Why Are My Lupin Leaves Turning White? [Causes & How to Treat]

The Lupin plant produces one of the brightest colored flowers, and they bloom from early spring into the summer. They are red, pink, white, purple, or cream and are often multi-colored, making them look beautiful and eye-catching. For this reason, many florists and horticulturists prefer to grow them on their lawns to add that aesthetic value.

When the lupin plant suffers from mildew disease, they appear white because of the powdery mildew deposits on its leaves. These mildew deposits form when the temperature is higher than usual, and the ground is dry for long periods. Infrequent watering is also often a cause.

This article will explore the causes of powdery mildew in lupin plants. I will also outline the various solutions and how you can use them to save your plants without breaking the bank.

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What Causes My Lupin Leaves To Turn White?

The fungus Erysiphe polygoni is responsible for powdery mildew on the lupin leaves. It is a highly specialized pathogen that closely associates itself with the host. Lupin leaves with powdery mildew are common in some US states like Oregon, Idaho, and Washington.

Erysiphe polygoni thrives in conditions that favor the plant, making it challenging to eradicate. Most of the pathogen’s body grows outside infected plant parts and sinks root-like structures into the plant to obtain crucial nutrients.

The fungus which causes this powdery mildew does not occur in isolation, and certain ideal climatic conditions contribute to its growth. These conditions include irregular watering, high temperatures, and high air humidity. When they occur, your plant is highly likely to host pathogens that cause mildew growth.

The following are the major causes of white powdery mildew in detail:

Irregular Watering Can Cause Powdery Mildew

One of the leading causes of powdery mildew is irregular watering. When you water your lupin plants in a non-uniform manner, they will likely develop mold.

Excessive watering followed by dry spells encourages the growth of fungi and other parasitic pathogens. These pathogens cause your plant leaves to curl, wither and develop these tell-tale white powdery deposits.

Lack of Exposure to Sunlight Promotes Mold

Plants stored in a dark room or close to each other often develop mildew. These pathogens thrive in darkness since it inhibits harmful bacteria and mold destruction. Therefore, it is typical for plants growing indoors to develop this white substance since fungi thrive in such conditions.

Poor Air Circulation Enhances Mold Growth

The spores that cause mildew and other fungi to grow naturally exist in the air. When you open your windows, they will come into your home and grow on various surfaces, including other indoor plants.

Poor ventilation encourages their growth since the humidity in the air is trapped, creating an ideal condition to multiply. This problem also affects plants growing outside where you plant your lupins too close together or near obstructions.

Low Temperatures Promote Humidity

The cold weather also contributes significantly to the formation of white powdery deposits on the lupin plant.

Mildew and other fungi growth accelerates in low temperatures and can quickly multiply if you do nothing. Low temperatures also promote water retention in the air, which fuels mildew growth.

Fluctuating Weather Conditions Promote Mildew

The lupin plant blooms in the summer when we see its bright colors in full glory. However, the lupin plant will likely develop mildew when summer brings sudden bouts of warm weather. These temperature fluctuations are expected in early spring when temperatures rise, and the snow is melting. 

Dirt and Grease Promote Fungal Growth

This problem is often associated with lupin plants that grow indoors. Just like humans and pets, fungi need a source of food to grow and develop.

The fungi find such food in accumulated dirt and grease, especially in the kitchen. When dust and debris accumulate, they form the perfect food source for mildew to grow and infect your lupin plants.

Read Why Are My Lupin Leaves Turning Yellow?

How To Treat Powdery Mildew on Your Lupins

Mildew growth on your plants poses a severe threat to them. These fungi can rob them of access to water and crucial nutrients, making them grow slowly, whither, weak, discolored, and bloom less.

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While this disease has various causes, it is not fatal. When you spot and detect them in good time, you can apply multiple interventions and save your plants from death.

Various natural and chemical interventions can reverse the impact of these fungi on your plants. In addition to ensuring your plants are exposed to sufficient sunlight, regularly watered, and adequately aerated, you can thin out vulnerable parts and remove dead or diseased foliage to prevent extensive growth and damage.

You can take the following steps to treat powdery mildew on your lupins once they have already manifested on the plant:


You can apply various fungicides to protect the plant from infections and eliminate existing ones. Experts recommend using a fungicide that protects and eradicates to enjoy complete protection.

