White spots on tomato leaves can be a disturbing plant problem. They cause delayed growth, lower productivity or lead to the death of tomato plants. The spots can appear on the upper side or lower side of the leaves. Explore possible causes of white spots on tomato plants in your garden, greenhouse or plantation field. With aid of pictures, learn how to identify, treat, control and prevent them.
Powdery Mildew on Tomato
Powdery mildew is one of the common causes of white spots on tomato leaves. In fact, potatoes and tomatoes are major plant hosts.
What causes powdery mildew on tomatoes? The fungi Oidium lycopersici, Oidium neolycopersici and Leveillula taurica are widely responsible for causing powdery mildew on tomatoes.
Infection occurs when spores land on tomato leaves, germinate and begin to reproduce. Even after reproducing, the fungi population can spread and multiply. The spores spread mainly by the wind that carries fungi spores from the host plant. Powdery mildew in tomatoes develops quickly in humid areas with an average measure under 85% relative humidity.
How to Identify the White Spots
Infection symptoms begin with the production of smaller pale yellow or light green spots on tomato leaves. These spots enlarge and turn brown quickly.
As infections advance, the fungus produces more spores and multiplies. This process is termed sporulation. Sometimes, dew staying on tomato foliage for longer hours can favor sporulation. As a result, the leaves have white spots, white growths or may appear dusted white.
Tomatoes infected by the fungus Leveillula taurica produce these white spots on the underside of leaves. Even though leaves rarely fall off their stems, entire infected leaves eventually die leading to substantial foliage loss. Symptoms produced by this disease in tomatoes are limited to leaves.
How to Treat Powdery Mildew in Tomatoes
The disease responds well to organic products as well as fungicides that are registered. Look for fungicides labeled specifically for the treatment of powdery mildew. Major agents of these fungicides include sulfur, copper and chlorothalonil. Apply them optimally to treat powdery mildew and get rid of white spots on tomato leaves.
Some organic products include potassium bicarbonate and botanical oil. Other products can contain Bacillus and Streptomyces. Re-apply these treatment products weekly until symptoms have cleared.
How to Control and Manage
Managing and controlling powdery mildew in tomatoes may be presented with challenges.
One, the spores can easily be carried in wind from infected tomato leaves. Two, there is a host range of plants and weeds. Three, infections can occur several times within a single growing season.
Below are ways to manage the fungus.
1. Grow Resistant Tomato Varieties
A successful choice of tomato variety resistant to powdery mildew may depend on:
- The climate of planting zones
- Weather changes
- Growing altitudes
For example, the following are resistant varieties of tomatoes grown in various regions of the Americas including the United States.
- Geronimo F1
- Granadero F1
- Striped Stuffer
- Massada F1
2. Carry Out Cultural Practices
Gardeners can control tomato powdery mildew through season-to-season good practices.
Cultural practices include a selection of healthy, disease-free planting materials and the removal of infected plants or plant parts.
3. Use Preventive Fungicides
This method of management relies on chemical control of the fungus. Many of the registered fungicide products contain copper, sulfur or potassium agents.
The New England Vegetable Management Guide lists below some fungicides for control of tomato powdery mildew fungus Oidium lycopersici.
- Bacillus pumilis strain QST2808 (SonataOG)
- Potassium salts of fatty acids (M-PedeOG)
- Potassium bicarbonate (MilStopOG)
- Phosphorous acid (K-Phite 7LP):
- Sulfur (Microthiol DisperssOG)
Cases of Oidium lycopersici fungus have been reported only in Australia.
Keep in mind that sulfur fungicides may cause a burning effect on leaves when subjected to high temperatures. Apply it mostly in cooler conditions preferably in the evening.
How to Prevent Powdery Mildew in Tomatoes
Prevention aims at stopping the plant fungus from spreading which helps control infections.
- Avoid excess application of nitrogen fertilizers
- Avoid handling tomato seedlings
- Space your tomato plants to allow for good penetration of light
- Remove all infected leaves on time before they get damaged
- Clear all host weeds and plants around your garden
Late Blight of Tomato (White Growths)
Late blight is another reason for white spots on tomato plant leaves. These spots occur in form of white growths.
What causes late blight in tomatoes? Late blight is caused by fungus-like tiny living things known as Phytophthora infestans. These fungus-like pathogens are also referred to as oomycetes. Oomycetes do not possess traits of true fungi.
How to Identify (Signs and Symptoms)
Small thin powder-like growths can identify white spots on tomatoes due to late blight. The growths are white in color. When present, you can notice these growths on leaves, stems and fruits of infected tomato plants.
These growths may be discovered on underside leaves when there is high humidity. Other symptoms to help you identify late blight include:
- Green lesions turn brown as they increase in size
- The brown lesions have dark-green edges
- In humid areas, lesions become water-soaked on younger leaves
- Dry and brown leaves as infection advances
- Dark round lesions or blotches on tomato fruits
- Dry brown rot on fruits
The leaves, stems and fruits eventually wilt and the tomato plant dies.
Treatment of Tomatoes With Late Blight
The use of treatment products goes hand in hand with correct identification. However, you need to observe your plants to identify the right symptoms.
Treat to save affected tomatoes from dying. What do you do? Spray your affected tomatoes with curative fungicides as early as symptoms have started showing up.
Consequently, protect healthy plants. Use preventive fungicide applications on those not affected.
How to Prevent Late Blight on Tomatoes
Prevention will prevent the oomycetes from spreading.
Instances of late blight recurring in your tomato garden are very likely if you don’t take bold preventive and management measures.
