Rust Spots on Leaves During Flowering | Causes and How to Fix

Rust Spots on Leaves During Flowering

Spots of color and leaves turning yellow of a plant’s precious leaves can be alarming, but don’t worry. The problem can often be alleviated by treating or improving the plant medium. As long as you properly identify the problem and fix it quickly, you can usually reduce your plant damage to a few parts. 

Fungal rust is a common cause of bright, alien-looking spots. What you see on rusty leaves or brown spots on leaves during flowering are reservoirs of reproductive spores. The spores can spread throughout the trees or surrounding vegetation as these spots mature. It’s critical to tackle the issue before it worsens. Let’s learn more about it.

Two Major Causes of Rust Spots on Leaved During Flowering

The two most common causes of rust spots on plants are fungal rust and calcium or magnesium deficiency. While rust spots usually appear during flowering, they can occur at any stage of development.

Rust Fungus 

rust spots on cannabis leaves

Much of the food you eat every day requires good growing conditions for plants. There are so many things that can go wrong, from bad weather to pests to fungi. Wheat was once particularly vulnerable to a fungus known as rust fungus. Modern wheat plant varieties have been developed to be much more resistant to these fungi, but just 100 years ago, farmers would have been very upset if they started seeing red spots or yellow along with the wheat leaf stalks of corn.

Occasionally, even modern wheat varieties can be affected by a new rust fungus that can be very harsh on the crop. Rust fungus is a fungus caused by the fungus Pucciniales. There are thousands of different species of rust fungus. They are usually red on the trees they attack, hence “rust.” 

 What are the Causes of Rust Fungus?

  • Rust fungus is a common problem for most green leafy plants, and it can thrive under certain optimal conditions. 
  •  Rust fungus is more likely to grow if you keep the temperature between 60 and 80 degrees F with high humidity. If these conditions sound familiar, that’s what you want your cannabis plant to thrive on. 
  • Also, if you give your plants too much water, making the soil very wet, but you don’t give them enough sunlight to evaporate the water, Rust fungus can occur.
  • If the air circulation in the growing space is not good, some fungus may be growing.

How do you Confirm a Case of Rust Fungus on Cannabis?

The fungus is prone to spore spread, so you can usually test for the fungus by simply rubbing the affected area with your finger. If part of the rust rubs against your finger, it is mold rust. If it doesn’t rub, it’s probably a nutrient issue. The spots caused by fungal rust are storage areas for powdered spores. The positive thing about fungal rust is that it is easy to diagnose, as fungal rust can be partially scraped off with a handkerchief or cloth. Wipe the spots and see if the color transfers to the material.

How to Prevent Rust Fungus in the Future?

Rust fungus is a common fungal disease affecting many ornamental plants, including chrysanthemums and perennials. Rusts like cool, mild temperatures and humid conditions. Infections reduce plant wellness and vigor, flower production, and crop value. In late summer, beetles and garden beetles may be at risk of becoming infected with certain rust pathogens.


The symptoms of rust are quite distinctive. Initially, the infected site appears as pale yellow spots on the upper surface of the leaves, then pustules emerge on the underside of the leaves below the lesions. Once the pustules burst, brown, rust-colored spores are released to create new foci of infection. In addition to brown rust, chrysanthemum gardens are also susceptible to white rust that causes white, cream-colored blisters on the underside of foliage.

Here are some tips to prevent rust in production: 

  •  Examine incoming species for signs of disease. 
  •  Regularly monitor sensitive species for signs or symptoms. 
  •  Monitor weather and environmental conditions. (Only 4.5 hours of leaf wetting or dew combined with the cool temperatures needed for the spores to germinate and infect the plant.) 
  • Prepare your rotation plan and use fungicides for prevention.

Planet Natural discusses preventing rust fungus in a much thorough manner. You may refer to their guide for more on this topic.

How to Deal with Rust Fungus?

Prevention is important because it is difficult to get rid of rust fungus once your plant is infested. If you want to get rid of rust fungus from a plant, first remove the infected plant and the debris in between and discard it. It’s best to burn it but get it out of the house. Spores move fast and do not want to infect other plants. After that, treat the rest of the plants with a fungicide. 

There are many chemical sprays available online, but one of the best remedies is to spray the plant with a natural homemade sulfur fungicide once every 10 days. A mixture of baking soda is also a good remedy. One liter of water + 1 teaspoon mixed them all. You can also mix 1/2 cup of chopped garlic and 1 quart of water to make a garlic spray. Leave it for 24 hours before spraying on the plants. A weekly sulfur dusting can help prevent and cure rust fungus. Neem oil, a natural fungicide, and insecticide are also effective against rust.

