Downy mildew and powdery mildew can look very much alike at first glance, but they are actually quite different. Both of these forms of mildew typically only affect the leaves, however you can identify downy mildew by the fungal layer underneath the leaf – this forms in moist weather and is normally paired with leaf spots on top of the leaf. Powdery mildew causes white, powdery, fungal growth on the leaf.
The Difference Between Downy and Powdery Mildew
Under humid, cool conditions, downy mildew spores pop up in large numbers on the undersides of leaves in a branch-like formation. The spores can germinate within four hours if there is water from recent irrigation, rain, or heavy fog.
Symptoms of Downy Mildew
- In wet weather, the undersides of the spots are covered with a layer of fungus that can be white to purple to nearly black.
- The spot is brighter on the upper leaf surface than on the lower leaf surface.
- The spots might turn brown or stay yellow.
- The entire leaf dies very fast.
- Older leaves are usually affected first, followed by younger leaves.
Prevention of Downy Mildew
- Improve air circulation and leaf drying; allow for wide spaces between plants.
- Avoid overhead irrigation.
- Water earlier in the day so that leaves can dry thoroughly.
Powdery mildew prefers moderate temperatures. These fungi don’t the leaves to be wet for them to infect the leaf as long as humidity is high.
Symptoms of Powdery Mildew
- A whitish, powdery, fungal growth is on the upper surface of plant parts.
- Fungal growth typically begins on the bottom of the crown leaves.
- In sever cases, leaves can become dry and brittle, or wither and die.
Prevention of Powdery Mildew
- Promote good air circulation and low humidity.
- Separate new plantings from old ones.
- Control weeds that can host the fungi.
It is very important to treat your plants if they have developed any type of mildew or mold. Spray infected plants with Pure 3-Way, a fungicide that incorporates natural ingredients like lemongrass oil, to eliminate the problem safely. Once you do this, your plants will be healthy before you know it!