For diseases to develop in a crop you need three things. First you need the disease vector or pathogen present. Second, you need a susceptible host and third, you need the right environmental conditions. Understanding these three things possibly helps explain why diseases may becoming more commonplace in crop production.
Disease pathogens are found in higher populations particularly in higher residue environments and where the same crops are grown more continuous. Some studies have shown significant shifts in populations of microbial communities with the repeated use of glyphosate in our crops. Some of the soil microbes that are less prevalent were instrumental in suppressing disease organisms. Xanthomonas bacteria disease is one of those which have increased due to this change in soil microorganisms. Goss’s Wilt is another which is suspected to be increasing due to microbial shifts.
Susceptible hosts are also needed for diseases to progress. We have seen that in recent years certain corn hybrids had little tolerance to Goss’s Wilt, Grey Leaf Spot or Northern Corn Leaf Blight whereas other hybrids had little effect from these diseases. If you know you are planting a hybrid or variety that has more susceptibility it would be wise to protect it from the start with a fungicide/bactericide. Healthy plants will also fend off diseases better than a stressed plant so cultural practices and nutrition can also influence your variety’s susceptibility.
You need the right environment for infection, survival and spread for the disease to become a problem. With some diseases you need a point of entry. Wind or hail damage can cause a physical damage that will allow entry of the disease. Higher residue environments may also create a more favorable environment for the disease organism to survive and be positioned for infection when the right conditions occur. Seems like we have had more wind in recent years. This can also carry some diseases into a growing area that may not overwinter there (ie. Rusts) or may transport insects which could vector the disease. Some diseases are favored by high humidity, rainfall or irrigation. Others are favored by hot dry conditions. Being able to predict weather conditions even a few days ahead may help predict whether a disease could potentially become a problem and justify a preventative treatment.
It is critical that producers become more familiar with diseases affecting their crops and understanding what factors can create the “perfect storm” for the disease to develop. It is also important to understand whether the products you are using to protect your crop is effective against a particular disease.