Crop Protection

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. 


There are other, more sophisticated methods of testing for the presence of late blight spores in growers’ fields, but that’s precisely the reason Eugenia Banks selected a very simple test for her 2016 project.

Post-harvest potato storage expert Todd Forbush of Techmark Inc. in Lansing, Mich., says quality potato storage requires just two things: quality storage facilities and quality potatoes to store.

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!).



July 27, 2016, Prince Edward Island – While some areas on P.E.I. got a thorough soaking over the weekend, others are still thirsty for moisture. Water levels are still low in some areas of the province, reports CBC. | READ MORE

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). 

June 28, 2016, Alliston, Ont. – Irrigation was the order of the day on June 27, writes Eugenia Banks, OMAFRA potato specialist, in her latest update. Banks checked a few fields near Alliston, Ont., for early blight but did not find any lesions. The fields had been sprayed recently and there was fungicide residue on the leaves.   

Banks did not see any damage caused by air pollution and weed control was good (Prism was applied after emergence). A good, steady rain is needed in most areas of the province. 

June 23, 2016, Manitoba – Potato crops across Manitoba in general look very good, according to Vikram Bisht of Manitoba Agriculture, Foods and Rural Development, in his latest report. The early planted crops appear to be about a week ahead of last year. Many of these fields have crop canopy nearly closed between rows, and have 0.5 to 0.75-inch tubers. Some of the later planted crops are between hooking and pea-size tuber size stage. 

Wide spread and well distributed rains have helped the potato crop in Manitoba grow very well. Recent rains (including overnight) have been also wide spread, and amounts reported range from 0.25 to 1.5 inches. There are reports of scattered hail in central potato growing areas of the province. The conditions appear to be favourable to late blight disease development. It is important that the crops be protected against late blight with protectant fungicides in fields nearing row closure. This is especially true for crops close to cull piles with volunteer potatoes growing in the cull pile. 

Disease Severity Risk Values (DSVs) for late blight are currently low across the province. 

An early incidence of late blight disease has been reported from Walla Walla County, Washington, on June 1 (, late blight strain US #8 (metalaxyl resistant strain).

May 27, 2016, Prince Edward Island – Prince Edward Island potato growers got a bit of a head start to planting this year, says Greg Donald, manager of the P.E.I. Potato Board. Donald estimated that between 65 and 75 per cent of the Island’s 2016 potato crop was in the ground mid-week. | READ MORE

April 28, 2016, Charlottetown – Christine Noronha, an entomologist with Agriculture and Agri-Food Canada’s Charlottetown Research and Development Centre, has designed an environmentally green trap that could be a major breakthrough in the control of wireworms, an increasingly destructive agricultural pest on Prince Edward Island and across Canada.

In this exslusive webinar hosted by Potatoes in Canada magazine, Christine will share details about the Noronha Elaterid Light Trap (NELT). Don't miss the opportunity to ask questions and learn more from Christine Noronha. 

Date: May 12, 2016

Time: 2 p.m. ADT (1 p.m. EDT)

Cost: $20

Register today!

April 26, 2016 – Eugenia Banks is offering free training sessions for potato scouts in May. 

The first session will be held Monday May 30 from 9:30 a.m. to 3 p.m. at the Shelburne Agricultural Society Community Centre in Shelburne, Ont.

The second session will be held Tuesday May 31 from 9:30 a.m. to 3 p.m. at the Royal Canadian Legion, Branch 190, Norwich, Ont.

Both sessions are free of charge. To register, please email Eugenia Banks ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it ) with the name and contact information of the registrant(s). 


Careful management of irrigated potato crops over the long-term may help maintain crop productivity and nutrient availability within acceptable levels for agricultural production. This is the conclusion Agriculture and Agri-Food Canada (AAFC) researchers reached when they did a field experiment the year after completing a long-term irrigated potato rotation study in Brandon, Man.

During that initial 14-year rotation study, Ramona Mohr, a sustainable systems agronomist at AAFC, worked with a team of researchers to identify economically and environmentally sustainable rotations for irrigated potato.

From 1998 to 2011, Mohr and her colleagues grew six different rotations: potato-canola, potato-wheat, potato-canola-wheat, potato-oat-wheat, potato-wheat-canola-wheat and potato-canola (underseeded to alfalfa)-alfalfa-alfalfa, and looked at their effects on various factors including crop yield and quality, diseases and weeds, soil quality and economics.

