Lupin Leaves Turning Brown: What You Need To Know

Healthy lupin plant leaves are usually grey-green with a dense coat of silvery hairs. Changes in the color, shape, or size of lupin leaves are clear signs that the plant is not healthy, and you need to inspect it further for signs of infection. Early diagnosis and treatment are crucial to saving your lupin plants.

Lupin leaves turn brown due to fungal diseases such as Brown Spot (Pleiochaeta setosa), Lupin Rust, and Lupin Anthracnose. Furthermore, infections by fungi such as Macrosporiuni sarcinaeforme can also cause the browning of leaves. In rare cases, viral infections can also cause leaf browning.

As you read further, you will learn more about the causes of browning in lupin leaves, diagnosing various diseases, and how you can mitigate the effects of fungal infections to save your lupins. I will also highlight some vital tips to keep your lupin plants healthy.

Table of Contents

What Causes Browning of Lupin Leaves?

Fungal infections typically cause the browning of lupin leaves. Excess water or humidity encourages fungal growth. Overwatering or maintaining poorly draining soils causes root rot, which may move to the leaves and causes browning.

Fungal infections can spread from one lupin plant to another through the following means:

Growing lupins in infected soil.
Propagating lupins using infected seeds, seedlings, or plant cuttings.
Splashing of fungal spores onto plants as it rains.
Cross-contamination during human activity.
Wind currents.
Infected compost or plant remains.

Untreated fungal infection in lupins can cause:

Stunted growth
Plant deformities
Compromised plant immunity
In severe cases, plant death.

To prevent these eventualities, farmers must familiarize themselves with the major fungal diseases that lead to leaf browning. This information will also help you identify the proper treatment procedures.

Brown Spot (Pleiochaeta setosa)

You can diagnose brown spot in lupins by inspecting for the following signs:

Small, dark brown spots on leaves, pods, and stems grow larger, forming a net-like appearance.
It reduced leaf sizes.
Distorted leaves.
Your lupin leaves will start dropping off.
The branch may develop large brown cankers, which encircle it.

This fungal disease is more prominent in wet, damp areas such as New Orleans and Louisiana.

Spores of the brown spot fungus drop from infected plants into the soil. Growing lupins in such soil will result in brown spot infection. The fungus can also spread through the splashing of spores onto the plant.

Seedlings are particularly susceptible to infection and suffer adverse effects from exposure to this fungus.

How Should You Manage Brown Spot?

Managing brown spot will require a combination of disease control methods. Crop rotation and fungicide application will help prevent infections in new lupin plants.

The following practices can also help to mitigate the effects of Brown Spot Disease in lupin plants:

Early sowing of lupins.
Ensuring plants receive adequate nutrients.
Planting lupins in well-draining soils
Variety Selection

Lupin Rust

Lupin rust appears as rust-colored spots on leaves surrounded by lighter discoloration (appearing like a halo around the areas). As the disease worsens, some lupin leaves may begin to die and drop off.

Fungal spores are light and are easily spread by wind currents or during human activity by attaching to clothes and tools/machinery.

Although lupin rust is not common in the US, farmers should be careful when visiting farms overseas, especially in Europe, Spain, Morocco, Egypt, Austria, and Portugal, where it is more common, to avoid bringing the pathogen into the US.

How Do You Manage Lupin Rust?

Manage lupin rust by removing any infected leaves to prevent further spread. Avoid splashing water on the infected plants, which can encourage further spread. Appropriate fungicide dressings are also necessary.

Additionally, variety selection by choosing the most disease-resistant seeds and enhancing drainage in the soil will assist in reducing the plant’s susceptibility to lupin rust.

Lupin Anthracnose

Lupin anthracnose affects all lupin plant species. All plant parts above the ground can get affected and show signs of infection.

These signs can help you determine whether your lupin plants are suffering from Anthracnose:

The deforming and twisting of leaves, with dark lesions appearing at the bent points.
Dark brown lesions with orange spores on the stems.
Stems that are bent over and deformed may eventually break off.
Loss of lupin pods and infected seeds.
Crop failure and loss of plant yields are eventualities.

Anthracnose is most prevalent in warm and wet climates, such as southern Florida. The fungus spreads mainly through wind current, rain splash, and human/animal activity through lupin fields. Blue lupins are often the most affected by anthracnose and are the most likely source of crop infestation.

