b'TATER TALES Tips to Reduce Heat Stress on PotatoesHow to save your spuds during hot temperatures.AS A CONSEQUENCE of climate change, Ontario has been experiencing summer temperatures that exceed whats ideal for the potato crop especially from late June through August. Yield is greatly reduced at high temperaturesabove 30 C during the day and 25 C at night. Heat and drought go hand in hand, with irrigation needed during heat waves. Irrigation is expensive, and for many farms, water is a reduced natural resource EUGENIA BANKS,with some fields only rain fed. To compound the potato specialistproblem, rainfall has been erratic, with some areas with the Ontario Potato Board receiving only two to four inches of rain per season. Periods of extended heat reduce yields dramaticallythe earlier a heat wave occurs, the more negative its impact. High temperatures during tuber initiation increase the respiration rate, which reduces tuber set. A high respiration rate in mid-to late-season may causeA tensiometer, used by WD Potato Ltd. during the 2022 the production of a second set of tubers that never sizegrowing season, has a digital rain gauge, and sends results to growers through a smartphone app or online uphigh temperatures slow down tuber bulkingapproximately 15 minutes after making readings.resulting in yield losses. In addition, second growth is aPHOTO: PATRICK DOL, WD POTATO LTD.common problem caused by heat waves.What can growers do to cope with heat stress? Herecool reducing evapotranspiration and crop stress. are some tips: Potato roots suffer when the soil warms in direct 1. S upplemental calcium applicationsJiwansun. Many fields in the province still have open Palta, an emeritus researcher at the University ofcanopies in early July, because of late planting.Wisconsin, and an expert on the calcium nutrition3. P lant late varieties in soils with the highest organic of potatoes, has shown calcium helps reducematter (OM) contentSoil organic matter the effects of heat stress. Heat stress causes theimproves soil health and improves water retention stomates of leaves to close until temperaturescapacity. drop. High calcium levels reduce the effect of heat4.Plant potatoes after small grains, corn or other stress by maintaining normal cell functions abovecrops that leave significant residues after harvest.28 C. This includes the opening and closing of5. Avoid fields that have saline, steep, or shallow soils stomates and cell enlargement. Palta recommendsor compacted soils with low soil porosity. the application of 100 to 150 pounds of soluble6. Avoid over fertilization, especially with nitrogen. calcium per acre through the irrigation water. This7.Monitor soil moisture during the season and total should be split into three or four applicationsschedule irrigation to crop needs. every two or three weeks starting at tuber8.Use dammer dikers which improve each plants initiation. For dryland production, one option isaccess to moisture and nutrients by trapping and to apply calcium at last hilling mixing the productholding waterthey prevent runoff and soil into the soil as much as possible. A less solubleerosion.calcium fertilizer such as gypsum should be usedPotato breeders around the world are trying to in sandy soils to reduce the risk of calcium loss bydevelop varieties that are more tolerant to heat and leaching. drought stress. Theres no doubt that such varieties will 2. P lant earlyIn Southwestern Ontario, usinghelp growers to maintain the production of a high-whole seed results in closed rows and vigorousquality crop as the weather gets hotter and drier and canopies by mid-June. This helps keep the soilrainfall becomes more erratic. 52SPUDSMART.COM Winter 2023'