“Generally accepted management practices were used during the 14-year rotation study,” Mohr says. “We soil tested on an annual basis and adjusted our fertilizer management practices accordingly.”

In the year after the rotation study ended, the researchers conducted a follow-up study to assess the impact preceding rotations had on phosphorus, potassium and micronutrient concentrations in the soil, as well as on soybean yield, quality and nutrient concentration.

For the follow-up study, the group picked a glyphosate-tolerant variety of soybean as an indicator crop to try to minimize possible confounding effects of the previous rotations with respect to disease, weeds and nitrogen.

It was a unique opportunity to study the relative effects preceding rotations have on crop productivity and nutrient status of the plant-soil system, given the limited information available for Western Canada.

“This rotation study was one of only two longer-term irrigated potato rotation studies conducted in Western Canada over the past couple of decades,” Mohr says.

Taking multiple soil samples from each rotation in the spring of 2012, the researchers were able to compare them with samples taken in 1997 at the beginning of the long-term study. They discovered that the soil nutrient levels and the yield and quality of the soybean crop were all typical of the region.

“We saw some differences in nutrient levels among the different rotations, but no substantial depletion or build up of nutrients, and no large differences in soybean yield among the rotations,” Mohr says.

Preceding rotations affected soybean yield to a limited degree. Soybean yield was six per cent higher following the potato-oat-wheat rotation than the potato-canola-wheat rotation, although the reason for this difference wasn’t clear.

“We also noticed when soybean followed potato, it had a slightly higher yield than following cereals or canola, we suspect, because of greater availability of water because the potato crop was irrigated and none of the other crops were,” Mohr says.

The samples also showed that where preceding rotations included alfalfa, seed protein increased and oil concentration decreased. The researchers believe the limited yield differences may have been due, in part, to the selection of soybean as an indicator crop. This likely minimized the differences among rotations arising from disease, weeds and nitrogen. Soybean had not been used in the rotation study and so was not susceptible to those diseases that had built up in the preceding rotations. Also, it is a nitrogen-fixing crop that could supply its own nitrogen. As well, by selecting a glyphosate-tolerant soybean, weeds could be effectively controlled regardless of the previous rotation.

For nutrients, the researchers looked at phosphorus and potassium in the top 15 centimetres of the surface soil and found they fell within the same general range of what they saw in 1997.

Soil test phosphorus was slightly higher except for the rotation that included alfalfa hay. That rotation saw a reduction of both phosphorus and potassium, which the researchers determined was likely a result of the high nutrient removal rates of alfalfa hay and their fertilizer management practices during the long-term study.

For example, Mohr says they applied phosphorus in the alfalfa establishment year, but not potassium because soil levels did not call for it. “When we saw a decline in soil potassium levels, we started applying potassium at that point.”

Soil test phosphorus levels were also found to be higher in the shorter rotations. “The two-year was greater than the three-year was greater than the four-year rotation,” Mohr says. Again, the researchers attribute this to their fertilizer management practices since they applied a higher rate because they broadcast the fertilizer in potato, adding more phosphorus than the potato crop removed.

“The more frequently we grew potatoes, the higher the soil test level we tended to see,” Mohr says. “Although we saw some difference in soil test levels, again they were within the range we see in agriculture fields.”

Mohr and her colleagues also looked at micronutrients during their follow-up study. “The site had sufficient micronutrients for the crop so we didn’t need to add any fertilizer,” Mohr says, although certain of the fungicides applied to potato would have contained some copper or zinc. While the preceding rotation had minimal effects on soil copper and zinc levels, soybean established after the potato-canola-alfalfa rotations or directly following a potato crop contained comparatively higher seed copper and zinc concentrations.

This suggests, Mohr says, that including mycorrhizal crops, like potato and alfalfa, might have increased the availability of micronutrients to the following soybean crop. “The roots of potatoes and alfalfa form a relationship with mycorrhizal fungi in the soil, which may increase the availability of micronutrients. We didn’t measure mycorrhiza in this study, but we know that based on previous studies.”

The results of the follow-up study in 2012 do suggest that careful, long-term management of irrigated potato systems may help maintain crop productivity and nutrient availability within acceptable levels for agricultural production. However, Mohr stresses the impacts of disease, weeds and nitrogen fertility on crop growth may have been minimized because the researchers selected soybean as the indicator crop in this study.

“If producers were to grow other crop species, there might be a greater impact on crop productivity,” she says.