Calcium and Magnesium Deficiencies 

This macronutrient deficiency may manifest as the yellowing of leaves with small brown spots or rust spots on the leaves increases. Increasing magnesium can solve this problem. Some fertilizer compounds include both calcium and magnesiumIf rust fungus is not the problem behind the spots on your plant leaves, other causes could be a lack of magnesium or calcium, not feeding them enough of these minerals, or because the plant is congested and cannot absorb them. 

The flowering period is when your plant starts to run out of magnesium and calcium, so if magnesium is lacking, this is when it will start to appear as rust or brown spots on the leaves. If left untreated, these spots will spread to all of your leaves and reduce flower production significantly. These deficits should be easily distinguished from fungi that cause rust patches on leaves.

How to Confirm a Ca or Mg Deficiency?

rust colored spot on weed leaves ca and mg Deficiency

Cal-Mag deficiency is difficult to identify in the beginning stages of a plant. As a result, it is critical to act as soon as you see the first indication. The first indications occur in the plant’s lower leaves. The leaf tips curl upwards and turn brown. From the bottom to the top of the plant, the brown spots grow in size and quantity.

The youngest leaves on the plant’s top also develop dark patches with vein discoloration. Too little magnesium or a blockage of this important mineral is often the cause of rusty spots on your plants. If your leaves turn yellow but the veins remain green, it’s a sign that your plant isn’t getting enough magnesium.

What to do about a Ca or Mg Deficiency? 

Before considering a solution, make sure that the nutrient deficiency problem is not a nutrient lockout. To find out, you’ll need to test your soil’s pH by testing the water from your pot. If you don’t have a pH meter, test paper should be fine. Note that calcium and magnesium need to have a pH between 6.5 and 9.1 for better absorption. If the pH in your soil is outside these limits, you know they’re locked in, and you need to adjust. 

Soil pH will affect your plant’s ability to absorb all the nutrients it needs, and pH levels out of the ideal range can lead to nutrient locking in your plants. Too little acidity (pH above 7) and your plants can’t absorb the important trio of NPK nutrients – nitrogen, phosphorus, and potassium. However, if the pH of your garden soil is in the range – and you want it close to 6.8 – then your plants need additional magnesium or calcium. This process will take a bit of trial and error, as giving nutrients to your tree too much can block the other. Take it carefully, evaluate the outcomes, and be calm.

Closing Thoughts on Rust Spots on Leaves During Flowering

In summary, there are several reasons for the appearance of rust spots on leaves during flowering. These include pests, fungi, nutrient deficiencies, and nutrient burn attacks. If you observe rust spots in the middle of the leaves, immediately start preparing for the treatment described in this article. If you do nothing, your plants will be stunted and yield low. So don’t take rust stains lightly and do what a smart gardener does by caring for every plant. 

Frequently Asked Questions

Rust spots on leaves during flowering can be caused by a fungal infection known as leaf rust. This fungal infection is common in plants that are grown in damp, humid conditions and is typically more severe during the cooler months.

Leaf rust can be identified by the presence of small, orange or yellow-brown spots on the leaves of a plant. These spots may be accompanied by a powdery, yellow-orange substance on the surface of the leaves.

Yes, leaf rust can cause significant damage to a plant if left untreated. It can weaken the plant and reduce its overall vigor, leading to reduced growth and flowering. In severe cases, leaf rust can kill a plant.

To prevent leaf rust from occurring on your plants, it is important to follow good cultural practices, such as avoiding over-watering and providing proper drainage. You should also avoid overcrowding your plants and provide adequate space for air circulation to help prevent the growth of fungal infections.

To treat leaf rust on your plants, you can start by removing any infected leaves and disposing of them away from the plant. You can also apply a fungicide according to the instructions on the product label. It is important to follow the manufacturer’s recommendations for application frequency and precautions to ensure the safety of your plants and yourself.

Leaf rust can return once it has been treated if the conditions that favor its growth are not addressed. To prevent the recurrence of leaf rust, it is important to follow good cultural practices, such as avoiding over-watering and providing proper drainage, and to properly treat and dispose of infected plant material.

Leaf rust can be transmitted to other plants through the movement of infected plant material or by wind-borne spores. To prevent the spread of leaf rust, it is important to properly dispose of infected plant material and to follow good hygiene practices when working with your plants. You should also avoid placing infected plants near healthy ones, as this can increase the risk of transmission.

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