This article appears in the September 2020 issue of Potato Grower.
By late summer and into early fall, it’s impossible not to be looking ahead and preparing for harvest and storage. But those last few weeks, days and even hours prior to potatoes being harvested are crucial, and taking the necessary steps during the tail end of the season can make or break a potato crop.
“As we get closer to the end of the season, it’s important to continue protecting potatoes,” says Glenn Letendre, agronomic service representative with Syngenta based in western Idaho. “Those plants and tubers need to be protected until the vines are completely dead or the potatoes are harvested from the field.”
Among the potential problems facing potato crops toward the end of the season in most growing regions is the dreaded and infamous late blight. The disease can strike right up until harvest, and Letendre cautions growers against letting their guard down as harvest nears.
“Sometimes growers have a tendency to cut back on fungicide application as the season draws to an end,” he says, “either to save money, or because they just don’t think it’ll be an issue. But if there are green leaves or vines in the field, late blight can infect the crop. In the worst-case scenario, late blight spores can drop to the ground and contaminate tubers as they’re harvested, which can lead to an entire cellar getting infected in storage.”
Despite its name, early blight also has the potential to wreak havoc late in the growing season. The disease is most prevalent in older, senescing leaves, but it has been known to infect tubers growing close to the surface and infect wounded tubers at harvest.
Letendre says that while the products he works with for Syngenta are “awesome tools for the potato industry,” there is no substitute for checking all the boxes at the correct time leading up to potatoes going into storage. Ensuring tubers have a strong skin set before harvest and minimizing bruising or cracking during harvest can be the difference-maker.
“A good fungicide program pushed all the way into the storage unit provides the best protection,” he says. “A grower can spend a lot of money on fungicides throughout the year, and then get in too big of a hurry at the end, which leads to problems.
“Storage doesn’t improve any potato over time. But the healthiest potatoes going into storage will typically be the healthiest potatoes coming out.”
Syngenta offers several products that can help potato growers as the season draws to a close:
Revus Top fungicide is an ideal choice for managing early blight and late blight infections in the fall. It is also active against black dot, brown spot and powdery mildew. Revus Top contains two active ingredients, mandipropamid and difenoconazole, and is compatible with many tank-mix partners. To further enhance Revus Top’s positive impacts on a potato crop, growers are encourage to us resistant or tolerant varieties whenever possible, plant the cleanest seed available, incorporate proper fertility and timely irrigation, and use proper forecasting tools for timely fungicide applications.
In the event of a late blight outbreak, growers can utilize Syngenta’s Orondis brand fungicides. Orondis Opti combines oxathiapiprolin and chlorothalonil to provide built-in resistance management as part of a season-long oomycete disease control program, and also suppresses Alternaria leaf spot pathogens. Orondis Ultra, with the active ingredients oxathiapiprolin and mandipropamid, provides preventative and residual disease control of late blight. Both Orondis products are rainfast within 30 minutes.
By eliminating vines and weeds, Reglone herbicide (active ingredient diquat dibromide) allows potatoes to develop a firm skin set, protecting harvest quality. With its flexible application methods, Reglone allows for a more efficient harvest through both ground and aerial sprayers and doesn’t leave harmful soil residues behind.