Rosemary Plant Problems: Diseases, Pests, and Other Issues

In herb gardening, rosemary is considered one of the easiest plants to grow. This herb is native to the Mediterranean region, so it can withstand harsh conditions, such as drought.

Generally speaking, rosemary requires minimal maintenance and attention, but this doesn’t mean that it comes free of problems.

Rosemary, like any other herb, can encounter several life-threatening issues as it goes through its life cycle. It might be a disease or a problem with the environment, and you’re here to be your rosemary’s inspector, guardian, and savior.

For me, it’s ultimately important that you sharpen your knife and learn all about rosemary’s problems before growing it.

In this article, I will investigate the problems rosemary could face so that you’ll be ready to confidently grow, protect, and treat your rosemary plant.

Rosemary plant problems

Rosemary and Illness:

Rosemary is immune to most diseases and has a relatively low probability of getting sick. In poor conditions, however, rosemary becomes more prone to being infected by pathogens that the plant is naturally less resistant to.

Diseases that gardeners face the most with rosemary are:

– Powdery Mildew

Powdery mildew is one of the most known diseases among herb gardeners. It affects a great range of plants, including rosemary.

The most prevalent and apparent symptom of this disease is the formation of white ash-like powdery spots on the leaves of the infected plant.

It is caused by some species of fungi that invade the plant gradually and start forming their spores on leaves. These whitish spores are capable of infecting surrounding plants by traveling to them through the air.

In general, powdery mildew isn’t fatal for plants, but it will weaken your rosemary and reduce the amount of harvest.

  • Prevention:

Powdery mildew usually spreads when the soil is overly moist or if there isn’t enough sunlight reaching your plant. Another reason that could contribute to the appearance of powdery mildew is bad air circulation and ventilation.

To boost your rosemary’s defense against the disease, you need to make sure that all of the above factors aren’t present. Keep your plant growing in the best conditions.

Overcrowding of plants and branches can be another reason why your rosemary might contract powdery mildew.

rosemary plant

Spacing your plants a few inches apart is vital to avoid creating the perfect medium for the fungi to duplicate. Also, regular pruning of your rosemary, which prevents branches from overlapping, helps your rosemary stay immune to the disease.

  • Treatment:

Treatment of powdery mildew includes mixing one tbsp of baking soda and a few drops of biodegradable liquid soap with a gallon of water and then using the mix to spray the leaves weekly until the disease disappears.

plant soap for disease

Neem oil is also an effective natural fungicide that can help you get rid of powdery mildew. It is used the same way as the soda and soap mix.

If the disease persists after trying these natural methods (which is unlikely to happen), you can purchase some organic or synthetic fungicides.

IMPORTANT! It’s better to use neem oil only if you’re planning on consuming your rosemary.

– Root Rot

When the leaves of a plant start to wilt, most people think that either there’s a problem with the leaves or that the plant is thirsty, but what they don’t know is that root rot can also be the reason behind this issue.

Root rot is usually caused by excessive watering that enables mold to spread all over the roots of the plant. Rosemary is highly prone to this disease since it isn’t adapted to moist environments.

In most cases, root rot is fatal. Unfortunately, when the roots of your rosemary decay, you can’t do much to revive them.

  • Prevention: 

In this case, prevention is key. It’s very important to monitor the amount of water you’re providing your rosemary.

Remember that rosemary is a drought-tolerant herb, so even if you’re growing the herb in a container or the weather is getting hotter, rosemary doesn’t need to be watered excessively.

Use a high-quality, fast-draining soil that doesn’t trap a lot of water and allows the roots to breathe properly.

rosemary

Also avoid applying a lot of amendments and organic matter to the soil because they retain a lot of water, and in most cases, rosemary needs a minimum amount of fertilizer to grow.

  • Treatment:

Root rot needs immediate treatment. If your rosemary’s leaves are gradually wilting and turning yellow for no apparent reason, you should check the roots.

Gently remove the plant from the soil and wash the roots for a few minutes with a lot of water.

Plants with root rot will have some of their diseased roots fall off when you touch them. Such roots may look black and feel mushy.

Use scissors to cut off all the diseased roots. Afterward, use some fungicides to spray the healthy roots to prevent the disease from spreading.

Bring a new container or clean the used one with a bleach solution. Fill the container with fresh, high-quality potting soil mix and repot your rosemary in it.

Remove the yellow and wilted leaves from your rosemary and cut back the plant to stimulate new growth.

Verticillium wilt

From its name, Verticillium wilt indicates that it is a wilt disease. It is also caused by a fungal infection caused by fungi from the genus Verticillium. Overall, it is not that common in rosemary.

The most common symptom of this disease is wilting of the leaves and stems. It affects the older foliage, and it usually spreads from the bottom to the top of the plant. Sometimes, one part of the plant can be affected, while other parts will remain healthy for some time.

This disease can easily kill rosemary seedlings, but it needs some time to take over an adult plant.

