Your potato crop is only as good as the seed you plant. Prepare and plant your seed tubers following Khalil Al-Mughrabi’s top tips checklist for best results.
It’s almost that time of year again. A key factor that affects the quality and quantity of potato crop yield under a grower’s control is seed tuber quality. You have decided which cultivar(s) to grow and how much seed you need. Soon it’ll be time to bring that seed home and prepare it for planting. Consider the following:
- The experience, expertise and integrity of the seed potato grower are the most important factors in the consistent production of good quality seed tubers. Choose a seed grower you know and trust.
- Make sure you and your seed supplier are in agreement on cultivar, clone, seed size, class, grade, quantity, price, date and method of delivery, etc.
- Use certified seed potatoes free from diseases or with very low disease incidence. However, for some diseases, one per cent infection is too high and risky (e.g. late blight, Dickeya, etc.).Viruses (e.g. PVY) should be below the maximum level allowed in seed potatoes destined for planting in a province or state.
- Make sure all paperwork is in order, such as certification, field inspection results, post-harvest test results, purchase agreement, etc.
- Disinfect the truck(s) that will transport seed.
- Disinfect all surfaces of the storage area where seed will be stored. Remember, quaternary ammonium disinfectant works best in cold water. Surfaces must remain wet for at least 10 minutes for the disinfectant to destroy pathogen organisms.
- Do not store seed in any area where a sprout inhibitor was used or where sprout inhibitor-treated tubers were stored.
- Are you familiar with Canadian seed potato regulations and tolerances? Check seed upon arrival and contact the Canadian Food Inspection Agency immediately if quality may be an issue and an inspection is needed.
- Keep records of conditions and weather/temperature during loading, unloading and handling. Good records can protect you if seed does not perform.
- Keep seed lots separate whenever possible.
- Keep the seed clean: provide disinfectant foot dips at all seed storage entrances. Make sure employees use them. Refresh foot dips regularly — a dirty dip is a useless dip.
- Avoid rough handling and bruising of tubers. Bruising stresses the tubers, decreases seed performance and invites pathogens to attack, and rot, your seed.
- After delivery, store seed tubers at 4 C to 5 C and 90 to 95 per cent relative humidity. To minimize damage during handling, slowly warm seed to 10 to 12 C over seven to 10 days prior to cutting.
- Cut seed with sharp, clean blades adjusted to deliver piece size weighing about two ounces. Disinfect the seed cutter daily and between seed lots.
- Apply seed piece treatments at the labeled rate and time of cutting and provide workers with appropriate safety gear.
- Cut seed pieces may be stored and wound healed at 12 C to 15 C, 95 per cent RH, and with adequate oxygen in piles no higher than six feet.
- Plant either freshly-cut seed (cut and planted on the same day) or seed that has been wound healed for about two weeks. Time the seed cutting operation accordingly.
- To control sprout growth if planting is delayed, cool the cut seed pieces down to <6 C, then re-warm prior to planting.
- Unless physiologically aged seed is desired, avoid storage conditions that promote sprout growth and avoid de-sprouting the tubers.
- Consider green-sprouting to promote an early harvest for seed production or to capture that lucrative, early table market. Place small whole tubers in continuous light at 12 C for four to six weeks prior to planting. Green-sprouting tubers advances the growing season by about two weeks.
Volunteer Potatoes: Potential Issue in 2019
Volunteer potato plants (potatoes growing from unharvested tubers) might be problematic in rotation crops during the 2019 growing season. These plants can be a competitive weed with most crops and act as a reservoir for diseases and insects.
In general, winter conditions in Canada are severe enough to control most volunteers (soil temperature below -2 C or 28 F) but winter survival is dependant on tuber health, temperature, snow cover, and burial depth.
When unharvested tubers survive the winter, volunteer potatoes are difficult to control the following growing season, and no one measure will guarantee success. An integrated approach, including harvest methods, cultural control, tillage methods, pre-crop control, and in-crop herbicides, is needed for proper volunteer management.
Tips for Volunteer Potato Control:
- Minimize the number of tubers left in the field following harvest. If a large number of tubers remain in the field in the fall, be prepared to deal with volunteers the following season.
- Avoid deep fall tillage that buries tubers. Leave tubers near the soil surface to be exposed to winter conditions.
- Delay planting the rotation crop to maximize volunteer emergence, then apply a herbicide or remove early volunteer growth by tillage.
- Select a competitive crop (i.e. barley) to follow potatoes, or a crop with a high potential for volunteer potato control (i.e. corn, Round-up Ready crops). Increase crop competitiveness with adequate fertility and higher seeding rates.
- Apply an appropriate in-crop herbicide treatment.
- Feeding from Colorado potato beetle, in combination with early herbicide treatment, may be enough to limit the impact of volunteer potatoes in cereal crops.
- Apply an appropriate pre-harvest herbicide if many volunteers are present, as certain pre-harvest herbicides can limit daughter tuber production and viability.
Seed Preparation Tips for Late Blight Prevention
- Visually inspect seed potatoes within 24 hours of delivery. Cut a sample of tubers and look for the reddish brown, dry rot characteristic of late blight tuber rot. A buyer has only 24 hours to request a re‑inspection after delivery.
- Test your seed for late blight before planting. Ask for a test certificate indicating freedom of late blight if buying seed.
- Grade seed potatoes before planting. It is important that seed is graded after it is cut and any late blight tuber rot removed before planting. Infected tubers can be a source of early field infections.
- Frequently disinfect seed cutting equipment (quaternary ammonium-based products).
- Treat seed with a recommended seed piece fungicide (mancozeb-based products) immediately after cutting.
- Construction of a good deep hill will help restrict spores from washing down through the soil and infecting the tubers.
- A preventive spray program at 80 per cent emergence is recommended for 2019. Systemic fungicides are used in a preventive program as part of an integrated pest management (IPM) program to control resistance. Effective control by fungicides requires good coverage of the leaves, proper rates of application and proper timing of applications. Read and follow label directions for best results.
- Monitor your crop. Scout fields where moisture persists after rains or dews such as low-lying areas and along treed edges. Have a good look at stems and leaves for symptoms of late blight. Stem infections do not die during dry periods and will easily re-activate in humid weather.
- When late blight is first identified, remove and destroy infected plants. When infected plants are rogued, they should be placed in plastic bags and then taken out of the field. Top kill or rogue an area twice the size of the area with infected plants.
- Bury cull piles before crop emergence. Infected tubers in cull and rock dump piles are major sources of infections. Buried tubers may germinate and grow. Rogue or treat these plants with a herbicide. Slivers and pieces of potato remaining from cutting operations should also be buried.
- Volunteer potato plants can be a source of infection. If there are volunteer potato plants in a field, an effort should be made to remove these plants by rogueing or herbicide treatment.
- Always report any suspect case of late blight immediately. If late blight is identified, roguers and other workers should wear pants and boots which can be disinfected with a bleach solution (diluted 1:9 with water) between fields or farms. Field equipment should also be washed and disinfected before entering other fields.
Cull Pile Disposal
Cull potatoes are a source of diseases, such as late blight, viruses, and bacterial ring rot. The presence of cull potato piles increases the risk of the new crop becoming infected with these diseases. Proper cull potato disposal is a necessary component of an effective disease management strategy. All cull potato piles must be disposed of prior to the deadline date set by a province or state. In New Brunswick and Maine, the deadline is June10thof every year.
Editor’s note: Watch for storage tips in Spud Smart Summer 2019by Dr. Khalil Al-Mughrabi, a pathologist for the Potato Development Centre at New Brunswick’s Department of Agriculture, Aquaculture and Fisheries.