We have a large Montmorency cherry tree in our backyard. The summer of 2016 we had a wonderful crop. March 2017 we pruned the tree back significantly to cut down on waste and droppings (rotting cherries all over the grass was an issue), but then summer of 2017 we had no cherries which I believe to be due to the stress of the pruning and an aphid infestation. My question is in regards to the aphids. Is there a way to prevent or get ahead of another infestation? We missed our sour cherry pies last year! Much thanks!
There are a number of possible causes when fruit trees fail to produce, including environmental, pollination and cultural practice issues. Sour cherries are self-pollinating, unlike sweet cherries which require a near-by tree with which to cross-pollinate, so pollination is likely not the issue here. A very cold winter can damage overwintering flower buds which can be seen as wilted or darkened pistils after the blooms emerge.
Cultural practices such as watering, fertilization and harvesting can also affect fruit production. Cherry trees should be watered infrequently, but deeply. Too much nitrogen will encourage foliage growth at the expense of flowers and fruit. You may want to get a soil test done to confirm the specific level of nutrients in your soil to guide your fertilization regime. You can find a list of accredited soil testing laboratories here.
Many fruit trees are susceptible to biennial bearing which is the tendency to produce less fruit following a previous year of abundant production. The setting of flower buds happens closely after fruit setting, which draws energy away from the production of flower buds for the next year. This tendency can be managed by reducing the fruit during a heavy production year through pruning or manual thinning of fruit before they begin to ripen. Given the heavy fruit drop you noted in the previous year this could be a possible cause of your lack of fruit last summer.
It is also possible that the heavy pruning you did the previous year cut out a significant number of the flower buds. The best time to prune is early spring before the buds swell. Pruning during too late in the fall or during winter can lead to injury if pruning is closely followed by freezing temperatures, as the tree cannot heal. Dormant pruning will also encourage the most new growth. Consider pruning moderately, but more frequently. OMAFRA has some helpful guidelines for pruning fruit tree here.
While aphids can damage foliage and fruit, its likely not the root cause of your low production last year. However, a dormant oil spray can be applied to branches in early spring which will smother the overwintering aphid eggs. Contact a reputable garden centre for the selection of an appropriate dormant oil and follow the manufacturer’s recommendations on timing and methods of application.
Good luck, and I hope you are back in sour cherry pies this summer!