It’s time to cut and plant those spuds. Potatoes (Solanum tuberosum) are different than most vegetables we eat. They aren’t propagated by seed. Plants are grown asexually, meaning they are clones. All plants in a field are genetically identical to each other. Sweet potatoes (Ipomoea batatas) are propagated slightly differently, but they are still asexually reproduced.
Few people would even give this a second thought, but it creates a potentially catastrophic situation when it comes to disease control. Large scale operators are aware of this and pay close attention to weather that could cause a suitable environment for certain disease organisms.
Favorable environment, susceptible host and virulent pathogen are the three corners of the disease triangle. Should any be absent, a disease would not occur.
Enter the potato. Should conditions be right for a disease to develop all plants in a field could be attacked. Late blight is a common potato pathogen.
Inoculation is at its peak under moist conditions and night temperatures between 50 and 55 degrees. Should late blight spores land on dew soaked susceptible leaves under these conditions, disease will spread. The Irish Potato Famine was a great example of this.
That’s why farmers must spray to control these problems. Regular fungicide sprays will control fungus diseases like late and early blights. Insecticide treatments to kill insects that carry viruses is also critical.
Planting resistant varieties is also another strategy. The problem is that market demands certain eating qualities of the crop. Avoiding disease is fine, but if proper specific gravity and other factors aren’t right, the final product may not be what the public wants.
For most seed propagated crops there is a certain degree of genetic variation. Self-pollinated crops like wheat are an exception. Back in the 1930s black stem rust of wheat consistently decimated wheat crops. Plant breeders developed resistant varieties to eradicate the disease, but it wasn’t easy.
Fruit trees are reproduced by grafting, so lack of genetic diversity is a problem too. It’s not like the Johnny Appleseed days when a broad genetic base of seedlings hedged against total crop failure.
Certain pear varieties can’t be grown in the eastern states because of a bacteria disease called fire blight. It’s rarely cost effective to chemically control bacteria diseases in plants. This is largely due to the speed that bacteria reproduce and adapt.
Overcoming disease pathogens that constantly adapt to our systems of crop managements provides more than enough challenges to crop breeders and plant pathologists. Add to that quality factors that the public demands, and the job is even more daunting.
Different geographic regions pose different challenges. As far as potatoes in eastern North Carolina are concerned, a potential selection characteristic is resistance to cold waterlogged soils. Weather can suddenly turn hot and dry and those conditions aren’t great for growing spuds either.
It’s somewhat true for growing anything. However, when raising clonal crops like potatoes and sweet potatoes, experience is the best teacher. Farmers and gardeners become familiar with strengths and weaknesses of certain cultivars. They can predict the best course of action when problems arise. Right now, prepare for muddy fields or wait.
Ted Manzer teaches agriculture at Northeastern High School (firstname.lastname@example.org).