Gordon Johnson, Extension Vegetable & Fruit Specialist; firstname.lastname@example.org
We have a report of blueberries that are delayed in leafing-out or have little or no leaves on branches in 2023. When perennial fruits are delayed in leafing-out or have reduced leaves in the spring this is a sign of stress or physiological changes in the plants related to leaf and flower bud formation the previous year.
Perennial fruits that were stressed in 2022 may have fewer leaves in 2023. Stresses include drought, excess water, high winter water tables, herbicide damage, root pruning, insect damage above and below ground, root diseases, diseases that caused leaf drop, trunk and branch cankers, leaf drop from fungicides such as copper based products, soil pH too high or low, high soil salts, salt spray, wind and storm damage, wildlife damage (deer, rabbits, voles) and other biotic or abiotic stressors. When perennial fruits drop leaves, fewer photosynthates are produced and stored (in roots, trunks, canes, crowns). Leaf-out the following spring is dependent on these reserves and if stores are reduced leaf formation will be delayed, leaves will be smaller or there will be fewer leaves.
Often individual branches or canes may not leaf out. This may be a sign of damage or disease on that branch or cane. Look for girdling from insects, wildlife, or disease cankers. In tree fruits, damage to the trunk or root system may show up with poor leaf out on a portion or the tree, often opposite of the damage, due to vascular connections being disrupted.
Peach branches with few leaves but with some fruits. These branches are in decline. Fruit should be removed. Photo Credit G. Johnson
When fruit plants experience poor leaf out, then they may go into decline and eventually die. This may take several years. Rarely do plants in decline recover.
Leaf buds are generally very resistant to cold temperatures; however, if freezing weather occurs after bud break, leaves can be damaged.
Another cause of delayed leaf development in certain fruits is inadequate chilling hours (cold period in the winter). Temperate fruits require temperatures between 32°F and 45°F to fulfill the chilling requirement of many plants. When temperatures dip below 32°F, very little, if any, chilling is received by the plant and when temperatures exceed 60–70°F for extended periods, chilling can be negated. Leaf and buds on the same plant can have different chilling requirements. Insufficient chilling can lead to delayed foliage formation, reduced fruit set, and poor fruit quality. This is often a problem in southern states but we may see this on Delmarva in some varieties if winters are too mild.
Southern highbush blueberry on the right that did not leaf out due to not enough chilling. Photo credit Eric T. Stafne, Mississippi State
A final cause of reduced leaf formation is related to flower and leaf bud balance. This is often a problem in blueberries.
The following is from Becky Sideman, UNH Extension Professor & Specialist, Vegetable & Berry Crops
“Every year one of the most common questions I get is about blueberry fruit load. It is very typical for some branches, or in some cases, entire bushes, to have too many fruit and not enough leaves.
Too few leaves! After bloom, when fruits have set and the new growth is taking off, it usually becomes apparent that some branches do not have very many leaves. It is not that the leaves fell off – they never formed to start with. In some cases, the entire bush may be affected, but it’s usually only select canes. Canes or bushes that have very few leaves tend to have abnormally heavy fruit set, and those with lots of leaves have comparatively few fruits.”
“What’s going on? During the growing season, the blueberry bush forms buds for the next year – in spring and early summer, it puts out new shoots and, on these shoots, it produces leaf buds; later in summer it produces fruit buds at the tips of those new shoots. Heavy fruit set this year means that the bush had sufficient energy to produce a lot of fruit buds last year. This may have been because yields were light last year (at least on that branch) so they weren’t spending energy ripening fruit. Many plants, including blueberry bushes, preferentially pour their energy into ripening fruit rather than leaves. This is why we often see branches that have either lots of fruit or lots of leaves, but not both.”
“One of the goals of winter pruning is to bring fruit and leaf buds into balance on the bush. Heavier pruning reduces fruit but increases leaf canopy the following year. Therefore, bushes that were pruned more heavily do not generally show this problem as much as those that weren’t pruned or that were pruned lightly. The goal is therefore to balance removing enough wood to stimulate new growth (future yields) with keeping fruit buds (current yields).
“Another complicating factor is that winter injury can weaken canes slightly without killing buds. Weaker canes have less energy overall, so this problem may be more apparent on exposed canes or older canes that were more susceptible to winter injury. The same goes for canes plagued by other problems – diseases, insect pressure, etc.”
Blueberry bush with flowers but few leaves. Photo Credit H. Bennett
In crops such as brambles and blueberries, additional nitrogen fertilization can encourage more cane and leaf production. Where there are too many flowers and not enough leaves, you