  • Prevention:

The most effective way of preventing this disease is by using disease-free soil. This can be ensured by choosing premium-quality soil.

Choosing a resistant cultivar is also another way of prevention. This can be hard to achieve, though, especially when the workers at your local nursery don’t answer your needs.

rosemary plants problems
  • Treatment:

Unfortunately, it is almost impossible to treat this disease once it infects your rosemary.

The best way to deal with Verticillium wilt is by getting rid of all the diseased plants and starting all over again by using new soil, new containers, and new rosemary plants.

Pests:

Rosemary is known to be a pest-resistant plant, but some insects can still land on this herb to live and reproduce. Even most of these, however, will leave rosemary alone.

– Aphids

Aphids are very small and usually appear as little black or pale dots on the plant. They grow fast in quantity and might be a big problem for weakened rosemary.

aphids rosemary

The problem with aphids is that they suck the food rosemary is producing for itself, depriving it of energy.

The best way to deal with aphids on rosemary is to spray the plant with a strong water jet every other day. We don’t use insecticides here in case you want to use rosemary in the kitchen.

– Mealybugs

Mealybugs are also small insects that suck on rosemary’s sap. Females are bigger and wingless, while males are smaller but have wings.

Mealybugs can be worrying and annoying, especially if you’re growing rosemary indoors.

You can prevent them by using neem oil, which is also an effective insecticide in this case.

Other Rosemary Problems:

– Overwatering

Being a drought-tolerant Mediterranean plant, rosemary doesn’t need much water.

Gardeners, however, don’t pay attention to this when they water their herbs. They usually water all of their potted plants on a schedule.

Rosemary doesn’t like water as mint does, for example, so you need to take that into consideration when you water your herbs.

Overwatered rosemary may show signs of wilting or slow-growing. Sometimes, leaves will turn yellow or black.

To make sure you’re not overwatering your rosemary, wait until the soil is very dry to water the plant. At the same time, make sure the container you’re growing rosemary in is draining water properly.

– Heavy Soil

Heavy soil, such as clay soil, is a major problem for rosemary. Not only does this kind of soil trap a lot of water, but it also prevents the roots from breathing. This is almost fatal for the plant, as the roots start to gradually die due to a lack of oxygen.

To avoid such a problem, always use a premium, well-drained soil for your rosemary.

– Lack of Light

A rosemary plant that gets little light and not enough warmth will grow stretched and elongated branches. It will also become weakened and more susceptible to diseases.

This problem is especially common in rosemary plants that are growing indoors and don’t get enough light during the day.

rosemary plant

Rosemary grows best with at least 6 hours of direct sunlight exposure per day, so in case you’re growing it indoors you need to find a sunny location for it.

If that’s impossible, you can use a full-spectrum LED light to help your rosemary get the right amount of light per day.

– Lack of Space

Rosemary plants that are growing in tight containers will start feeling claustrophobic at some point.

As your rosemary grows more branches and foliage above the ground, it also develops more root systems below ground.

Rosemary will stop growing as it should when its roots are unable to extend anymore. This will make it more weakened and fragile.

Make sure you repot your rosemary every year or so to guarantee that the roots don’t bump against the walls of the container.  

– Pruning

Pruning your rosemary is necessary to stimulate the growth of newer and more flavorful foliage and to prevent it from turning woody and susceptible to disease.

Rosemary is an evergreen perennial herb, which means it can stay alive throughout the year if the climate is suitable.

One of the mistakes gardeners make is that they prune rosemary just before winter begins. This makes the plant too unstable and weak to survive during cold weather.

If you’re growing your rosemary under unregulated conditions, avoid cutting it back when the weather starts to get colder.

Have fun growing your rosemary, and don’t forget to share all your thoughts and questions in the comments below!

Blogger, Gardener | + posts

I'm Jad, a biologist, blogger, and experienced indoor gardener. I am knowledgeable in plant biology, particularly in plant cultivation and propagation. I founded HerbsWithin.com in 2019 to share my knowledge in indoor gardening with passionate home growers.

4 thoughts on “Rosemary Plant Problems: Diseases, Pests, and Other Issues”

  1. I found some fungi on the roots of my plant in the garden. It is white in color the shape and size varies from that of a chickpea to a pecan.
    When I peeled some skin off the larger one it had 5 segments each filled with what looked like caviar.
    The plant was dying back so I pulled it out and I want to replace it.
    Is this something I have to be wary of.

    Reply
    • It seems like your plant is infected with a soil-borne fungal disease that is causing its roots to rot.
      Try growing a new rosemary plant in a clean container away from the contaminated soil and if you see any fungus gnats in the garden, make sure to get rid of them.

      Reply
    • Hello Denise,

      It’s generally okay if the number of broken branches is relatively low.
      Treating your rosemary plant with pesticides in such a case is not necessary and wouldn’t be worth it.

      Reply

Leave a Comment