Why Does Your Sage Have White Spots? 4 Causes and Fixes

If you frequently harvest fresh sage from your garden to use as an ingredient for cooking a meal, it might be shocking to find the leaves have white spots. If it’s the first time you’ve seen these spots on your plant, you should know that it is a sign of an infection. 

Your sage may have white spots due to any of the following reasons:

  1. Your sage has powdery mildew.
  2. There are spider mites on the sage.
  3. Your sage has a white mold infection.
  4. Whiteflies are using your sage as a host.

This guide will help you identify the root cause of the white spots on your sage plant’s leaves. It also covers solutions you can implement to ensure you won’t face this problem in the future. 

1. Your Sage Has Powdery Mildew

A common reason you’re noticing white spots on your sage leaves is a plant disease known as powdery mildew. It’s caused by fungi and can spread to the shoots and nearby flora via rain or wind.

Fortunately, not everything is lost if your sage has powdery mildew. It isn’t fatal even when your plants suffer from a severe infection. However, it may reduce the yield.

The problem with powdery mildew is that it can survive during the colder months. By staying on plant parts and debris, it withstands the harsh winter. Once the weather warms up next season, the fungi become active.

Powdery mildew may start on one sage plant but can quickly spread to other flora in your garden. Once the temperature exceeds 60 °F (15.5 °C), it’ll focus on spore production.

The plant surface doesn’t need to be wet for the fungi to catch on. As long as relative humidity meets its requirements, it will spread.

Powdery mildew on a zucchini plant

Relative humidity plays another role in influencing the behavior of fungi. When it is high, the fungi start creating new spores. As the relative humidity drops, they focus on spreading their spores.

This is because the fungi consume the nutrients that go to the plant cells. As a result, growth slows down, and the flora no longer looks healthy. 


One fact you should know is that you may not see white spots on your plants right away. If the sage in your garden has this disease, you should examine the new growth.

Curled, discolored, or twisted leaves are usually the first signs that your flora is contaminated. Only when the disease spreads throughout the plant will you start to see white spots. 

If powdery mildew grows unchecked, the contaminated leaves will turn yellow. Over time, the infected foliage will dry up and fall off the sage.


Luckily, there are several ways to combat powdery mildew.

Below are handy tips to follow to decrease the chances of dealing with powdery mildew:

  • Before buying sage from a nursery, inspect all plants for powdery mildew. This includes white spots or curled, discolored, or twisted new growth in the flora. 
  • Ensure there is sufficient space for each sage plant to grow. This prevents overcrowding, which tends to increase the relative humidity in the growing area.
  • Trim or thin the plants, not more than ⅓ of the total foliage. This technique also helps avoid overcrowding in your garden.
  • Always pour water directly into the soil. Overhead watering increases the relative humidity in your garden as the water evaporates from the plant parts. Also, this technique makes your sage vulnerable to other diseases.

What if powdery mildew has already gotten a hold of your sage plants?

In this case, you should follow these tips to control this disease:

  • Avoid over-fertilization, especially with products that are nitrogen-heavy. Nitrogen promotes new growth in sage, which are susceptible to these fungi. 
  • Remove all infected plant material and discard them immediately. Don’t add it to your compost pile, as the fungi will survive and spread to new flora. 

Once you’ve started to get this disease under control, you should monitor your plants the following season. This way, you can tackle the issue before it becomes a severe problem in your garden. 

2. There Are Spider Mites on the Sage

From a distance, spider mite infestations can look like white spots. Only upon closer inspection and along with a magnifying glass will you be able to see that they are not white spots but rather insects with webbing.

There are two ways they will appear on your plant. The first method is via wind, which blows them from neighboring infected flora to the sage in your garden. Otherwise, they travel through contaminated plant material.


Spider mites consume everything inside the plant cell, barring the cell wall. As a result, the sage leaves will start to have white spots. 

However, this is only the initial phase of the infestation. As it progresses and becomes severe, the contaminated flora will sometimes change from green to yellow or even gray. 

If the infestation reaches this point, you’ll also see webbings throughout the plant. This is how spider mites get their name. 


