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.
Sept. 29, 2016 – Second growth is a physiological potato problem induced by soil temperatures of 24 C or above and water stress. These two factors interact to limit the tuber growth rate, causing second growth. Inadequate soil moisture alone does not result in the initiation of second growth.
Heat and drought prevailed during the 2016 Ontario growing season, which explains why second growth has been reported in some fields.
Potato varieties differ in their susceptibility to second growth. European varieties appear to be more susceptible because they were bred and evaluated in countries where the growing seasons are rarely hot.
There are three distinct types of second growth:
Tuber chaining: A series of small tubers are produced on a single stolon.
Heat sprouts: Sprouts develop from stolons or daughter tubers. The sprouts may emerge from the hills developing into leafy stems.
Secondary Tuber: Small tubers form on daughter tubers. The secondary tubers are formed on short sprouts or directly on the tuber surface. This disorder is usually associated with physiologically old potatoes. High temperatures and water stress during the growing season are major factors contributing to the physiological aging of potatoes.
Cultural practices that promote uniform growth of plants and tubers throughout the season help minimize second growth. Among them are:
● Do not plant physiologically old seed in cold, dry soil.
● Space seed pieces as uniformly as possible at planting.
● Apply an adequate amount of fertilizers.
● Maintain uniform soil moisture sufficient to meet crop needs (this was easier said than done this past season!).
August 26, 2016 - According to Dr. Vikram Bisht, of Manitoba Agriculture, aphid counts in weeks 8 in all but one sample were low. There was one Green Peach Aphid (GPA) trapped in southern seed growing area, but not anywhere else. Potato aphids were trapped in southern and central areas. One field showed a sudden influx of aphids, probably from nearby crops being harvested or desiccated. There were low counts of Aster leafhoppers were trapped in all seed areas.
Some of the seed fields are being desiccated, so Bisht reports there will be one more week of aphid monitoring. The results from suction and pan traps in seed fields for the 6th and 7th week of sampling can be seen in a chart (please click here):
In 2016 season, as in 2015, as part of the Canadian Hort Council, Growing Forward 2, Canadian Potato Psyllid and Zebra Chip Monitoring Network project, yellow sticky cards are being sent to Dan Johnson, Univ of Lethbridge. One potato psyllid adult was confirmed today (August 22) in a card (in field July 12-18) from Northfolk-Treherne Rural Municipality. This is the first find for 2016 in a province outside Alberta.
North Dakota has also reported occurrence of potato psyllids in their fields. "We have confirmed that psyllids are present potato fields in western ND. Psyllids are the vector of zebra chip disease and can do damage without the Lso bacterium (Gary Secor, NDSU)".
August 15, 2016 - New late blight finds were reported on potato from Carman, Winkler areas and on tomato crops east of East of Portage and east of Highway #75, according to Vikram Bisht. Frequent fungicide applications are being applied to control the disease; and in one case the tomato plants have been pulled out and destroyed.
Samples have been collected for strain identification. All of the previous samples, tested by Lethbridge Research and Development Center were determined to be US-23 strain.
"There is increasing metalaxyl insensitivity in the Pi from these samples and the use of Ridomil would probably have only marginal benefit," says Bisht.
It is important, he continues, to scout for late blight, especially in low lying, irrigation pivot center, wheel tracks of irrigation systems (guns/pivots), tree-line protected areas and under hydro-power lines (areas where applicators may have difficulty covering).
It is also critical at this time to monitor potato and tomato plants in home gardens. The DSVs (late blight risk values) accumulated over 7-days at various weather stations suggest mostly moderate risk in most of the province. There is forecast for rain and risk of thunderstorms today afternoon in many potato growing areas. Full fungicide coverage of foliage in high risk areas should be maintained.
Due to continued high moisture levels in many fields, it may be helpful to harvest the low lying areas last, so it will be easier to manage the storages.
Also, a post-harvest treatment with phosphorus acid / phosphite fungicide could be considered for such fields, adds Bisht.
Heat edema has been observed in Ontario, and should disappear when humidex values drop below 30 C. Photo courtesy of Eugenia Banks.
July 27, 2016, Ontario – Two potato problems have developed due to high temperatures, writes Eugenia Banks in her latest Ontario potato update.
