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.”
Potato seed infected late in the season with Dickeya (new blackleg) usually does not show symptoms in the field before harvest nor in seed storages. This is because Dickeya requires high temperatures for the development of visible symptoms. The optimum temperature for Dickeya is above 25 C.
By contrast, the old blackleg (Pectobacterium) can develop at cool temperatures (8 C to 10 C), and symptoms are usually visible when cutting seed.
Banks says she received two questions about Dickeya:
Q: If dormant infection of Dickeya is suspected, could you incubate a sample of tubers at 25 C to 30 C so the tubers will show Dickeya symptoms in about 2 weeks?
A: Banks asked Steve Johnson (Maine) and Gary Secor (North Dakota) this question and both said no. It takes more than two weeks for the symptoms to develop. Banks says the first time she saw Dickeya symptoms developing from seed tubers with dormant infection was in late June (the seed tubers had been planted by the middle of May), and both Johnson and Secor agree.
Q: Are Dickeya lesions smelly?
A: We all know how smelly the old blackleg is. The slimy, black stems smell like rotten fish, a disgusting smell noticeable at least 30 feet away from an infected plant. Usually Dickeya is not smelly. The bacterium grows inside the stem moving up in the vascular tissue. Dickeya-infected stems are usually dark brown, not inky black, slimy and smelly like the old blackleg. Eventually, the infected stems may be invaded by secondary bacteria that cause a black rot. If, shortly after emergence, you see small, wilted plants with a black stem base, it is probably the old blackleg. If the summer is cool and wet, probably the old blackleg will prevail. In hot summers, Dickeya will be the prevalent disease (wilted foliage is also a symptom of Dickeya).
The field trial conducted by The Sainsbury Laboratory (TSL) in Norwich involves incorporating late blight resistant genes from a wild potato relative into a cultivated Maris Piper potato. READ MORE
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.
Harvest management, in large part, is bruise management. Bruising also affects tuber quality significantly. In order to harvest potatoes with minimum tuber damage, growers need to implement digging, handling and storage management practices that maintain the crop quality for as long as possible after harvest.
Assuming all harvest and handling equipment are mechanically ready to harvest the crop with minimum bruising, there are several tips to preserve the quality of potatoes crop during harvest:
- Timely Vine Killing. Killing the vines when tubers are mature makes harvesting easier by reducing the total vine mass moving through the harvester. This allows an easier separation of tubers from vines.
- Timely Harvest. Potatoes intended for long term storage should not be harvested until the vines have been dead for at least 14 days to allow for full skin set to occur.
- Soil Moisture. Optimal harvest conditions are at 60-65% available soil moisture.
- Tuber Pulp Temperature. Optimal pulp temperatures for harvest are from 500F to 600F. Proper pulp temperature is critical; tubers are very sensitive to bruising when the pulp temperature is below 450F. If pulp temperatures are above 650F, tubers become very susceptible to soft rot and Pythium leak. Pulp temperatures above 70°F increase the risk of pink rot tremendously no matter how gently you handle the tubers if there is inoculum in the soil.
- Tuber Hydration. An intermediate level of tuber hydration results in the least bruising. Overhydrated tubers dug from wet soil are highly sensitive to shatter bruising especially when the pulp temperature is below 450F. In addition, tubers harvested from cold, wet soil are more difficult to cure and more prone to breakdown in storage. Slightly dehydrated tubers dug from dry soil are highly sensitive to blackspot bruising.
- Reducing Blackspot Bruising. Irrigate soil that is excessively dry before digging to prevent tuber dehydration and blackspot bruising.
- Bruise Detection Devices. Try to keep the volume of soil and tubers moving through the digger at capacity at all points of the machine. If bruising is noticeable, use a bruise detection device to determine where in the machinery the tubers are being bruised.
- Do not harvest potatoes from low, poorly drained areas of a field where water may have accumulated and/or dig tests have indicated the presence of tubers infected with late blight.
- Train all employees on how to reduce bruising. Harvester operators must be continually on the lookout for equipment problems that may be damaging tubers. Ideally, growers should implement a bruise management program that includes all aspects of potato production from planting through harvest.
- Harvest when day temperatures are not too warm to avoid tuber infections. Storage rots develop very rapidly at high temperatures and spread easily in storage. If potatoes are harvested at temperatures above 27o C and cool off slowly in storage, the likelihood of storage rots is increased. If warm weather is forecast, dig the crop early in the morning when it is not so warm.
The warm conditions has slowed the harvest of some processing fields, to prevent bringing warm tubers into storage. The seasonal accumulated precipitation has been 50-70% of normal in the potato growing areas (Fig1). The soils are generally on the dry side (Fig 2), but irrigated fields have sufficient moisture for a good harvest. READ MORE
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