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Agricultural disease vectors and hosts
Dr. Victor Martin

The Drought Monitor report no real change except for our area but an intensification in extreme Southwest Kansas. Also appearing is a swath of abnormally dry counties just to the north of Barton County. The six to ten day outlook (April 29 to May 3) indicates above normal temperatures and below normal precipitation for the state. Good news for area corn producers for corn planting. Wheat producers should be better able to evaluate potential freeze damage from the extremely cold temperatures. Looking out eight to 14 days (May 1 to 7) also indicates above normal precipitation and temperatures. Does this means the frost danger is over? Hopefully, but we have snow in recent years the first of May. The 30 day outlook (May) is still calling for of equal chances of below or above normal temperatures and above normal precipitation with the 90 day (May through August) outlook predicting equal chances of above or below normal temperatures and above normal precipitation. Before today’s topic, a brief note. Some damage to developing wheat heads and tillers is being observed in our area. Over the next week or more, likely more damage will become visible. It doesn’t mean we have “lost” the crop but have at least seen the top come off some fields.

With Covid-19 being foremost in people’s minds, let’s discuss diseases in crop production. Some of this applies directly with what is happening in society currently and may help us understand why the current steps are in place. There is a concept termed “The Disease Complex”, that is conditions necessary for an infection.  Here they are:

• There must be an organism capable of causing the disease: a fungus, bacteria, virus, or nematodes for example.

• There must be a susceptible host plant. This is why crop producers do their best to provide crop conditions to minimize stress to the plant (fertility, moisture, etc.) and breeders work to develop plant varieties/hybrids with tolerance or resistance to a disease.

• There must be a favorable environment for disease development. For something like wheat rust, as an example, humid, wet, warm conditions.

• A vector to spread the disease is required. Using a human example, West Nile Virus is “vectored” to human beings through certain mosquito species.

• Finally, all of the preceding needs to occur at the same time. If any one of these factors of the disease complex is missing, the disease won’t occur.

In crop production, there are various ways to deal with potential diseases and an approach termed Integrated Pest management is employed.  First, what about hosts? Obviously, the plant we are trying to protect are hosts but producers must focus on other hosts where the disease can “hang out” and survive until it can infect the crop. This may be volunteer wheat serving as a “green bridge” for wheat streak mosaic virus or barley yellow dwarf. The alternate host may be crop residues or weed species. So through sanitation producers work to eliminate the alternative hosts. They may also disrupt continuity through crop rotation.

Secondly, producers have to cope with vectors, how the disease gets to the plant. Vectors can include insects and insect-like pests such as mites, wind, raindrop splashing, and even something as simple as equipment tires and farmers boots. Some of these producers can interrupt but many are out of their control to eliminate. So then a producer tries to eliminate the presence of the pathogen so it can’t be vectored to the crop. Hopefully it is obvious with what we are dealing with, why the measures in place were taken.

Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207.