What is the Difference Between Powdery and Downy Mildew

The main difference between powdery and downy mildew is that powdery mildew looks like spilt powder on leaves, whereas downy mildew causes leaves to droop and develop yellow and brown spots. Furthermore, the spores of the powdery mildew occur on both sides of the leaves. But, the spores of the downy mildew occur on the underside of the leaf. In addition to these, powdery mildew produces a thick web of white spores, covering leaves, stems, and shoots, while downy mildew the spores appear as a grey or white fuzz on the underside of the leaves.  

In brief, powdery and downy mildew are two types of fungal infections in plants. Generally, powdery mildew is an ascomycetes fungi, while downy mildew is an oomycetes fungi. 

Key Areas Covered 

1. What is Powdery Mildew
     – Definition, Characteristics, Infection
2. What is Downy Mildew
     – Definition, Characteristics, Infection
3. What are the Similarities Between Powdery and Downy Mildew
     – Outline of Common Features
4. What is the Difference Between Powdery and Downy Mildew
     – Comparison of Key Differences

Key Terms 

Downy Mildew, Fungal Infections, Powdery Mildew, Spores

What is Powdery Mildew 

Powdery mildew is the most common type of mildew infection in plants. It belongs to the family Erysiphales, and it mainly occurs in ornamental plants including phlox, monarda, azaleas, roses, lilac, privet, dogwood, crab apple, grape, squash, and turfgrass. However, there are different types of powdery mildew specific to different plants. Importantly, the main characteristic feature of powdery mildew is the production of white cobweb-like growth of the fungal mycelium on the upper surface of the plant. 

Figure 1: Powdery Mildew

Furthermore, this infection can occur on the underside of the leaf, on buds, flowers, young fruits, and stems. The infected leaves often become curled and distorted, and the colour changes into brown or yellow. Ultimately, these infected leaves may fall off prematurely.  Although the powdery mildew weakens the plant, it rarely kills it.  

What is Downy Mildew 

Downy mildew is a less common type of plant infection of fungi. It belongs to the family Oomycetes. Although it is less common, downy mildew is very damaging to the plants. Importantly, it infects a wide variety of plants including the mint family, roses, butterfly bush, coreopsis, pansy, snapdragon, viburnum, and cucumbers. Though the symptoms vary depending on the type of plants, the most common symptoms of the downy mildew include yellow, dark green, brown or black spots on the upper surface of the leaves.

Figure 2: Downy and Powdery Mildew

Moreover, with the dispersion of the infection, the whole leaf turns into brown and drop from the plant. Notably, the main reason behind the increased damage by downy mildew is their invasion of leaf tissue to obtain nutrients. 

Similarities Between Powdery and Downy Mildew  

• Powdery and downy mildew are two types of fungal infections that mainly occur in the leaves of the plants.  
• Both are types of fungi.  
• However, preventing and controlling is easy with the correct understanding of the type of fungal infection. 

Difference Between Powdery and Downy Mildew 

Definition 

Powdery mildew refers to the most-commonly reported fungal disease, affecting a wide range of plants while downy mildew refers to any of the several oomycetes fungi that are obligate parasites in plants. 

Taxonomy 

While powdery mildew belongs to the family Erysiphales, downy mildew belongs to the family Oomycetes. 

Characteristics 

Furthermore, powdery mildew looks like spilt power on leaves while downy mildew causes leaves to droop and develop yellow and brown spots. 

Growth Conditions – Temperature 

Also, powdery mildew requires nighttime temperatures of 60 °F and daytime temperatures of 80 °F, but downy mildew survives at 40-80 °F. 

Growth Conditions – Humidity 

Besides, powdery mildew requires nighttime humidity of 90-99% and daytime humidity of 40-80%, while downy mildew requires a humidity of 85%. 

Sides of Leaves Where Spore are Produced 

Notably, the spores of the powdery mildew occur on both sides of the leaves, but the spores of the downy mildew occur on the underside of the leaf.  

Sites of Spore Production 

Moreover, powdery mildew produces a thick web of white spores, covering leaves, stems, and shoots, while downy mildew the spores appear as a grey or white fuzz on the underside of the leaves.  

Morphology of Spore Production 

Also, powdery mildew produces spores in a tree-like formation, while downy mildew produces spores in chains. 

Transmission of Spores 

The spores of the powdery mildew transmit through the wind, while the spores of the downy mildew transmit by splashing water. 

Symptoms of Leaves 

In addition to the above, the leaves turn yellow and fall off as a result of the powdery mildew, but leaves produce yellow blotches as a result of downy mildew. 

Invasion of Plant Tissues 

While powdery mildew does not invade plant tissues, downy mildew invades plant tissues for nourishment. 

Degree of Damage 

Another difference between powdery and downy mildew is that powdery mildew causes less damage, while downy mildew causes high damage. 

Conclusion 

Powdery mildew is a whitish, powdery fungal growth on the upper surface of the leaves of plants. It belongs to the family Erysiphales. However, the spores of the powdery mildew occur on both sides of the leaf. In addition to these, plant leaves with powdery mildew may turn into yellow and fall off. Meanwhile, downy mildew is the other type of fungal growth on plant leaves, producing yellow spots on the upper surface. Its spores occur on the underside of the leaf. Downy mildew belongs to the family Oomycetes. Therefore, the main difference between powdery and downy mildew is the type of mildew and the symptoms. 

References:

1. Karen. “Differences between Powdery Mildew and Downy Mildew.” KarensGardenTips.com, 13 Sept. 2012, Available Here.

Image Courtesy:

1. “Uncinula tulasnei – powdery mildew – Echter Mehltau 04” By Norbert Nagel, Mörfelden-Walldorf, Germany – Own work (CC BY-SA 3.0) via Commons Wikimedia   
2. “Downy and Powdery mildew on grape leaf” By The original uploader was Agne27 at English Wikipedia. (Public Domain) via Commons Wikimedia