How Do You Manage Lupin Anthracnose?

Applying thiram-based fungicide and permitted foliar sprays to anthracnose-infected plants can help reduce yield loss. You can also mitigate anthracnose spread by cleaning tools and farm equipment in between use. Pulling out severely affected plants and disposing of them will also help to reduce the spread.

Other steps you can take to minimize the spread of anthracnose in lupins include:

Sowing seeds with higher resistance: avoid growing blue lupins in higher-risk areas.
Allow about four years between planting lupin crops in the same paddock.
Space out lupin plants adequately to allow unrestricted airflow for plants and soil.
Separate infected plant parts from plants at all costs: do not even add them to compost, as reinfection can occur.

Impatiens Necrotic Spot Virus

In rare instances, a virus is to blame for lupin leaves turning brown. Impatiens necrotic spot virus may affect only some parts of the plant, with the rest maintaining a healthy appearance.

Signs of impatiens necrotic virus infection on lupin plants include:

The presence of light discolored, sunken lesions with dark brown edges (or ring spots) along the leaf margins.
Distorted leaves.
Wilting and falling off of the leaves.
Stem streaks, which may be purple or black.
Other signs may vary depending on the season.

Managing Impatiens Necrotic Virus

Inspect plants for signs of impatiens necrotic virus, and immediately isolate any plants you suspect are infected. The virus can rapidly spread from one infected plant to the entire lupin plantation.

In such a case, you would have to destroy all your lupin plants since there is no remedy for infected plants.

Nonetheless, preventing initial infection by the virus is the most effective way to protect your lupin plants. Other effective methods you can use include:

Plant virus-resistant lupin varieties.
Practice proper pest control methods, since some pests such as aphids, act as carriers.

Read Lupin Leaves Turning Purple

Lupin Plant Care Essentials

Whether you are growing lupins in a garden or a pot, there are essential conditions you must maintain to keep the plants healthy.

The biggest threats to lupin plants are the following:

Fungal infections.
Viral infections.
Pests.
Adverse environmental conditions.

Therefore proper care includes mitigating their effects.

Below is a summary of essential plant care tips:

Variety selection, as mentioned earlier, helps you sow high-quality seeds that are less susceptible to plant diseases, which simultaneously produce vigorous and quality yields.
Inspect seeds, seedlings, and plant cuttings for signs of infection before planting.
Lupins do best in slightly acidic to neutral soils, so you need to maintain a pH of between 6.5 and 7.
Opt for rich, well-draining soils to plant lupins, as water-logged soils encourage fungal growth and root rot.
Water regularly, especially at the seedling phase and during hot seasons, but check that the soil does not become soggy.
Allow the lupin plants at least six hours of full sunlight, but provide a shade for seedlings when temperatures are too high.
Conduct regular, thorough checks on plants and soil to identify any abnormalities which may indicate infection.

Choosing the appropriate chemical treatments for lupins is part of essential lupin care. You should carefully apply herbicides, fertilizers, fungicides, pesticides, and insecticides to prevent chemical burns on lupins. Here is what you need to know about chemical treatments on lupin plants:

Diagnose the plant problem critically before selecting a chemical treatment.
Study the dressing instructions carefully to prevent over-application for regular treatments such as fungicides.
Use the recommended personal protective equipment when handling the treatments.
Only use certified or registered treatments on your plants.
Opt for environmental and animal-friendly treatments to protect the environment and wildlife/domestic animals from poisoning.
Familiarize yourself with homemade remedies because their ingredients may be more gentle on plants, soil, and the environment.
Purchase treatments only when necessary because some tend to have a short shelf-life, and buying them too far in advance will cause you losses.

Overall, we cannot overlook the importance of consulting an expert during diagnosing lupin plant diseases, selecting suitable treatments, and practicing proper plant care.

Final Thoughts

Lupin leaves turn brown from fungal and viral infections, which attack the plant and cause other changes in the shape, size, and appearance of various plant parts. When untreated, these infections can lead to the death of the plants. Therefore, prompt identification, diagnosis, and treatment are critical to plant survival.

Isolation and destruction of infected plant parts are one of the most efficient ways to control the spread of fungi and viruses in lupins.

Proper selection and application of chemical treatments on lupins is a major contributing factor to overall plant health.