I recommend the Garden Safe Brand Fungicide3 which is Organic Materials Review Institute (OMRI) listed as a safe, organic solution to fungal growth on all plant types.

 Consider using fungicide during the onset of the disease because once mildew growth is extensive, control with any fungicide becomes more difficult.

Plant-Based Oils

Plant-based oils such as neem or jojoba oil effectively treat powdery mildew growth on lupin plants. You can use them to eradicate mild to moderate infections.

Alternatively, you can use horticultural oils like neem oil, which work just as well. However, be careful not to apply these oils to drought-stressed plants or when temperatures are over 90 degrees Fahrenheit (32°C).

Biological Fungicides

Biological fungicides such as the Monterey Complete Concentrate Fungicide & Bactericide offer an active ingredient, Bacillus amyloliquefaciens. These bacteria help prevent the powdery mildew from infecting the plant.

When sprayed on the plant, this ingredient destroys fungal pathogens and is nontoxic to people, pets, and beneficial insects. It has not proven to be as effective as oil or sulfur in controlling this infection.

Garden Safe Fungicide, Prevents Fungal Diseases, Controls Black Spot, Rust and Powdery Mildew, Aphids, Whiteflies, Spider Mites, (RTU Spray) 24 fl Ounce

Natural Remedies To Remove the White on Your Lupin Leaves

Although most products are currently available in the market to target the prevention of the growth of powdery mildew, there are many home remedies to treat an existing infection.

These remedies are cheaper to make than those available in stores but are as effective. They take between three to four weeks to eliminate existing infections.

Remember to coat all the affected areas thoroughly since they will only kill the mildew once they come into contact with each other. If possible, make several applications.

The following segment will highlight such remedies that effectively reduce the impact of these fungi and eliminate their growth:

Baking Powder Solution

  1. Mix one tablespoon of baking powder and liquid soap of similar proportions in a gallon (4.55 liters) of water.
  2. Proceed to spray the plant liberally, paying attention to the top and bottom leaf surfaces and any affected areas.

Use this primarily as a preventative measure instead of a curative one. However, it can still have some effect on existing powdery mildew.

Milk Treatment for Powdery Mildew

  1. Mix at least five ounces (148 ml) of milk with ten to fifteen ounces (296-444 ml) of water to make this solution. You can increase the amount of milk and water depending on the plants you intend to spray.
  2. Just like other solutions, make sure to spread it liberally across the entire plant for maximum effectiveness. Experts believe that some compounds in milk mitigate mildew growth.

Pruning and Trimming To Prevent White Mildew

  1. Remove the affected leaves, stems, or buds from the plant and discard them. You can cut some of these parts for new ones to emerge.
  2. Do not compost the trimmed or pruned sick leaves. Remember, the spores can sprout and spread in the composite material. It is noteworthy to disinfect all the tools used on infected plants.

Potassium Bicarbonate Solution Treatment

  1. Mix one teaspoon of potassium bicarbonate (potassium hydrogen carbonate/potassium acid carbonate) with half a teaspoon of liquid soap in a gallon (4.55 liters) of water. Do not use detergent.
  2. Spray the solution on all infected parts of the leaves, especially those hidden from direct light, such as stems and leaves.
Why Are My Lupin Leaves Turning White
Why Are My Lupin Leaves Turning White

Why You Have White Powdery Stuff on Your Lupins

Lupin flowers are easy to grow and can survive challenging climatic conditions. However, like every other flower, lupin flowers also have their share of problems. In addition to some of them being poisonous, the green ones are more susceptible to mildew disease than the colored ones due to multiple issues.

The white powdery deposits on the lupin leaves are mildew, affecting all the lupin species. They are often seen as white growth on the plant’s stems, leaves, and pods. It mainly occurs during the summer months due to the high temperatures and negatively affects the plant’s growth cycle.

This fungus often starts as a white isolated growth and, if not controlled, can cover the entire leaf surface. You may notice some lesions on the widely scattered plants. However, it should mostly happen early in the season. Tiny black dots may be seen later in the white areas.


Like other plants, Lupins have their share of problems, and one of the significant issues is white powdery mildew growth. This disease is a common problem that most florists and gardeners face, and the weather and various practices cause the issue.

It is not a fatal disease; your plants can spring back when you use different chemical and organic solutions. Additionally, various DIY solutions can help you care for your Lupin plants all year.

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