Tomatoes With Sclerotinia Stem Rot – How To Treat Tomato Timber Rot
By: Kristi Waterworth
It’s no wonder that tomatoes are the favorite plant of American vegetable gardener; their sweet, juicy fruits appear in a huge range of colors, sizes and shapes with flavor profiles to please nearly everyone’s palate. Tomatoes are also hugely popular with fungus, including those responsible for tomato timber rot.
What is Timber Rot?
Tomato timber rot, also known as sclerotinia stem rot, is a fungal disease caused by the organism known as Sclerotinia sclerotiorum. It appears sporadically around the time tomatoes start to flower due to the favorable conditions that heavy tomato foliage cover creates. Timber rot of tomatoes is encouraged by prolonged periods of cool, wet conditions caused by rain, dew or sprinklers and the high humidity that builds between the ground and the lowest tomato leaves.
Tomatoes with sclerotinia stem rot develop water-soaked areas near the main stem base, at lower branch crotches or in areas where there has been serious injury, allowing the fungus access to internal tissues. The fungal growth that begins in these areas progresses outward, girdling tissues and developing white, fuzzy mycelium as it grows. Black, pea-like structures about ¼-inch (.6 cm.) long may appear along infected sections of stems, inside and out.
Control of Sclerotinia
Timber rot of tomatoes is a serious, difficult to control problem in the home garden. Because the disease-causing organisms can live in the soil for up to 10 years, breaking the lifecycle of the fungus is the aim of most control efforts. Tomatoes with sclerotinia stem rot should be promptly removed from the garden – their death is inevitable, pulling them at the first signs of infection can protect unaffected plants.
You should aim at controlling the conditions that allow this fungus to germinate, amending your tomato bed as needed to increase drainage and watering only when the top 2 inches (5 cm.) of soil are completely dry. Spacing tomatoes further apart and training them on trellises or tomato cages may also help, since dense plantings tend to hold in more humidity.
The spread of sclerotinia during the growing season may be halted by removing affected plants along with the soil in an 8 inch (20 cm.) radius around each one, to a depth of about 6 inches (15 cm.). Bury the soil deeply in an area where non-susceptible plants are growing. Adding a plastic mulch barrier to remaining plants can also prevent the spread of spores originating from the soil.
At the end of each season, make sure to remove spent plants promptly and completely remove any leaf debris before plowing your garden. Do not add spent plants or plant parts to compost piles; instead burn or double bag your debris in plastic for disposal. Applying the commercial biocontrol fungus Coniothyrium minitans to the soil during your fall clean-up can destroy many of the infectious sclerotia before planting in the spring.
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Here are tips on how to identify, control, and prevent the fungal plant disease white mold.
What Is White Mold?
White mold, also known as sclerotinia, is a fungal disease that affects over 360 different plants, including beans, peas, lettuce, and members of the cabbage family. White mold is sometimes called timber rot when it affects tomatoes. Mold symptoms appear on blossoms, stems, leaves, and pods that have water-soaked spots. Leaves will wilt, yellow, and die pods may rot.
Host crops are most susceptible during flowering, but young seedlings are also very vulnerable. White mold typically infects the plants early in the spring or summer and then develops unnoticed for a while. White mold fungus releases spores when the weather is cool, and these spores can be carried by the wind and infect other plants. This is why it is so important to catch white mold and destroy infected plants quickly.
Early blight is caused by the fungal pathogen Alternaria solani. Also known as Alternaria leaf spot, this disease appears as black or brown spots 1/4 to 1/2 inch in diameter on leaves, stems and fruits and a premature loss of older leaves. This fungus can also impact fruit, creating large, sunken areas with a velvety black appearance and concentric rings at the stem end of the fruit. Early blight survives in the soil on plant debris and disease spores spread via wind or splashing water. This disease is only problematic when weather is warm and wet, and develops most rapidly after fruit set. Good sanitation practices including the destruction of volunteer tomato plants and nightshades and the removal of all plant debris at the end of the growing season will help prevent early blight.
