[deck]The devil is in the details in the battle against post-harvest fungal infections in potatoes.[/deck]
Every grower has seen it at one time or another: the signs of pink rot spreading through the bin, and the dollar signs flying out the window. Fungal infections post-harvest can cause significant losses in a short period of time. The good news? Growers have an increasing number of options for controlling these diseases. And according to the experts, attention to detail and using the right products can mean the difference between a pile of rotting spuds and healthy profits this fall.
Some of the newest and best of the tools available for protection against fungal diseases in storage are phosphorus acid-based products, including Confine, Phostrol and the newly-registered fungicide Rampart, among others. According to Khalil Al-Mughrabi, a pathologist at the Potato Development Centre at the New Brunswick Department of Agriculture, Aquaculture and Fisheries, these products — referred to collectively as phosphites — can be very effective against late blight, pink rot and silver scurf when applied at the correct label rate.
If applied in the field rather than post-harvest, these products should be applied before foliage infection takes place, according to Al-Mughrabi. “Although they may not control late blight on the foliage, they have residual activity which protects harvested tubers from tuber late blight and pink rot,” he explains.
“They have no curative activity,” Al-Mughrabi adds, “and therefore, if they were applied after harvest on a tuber that is already infected, it will not be cured.”
Phosphites can also be applied post-harvest, however, and for many growers this is the preferred method. “Phosphites are very effective in protecting against late blight, pink rot and silver scurf when applied immediately after harvest as the tubers are loaded on the bin piler,” says Al-Mughrabi. He adds that seed potato growers should be cautious about using phosphites, as safe rates for seed potatoes have not yet been determined.
The right concentration, the right water volume, at the right time and frequency of application using calibrated equipment will improve the efficacy of the product and reduce losses.
– Khalil Al-Mughrabi
Trial and Error
What appears to be a one-size-fits-all solution to fungal damage in stored potatoes actually varies from operation to operation, however. Variables include size and power of pump, type of applicator and nozzle configurations. Most growers have come up with systems that work for them through trial and error over the years.
My recommendation to other growers would be to use the spin-type applicator and apply the product over a roller table. This should give the best coverage on the tubers.
— Peter Loewen
At Kroeker Farms, a family-owned operation spanning close to 2,500 hectares between Winkler and Carman, Man., the Kroeker family and staff have been growing healthy potatoes for more than 50 years for both conventional and organic markets. According to Marv Dyck, Kroeker Farms’ assistant farm manager, silver scurf, pink rot and late blight are perennial problems, and one of the solutions is applying phosphites post-harvest rather than in the field.
“We think we get the best bang for our buck that way. We use both Confine and Phostrol, and the way we decide between the two is strictly price, as they’re equivalent products,” says Dyck.
“We need something that controls silver scurf in the bin, and silver scurf isn’t controlled through a foliar application,” he explains. “That’s a big problem for us because we grow chip potatoes, and they need to be kept at warmer temperatures around 47 degrees [Fahrenheit].”
Kroeker Farms’ storage manager, John Wall, says the company had developed a system for spraying potatoes headed in or out of storage years prior to Phostrol or Confine coming on the market. For example, they applied Actara on seed potatoes while loading trucks at planting time, so it made sense to use the same system for phosphite application. “We get Confine pre-mixed by a company in town,” explains Wall. “We have a pump system, and a spray bar with three fan-tip nozzles. We apply it right where the potatoes are going into the bin piler.”
At Garden Valley Vegetable Growers, also based near Winkler, Man., Peter Loewen, along with brothers Abe and Len and cousin Bitz Loewen, grow red- and yellow-fleshed potatoes for the fresh market on just over 2,300 acres.
Loewen says they developed their system for phosphorus acid application by trial and error, experimenting with nozzle sizes and calibrations until they felt they had the best coverage.
“We apply phosphorus acid to the tubers as they pass from the elevator to the boom on the bin piler,” says Loewen. “We designed and put together a series of hollow cone spray nozzles. The product is mixed and stored in a plastic tote. A sure-flow pump provides sufficient pressure and volume to the nozzles.”
Initially, the Loewens experienced some issues with wind, and had to modify the system to ensure even coverage. But if ‘trial and error’ has helped the Loewens achieve great results, they are also open to new products that can make the process even smoother.
“New products are always showing up, and one that I have seen is a spin-type applicator. It requires less volume and gives better coverage than nozzles,” says Loewen. “My recommendation to other growers would be to use the spin-type applicator and apply the product over a roller table. This should give the best coverage on the tubers.”
New and Improved
Al-Mughrabi emphasizes following the label to the letter as a key component in using fungicides most efficiently. “The right concentration, the right water volume, at the right time and frequency of application, using calibrated equipment, will improve the efficacy of the product and reduce losses,” he says.
Additionally, proper maintenance of equipment can make a huge difference in coverage. “Growers need to use the correct nozzle, [and these] should be replaced at the beginning of the season to ensure performance,” says Al-Mughrabi. In addition, sprayers should be calibrated prior to each use, which will improve machinery performance and efficiency.
For growers who are invested in finding new solutions to old fungal problems, there are a range of options for post-harvest fungal control newly coming to market. For example, growers can consider using “biocides” as an alternative to the use of fungicides, according to Al-Mughrabi.
“Some are already in the market and are registered for use on potatoes. One of the products is called Bio-Save 10 LP. We experimented on this product and found it effective against fusarium dry rot and silver scurf,” he explains. Other products include Serenade Max, which contains disease-fighting Bacillus subtilis bacteria and is registered in Canada for early blight management.
For growers like Peter Loewen, biocides are a welcome addition to the fight against post-harvest fungal infections. “Farmers are managers of the earth and need to continue improving how we care for the land that feeds us all,” he says. “Better ways to control pests without harming other beneficial insects is a definite improvement to that care.”
[sidebar]
Options for Post-Harvest Fungal Control
According to Khalil Al-Mughrabi, pathologist with the Potato Development Centre at the New Brunswick Department of Agriculture, Aquaculture and Fisheries, there are a variety of options for growers looking to save themselves from headaches this fall. “These fungicides are effective only when the total surface of each tuber is covered and recommended rates are used,” says Al-Mughrabi.
The following is a guide to some of the available anti-fungal products registered for use in Canada this year. Growers should always take care to read and follow label recommendations.
Bio-Save 10 LP — Registered for fusarium dry rot and silver scurf.
Confine — Registered for late blight, pink rot and silver scurf.
Dithane F-45 — Registered for fusarium dry rot.
Mertect SC — Registered for fungal diseases caused by fusarium, phoma and rhizoctonia, as well as the diseases silver scurf and skin spot.
Phostrol — Registered for late blight and pink rot.
Rampart — Registered for late blight and pink rot.
StorOx — Registered for fusarium dry rot, bacterial soft rot and silver scurf.
Information courtesy of Khalil Al-Mughrabi.
[/sidebar]
