MECHANICAL FRUIT THINNING INFLUENCES FRUIT-QUALITY, YIELD, RETURN FRUIT-SET, AND COLD INJURY OF PECAN

Pecan [Caryaillinoinensis (Wangenh.) C. Koch] fruit were thinned from 'Mohawk' trees in Oklahoma and 'Giles' trees in Kansas with a mechanic al trunk shaker. All trees bore an excessive crop load before shaking. Fruit thinning improved the kernel percentage, individual nut weight, and kernel grade of 'Mohawk', but nut characteristics of 'Giles' were not affected by fruit thinning. Cold injury, caused by a sudden tempe rature drop in November, was positively related to the percentage of f ruiting shoots in both cultivars. Fruit set in 1992 was negatively rel ated to the percentage of fruiting shoots in 1991 in both cultivars. C onsistent annual fruit set could be induced in 'Giles' by fruit thinni ng, but return fruit set in 'Mohawk', even at high levels of thinning, was low. Fruit thinning reduced yield the year of thinning in both cu ltivars. Thus, 'Mohawk' trees should be thinned so that 50% to 60% of shoots bearing fruit at mid-canopy height would remain, and 'Giles' tr ees should be thinned similarly to 65% to 70%.