With few available treatments, a process called biofumigation is being used by some growers to manage PED. The process involves tilling mustard plants into the soil at a specific stage of growth with enough heat and moisture in the ground to induce a chemical breakdown of the plant material.
“As the mustard decomposes, it releases a chemical that reduces Verticillium wilt pathogens without adverse effects on the environment,” explains Dahu Chen, AAFC plant pathologist at the Fredericton Research and Development Centre.
As a side-effect, mustard biofumigation also delivers green compost into the soil, improving soil health. There is some evidence that the severity of PED symptoms is reduced in healthy soils.
“The disease has been around for a long time, but it is now identified to be a major factor limiting tuber yield in New Brunswick,” says Chen, who is studying the problem with colleague, AAFC researcher Bernie Zebarth.
“The pathogen can survive in the soil for a long time, even through the harshest winter conditions of eastern Canada,” explains Chen.
Chen and Zebarth are now working with industry partners, including Potatoes NB and McCain Foods Canada, to determine the effectiveness of mustard biofumigation through trials in commercial fields.
Dahu Chen, AAFC plant pathologist, examines the leaves of a potato plant for signs of disease. (Photo courtesy of AAFC)
Two spore traps are located in the Shelburne-Melancthon areas at D & C Vander Zaag Farms Ltd. and two others in the Alliston area at Mark and Shawn Murphy Farms. In the Delhi area, two spore traps are set up at Joe Lach's Farm and Fancy Pak Brand Inc. The final two spore traps are located in the Leamington area at Harry Bradley and Sons Farm.
Alliance Agri-Turf, Bayer CropScience, FS Partners, Holmes Agro and Syngenta provided funding for the 2018 late blight spore trap project.
A&L Laboratories in London, Ont. will conduct the polymerase chain reaction (PCR) tests to identify the presence of late blight spores.
In the past two years, Eugenia Banks, a former potato specialist for the Ontario Ministry of Agriculture, Food and Rural Affaris (OMAFRA), led a project evaluating passive spore trapping technology to help growers improve late blight management. The project recorded positive results. Spores were detected 15 days on average before late blight lesions were seen in a few fields. A previous Potatoes in Canada article goes indepth into the project and how effective spore traps are for preventing late blight.
“Spore traps represent another tool to be added to the potato growers’ arsenal to combat late blight,” Banks says. “If late blight spores are not detected by the traps, growers should still follow a preventative fungicide program and apply a fungicide spray before rows close. Also, fields should be scouted regularly.”
Stronger potato varieties will increase yields for Canadian growers, which translates into higher profits.
Dr. Benoit Bizimungu, head of potato breeding at the Fredericton Research and Development Centre, said a number of hybrids bred from these wild varieties could be ready for industry trials next year.
Bizimungu selected the German plants because of superior traits such as high yield, as well as strong natural resistance to PVY, late blight, drought, and insects like the Colorado potato beetle.
“Although the primary interest was multiple disease resistance and high yield potential, a number of progenies show a nice deep yellow flesh color, which is usually associated with carotenoids,” Bizimungu explains. This is great news for consumers who want more antioxidants in their diet.
“What is really exciting is that some of these wild species have never been used in potato breeding before now,” he says. “Using these new parents broadens the genetic base.”
“It’s good to have multiple sources for breeding, especially for things like late blight where it keeps changing.”
Dr. Bizimungu obtained this unique plant material as a result of his collaboration with potato geneticist Dr. Ramona Thieme of the Julius Kuhn-lnstitut (JKI) at the Federal Research Centre for Cultivated Plants in Braunschweig, Germany.
The imported species come from wild potato cultivars that originated in South America, the birthplace of the potato.
Syngenta Canada Inc. has received registration for Revus fungicide as a potato seed treatment for the suppression of pink rot and control of seed‑borne late blight in potatoes.
Pink rot is a devastating, soil-borne disease caused by the pathogen Phytophthora erythroseptica that thrives in wet, poorly drained soils. Infection typically takes place pre-harvest, as the pathogen enters tubers through the stem end and lenticels.
Tubers infected with pink rot will often decay during harvest and handling, which allows the pathogen to spread quickly from infected tubers to healthy tubers while in storage.
“Every field has the potential for pink rot,” says Brady Code, eastern technical lead with Syngenta Canada. “It takes a very small number of infected tubers going over harvest equipment or getting by on the belt to put an entire season of work in jeopardy, and leave growers with far fewer healthy potatoes to ship.”
Revus contains the active ingredient mandipropamid (Group 40), and works by protecting the daughter tubers from becoming infected with pink rot. It also provides control of seed-borne late blight (Phytophthora infestans), according to a company press release.
Revus is applied at 5.9-11.8 mL per cwt of seed (13-26 mL/100 kg of seed).
Following a seed treatment application of Revus fungicide, the first foliar fungicide application should be a product that does not contain a Group 40 active ingredient.
Maximum Residue Limits (MRLs) for mandipropamid have been established for markets including Canada, the United States, Japan, and South Korea, in support of the seed treatment use pattern.
Usually wet seasons favour crop development, but incidence of storage rots is a concern, especially if rainfall occurs late in the growing season, advises Eugenia Banks, Ontario potato specialist.
