Powdery Mildews

Leaf Diseases of Hardwoods

Powdery Mildews

Powdery mildew with the white mycelium covering the surface of the leaves.

Powdery mildew with the white mycelium covering the surface of the leaves.

Powdery mildew on squash growing in the greenhouse. The white surfaces produce large numbers of conidia.

Powdery mildew on squash growing in the greenhouse. The white surfaces produce large numbers of conidia.

Advanced stage of powdery mildew showing a very powdery appearance

Advanced stage of powdery mildew showing a very powdery appearance

Powdery mildew conidia forming on a grape leaf (From Australia Agriculture and Food). Chains of conidia are formed on conidiophores.

Powdery mildew conidia forming on a grape leaf (From Australia Agriculture and Food). Chains of conidia are formed on conidiophores.

Illustration of conidia produced on leaf surface. Conidia, conidiophores and haustoria are shown.

Illustration of conidia produced on leaf surface. Conidia, conidiophores and haustoria are shown.


Oak leaf showing powdery mildew and cleistothecia (black dots). This was  a part of the sample you had in your lab kit.

Oak leaf showing powdery mildew and cleistothecia (black dots). This was a part of the sample you had in your lab kit.

Cleistothecia (also called Chasmothecia) produced on the oak sample.

Cleistothecia (also called Chasmothecia) produced on the oak sample. This was one of the unknowns in your lab kit. Look closely to see the features on the appendages. See handout to determine what this powdery mildew is named.

Another view of the powdery mildew on oak.

Another view of the powdery mildew on oak.

Willow leaf with powdery mildew and cleistothecia (small black dots).

Willow leaf with powdery mildew and cleistothecia (small black dots). You have a sample of infected willow leaves to observe with your pocket microscope.

 

Cleistothecia from the willow leaf that was in your lab kit.

Cleistothecia from the willow leaf that was in your lab kit. Note the outer ends of the appendages. See handout to identify this powdery mildew.


Other powdery mildews that were not in the lab kit:

A cleistothecia with one acus that was broken out of it (round structure at bottom - you cannot see the ascospores in it but when mature it would have 8 ascospores inside).

A cleistothecia with one acus that was broken out of it (round structure at bottom - you cannot see the ascospores in it but when mature it would have 8 ascospores inside). Note end of appendage with ornamentation. What is this powdery mildew called?

 

This powdery mildew is from grape leaves. The cleistothecia was broken open and many asci are present Each ascus has some ascospores developing.

This powdery mildew is from grape leaves. The cleistothecia was broken open and many asci are present Each ascus has some ascospores developing. Note appendages with ornamentation. What is this powdery mildew called?

 

A drawing from the 1800's showing a few different types of powdery mildews with different appendages on the cleistothecia

A drawing from the 1800's showing a few different types of powdery mildews with different appendages on the cleistothecia