Plenty of options are available regarding tackling spider mites on sage plants.

Check out all the solutions and pick one you feel comfortable using in your garden:

  • Decrease plant stress as much as possible. Sage doesn’t like over-watering and is relatively drought-tolerant. Spider mites like dry conditions, which is why they tend to attack the sage in your garden.
  • Spray water on the spider mites and their webbings. This will make it harder for these organisms to establish themselves, reducing their population. However, this won’t work if there are hundreds or thousands of spider mites. 

Use Biological Control Agents

So, what can you do when the population of spider mites is out of control?

In this case, you can go for the following biological control agents. 

If spider mites attack the sage during summer, you should use insects that can withstand high temperatures, like the Swirski mites. These predatory mites will feed on the spider mites and tend to be aggressive. 

Another predatory mite that does well against spider mites is the Persomillis mite. They work best during spring and fall but aren’t as effective if the temperature exceeds 85 °F (29.4 °C).

If you want to take preventive action (i.e., ensure spider mites never get hold of your sage), Californicus mite is an excellent option. Depending on how many plants are there in your garden, you can have 1-5 mites for every square foot (0.09 sqm) of space.

Unfortunately, you can’t use any of the above predatory mites if you are growing your sage indoors. In this case, you can turn to Mesoseiulus longipes, which will help keep a check on the pest population.

You only need 1-3 of these mites on every leaf. You should ensure that the relative humidity is low to give them the best chance of survival.  

When Should You Use Chemical Solutions?

As highlighted earlier, predatory mites control the spider mite population well. Should their numbers increase to a point where you have a full-blown infestation, you need stronger solutions. 

There are two options in this case – you can consider horticultural oils, which effectively target these pests. Go for cinnamon, clove, or rosemary.

The second option is to apply insecticidal soaps. Like the horticultural oils, these chemical miticides will make it harder for the pests to breathe. 

However, predatory mites are also vulnerable to these products. Make sure you only use it when necessary. Fortunately, once the product dries up, you won’t have to worry about accidentally killing the predatory mites as it will become ineffective. 

You should never use insecticidal soaps if the temperature exceeds 90 °F (32.2 °C). This can damage the sage foliage. Also, if the weather in your area is arid, don’t apply these products to the plant. 

3. Your Sage Has a White Mold Infection

If there is one problematic plant disease you need to keep an eye out for, it’s white mold. Caused by Sclerotinia sclerotiorum, a plant fungus, it may already be too late by the time you notice this issue. In other words, it will likely result in the death of the plant

Yellow cucumber flower covered with Sclerotinia sclerotiorum

Another problem with white mold is that it can spread through the air or soil.

For air germination, the plant must continuously be wet for at least 10 days. However, the moisture levels should be constant; otherwise, the spores won’t develop. 

The other mode of germination starts from beneath the soil surface. With sufficient levels of nutrients and moisture, the pathogens will infect the plant and spread the contamination throughout the healthy tissues. 


Because it looks similar to other diseases, it can be hard to identify this issue. For example, one of the signs of white mold infection is the sudden mycelial growth in the infected areas. This is confusing because you may mistake it for another type of fungi that generally appears when organic material starts to decompose. 

However, you can look for other structures which indicate an infection.

For instance, apothecia is a tan-colored fungal structure shaped like a cup. You’ll find it close to the infected plant or soil. The role of apothecia is to store spores known as ascospores, which it spreads to infect other flora.

Another sign of a white mold infection is if you notice the formation of sclerotia. This rigid structure is black in color and has an oval shape. You may find it inside or outside the sage plant. 

If you don’t pick up on these signs, the infection may reach a point where you can no longer save the sage in your garden. In this phase, you’ll want to look for the symptoms of infection to prevent it from spreading.

The first symptom of this disease is the formation of lesions. They look like they contain water and will start to appear everywhere on the sage. In the early stages, it’s brown before it changes to a greyish-white hue. 

Another common symptom is that the infected plant parts break easily. You’ll also notice that the foliage wilts and falls off the plant. Look for fungal growth, which is generally white and hairy. Unlike powdery mildew, this will be furry. 

