Happy (belated) Robigalia!

Robiga-what?

The ancient Romans dedicated April 25 to a festival called the Robigalia. It was celebrated with chariot races and a dog sacrifice. The dog had to be rust colored, as it was an offering to the gods to protect the cereal crops from rust, a group of plant diseases.

There are thousands of different species of rust which cause disease to a wide range of host plants. Rusts have some of the most complicated life cycles of any fungal pathogen, with some species requiring two host plants and producing up to 5 different spore types.

One of the most important hosts is wheat, which can be a host to several different rust diseases. The Latin word "robigo" refers to rust on both metal (as oxidation) and on plants (as disease). Over time, sacrifices were made to the minor god Robigus (or possibly the minor goddess Robigo) who could protect the all-important cereal crops from disease, including the dreaded rust.

Wheat leaf rust on an individual plant; note the raised, rust-colored pustules on the leaf surface

Wheat leaf rust in a severely infected field

Today the cities of Urbana and Champaign are hosting, not chariot races, but the Illinois Marathon. Most of the major roads in town have been shut down to form the route. Hopefully the gods will be content with the sacrifice of sweat and inconvenient traffic, and will overlook the fact that it's a day late and we're missing the dog.

Happy Robigalia, and may our plants be free from disease in 2014!

The Naked Truth: Trees

Happy Spring! It’s been a month since the spring equinox and it’s finally starting to warm up and, more importantly, green up. Crocuses, snowdrops, daffodils (and early-season weeds) are blooming and the pussy willow is in full flower.

Tree buds are fully swollen and many of the maples are in bloom. While we’re waiting for trees to leaf out, this is the perfect time to examine trees “in the buff.” We can check for damage to limbs and branches that will become hidden once the leaves cover the tree.

Here are two examples of common twig problems from a recent walk:

OAK TWIG GALLS

The balls decorating the twigs of this mature oak tree are galls caused by a variety of parasitic wasps. There are a number of types of galls, caused by an even greater number of species of tiny wasps. The two most common twigs galls in our area are horned oak galls and gouty oak galls.

Galls are tumor-like structures and they’re formed of tree tissue. Tiny, non-stinging wasps induce the tree to form galls which act as protection for the wasp eggs and developing larvae. While they may not be aesthetically pleasing, they usually aren’t harmful to healthy, well-established trees. The galls can be pruned out of the tree, though that quickly becomes impractical as the tree grows. The general recommendation for oaks infested with galls is to maintain good tree health through watering during dry periods, fertilizing when necessary, and responding quickly to other insect or pathogen problems.

WITCH'S BROOM

This picture shows the crown of a majestic sycamore tree. The arrows indicate portions of branches where a proliferation of slender, closely-spaced twigs arise. These bunches of twigs are known as witch's brooms. They are caused by a fungal disease known as anthracnose. Anthracnose is a very common disease and can affect a wide variety of plants, though it doesn’t always cause witch's broom in other hosts. In sycamores, anthracnose can also cause lesions on leaves and cankers on branches.

The twigs in witch's brooms tend to be thin and poorly-spaced; as a result, they don’t leaf out well and tend to break easily. Much like the oak galls, witch's brooms usually won’t cause too much injury to a healthy, mature tree. Management includes sanitation, or the removal of infected plant tissue (in this case, raking and bagging or mowing leaves and twigs affected with anthracnose), and maintaining good tree health.


OTHER ISSUES

This is also a good time to look for limbs damaged by wind or ice over the winter. Dead or damaged limbs, branches that are crossing and rubbing against another branch or the trunk, or ones that attach to the tree at a small angle, need to be pruned out of the tree to ensure good tree health. Make sure to prune correctly, leaving the collar around the branch intact to allow for proper wound healing. 

Welcome to my new blog: Plants, Pests, and Pathogens! I'll be updating with interesting facts and stories about ornamental and agronomic plants, and the pests and pathogens that threaten them. But first, a little bit about me:

My name is Diane. I'm a Horticulture Educator with the University of Illinois Extension, serving Champaign, Ford, Iroquois, and Vermilion Counties. I grew up in central IL and received a bachelor's of science in Crop Sciences from the University of Illinois, and a master's of science in Plant Pathology from the Ohio State University. I worked at the University of Illinois Plant Clinic as an undergrad and after completing my MS. My passions in life include plant pathogens and my two pet rabbits (who, when they go outside, quickly become plant pests).

I love spending time outdoors. Nature is a complex and beautiful thing, and the relationships between plants, pests, and pathogens can be awe-inspiring. I hope this blog introduces you to new ideas, images, or facts. Join me in the fascinating world of plants and their problems!