These include the following.
a. Destroy All Affected Plants
Begin by uprooting the affected tomatoes and other plants with similar symptoms. Destroy them by burning them.
b. Clear All Host Plants
Another sure preventive measure is by clearing plants known to host the oomycetes. These include weeds and plants such as:
- Nightshade plants
- Jimson weed
- Golden henbane
c. Plant Resistant Varieties
Select and plant well-adapted, resistant tomato varieties including:
- Mountain Merit Hybrid
- Plum Regal Hybrid
- Mountain Magic
- Matt’s Wild Cherry
d. Grow From Seeds
Purchase clean certified seeds from your local seed manufacturer. In case of regular occurrences of late blight in transported seedlings, consider growing from culturally produced seeds.
Evidently, infection of seeds is unlikely to happen since “Phytophthora infestans does not survive in or on tomato seed.”[ag.umass.edu]
More importantly, preventive measures to control the spread of Phytophthora infestans must have been put in place.
e. Other Preventive Measures
- Application of preventive fungicides on healthy plants
- Plant your tomatoes early to help your plants evade conditions that favor the spread of oomycetes
- Do a regular inspection of greenhouses and fields of tomato plants
Light Patches & Leaf Discoloration in Tomato Plants
Sometimes, spots on plants may present as light spots and patches. Tomato plants are vulnerable to these spots. Fruits may also be discolored. Apart from nutrient deficiencies, little care could be a root cause of light patches or leaf discoloration. These problems could also be due to improper care of tomato plants.
Here are possible reasons to highlight why light patches occur on your tomato plants.
- Heavy and irregular watering that favors the growth of mold
- Injury caused by glyphosate spray to control weeds
- Sudden exposure of tomato plants to intense sunlight can cause sunscald spots on fruits
- Lack of nitrogen in the soil
Remedies for White Spots on Tomato Leaves/Plants
The use of certain household products can help fight the fungal effects. As a result, applying home remedies can give tomatoes a survival boost and evade severe infection effects.
Try these home remedies as soon as fungal infection symptoms appear.
Use Milk Spray
Add whole parts of powder milk to water in a ratio of 2:3 respectively. Use a hand sprayer kit to apply to all tomato plants.
Apply milk spray on time for mild to moderate powdery mildew symptoms on your garden tomatoes. Repeat spraying every 5 days until the signs disappear.
Sprinkle Cinnamon Powder
Sprinkle cinnamon powder on tomato plants whose leaves have started growing white powdery little things. We recommend cinnamon that people spray in living rooms during winter.
Spray Baking Soda + Hand Soap Solution
Combine 1 tablespoon of baking soda with 2 mg of hand soap solution. Add this mixture to 4 liters of water. Stir well. Pour into your hand spray kit and spray directly on leaves with white mold-like spots.
This trick works fine in controlling powdery mildew at the early stages of infection. Repeat as necessary for improved fungus control.
Such home remedies are simple and safe to use anywhere. However, not all work to produce the expected results. They cannot serve as a direct substitute for specified treatment. Therefore, on a commercial scale, they might not be very effective and reliable.
FAQs on White Spots on Tomato Leaves
Q: Do the white spots on leaves kill tomato plants?
A: Yes and No. The white spots caused by powdery mildew will not lead to the death of your tomato plants. However, tomatoes don’t do well in terms of productivity. And with time, they get weakened because of the loss of nutrients to fungi. However, late blight can cause the death of all affected tomato plants if not well treated.
Q: Can powdery mildew spread to other tomatoes?
A: Yes. As stated above, the spores can be carried by the wind from one leaf or plant to another. Insects and other small animals
Q: Can you eat tomatoes with powdery mildew?
A: In most cases, the disease does not cause any symptoms in humans. However, it is generally safer and healthier to eat treated and disease-free tomato fruits only.
Sources & Reference
- TOMATO DISEASES & DISORDER. Clemson Cooperative extension. https://hgic.clemson.edu/factsheet/tomato-diseases-disorders/. Accessed online on 30 August 2021
- POWDERY MILDEW OF TOMATO. The Connecticut Agricultural Experiment Station. Accessed online 30 August 2021
- Center for Agriculture, Food, and the Environment: Late Blight and Tomato Transplant Production. Accessed online 30 August 2021
- Septoria leaf spot on tomatoes: More ways to prevent spots before your eyes. MICHIGAN STATE UNIVERSITY, MSU Extension. https://www.canr.msu.edu/news/septoria_leaf_spot_on_tomatoes_preventing_spots_before_your_eyes. Accessed online 9 Feb 2023
- White Spots on Tomato Leaves: How to Prevent This Unsightly Problem. Evergreenseeds. https://www.evergreenseeds.com/white-spots-on-tomato-leaves/. Accessed online 9 Feb 2023
- Oidium neolycopersici. ScienceDirect. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/oidium-neolycopersici. Accessed online 9 Feb 2023
- Reduction of Oxalate Levels in Tomato Fruit and Consequent Metabolic Remodeling Following Overexpression of a Fungal Oxalate Decarboxylase. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3641215/. Accessed online 9 Feb 2023
- Chakraborty N, Ghosh R, Ghosh S, Narula K, Tayal R, Datta A, Chakraborty S. Reduction of oxalate levels in tomato fruit and consequent metabolic remodeling following overexpression of a fungal oxalate decarboxylase. Plant Physiol. 2013 May;162(1):364-78. doi: 10.1104/pp.112.209197. Epub 2013 Mar 12. PMID: 23482874; PMCID: PMC3641215.