During three years of sampling for potato psyllids (Bactericera cockerelli) across Canada, we found
small numbers in Alberta (2015-2017, increasing annually), Saskatchewan (first time in 2016), and
Manitoba (first adults, 2016). No potato psyllids have been found on sample cards from any sites
east of Manitoba.
In southern Alberta, the range of potato psyllids has expanded to sites throughout the potatogrowing area, where in 2017 they appeared on sampling cards of over 70 per cent of 45 sites regularly sampled (we thank the growers for co-operation and access to University of Lethbridge samplers at 45 sites, with a minimum of 4 sampling cards per field, and Crop Diversification Centre South for managing two additional sites and sending sample cards). For the full story, click here.
An infected potato psyllid insect carries the Lso (Candidatus Liberibacter solanacearum) pathogen that can cause zebra chip disease in potato crops.
Zebra chip has affected potato crops in the U.S., Mexico and New Zealand and caused millions of dollars in losses. Potatoes with zebra chip develop unsightly dark lines when fried, making affected potatoes unsellable.
The first detection of Lso came from sampling cards collected at one site south of Highway 3, near Lethbridge, Alta. For the full story, click here.
Researchers are hoping Canadian potato growers will soon be able to use an innovative approach to control wireworms. This method uses just a few grams of insecticide per hectare applied to cereal seeds that are planted along with untreated seed potatoes. It provides very good wireworm control for the whole growing season, with a lower environmental risk than currently available insecticide options.
Just because black cutworms don’t overwinter in Canada doesn’t mean they aren’t a threat to potato crops. The insects spend their winters in the southern United States but travel north on low-level jet streams and, once they cross the border into Canada, they look for a tasty food source. Black cutworm moths prefer some of the weeds that grow in and around fields and, while potatoes are not their favourite food, they will adapt and can wreak havoc on an unmonitored field.
A researcher at the University of Minnesota says the cutworms’ new interest in potatoes could be the result of a change in potential host plants. If the moth’s desired weed is being well controlled in a field, it will eat what is available where the wind sets it down.
“Black cutworm moths are active flyers,” explains Ian MacRae, the extension entomologist at the university’s Crookston research station. “These insects can travel hundreds of miles in a short period of time aided by an extremely efficient bug highway [a jet stream].”
MacRae says if the wind and temperature are conducive and Canadian potato producers are able to get their crop planted in good conditions, there is a chance the moths will arrive about the same time as the plants are emerging. The possibility exists that early arrival could spawn a second generation of the insects later in the season. He says, once landed, reproduction occurs when the moths lay eggs. The emerging larvae will feed on the foliage, but once at the fourth or fifth larval stage they will begin actively eating near the base of the host plant, cutting it off.
“The first you might notice a cutworm problem will be plants that are cut at the base or wilting,” MacRae explains. “At night, the worms burrow into the soil and if the tubers are close to the surface, they will burrow into the tuber. They can do more damage to tubers in dry conditions because cracks in the soil will give the cutworms access to what is underneath.”
Damage to potato crops early in the season can be a greater problem because the young plants will not recover from being chewed off. There is a possibility that the seed piece might send up another shoot, but the crop will be set back. MacRae suggests early scouting will help identify the problem and allow time for control. There are effective insecticides for control of black cutworm and there are sources of natural mortality, such as predators or parasitic wasps. Birds may be less effective because of the location of the worms and their habit of eating at night.
“If you find yourself at a threshold of about 30 per cent of your plants cut, you may want to apply an insecticide,” MacRae says. “If defoliation is this high, it may be that natural mortality sources are not functioning well.”
Ensure proper identification of the larvae as black cutworms so the correct product can be chosen for control. Combining regular field scouting with pheromone or light traps to catch the male moths is an effective way to identify the insects.
“When scouting, look for stalks at an odd angle or wilting,” MacRae suggests. “Look in the evening when the cutworms come out to feed, and look as much as a half metre away from the plant because they are good walkers. Black cutworms are aptly named because they are a dark caterpillar with a waxy appearance. They will often curl into a C if disturbed. They hang out during the day under clods of soil or in cracks.”
MacRae says climate change may be the reason black cutworms are being seen farther north. He doesn’t believe they will begin to overwinter in Ontario or the Prairies, but a warmer climate means they develop faster and may overwinter in more northern states, making the migration north earlier and causing greater problems.
“Black cutworms have certainly become a problem in Ontario in the last few years,” MacRae says. “They can be a significant pest issue.”
MacRae adds there are some cultural practices that may minimize the impact of black cutworms when they arrive. Planting late can put new, young plants directly on a collision course with the moths and their offspring, so plant early, if possible. He says controlling weeds will reduce the areas where the moths might lay eggs. Growers in the United States use pre-plant tillage to turn over the soil to destroy potential habitat.
To date, there is no accurate monitoring system in place for potato crops, according to MacRae, but the cutworms also like corn and the corn growers in some states, such as Iowa, have a black cutworm monitoring network. “The moths seem to appear in Ontario about three weeks after they are seen in the United States,” he says. Ontario growers could tap into the monitoring networks south of the border and use that information as an early warning system, he suggests.
Black cutworms could be considered a stealthy yield robber because by the time you begin to notice a problem, it could be a challenge to execute effective control. The best defence is early and frequent field scouting and adopting cultural practices that could minimize the attractiveness of the crop. MacRae believes Canadian potato growers will see black cutworm more often in the coming years, so preparation for and understanding of the pest is a wise approach.
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