Alternaria leaf spot in the garden is a real problem for growers of brassicas, but it also makes life miserable for tomato and potato growers, causing plaque-like spots on leaves and fruits. Treating Alternaria can be difficult, so many gardeners do what they can to prevent this fungus from getting a toe-hold in their plots. Let’s learn more on what is Alternaria and how to treat this gardener’s nightmare.
The fungal pathogens in the genus Alternaria can be devastating to plants year after year. The spores overwinter on old plant debris and attach themselves to seeds, making Alternaria leaf spot especially tricky to completely eliminate if you save your own seeds. Garden vegetables are common targets of these wind-blown spores, but Alternaria is not discriminatory in the plants it attacks– apples, citrus, ornamentals, and weeds have been known to develop leaf spots caused by this fungus.
Alternaria symptoms once infection begins include small, dark, circular spots that regularly reach ½ inch (1 cm.) in diameter. As they spread, Alternaria leaf spots may change in color from black to tan or gray, with a yellow halo around the outside. Since spot development is heavily influenced by the environment, there are frequently noticeable concentric rings that spread from the initial point of infection. Sporulation causes these spots to develop a fuzzy texture.
Some plants tolerate Alternaria spots better than others, but as these spots increase on tissues, leaves may wilt or drop, leading to sunburned crops or weak plants. Fruits and vegetable surfaces can be infected with Alternaria spots as well, the lesions making them unsightly and unmarketable. Alternaria can invade tissues invisibly so eating spot-covered produce is not recommended.
Treatment for Alternaria requires fungicide to be sprayed directly on infected plants, as well as improvements in sanitation and crop rotation to prevent future outbreaks. Organic gardeners are limited to sprays of captan or copper fungicides, making control much more challenging. Conventional gardeners can use chlorothanil, fludioxinil, imazalil, iprodine, maneb, mancozeb, or thiram on plants listed on the label of their chemical of choice, but should still strive for prevention in areas with known Alternaria pathogens.
Mulch can help to slow the spread of Alternaria spores already in the soil when applied immediately after planting. Experiments at the New York State Agricultural Experiment Station showed that mulched kale crops experienced fewer and less severe problems with Alternaria leaf spot than the control plants, with straw mulches significantly more successful at suppression than black plastic or biodegradable plastic mulches. The straw mulched plants also grew much taller than other plants in the experiment.
Crop rotation is vital to preventing Alternaria fungal spores from germinating– although the many Alternaria fungal diseases look similar, the fungi themselves are often very specialized in the type of plant they will attack; gardens on four year rotations can avoid Alternaria building in the soil.
Cleaning up fallen leaves and spent plants as soon as possible will also limit the number of spores in the soil. Healthy, well-spaced plants tend to suffer less severe damage from Alternaria than their overly-stressed kin.
Several kinds of diseases can plague tomato plants. If you keep a close eye on your plants' leaf health, watering status, and growth patterns, there's a good chance you'll be able to catch the disease early to treat or eradicate it.
Alternaria leaf spot describes a broad group of fungal diseases that infect several common garden plants. As with many common fungal diseases, several species of closely related fungi cause this leaf-spotting disease. Some target specific plants, but others strike entire plant families. In the case of brassica vegetables such as cabbage, broccoli, cauliflower, and Brussels sprouts, several forms of the disease affect a single family.
Alternaria leaf spot thrives with warm temperatures and prolonged periods of high humidity. Overcrowded gardens encourage its development, as spores spread via wind, splashing water, garden tools, and even gardeners' hands and clothes. The fungi survive from year to year on infected plant debris left to overwinter in the garden.
Alternaria Leaf Spot Identification/Symptoms: Alternaria leaf spots often have different common names based on the plant and fungal species involved. The diseases that target brassicas include those commonly called brown spot, black leaf spot, and shot hole disease. Early blight in tomatoes and late blight in carrots are closely related to these brassica diseases.
As with early tomato blight, the first brassica symptoms are small, circular leaf spots that develop dark, target-like rings with a yellow outline. As the disease progresses, the spots merge and entire leaves become yellow or brown and scorched. Spot centers die and fall out, leaving a shot-hole behind. Spots may develop on stems and stalks as well as leaves.
In some plants, Alternaria leaf spot problems are mostly cosmetic, but brassicas sustain damage that leads to deterioration and rotting, storage problems, and general crop loss.
How to Control Alternaria Leaf Spot: Preventive treatments and regular applications of effective fungicides help protect brassica crops against Alternaria leaf spot. Daconil ® fungicides from GardenTech ® brand offer highly effective three-way protection to prevent, stop, and control Alternaria leaf spot and more than 65 types of fungal disease. These products treat broccoli, Brussels sprouts, cauliflower, and cabbage right up to harvest day:
Alternaria Leaf Spot Tips: Avoid overhead watering to limit leaf wetness, and allow enough space at planting time for good air circulation and ample sun penetration. Keep your garden free of fallen leaves all season, and especially thorough at fall cleanup time.