The long and relentless heat wave that is affecting Ontario has provided favorable conditions for diseases and physiological problems that we do not often see. One of them is Fusarium wilt caused by Fusarium oxysporum, a relatively common soil fungus that thrives when soil temperatures are around 29 C.
A grower found patches of Fusarium wilt this year in a field of Andovers. Also wilted plants here and there were noticeable in the field. The base of the stems emerging from the seed was woody. At ground level the stems were dark brown, rotten or hollowed but did not have a strong fishy smell. The upper part of the stems was still green but wilted. Most of the plants pulled had rotten seed, but with no fishy smell.
Gary Secor from North Dakota State University helped with the identification of this problem. He isolated Fusarium oxysporum from the diseased stems. There was no sign of blackleg, dickeya or verticillium.
How to control this disease?
Fusarium oxysporum is more prevalent in very hot summers, just like our 2016 growing season. There is nothing that can be done about the weather, but:
● Avoid ammonium nitrogen as a source of N
● Keep potassium levels adequate
● Acid soils favour Fusarium wilt. Liming soils help, but may increase the risk of common scab.
This problem has been observed in two fields of the variety Canela Russet, growing in two different production areas. Small bumps form on the leaves that, with time, rupture leaving round, brown necrotic spots. The centres of the spots often drop out leaving holes in the leaves. Holes in leaves usually means insect feeding, but there were no insects in the fields. Ian MacRae, an entomologist at the University of Minnesota, did not think that the holes looked like insect feeding. Jeff Miller from Miller Research in Idaho suggested heat edema, a physiological disorder. Edema is related to water retention (see page 122 in the Potato Field Guide), but heat edema is different. The cells expand trying to diffuse the heat and eventually rupture. Because it is a physiological problem, heat edema should disappear when humidex values (temperature plus humidity) drop below 30 C. Yesterday, I checked one of the fields and noticed that, because of the hot weather, necrotic spots were developing on new leaves.
Prolonged heat waves bring all sorts of different problems to potato plants. Working with potatoes is a never-ending learning experience!
July 27, 2016, Manitoba – Several fields in western Manitoba (Carberry area) reportedly have light blight symptoms, according to Vikram Bisht's latest potato disease reports.
Some photographs of the diseased leaves show symptoms typical of late blight. Three samples received have been confirmed to have sporangia. The infections are mostly on the top foliage and found in pivot wheel tracks, along the irrigation gun run and edge of field in low areas. There are very few infected plants in the fields and they are difficult to find. The five-day spray schedule in these high risk fields may have kept the infection low.
So far, there is no report of late blight from any other part of Manitoba. The DSVs (late blight risk values) accumulated over seven days at various weather stations continue to suggest high late blight risk in most of the province.
It is extremely important to scout for late blight now, especially in low lying, irrigation pivot center, wheel tracks of irrigation systems (guns/pivots) and tree-line protected areas. It is also critical at this time to monitor potato and tomato plants in home gardens.
There is no forecast for rain events for rest of the week, but it will be warm.
June 28, 2016, Manitoba – The crops continue to look very good, says Vikram Bisht in the Manitoba potato report from June 24. Most early planted crops are row closed and many are nearly so. The rainfall distribution has been very good, and very few fields need irrigation. The accumulated Disease Severity Risk Values (DSVs) for late blight are currently low and below the critical value of 18 across the province; however, it will be helpful to have at least one protectant fungicide application before complete row closure to protect the lower and hidden canopy. It is good to see that many farms are now clearing away the cull piles near their yard and fields.
A few fields are showing herbicide drift injury symptoms. It is important that the applicators are cognizant of the crop injury potential to potatoes, and avoid spraying when the wind speed is above an acceptable level, toward the wrong direction or it is dead calm (no air movement).
First identified in Ontario potatoes in 2015, Dickeya is shaping up to be a problem. Photo courtesy of Tracy Shinners-Carnelley.
Potato growers are familiar with the problems that stem from blackleg and are adept at managing it. However, two new strains have been identified and one has been spreading in North America for the last two years. Dickeya dianthicola has been affecting potatoes in Europe since the 1970s, but is now found frequently in the United States, particularly in Maine and south along the eastern seaboard. Dickeya is most probably spread on seed and is shaping up to be a problem in North America.
