b'temperatures between 31o to 34o F (-0.5ostems, and a non-uniform stand in the to1.1oC).Thismayoccurwhilethefield. In the field, hot soil temperature is crop is still in the ground before harvest,the main cause of seed aging.in transit, or in storage. Little potato disorder or no top:New Chillinginjuryisnotvisibleonthetubersareproduceddirectlyfromthe tuber surface but causes pinkish-red tosprouts, without emergence.reddish-brown or gray discoloration of theflesh.(Thereddish-browndiscol-orationsymptomiscalledmahoganyFreezing injury effects on tuber. (John Nordgaard, Black Gold Farms)browning). The vascular tissue is very sensitive toFrozen Sproutschillinginjury.ChilledcellsarenotFreezingtemperatureskillemerging frozen, and tissues do not break downsprouts.Newsproutsregrowfrom rapidly. Little potato tuber disorder or no top. healthy tissue emerging at a 90-degree(Andy Robinson, North Dakota State angle to the stem. This delays emergenceUniversity/University of Minnesota)Chilled potatoes should not be used forfor at least a week and stand is not uni-seed. Cut surfaces do not heal properly,form. andseed-piecedecayislikely.SproutsHair Sproutsfrom chilled potatoes usually die off.High soil temperature toward the end of the growing season causes this disorder. Hairsproutdisordermaydevelopon physiologicallyoldtubersalongwith the formation of little potatoes resulting in poor stands. Hair sprouting is also a symptom of infection with the black dot fungus. (Fig. 13b) Chillinginjurytotuber.(Eugenia Banks, Ontario Potato Board)Frozensproutdamage.(John Freezing InjuryNordgaard, Black Gold Farms)Soil temperatures below 28o F (-2o C) for several hours kill the tuber tissue closerHairsprouts.(SteveJohnson, Physiologically Old Seed UniversityofMaineCooperative tothesoilsurface.SymptomsbecomeSeedthataccumulatedmanygrowingExtension) visible as the tubers begin to thaw result- degree days or stressed in the field prior inginfreemoisture(weeping)ontheto harvest, was not properly stored, orBlackheart tuber surface. stressed by excessive handling can pro- Canoccurduringtuberdevelopment ducerecognizablesymptoms.Ithasand/orstoragebythelackofoxygen, Later, cellular breakdown causes the tis- sprouts, or second growth, and/or it canleadingtodark,necroticcavities. sue to turn brown, grey, or black. A dis- be spongy or dehydrated. Planting seedIncreasedtemperaturecanintensify tinct line is visible between healthy andwith these symptoms can result in miss- blackheart, especially after vine kill and frozen tissue. ingplants,slowemergence,multiplewhen soils are saturated. Seed with12 POTATO GROWER MAY/JUNE 2023'