spacing, pruning and ventilation, farmers should try to enhance air circulation as well and help in reducing black spots tomato stems. Irrigation should be carefully governed to prevent unneeded periods of leaf wetness and overhead watering should be avoided if possible. Regularly check surrounding plants as new infections can occur if there are cool, humid or wet weather conditions around them.

Biologicals or other disease-management products can be included in an integrated program, as needed. There should be a combination of several precautions that should be taken and not the use of one precaution.

How to naturally remove gray mold on tomatoes for farmers?

The first step to solve grower problems on how to get rid of white fungus on tomato plants is to remove diseased material from the plants. In extreme cases, badly affected leaves, stems, flowers and fruit should be removed from plants and disposed of properly (not in the crops) but not discarded next to healthy plants.

Other measures by farmers can decrease disease-promoting conditions such as increased ventilation, minimum canopy humidity, no unnecessary overhead irrigation, and speeds up foliage removal. Pruning or other plant handling should be done when plant foliage is dry to minimize opportunities for pathogen movement through handling of wet plants.

Tomato debris and weed clearing at the end of the season may help to decrease potential sources of Botrytis spores. Good sanitary practices must therefore not cease after fruit removal for market, but should continue after harvest.

What Should be the Correct Tomato Leaf Mold Control Measure for Farmers?

Tomato leaf mold treatment should not be chosen just on the basis of being able to see some fungus growing on the plant. Botrytis cinerea and Botrytis on tomato leaves may not be a single disease so accurate identification should be the first step.

However, before applying a grey mold on tomatoes, farmers should be able to separate out gray mold from other types of leaf diseases on the plants. Humidity reduction, sanitation, proper irrigation, adequate ventilation and guarding healthy foliage prior to extended wet periods should be part of management strategy.

If fungicides must be used, growers should apply those registered for the crop and manage disease and prioritize the use of products in line with the instructions on the label. Farmers should also be aware that fungicides are mainly effective as a preventive method of protection and may not be effective at controlling infections already present.

Does an Organic Fungicide have a place to treat Gray Mold of Tomato?

Biological products can be used in an integrated disease-management program by farmers looking into an organic fungicide to treat gray mold program against grey mold. Use of beneficial microorganisms as biological fungicides can be a preventative option for growers looking to decrease their use of chemical fungicides.

The fungus, Trichoderma harzianum, organic tomato fungicide, is part of a group of fungi used for microbial disease management. It can kill pathogens through other mechanisms such as competition for nutrients, competition for space, through mycoparasitism or by synthesizing enzymes which break down the mycelium.

In the selection of organic fungicide for tomatoes, farmers should check whether the product has been registered or approved in their area with respect to the disease and crop. Not all biological fungicides will be registered for all fungal diseases, so growers are advised to always use the product as directed.

FloraEgis: Can Trichoderma harzianum help with the management of gray mold of tomato?

Novobac's FloraEgis is the best organic fungicide for tomatoes, based on the Trichoderma harzianum strain TH17, presented as a natural foliar biofungicide for farmers who need an organic tomato fungicide. Novobac gives Botrytis as one of its target diseases and fruiting vegetables as one of its common crops (as recorded in supplied product information).

Application of the active microorganism trichoderma harzianum is capable of maintaining the natural disease management through colonizing the plant's surface and competing with harmful fungi. The information provided also explains mycoparasitism, which refers to the breakdown of the hyphal parts of the fungi by enzymes secreted by T. harzianum.

Tomato farmers can use FloraEgis as part of a comprehensive tomato leaf mold treatment strategy which includes canopy management, irrigation control, regular crop monitoring, and sanitation. It is important to view it as a part of an integrated solution, but not a stand-alone solution as this would not represent good cultural practice.

If growers already know they are looking for a tomato leaf mold solution, it is essential that they make a correct diagnosis first. Novobac says that preventive use or handling should be used when signs of disease first are seen; multiple applications should be dependent on disease pressure. 

The best organic fungicide for tomatoes: FloraEgis

Prevention Methods for Grey Mold on Tomatoes

How to get rid of white fungus on tomato plants? Good prevention of effective grey mould on tomatoes starts before the disease is established. Farmers should begin with clean planting material, and try and maintain proper plant spacing in order to allow air circulation through the canopy. There is a need to focus on ventilation and humidity control in particular for greenhouse producers.

Another key element of prevention is good irrigation techniques. Wherever possible, avoid prolonged wetness of leaves, especially in a protected set-up. Pruning may also help increase ventilation and alleviate areas that are overly compact to encourage moisture to drain away.

After harvest, it is recommended to clean orchards of crop residues which are potential habitats for Botrytis. Periodic monitoring during the season will allow a grower to recognize early symptoms and make control measures in time to prevent the infection from spreading.

Farmers thinking about adopting the best organic fungicide for tomatoes may wish to use a combination of biological programmes with sanitations and environmental management. Trichoderma harzianum registered products (where appropriate where locally registered) may be part of a disease management program when outbreaks are preventable and not just when they are present.

For growers seeking organic tomato fungicide, the decision will be based on the disease, whether or not it is registered in the area, the crop stage, disease pressure, and any directions. Similarly, prevention and control of the white fungus on tomato plants starts with proper diagnosis.

References:

1. Harel, Yael Meller, et al. “Systemic resistance to gray mold induced in tomato by benzothiadiazole and Trichoderma harzianum T39.” Phytopathology 104.2 (2014): 150-157.
2. Imran, Muhammad, et al. “Biocontrol potential of Trichoderma harzianum and zinc nanoparticles to mitigate gray mold disease of tomato.” Gesunde Pflanzen 75.1 (2023): 151-163.