Ag Acres

Microbes are extremely important in agriculture. All of us depend on plants, which in turn depend on microbes to help them grow. Some microbes can be pests on plants. Other microbes are necessary in agriculture. They can help plants by fertilizing them; microbes can kill unwanted plants pests such as insects, and microbes build healthy soil.

Some nasty microbes kill or damage plants. In fact, of all the crop destruction by insects, drought and microbes, microbes are responsible for most problems. Microbes cause plants to rot, wilt, spot, lose leaves, pale in color, become stunted, grow tumors, overgrow and die. Microbes causing plant disease include fungi, viruses, and bacteria.

Fungal Diseases:

Most plant diseases are caused by pathogenic fungi.

Rust Fungi
There are more than 20,000 species of rust fungi. These fungi often create rust-colored patches on plant leaves.

Rhizoctonia
This fungus causes root rot of various plants. Rhizoctonia solani causes root rot in tomatoes.

Viral Diseases:

Some plant diseases, like animal diseases, are caused by viruses.

Tobacco Mosaic Virus
This rod-shaped virus contains RNA as its chemical blueprint for invading tobacco cells.

Bacterial Disease:

Many bacteria cause plant diseases.

Agrobacterium tumefaciens
This bacterium produces tumors called galls (growths) on the stems of plants.

Burkholderia cepacia
This bacterium rots onion roots.

Some microbes add nutrients to the soil. Some add nitrogen by fixing it from the atmosphere. These include Rhizobium and Azotobacter which are discussed in the root cellar. Other microbes, such as Mycorrhizal fungi, help supply plants with phosphorus. Please visit the Root Cellar to find out more about microbes that help fertilize the soil.

Wouldn't it be great if farmers didn't have to spray crops with chemicals (pesticides) to kill unwanted destructive insects? Well, thanks to microbes, farmers don't need to use as many chemicals. Farmers are now using microbes to kill unwanted insects. Using organisms such as microbes to kill unwanted pests is called "Biocontrol." Several different microbes are used to kill insects. These microbes can be either viruses, bacteria, fungi or protists.

Bacillus thuringiensis
This bacterium is the most widely used microbial insecticide. B. thuringiensis contains a poison which looks like a crystal. This poison (toxin) is called BT toxin. BT toxin kills lepidopterans such as cabbage worms, tent caterpillars, and gypsy moths; dipterans such as mosquitoes and black flies; and coleopterans such as Colorado Potato Beetles, Japanese beetles. At least 412 preparations of Bacillus thuringiensis and the BT toxins are registered for sale in the United States.

Baculovirus
This virus is widely used to combat many caterpillars, moths, and flies. Although there are over 450 viruses found to kill insects, the most widely studied viruses are the Baculoviruses.

Soil is not just the stuff that gets your hands dirty when you play on the ground. Soil is a complex, living environment necessary for the growth of plants. But how is soil formed? By an interaction of five factors including the action of microbes and other life.

The other factors forming soil are weather, topography, parent material, and time.

When soil is first made, for example after a volcano, some nutrients are missing, including nitrogen and carbon. Therefore, the first organisms to colonize the soil are generally nitrogen fixers and photosynthesizers that fix carbon.