Knowing Your Roots

Blog 44

As the mercury dips into the negative once again, the snow whistles and forms those ever creeping drifts and the kids are out of school yet again, it’s hard to imagine that anything positive could come from it all. If you are a Wisconsin potato grower, however, you are looking out the window now and rubbing those hands together in anticipation of good things to come!

Almost all the potatoes in the US are grown in the northern states—think of Idaho, Washington, Wisconsin, Colorado and Maine and you have the top potato states in the country. There is a simple reason for this—we all have miserable winters! Those winters may be hard on us mortals, but they are even harder on the enemies that are lined up to attack the humble potato.  

The most destructive bugs on potato all wimp out when it comes to our Wisconsin winters and survive only in the sunny south. The potato leafhopper, which can reduce healthy vines to stunted brown sticks with its toxic saliva, overwinters in the Gulf states and must fly upwards of a thousand miles just to get here. By the time its offspring are numerous enough to cause damage, the season is already half over and the growers can easily nip it in the bud. The tiny green peach aphid, renowned for its deadly role as a virus vector, can’t survive winters here either and must be blown in from the south each year. The ever-ingenious potato growers outwitted their spring arrival long ago by creating the nation’s first virus-free seed certification program in the northernmost counties of the state where the aphids are late to arrive and easier to manage.

Ironically, the Colorado potato beetle, the most destructive bug on potatoes worldwide, is not even a pest in its namesake state of Colorado because the winters are too cold there! In Wisconsin, the striped adult beetles that chew our potatoes to shreds every summer are killed by freezing at a mere 26 degrees F.  They can only survive by digging into the soil on field edges where snow drifts accumulate and provide enough insulation to keep them alive. Everywhere else, they are killed outright, keeping the overall population at a level we can handle. Survivors must walk to find the next potato crop in the spring, and the wily growers are onto those survival spots and carefully plan crop rotations to make the potatoes harder to find. Some crafty growers have even ventured out in the coldest of weathers and plowed the insulating drifts away to eliminate the sleeping pests.

As effective as the winter is in helping to keep bugs at low levels, however, nowhere are the benefits of cold more important than in keeping the late blight fungus at bay. Late blight is best known for its catastrophic impact in the 1800s when it destroyed the potato crop in Ireland. The potato famine caused widespread starvation and consequently death. This destructive disease is still present throughout the world and requires constant vigilance using state of the art science to keep it under control. In Wisconsin, our winters are an essential weapon in the late blight arsenal. Unless two different strains of the fungus mingle and produce a resting spore, the disease cannot survive in the cold Wisconsin soils and must reinvade every year. Thankfully, this is the usual pattern and researchers have developed sophisticated ways to predict and manage the disease if and when it does show up. Were it not for the miserable cold of a Wisconsin winter, this destructive disease would be ever present—crop destruction and high prices would be the norm.

Therefore, when the next polar vortex drops temperatures to unbearable levels, don your warmest woolies or join those bugs in Florida, but be thankful that even the most miserable cold is benefiting us in ways we never suspected!

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