White Spots On Lettuce: 3 Causes

You may think that lettuce and fungus problems go hand in hand.

These leafy greens, as well as many virulent fungi, love moisture and cool temperatures.

If you’re seeing white spots on your lettuce, it’s usually a safe bet that a pathogen has infected your plants.

But it’s not just fungi that can cause white spots on lettuce leaves.

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There’s also a pest that strongly resembles a fungal disease and has fooled more than one experienced gardener into thinking that their crop had some sort of disease, when really it was an infestation.

You may need to refresh your memory about Check out our guide on how to grow lettuce.

In this article, we’ll help you narrow down the cause of white spots on your lettuce and figure out how to treat the problem so you can get back to enjoying your favorite salad.

Here’s the lineup:

If you’re seeing spots, you need to act sooner rather than later, so let’s dig right in and look at the three common issues that cause white spotting on lettuce crops.

1. Downy Mildew

The symptoms of Downy Mildew are quite distinct.

The water mold (oomycete), which causes this disease. Bremia lactucaeThe top surface of leaves is covered with angular yellow or light-green spots.

On the undersides, you’ll find blotches and spots of white fluff.

If the disease is not treated, the leaves may die.

It usually starts on older leaves, and spreads rapidly to new growth. If the mildew starts at the seedling level, the plant may die.

All species are affected by the pathogen Lactuca genus – and a few other genera, too – and thrives in moist, cool conditions. Rain, high humidity and irrigation are all ways to spread it.

Beyond reducing moisture by watering at the soil level and spacing plants appropriately, you can use a preventative fungicide if the conditions in your garden are conducive to the disease – or you have experienced it before.

Otherwise, it’s best to plant resistant cultivars and there are lots to choose from. Here are a few examples of resistant cultivars to downy mildew.

• ‘Adriana’
• ‘Antonet’
• ‘Australe’
• ‘Auvona’
• ‘Bauer’
• ‘Blend’
• ‘Bluerock’
• ‘Breen’
• ‘Butterhead’
• ‘Carlsbad’
• ‘Cherokee’
• ‘Conversion’
• ‘Edox’
• ‘Elf Ears’

• ‘Frisygo’ 
• ‘Green Star’
• ‘Gondar’
• ‘Intred’
• ‘Milagro’
• ‘Mottistone’
• ‘Optima’
• ‘Powerhouse’
• ‘Red Cross’
• ‘Red Rosie’
• ‘Starfighter’
• ‘Teodore’
• ‘Willow’

Note that resistant doesn’t mean immune so if you have a bad outbreak in your garden, even these may become infected.

By the way, I love ‘Optima.’ It’s one of the few cultivars that I have never, not once, had a problem with. It’s a butterhead type that matures in just 52 days.

‘Optima’

Seeds are available in different sizes. High Mowing Organic Seeds.

In our guide, you can find out more about downy mildew and other common lettuce illnesses..

2. Powdery Mildew

The powdery growth starts off looking like someone has splattered flour patches on the leaves. Before you know it, this powdery growth covers the entire head.

The disease can also cause the leaves to become deformed, dried out and brown.

If you’re seeing these symptoms, it’s likely that your crop is suffering from powdery mildew, a disease caused by the fungus Golovinomyces.

Powdery mildew can be a very common problem. There are many ways to treat this condition.

You can choose from a variety of treatment options, including milk applications and sophisticated fungicides. Read about it in our guide.

3. Mealybugs

Wait, what? We’re talking about white spots on lettuce here, not bugs.

Mealybugs, sap-sucking insects of the Pseudococcidae family, can easily trick you into believing that your crops are infected.

Mealybugs have a flattened shape and move very slowly. So when you go to check out your plant, it looks like white waxy lumps growing on the foliage – but those aren’t lumps, they’re insects.

These can also have a slightly yellow color or be grayish. They like to hide in areas such as under the leaves, on the stems or at the center of a rosette.

We usually know they’re around because we see the insects themselves, but they can also cause stunted growth and yellowing as they suck the life out of your leafy greens.

Check out our guide for dealing with mealybugs You can learn to manage these pests.

You’re a Damned Spot

Since it’s the leaves of the plant that we eat and not the fruit it produces, it’s all the more devastating when the foliage develops white spots.

You should monitor your garden regularly for these signs. You can save your crops if you act quickly when you spot them.

Are you seeing spots? What is your enemy? Do you have trouble figuring out the situation? Let us know in the comments section blow and we’ll try to help.

You might also be interested in our other guides for growing lettuce.