potato 5-9-12 CLEAN - Vegetableipmasia.org

ORGANIC POTATO PRODUCTION 7. PLANTING METHODS7.1 Seed SourcesA certified organic farmer is required to plant certifiedorganic seed and is strongly advised to also plant onlyphytosanitary certified seed. If organic seed is notavailable in the preferred varieties, check with organiccertifier to determine options.While it may seem advantageous for organic growers tosave their own seed, it is not recommended. Diseased seednot only affects the plants that grow from it but also putsthe rest of the field and the whole farming operation at riskbecause cutters, planters, and other equipment can spreadmany diseases. In the case of late blight, diseased plantsfrom affected seed tubers serve as the primary inoculumsource from which other plants in the field can be infectedas the inoculum is spread by wind, rain, and insect activity.This is the same risk posed by leaving cull piles exposed inthe vicinity of production fields. A grower often cannot tellby looking at tubers whether they will be good for seed.See the New York seed directory, Maine seed directory,and the Colorado seed directory.H (References 32-34) formore information about the certification program, varietiesand lists of phytosanitary certified seed suppliers. Carefullyinspect seed at the time of receipt. If possible, evaluate theseed before it is shipped. For a guide to potato seedevaluation, see Reference 55.7.2 Seed Preparation and HandlingWhen handling seed, growers should maintain lot identityand prevent contamination. Trucks, storage, and handlingequipment must be clean and disinfected (see Table 10.3.1)between each lot of certified seed. Seed tubers should bestored at 38°F and high humidity to prevent prematuresprouting and dehydration. Physiological disorders thatresult from lack of oxygen and excessively coldtemperatures during storage or transit contribute to seedpiece problems and poor stand establishment.Optimum seed will have medium to young physiologicalage. Factors that contribute to aging of potato seed includetemperature, stress, physical damage to tubers, and otherfactors influencing seed during growth and storage. Whileold seed will sprout earlier, it will have more stems, highertubers set, smaller tuber size and less vigor. Young seedwill take longer to sprout, have fewer stems, larger tubersand more vigor. It is difficult to visually determinephysiological age of seed, but a simple test will give someidea: warm up (55-60 F) a sample of potatoes in midwinterand observe how quickly they sprout. The longer aseed lot takes to sprout, the younger the seed.Tubers should be warmed to 50° to 60°F before beinghandled or cut. If not using whole seed, precut and healseed before planting. Curing cut seed (suberization) is bestaccomplished by placing seed in half-full pallet boxes orspread out in piles only a few feet deep with adequate aircirculation, temperature between 55° and 60°F, and about90 percent relative humidity. After cut seed has been heldat optimal curing conditions for one week, the storagetemperature should be lowered to between 40° and 45°F tomaintain vigor and avoid excessive sprout growth. Seedshould be warmed to 50 to 55F for 7 to 14 days beforeplanting.Green sprouting or “pre-sprouting,” is the practice ofexposing seed potatoes to conditions that promotenumerous uniform, stubby, dark green sprouts that emergequickly after planting. Potatoes thus treated may beharvested early and may avoid late blight and other insectsand diseases that develop later in the season. Healing(suberizing) and greensprouting require different conditionsand need to be done sequentially for best results. Greensprouting is more practical for hand planting. Read moreabout this in the Maine Organic Farmers and GardenersAssociation newsletter. (Reference 35).For most varieties grown in New York State, seed weight of1.5 to 2 ounces is optimal. Cut seed should be blocky inshape to reduce the cross-sectional area and facilitateuniform planting by equipment. Mechanical seed cuttersshould be adjusted to seed size and shape, and seed shouldbe graded to a uniform size before cutting. See Table 7.2.1.Table 7.2.1 Potato seed (cwt) required to plant one acre. 34” between rows 36” between rows Distance between Weight of seed pieces (oz) Weight of seed pieces (oz) seed in row 1 1.5 1.75 2 1 1.5 1.75 2 inches cwt 6 19 29 34 38 18 27 32 37 8 14 22 25 29 14 20 24 27 10 11 17 20 23 11 16 19 22 12 10 14 17 19 9 14 16 18 15 8 11 14 16 7 11 13 14 152012