“Dickeya may have two problem features,” says Amy Charkowski, a potato specialist at the University of Wisconsin. “It needs fewer cells to cause disease and it can remain in a kind of dormancy until the right conditions trigger the disease.” She adds the bacteria thrives under wet conditions and is an equal opportunity pathogen so can be found on other vegetables and some ornamental plants. Dickeya does not seem to favour grains and legumes, which makes crop rotation a good option to lessen its spread.
Blackleg seems to resemble the common cold because it changes. Growers use management practices to control the disease, but this new species is not so easily harnessed using this familiar method. Crop protection products are not effective on Dickeya dianthicola. Meanwhile, researchers have identified Dickeya solani in Europe that is very aggressive and is not easily controlled, but it has yet to cross the ocean. This proves that complacency, when it comes to blackleg control, is not an option.
“We found Dickeya in Ontario potatoes in 2015,” says Gary Secor, a plant pathologist from North Dakota State University in Fargo. “The seed came from Maine, which is an example of how easily it spreads.”
To minimize the spread of Dickeya, both Charkowski and Secor recommend not cutting seed and, instead, using the whole tuber. Since it does not survive well in soil, they also recommend diligent crop rotation. “There are no food safety issues, but there is still a lot we don’t know about Dickeya,” Secor says. “We also don’t have any idea what the economic thresholds might be.”
“We are applying for grants to allow us to focus more research on Dickeya,” Charkowski says. “We want to learn what breeders need to know to enable them to breed for resistance, and we need to determine what the thresholds are for seed.
The symptoms are similar to the strains of blackleg growers are familiar with, so tubers need to be tested to identify Dickeya. “If it is present the most noticeable symptom is plant wilting,” Charkowski explains. “There will be rotten potatoes at harvest and there could be rotting at plant emergence.” She says determining an accurate laboratory test may be part of the planned research, but a field assay would be more helpful. Knowing the strain may help determine the most effective control as well.
“A lot of co-operation is required with all agencies working together to make progress on identification and control,” Secor admits. “Certification agencies need to determine if it requires certification at the seed stage.”
According to Tracy Shinners-Carnelley of Peak of the Market in Winnipeg, the Canadian Food Inspection Agency’s seed potato inspection program has strict tolerance for blackleg infection. “This is likely a factor in how the incidence of blackleg in Canada is quite low,” she says. In the United States, she adds, blackleg is not part of the industry’s seed certification process, which puts Canadian growers at a bit of an advantage when seed changes hands because it is screened. However, accurate tests for particular strains of Dickeya may be necessary if the more virulent versions enter North America.
“Canadian growers need to be aware of the risks and be proactive in order to prevent the introduction or establishment of any new disease,” Shinners-Carnelley continues. “My main message to growers is to follow best management practices and this, combined with the use of certified seed, will help to reduce the risk and spread of Dickeya.”
June 2, 2016 – Blackleg, caused by strains of soft rot bacteria known as Dickyea, has traditionally had little impact on North American potato production, but it now appears to be on the move throughout Europe and could increasingly threaten growers in the Eastern United States.
The Plant Management Network (PMN) has released a new presentation entitled “Dickeya: A Scottish, UK and European Perspective” to provide growers and crop consultants with an overview of the history of the disease in Europe and an introduction to Dickeya solani, a new aggressive pathogen strain contributing to the increase in incidence and spread of blackleg.
The webcast, developed by Gerry Saddler, deputy head of science and advice, Scottish Agriculture with the Scottish Government, details their country’s potato production practices and explains why they have adopted a national zero-tolerance approach to the presence of Dickeya strains.
The presentation discusses in detail:
• Causes of blackleg and symptoms exhibited by different strains
• Conditions that encourage infection and common transmission methods
• Inspection and testing practices employed in Scotland
• Effective control measures to limit spread
The 40-minute presentation will remain open access through July 31 in the Focus on Potato (www.plantmanagementnetwork.org/fopplantmanagementnetwork.org/fop) webcast resource.
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2018 Herbicide Resistance SummitTue Feb 27, 2018
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Canadian Horticultural Council’s AGMTue Mar 13, 2018