How to Store Your Tomato Harvest
Are you wondering what to do with your end-of-season surplus of green and ripe red tomatoes? Some can be kept in boxed storage to continue to ripen and enjoy fresh. But for a bumper harvest, long-term preservation is often needed. Find all the details on how to store your homegrown tomatoes right here. Read more now.
Caused by Water Molds
Formerly classified as types of fungi, water molds have been reclassified in their own class – the Oomycetes.
They include some of the most devastating plant pathogens known today.
13. Late Blight
The water mold Phytophthora infestans can cause severe infections on tomatoes and potatoes. This is the organism that was responsible for the Irish potato famine, resulting in the death or emigration of millions of people.
The first symptoms are areas of the leaves that appear water-soaked. They rapidly enlarge to form oily purple blotches. Rings of grayish-white mycelia may appear on the lower sides of the leaves.
The entire leaf can die, and the disease can spread to the young stems and petioles.
The fruit is usually infected on the shoulders, because the spores fall from above. These fruits turn brown, but they stay firm unless other organisms infect them as well.
The spores easily spread to other plants, so you should act quickly if your tomato plants have this infection. Not only are your plants at stake, those growing in your neighbors’ gardens are as well.
Infection can occur in just 10 hours at high humidity (above 90 percent) with temperatures of 60-78°F.
This organism overwinters in the debris of tomato, potato, and other nightshade plants.
You should ruthlessly cull any infected plants and remove them from your property. Just to be safe, you should also remove any plants nearby that could be infected, even if they are not showing symptoms.
14. Phytophthora Root Rot/Buckeye
This disease may be caused by Phytophthora parasitica and P. capsici. Since these soil-borne pathogens are water molds, they may infect plants at any stage of growth when the soil is moist.
Symptoms include the death of many or nearly all of the roots. The plants respond by wilting or dying – particularly in hot weather.
In seedlings, this disease is one of several that can cause damping off.
Keeping soil moisture constant and avoiding broad fluctuations can help to control this disease, as does providing good drainage and preventing flooding.
When these organisms infect the fruit, this disease is called buckeye rot and it manifests as leathery tan or brown spots.
Keeping the surface of the soil dry can help minimize the likelihood of damage to the tomatoes.
The use of cereals as a rotation crop may help reduce the levels of these pathogens in the soil.
In extreme cases, the use of fungicides may be necessary.
Vegetable Pesticide Application
There are several effective ways to deal with pests. If you want to use pesticides on your vegetable crops, you may need a license. You must fulfill a continuing education requirement if you want to maintain a valid private pesticide applicator license in Pennsylvania.
Penn State Extension provides a number of workshops for anyone who is looking to become certified or recertified. The courses available include the Private Pesticide Applicator Short Course in Spanish and English. A pesticide spray record-keeping spreadsheet is also available.
If you want to take the guesswork out of spraying there are smartphone and tablet apps you can use to help in sprayer calibration, nozzle selection, tank mixing, and product selection.
How can you prevent blossom end rot?
There are lots of ways you can take precautions for next year's crop!
- Carefully harden off young seedlings gradually to protect them from extreme temperatures and conditions.
- Select a planting area with good drainage.
- Avoid setting out plants too early in the season, which can expose them to cold temperatures and cold soil. Allow soil to warm before planting.
- Work in plenty of compost and organic matter into the soil before planting, so that the plantвЂ™s root system has a better chance to grow strong and deep.
- Add quick-release lime when planting tomatoes so that thereвЂ™s plenty of calcium in the soil and itвЂ™s absorbed quickly. Tomatoes grow best when the soil pH is about 6.5.
- Keep your tomatoesвЂ™ water supply even throughout the season so that calcium uptake is regular. Tomatoes need 1-3 inches of water a week. They perform best when watered deeply a couple of times a week rather than superficially every day.
- Mulch plants once established to maintain moisture levels.
- Once blossoms emerge, apply tomato fertilizer that is high in phosphorus (the second number in a fertilizerвЂ™s three-number series), like 4-12-4 or 5-20-5. Too much nitrogen (the first number) or large amounts of fresh manure can prevent calcium uptake.
- Cultivate carefully around tomato plants to avoid damaging root systems. Try not to dig more than an inch or two deep around plants.