Always read product labels thoroughly and follow instructions, including guidelines for treatable plants, application rates and frequencies, and pre-harvest intervals (PHI) for edible crops.
GardenTech is a registered trademark of Gulfstream Home and Garden, Inc.
Daconil is a registered trademark of GB Biosciences Corp.
While you can’t do many things to save your tomatoes once they were affected by late blight, there are a few things you can do to treat early blight.
Once you’ve seen the first signs of early blight affecting your plants, one of the best solutions is to apply a fungicide treatment.
Since the disease is caused by a fungus, a fungicide is one of the most efficient solutions.
You need to closely watch for the first signs of early blight, which are the appearance of brown dark spots on the leaves at the bottom of the tomato plant.
Remove the affected leaves (you can also remove any leaves that are very close or hanging on the soil) and throw them away or burn them once they dry out.
Do not use those for your compost (here’s my composting guide) since you risk contaminating your next generation of tomatoes or potatoes when you use the compost.
I found a supposed organic remedy for early blight on Jeff Bernhard’s YouTube channel.
Even though I haven’t tested yet, I’m going to list the ingredients here.
You’ll first need a spray bottle. If you don’t have one already, you can buy one from Amazon for a few dollars.
Mix all the ingredients together and spray the solution on the affected tomato or potato plants.
According to Jeff, this is going to create a solution that should prevent the fungus spores from being able to survive on the leaves or on the stems of the plants by increasing the pH level.
You can spray the finished solution early in the morning or late in the evening.
It is possible to control Septoria if you catch the infection early enough. Aggressively remove the infected leaves and purge them from your property.
Do not add the material to your compost pile, and dispose of it in the trash, away from your garden.
Simply removing infected plant matter will not control early or late blight. You will need to use fungicides to manage these infections.
Fortunately, you have several options.
You can use the same kind of fungicide to treat each of these diseases. Apply them every seven to 10 days throughout the season.
If your weather is conducive to the spread of these diseases (i.e. humid and/or rainy), you can also consider using preventative sprays before the onset of an infection.
While the products described here have all been shown to be effective, fungi can develop resistance to fungicides if they are used frequently.
Check your plants periodically to ensure that the treatment is still working. If it isn’t, you may need to change which type of fungicide you are using.
Fortunately, all of the fungicides recommended here are in different classes, so you should be safe switching between them.
If you are looking for an organic fungicide to use, you are in luck!
Copper will kill all of these organisms. You can buy Bonide Liquid Copper Fungicide from Arbico Organics.
Many of the fungicides commonly used to treat tomato diseases will treat all of these blights.
One thing to remember with the fungicides listed here is that you should stop using them five days before you plan to harvest your tomatoes.
1. Chlorothalonil – Bonide Fung-onil Concentrate, available from Amazon
One of the microbes commonly used in the biological control of plant diseases is effective against early blight.
It is a strain of the bacterium Bacillus subtilis, which is also known as Serenade in a commercially available form.
Cucumbers commonly face three kinds of blight. All lead to the same outcome: a slow, lingering death. If a stroll through your cuke patch reveals suddenly wilting branches with discolored leaves, some form of blight could well be the culprit. For tips on how to keep these nasty diseases away from your cukes, keep reading.
As fungal diseases, cucumber blights can spread into the garden on wind currents and throughout it by splashing water. Most active during warm, rainy weather, they survive for long periods in infected plant debris. The blights most commonly affecting cucumbers include:
Alternaria attacks from the soil up. It surfaces with tiny brown leaf spots, often ringed in yellow. As the infection spreads, the leaves become completely brown before withering and dying.
Gummy stem blight infects cukes at all stages. It affects an entire vine except the roots. On young seedlings, it surfaces with brown leaf spots. Older vines have yellowing leaf margins followed by brown leaf spots and fruit with mushy, sunken areas that ooze sticky black fluid when pressed.
Phytophthora also devastates cucumbers in all stages. Vines experience sudden, permanent wilting from their bases to their tips although their foliage stays green. As the infection worsens, they become brown and mushy at the soil line, with expanding, yellow or brown spots. Water-soaked areas covered in stringy white mold cover the fruit.
Expert gardener’s tip:These diseases also threaten other members of the cucumber family, including:
When you’re battling cucumber blight, prevention is always preferable to control.
To keep blight out of the cuke patch, regularly remove plant debris and cover the soil with 2 inches of organic compost. It will stop blight spores from splashing onto the vines. Use drip irrigation or a soaker hose to prevent splashing. Trellis your cukes and prune excessive foliage periodically for better in air circulation.
Expert gardener’s tip: To avoid spreading disease, disinfect your pruning tools between cuts and after use in a solution of 1 part household bleach to 4 parts water.
Spray your cukes with organic liquid copper two weeks before blight usually strikes in your area or whenever you’re expecting extended rain. If you see symptoms, spray immediately and repeat every week to 10 days until the symptoms and wet conditions subside. Always follow the label’s instructions regarding dosage and spraying frequency.