Potatoes are a high input, high value crop and ensuring their success should not be left to chance. Certain variables, like the weather, cannot be predicted or controlled, but monitoring the weather can certainly help assess if problems affected by weather can occur. But suspecting there could be a problem is not the same as knowing for certain the crop needs more attention than just a drive-by glance provides.

Growers with numerous acres sown to different crops or with fields scattered across many miles may not have the time to monitor each and every facet of their farming operation. Sometimes it pays to hire experts. Many growers understand the value of hiring field scouts to monitor the activity in their fields, to alert them to possible problems and to advise them on solutions.

According to Eugenia Banks, an Ontario potato specialist, “field scouting is the backbone of a potato integrated pest management program.” In 2015, Banks offered classes on field scouting through the Ontario Ministry of Agriculture, Food and Rural Affairs to assist scouts in understanding more about the issues facing potato crops.

“The information collected by scouts is reported to growers who can make important pest control decisions based on their findings,” Banks explains. “A scout can provide timely information on the status of the crop, the level of insect populations and their distribution in the field, incidence of diseases and other problems caused by weather conditions, and potential issues with weed infestation. This information helps growers to time the application of crop protection products, and scouts are able to monitor the efficacy of the pesticide chosen. In addition, field scouting allows growers to do spot treatments for pests, which are possible when pests are concentrated only in specific areas of fields. Spot treatments help growers enhance farm sustainability and environmental protection.”

Professional scouts make timely visits to a field to assess aspects of crop development and watch for disease, insects and weeds that could impede that development. By hiring a scout, growers can focus attention on other aspects of the operation, such as preparing storage to accept the crop or ensuring harvest equipment is ready to go to work. For a scout, the main focus is the crop and having a scout regularly walking the field is worth the fee. Most scouts contract to walk a field once a week, but many will visit more frequently depending on potential pest pressures or changes in the weather that could affect pest or disease development.

“Scouts can help prevent diseases because we are in the field at least once a week,” says Karen VanderZaag. She became a scout five years ago when her father hired her to scout his fields near Alliston, Ont., as a summer job. After discovering she liked the work, she takes Banks’ field scouting update courses annually.

“It’s important for a scout to refresh their knowledge every year and to learn what might be something new to watch for,” she explains.

“It can take an hour with multiple scouts to scout a field, but as much as two or three hours if the field is large or the risk of disease is high. You want to see the disease before it becomes a major problem across the field.”

VanderZaag takes a close eye to the field, looking for pests, diseases, and anything else that may affect the crop. “My main concern is late blight, but I scout for everything from weed pressure at the beginning of the season to insects throughout the season. In 2015, Colorado potato beetle was identified as a problem early in the season and I considered insect pressure and thresholds before making a recommendation.”

Scouts offer “a close extra look or inspection while walking through the field,” according to VanderZaag. In her observation, not all growers hire scouts, but the benefits are hard to deny. An example of the value a scout can bring to an operation is the need to regularly watch for late blight. “If you don’t have someone scouting your field and you aren’t doing it regularly yourself and you have late blight, it can cross the entire field and will be in the neighbour’s field by the time you notice,” VanderZaag cautions.

Scouts can be hired on an hourly basis or through a crop protection dealer, who may offer scouting services as part of a package that includes custom spraying. For VanderZaag, scouting is her summer job while she completes her education in agriculture. But there are also businesses that offer scouting services. On average, expect to pay close to $6,000 annually for a scout. The value can vary, depending on whether you are hiring hourly or on a contract and how much you expect your scout to do.

Staying current is also part of a good scout’s resumé, which is why many take the courses offered by Banks or other experts. Most growers are too busy to maintain their knowledge of pests and disease identification, and with new pests arriving regularly, getting to know new ones is time consuming. A scout’s job is to know what is new or which old pests may be a problem in any given year.

Averting such disasters as crop failure due to late blight, or losses due to a beetle infestation, will likely make up for the cost of the scout. Hiring a scout isn’t just about identifying pests and getting advice on spraying – it also buys peace of mind. Knowing your crop is in good hands is worth the cost. 


Nov. 20, 2015, Prince Edward Island – A former manager of the P.E.I. Elite Seed Potato Farm says he’s been hearing there have been no outbreaks of bacterial ring rot in Prince Edward Island potatoes in five years. But the good news is tempered by the provincial government’s decision to discontinue its potato disinfection services by year’s end. | READ MORE

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