Bur oak blight

This can leave the tree susceptible to greater insect predation, secondary infections from other pathogens, and death.

A distinguishing characteristic of T. iowensis is the formation of black crustose asexual fruiting bodies at the base of the petioles that are retained until the following year.

These distinctive fruiting bodies are pycnothyria (conidiomata) with radiating setae-like hyphae that form along the necrotic veins.

In spring, black crustose conidiomata (pychnothyria) that have served as the overwintering mechanism of the disease release conidia.

Secondary infection could occur during abnormally wet periods in the summer given this pathogen's polycyclic potential.

[4] According to the National Oceanic and Atmospheric Administration, or NOAA, over the previous two decades the state of Iowa has received more early season rainfall than in years past.

Several changes have been documented in the Iowa annual cycles including warmer nighttime temperatures, more humidity, more spring and summer rainfall, and a shift from the normal late season precipitation.

[6] In the latter part of April and into May rains help BOB during its most critical period by slashing conidia from the crustose pychnothyria on the upper surface of the leaf.

Repeated defoliations due to high concentrations of BOB conidia will eventually lead to a depletion of the bur oak’s food reserves and ultimately cause death.

Due to the fact that BOB overwinters on leaf petioles that stay on the tree, removing fallen infected leaves will do little in terms of disease control.

These organisms would either have to find another food source, move to a new area, or may perish due to a lack of resources.