b'Andys Advice:Understanding TuberGrowth Cracks And Thumbnail CracksBy Andy Robinson, Extension Potato Agronomist, NDSU/UMNcrackscanvarytremendouslyin whileshallowcrackinghappensseveritywithsometubercracks later in bulking. As tubers continuebeing shallow and small that do not todevelop,growthcrackswillaffect the grade, while others can be suberize and heal. deep fissures that expand across thetuberandaroundthebudend. Herbicide exposure to potato plantsSometimes there is nothing that can candisrupttubergrowthresultingbe done to prevent growth cracking ingrowthcracks,oftenseverebecause of the environmental con- growthcracks(Figure4).ditions potato plants are exposed to Translocatingandcontactherbi-duringtuberdevelopment.For cidescancausegrowthcracks.example,someyearsweseefew Herbicides such as glyphosate, planttuberswithcrackingwhileother growthregulatorsorthosethatyearstherearemanytuberswith inhibitacetolactatesynthase(ALS-Tubercrackinghasbeenfartoo crackingandresultingeconomic inhibitors) commonly cause severecommon in our area in 2020. There loss.cracking when plants are exposed inaretwotypesoftubercracking, earlybulking.Herbicidesresiduesgrowthcracksandthumbnail Tubergrowthcracksarecaused that remain in the soil are taken upcracks/airchecks.Growthcracks when the internal core tissue grow- byplantrootsandcanresultin(Figure1)occurduringthegrowth ers faster than the surface tissue or cracked tubers (Figure 5). Exposureanddevelopmentoftubersasa periderm when tubers are enlarging. at late bulking may result in shallowresult of a physiological response to This often occurs from a period of cracking, of what may appear as airenvironment stress, herbicide injury low soil moisture, followed by rapid checks or elephant hide (Figure 6),ordiseasepressure.However, water uptake, causing rapid changes ornosymptoms.Theseverityofthumbnailcracks(Figure2)area in tuber turgidity and growth rate. cracking is affected by the interac-resultofimpacttotubersduring Otherrapidchangesintuber tion of cultivar, herbicide chemistry,tuberhandlingorexposuretoair growthreportedtoencourage herbiciderate,plantgrowthstagewhenliftedfromthesoil.Tuber growth cracks can come from poor andenvironmentalconditions.cracking is not desirable in any situ- nitrogen management during bulk- Testing tubers for herbicide residuesation. The quantity and severity of ing, planting cultivars that tend to atareputablelaboratorycanhelptubercrackingwillvarybasedon have larger sized tubers, or low-den- determineifherbicideinjuryisthegrowingenvironment,variety, sityplanting.Tubercrackingmost causing cracking. disease pressure, handling and cul- commonly occurs at the bud-end oftural management.thetuberandstretcheslengthwise Research has reported that a num-acrossthetuber(Figure3),but berofpathogenscancausetuberGrowthcracks,asthename cracking can happen anywhere on cracking, likely because they disruptdescribes are cracks that develop in the tuber. Deeper growth cracks are normaltuberdevelopmentwhenthetubersasitisgrowing.These aresultofstressinearlybulking, plants are infected. Potato mop-top12 POTATO GROWER NOVEMBER/DECEMBER 2020'