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Potato Handling, Cutting, and Sanitation

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Potato Handling, Cutting, and Sanitation

Handle seed gently at all times up to and during planting. Impacts should be minimal and changes in temperature should be gradual. Seed should be protected from drying out and overheating in truck beds by tarping and minimizing time in the field, especially in warm weather. If seed must be stored more than a few days between cutting and planting, measures should be taken to provide aeration and cooling as needed. Typically, cut seed held more than a few days should be kept at 50-55F and high humidity with good air movement (see "Storage" at this site) to promote suberizing and healing.

Seed should be warmed to about 50oF a few days before cutting. Warm seed not only cuts better with less tissue tearing, but is also more physiologically active and heals faster than cold seed. Seed pieces should average 1.5 to 2 oz. and have a minimum of cut surface; that is, blocky seed pieces are preferred over slivers and slabs. Each seed piece should have one to several eyes depending on the variety. Some varieties may have few eyes near the tuber stem ends and produce a high percentage of "blind" (eyeless or budless) seed pieces unless special care is taken. Such varieties may call for larger seed pieces. (Ever wonder why tuber buds are called "eyes"? Because they have "eyebrows" which are actually rudimentary leaf scars.)

Before and during cutting, inspect seed for common diseases and pests such as bacterial soft rot, bacterial ring rot, Fusarium decay, powdery scab and rootknot nematodes. Excellent descriptions and control recommendations for common potato pests and diseases are available through the following sites and many others listed under Pests and Diseases:

Seed pieces should be treated with a recommended, currently labeled (see CDMS for current labels),  fungicide such as Maneb, Mancozeb, Thiabendazole or Thiophanate-methyl  immediately after cutting. When possible, seed should be planted soon after cutting into warm (above 45F), moist but not wet soil. For rapid growth and emergence, sprouts should be "peeping" (slightly enlarged) at planting and physiologically active in preparation for rapid growth and emergence.

Extreme care should be taken to maintain seedlot identity throughout the cutting and planting operation. Sanitize cutters and other equipment between plantings to prevent the spread of bacterial diseases, especially bacterial ring rot. Good planting sequence records, sanitation, and isolation of lots is essential in proving the source of ring rot seed in the event of lawsuits.

Bacterial ring rot (Clavibacter michigansis subsp. sepedonicus) is the scourge of the potato industry. It is always introduced to seed farms via seed, soil, or equipment contaminated with the organism. It survives for extended periods (years) only in living potato tissues. In the unlikely event that bacterial ring rot (BRR) is present in seed lots, precautions should always be taken to minimize spread in order to contain the epidemic and identify the contaminated seed lot for possible compensation. The following steps will help reduce BRR infection.

  • Use only certified seed potatoes at all times.
  • Plant whole, single drop seed when possible and avoid using picker planters because picks spread the disease.
  • Disinfect cutting knives at least three times a day when cutting a single lot of potato seed.  Always disinfect before cutting a new seed lot.
  • Disinfect storage bins, tools, trucks and other equipment frequently during cutting and planting operations. Always clean extensively before beginning seed handling operations at the start of the season.


The following disinfectants or fumigants are effective against BRR. In general, disinfect by wetting the surface with the product for at least 10 to 45 min and then thoroughly removing residues with water (see also Tables 2 and 3 below).

  • Quaternary ammonium compounds at 1.6 cups of a 10% solution/10 gal water
  • Trimethylammonium chloride at 1 oz of a 10% solution/2 gal water (400 ppm)
  • Calcium or sodium hypochlorite in a 1,000 to 2,000 ppm chlorine solution; for example, 1 gal of 5.25% calcium or sodium hypochlorite (household bleach) /10 gal water
  • Chloropicrin at 1 to 1.5 lb/1,000 cu ft of space. For storage fumigation, surfaces must be moist for effective control. Use a professional applicator for safety.
  • Copper 8--Quinolinolate (Mitrol PQ 57). Use a 5% solution in a 1:99 dilution


Recommended planting dates for Oregon range from early March in the Columbia Basin through early June in Christmas Valley. High elevation areas tend to be planted late because of cold soils and the danger of late frosts. By comparison, some Willamette Valley plantings on heavy soils can be delayed into June because of prolonged spring rains.

 Table 2.  1998 Ohio Potato Production Guideline (Bulletin 672) Disinfectant Ratings for Control of BRR

Effectiveness of Disinfectants for Control of Ring Rot Bacteria1
Disinfectant Metal Wood Burlap
Betadine* g g g
Chlorine Bleach (10%) s s g
Coal Tar g g g
DeBac** g g g
Ethyl alcohol (95%) s g g
Formaldehyde (1%) s g s
Formaldehyde (2%) g g g
Formaldehyde (4%) g g g
Vesphene* u u s
Zephiran** g g g
Lysol concentrate u u s
Lysol spray s g s
Phenol (5%) s s s
Water u u u
Soapy water u u u

1Materials may not be labeled for use in all production areas; read labels carefully before using.
*Hospital disinfectant
**Quaternary ammonium compound
g = good control after 15-20 minutes
s = very slight survival of bacteria after 15-20 minutes
u = unacceptable control

Table 3.  Materials shown in the following table are commonly used for disinfecting potato
handling equipment and storage facilities for both seed and commercial potato operations1

  Effectiveness Inactivation           
Material Wet Bact, Slime Dry Bact,
Slime
Org. Matt. Hard
Water
Corrosive ness Safety Conc. Exp. 
Time
Shelf 
Life
Quaternary 
Ammon. Cpds.
Ex. Ex. Slight No Slight Caution See 
Label
10 min 1-2yr
Hypochlorites, 5.25% bleach Ex Ex. Yes No, ex. Iron Yes Irritant, 
caustic
1:50, 0.1% 10 min 3-4 mo. 
undiluted
Iodine Cpds. Ex. Ex. Slight No, ex.
iron
Yes Caution See 
Label
10 min 1-2 yr.
Phenolics  Ex. Ex Slight No No Oral 
Poison
See
Label
10 min 1-2 yr.
Formaldehyde Gd. Poor No Yes No Unsafe 
Vapors
0.37-1.0% 30 min 1-2 yr.
Copper Sulfate Gd. Gd. No Yes Yes Caution 10lb/100 
gal 
30-60 min >10 yr. as
solid

1Materials may not be labeled for all producing areas; read labels carefully before using.
Adapted from: Disease Control Guidelines for Seed Potato Selection, Handling, and Planting, Extension Publication PP-877, North Dakota State
University. Registrations may vary. Check with local authorities.

Comments:
Quaternary Ammonium Compounds--Diluted solutions are relatively safe but concentrated form is poisonous. Slightly corrosive, use stainless.
Hypochlorites, 5.25% bleach--Quick acting, inexpensive; caustic to skin and clothing. Use at 1:50 when mixing with water only. For maximum effectiveness, use 1 part 5.25% bleach: 200 parts water; 0.6 parts white vinegar. Very corrosive.
Iodine Compounds--Not for internal use. Becomes ineffective as yellow-brown color is lost. Tamed iodophor compounds work best.
Phenolic Compounds--Provide residual action. These compounds show "phenol" in the list of of ingredients.
Formaldehyde--Use may be canceled. Produces irritating, choking fumes. Not generally recommended.
Copper Sulfate--Not widely used; mostly for soaking crates and bags.

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