Diseases 2012 – issue 1
Wendland ag agronomy
Diseases 2012 – Issue 1
WEndland WEndland Ag Ag Agronomy Agronomy
FOOD FOR THOUGHT Why the buzz about plant diseases?
S
o, why all of sudden these All of these types of fungi are last few years do we have called Pathogenic fungi. There so many diseases? If we are a lot of other fungi on and think about the disease triangle around plants that will not cause we need a pathogen (disease), any harm. Pathogenic fungi are Bennie favourable weather conditions spread by wind, water, soil, seed Dunhin and a susceptible host for disborne and contact with infected ease to form. We have the host tissues. All that is needed for inplants which are the crops we fection is a spore (reproductive grow, and the last several years’ weather con- part) to fall on a susceptible host leaf and when ditions were optimum for disease develop- the climate is perfect the spores will germinate ment. Spores are blown in from the south in and infect the plant. air currents and some pathogens overwinter in For Bacteria to infect it typically needs our fields which cause a build up of inoculum some sort of mechanical injury such as hail, (disease spores) in our soils and stubble. We frost, injury due to feeding (insects or animals) are heading for our third wet season; there- or equipment. It grows within the plant and fore, we can expect another big disease year. secretes enzymes that destroy plant cells. BacTo understand diseases and why we need teria are typically less destructive than fungi. to control them, we need to understand what Because of bacteria’s nature of infection, it is diseases are and how the infection process very difficult to control and not a lot of prodworks. There are 3 major types of diseases: ucts are available to control it. Therefore, after Fungi, bacteria and viruses. mechanical injury we always recommend a foFungi are responsible for most of the plant liar nutrition product to try to keep the plant as diseases we deal with in agriculture and are healthy as possible so that the plant’s natural mostly the only type that we can control suc- resistance mechanisms can work as optimal as cessfully. It infects living plant tissue, destroys possible. it and then lives off of it. Because of this, photoViruses, along with bacteria, also need synthesis is reduced dramatically which means some kind of mechanical injury present (feedthat the plant doesn’t have enough energy to ing, hail, frost, etc.) to infect the plant. Due to grow. Some fungi will attack the stems of the the small size of viruses, they can often infect plants which (like Sclerotinia) will cause the through microscopic wounds/cracks and need whole plant to die. Others will reduce the leaf to live off the plant cells. Therefore viruses surface (leaf diseases) that will reduce yield. don’t normally kill plant tissue, but because
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