As Sclerotinia sclerotiorum is present in contaminated soils, it will grow after rainfall. These fungi need rain, especially on the sage leaves, to infect the plant. If water remains on the foliage for 48-72 hours, it increases the chances of these fungi growing on the flora.

It will become a problem if you grow your herbs in a cool environment but with high relative moisture levels. 


Several solutions are available to prevent white mold from infecting the sage plants in your garden.

Follow the points highlighted below as they make it harder for these pathogens to get a hold of your herbs:

  • Always remove any weeds that grow along with the sage in your garden. White mold pathogens often rely on weeds as their host before making the jump to their next target, in this case, your sage.
  • Ensure there is sufficient space between sage plants to avoid overcrowding. Higher humidity favors white mold growth. Adequate space improves airflow, reducing moisture levels.
  • Use nitrogen-rich fertilizers only when required. Excess nitrogen increases plant growth, boosting the production of white mold spores.
  • Avoid overhead watering, including using sprinklers as much as possible. Stick to drip irrigation, as this will ensure the surface plant material isn’t moist.  

Fungicides and herbicides are effective when fighting against this fungal disease. However, they are only helpful when protecting your plant against these pathogens.

Once the infection spreads to the sage, you’ll need to remove it. Do not mix the infected plant material with your compost, as it will only contaminate the whole pile.

What if you already notice white mold growth on your sage?

In this case, you’ll have to be careful while handling the plant. For instance, you must sterilize all tools you use while interacting with your sage. This prevents the pathogens from infecting new flora in your garden.

White mold can survive up to 3 years without a host, which is why it can occur every growing season. If your sage has an infection, rotate it with a different plant for 2-3 years until the pathogen dies.

Here is a list of flora resistant or partially resistant to this disease.

  • Common/soft rush
  • Pearl millet
  • Taro
  • Weeping brown sedge

4. Whiteflies Are Using Your Sage as a Host

Initially, whiteflies can look like white spots because of their small size. They are pests, and you’ll usually find them on the bottom side of the leaves. These insects also lay their eggs on the same side.

By feeding on plant sap, they leave a residue known as honeydew. This attracts other pests like ants, which may destabilize your garden’s predator insect population.

It can be challenging for whiteflies to infest plants because of natural predators. However, if you used pesticides or insecticidal soap and killed predator insects accidentally or allowed the infestation to become severe, there’s a high chance you’ll face this problem. 


They like using sage plants as hosts because it provides them with plant sap. These insects target tissues that are responsible for transporting food throughout the flora.

Over time, the infested foliage will turn yellow before falling off. Also, you’ll notice that the plant no longer looks healthy. 


If you notice whiteflies in your garden, you should avoid using systemic insecticides. While they can help control the whitefly population, it also kills beneficial insects and other natural predators. As a result, if you don’t get rid of these pests, the infestation will only get worse by the day. 

Here are two easy ways to deal with whiteflies.

  • Remove whiteflies from the sage plants by spraying them with water. This is only effective during the initial phases of infestation (i.e., their population is low). 
  • Use safe and homemade insecticides. Insecticidal soaps and neem oil spray can effectively decrease the number of whiteflies in your garden. However, it won’t bring down their population to zero.

You should also be proactive when dealing with whiteflies on your sage. When you see contaminated leaves, remove them from the plant immediately. 

If the infestation is severe, pull the contaminated plant and discard it. As always, never add this debris to the compost pile. 

Final Thoughts

If you see white spots on your sage, you may be dealing with plant diseases like powdery mildew and white mold. Pests like spider mites and whiteflies may also look like white spots to the untrained eye. 

When dealing with these problems, it’s best to use safe and natural solutions like introducing beneficial insects to your garden. In contrast, pesticides risk killing even the beneficial insects, making your sage plants vulnerable to other pests and diseases. 

By implementing the solutions suggested above, you can control these infections or infestations and ensure your sage stays healthy during the growing season.

Alexander Picot

Alexander Picot is the founder of TheGrowingLeaf.com and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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