b'Andys Advice:Understanding Plant Growth Regulators Use on SeedBy Andy Robinson, Extension Potato Agronomist, NDSU/UMNnumbergoesdown,tubernumberlators have been used to manipulate decreases,andaveragetubersizethe growth of plants. You may ask, increases.Dependingonthetuberwhydotheyaffectplantgrowth? size profile needed for your market,The answer is there are many natu-attentiontostemnumbercanrallyoccurringgrowthregulators increase marketable tubers and prof- thatsignaltotheplantvarious its.processes, such as sprouting or stem elongationortuberinitiation. TherearethreecommonmethodsWhen we apply some type of plant toadjusttubersizeprofile.growthhormone(Iwillreferto Adjusting within-row spacing, phys- these as plant growth regulators) at iologically aging seed, and applyingextremely low rates we can manipu-plantgrowthhormones.Eachlate plant growth. One of the most Potatogrowersknowthattubermethodintendedtochangetubercommon regulators used by potato numberandsizematters!Seedsize profile has its risks, limitations,growersisgibberellicacid,often growerswantmanysmalltubers,andfinancialcosts.Iwilldiscussreferred to briefly as GA or Gibb. For while fresh growers want the correctthis third option more in depth asexample, gibberellic acid is used to ratio of C, B, and A-sized tubers, andmore attention has been placed onencouragemorerapidsprouting chip and russet growers have a spe- this recently as growers seek smalland increase stem number which in cifictubersizerangeforfinishedadjustments to maximize quality. turnaddstotubercountand product. Tubers that are too big candecreasestubersize.Otherplant increase bruising, take up space inFor a long time, plant growth regu- growth regulators are used to adjust trucksandstorage,andcanhave poor quality. Undersized tubers are not marketable, can reduce airflow in bins, and take resources from the plants that could have been used for sizing desirable sized tubers. When tuber size is not correct, returns are diminished.A general principle is as stem num-ber goes up, tuber number increases, whileaveragetubersizedecreases. The opposite is true as well, as stemFigure 1. Effect of plant growth regulator treatments on Sangre and Dark Red Norland emergence and stem number. 12 POTATO GROWER APRIL 2022'