Many of us harvested fewer fruit last year. This was almost entirely due to the cool, damp La Niña weather last spring and early summer. In July 2011 only one day met the criteria for “sunny” at SeaTac, tho August finally turned warm.
To get fruit: flower buds were formed the previous year, flowers were free from diseases at bloom, pollen matured and exited the stamens, pollinating insects flew during bloom, and pollen reached the flower’s ovary to accomplish fertilization.
Fruit trees set up flower buds the previous summer and if they are stressed by drought or over production (biennial bearing), fewer flower buds are produced. Huge old trees on seedling rootstock can withstand drought but trees on dwarfing rootstocks are smaller precisely because of their smaller root systems—they cannot forage far for water. Our area has a summer drought every August and perhaps in July and September too. It’s important to water then and to thin developing fruit promptly after bloom.
Some fruit tree diseases including scab, powdery mildew and brown rot infect flowers and destroy their ability to produce fruit. These diseases thrive in cool, damp weather. Pseudomonas can be bad in Oriental pears, especially if a frost occurs in early spring. There are protective sprays against these fungal and bacterial diseases but last spring it was hard to find windows of dry weather for spraying. Rain shields could be erected over small trees to protect them during the winter and spring until petal fall. Rain shields over peaches protect against peach leaf curl.
During bloom fruit trees need enough heat units to release mature pollen from the anthers. Even with such pollen grains present, blossoms may not get pollenized if it’s too cold for pollinators to fly. Not only was it too cold and wet for honeybees but mason bees and our hardiest pollinator, bumblebees, often didn’t take wing last year until after petal fall.
Here’s another hurdle: even if pollenized, blossoms don’t produce fruit unless the pollen grains can grow pollen tubes down the flower’s style to the ovary and accomplish fertilization. This process is temperature dependent, and under too cool conditions pollen grains die before ever reaching the flower’s ovary.
What can we do now to help our trees this spring? Sanitation is a biggie. Get those scabby leaves raked up and buried or out of the area. It’s hard to compost hot enough to destroy the scab spores. Remove all fallen fruit, prunings and of course any old fruit still on trees. Inspect apple trees in dry weather for small pointed terminal buds which have a whitish coating on the twig. These harbor powdery mildew spores under the bud scales which will burst forth during bloom. Simply prune these off. (While thinning fruit this spring carry a bag and pruners to remove any you missed.)
It’s possible to reduce bacterial canker in stone fruits by applying copper sprays at leaf fall. A serious disease occurring more in our recent damp springs is apple anthracnose. It may be reduced by copper sprays too. Inspect your trees for any cankers over winter and treat them in dry weather, by cutting out or by burning with a small plumber’s propane torch.
This year think about growing lots of flowers to aid pollinating insects. Insects are attracted to clumps of flowers rather than to scattered individual plants. Flowers attracting bees are of course the natives as well as dandelions, cosmos, coreopsis, clover, mint, etc. Don’t worry that flowers will divert Osmia; they feed on dandelions and other early flowers but prefer fruit tree blossoms and other roseaceous flowers.
Clean the nest blocks for our native Osmia now, before bloom, Some small solitary pollinators like to nest in undisturbed bare earth and bask on dark rocks to get up to flight temperature in the morning. They need just a sunny square foot or two. Bumblebees are our best pollinators and would appreciate a bit larger area with a pile of straw, twigs and dried grass per nest. Their favorite nest site is an old mouse nest but these are hard to find.
Look at the area surrounding your fruit trees. Have ornamentals grown up and cut off the sun? Maybe the fruit trees could use thinning during dry periods this winter to provide air circulation and light penetration. Save any downsize pruning for the first week of August, to reduce regrowth. It is helpful to remove vegetation at least a couple feet from the trunk to reduce vole damage and lessen root competition. It’s fun to plant crocus or snowdrops in this circle. Trunk guards also can help inhibit voles, sun scald and cracking in young trees.
During especially wet periods, brave the weather and check for drainage. Standing water problems must be addressed. Pears tolerate just a bit more wet than other fruit trees. Among small fruits raspberries are very susceptible to phytophthora root rot if too wet.
Looking really far ahead…..Our area is predicted to be one of the last to feel climate warming. But we are predicted to experience increasingly cool, cloudy weather in spring and summer. Why? Each spring the land mass east of the Cascades will start to become ever warmer as the climate warms and will have a lower air pressure over it than the higher air pressure present over the cold ocean. This means that cool, cloudy ocean air will be sucked over us toward Eastern Washington for more and more days in spring and summer while Eastern Washington bakes.
Think about choosing short season cultivars which can still thrive with lower heat units (choose Early Fuji over Mutsu or Goldrush apples). Choose cultivars which are disease resistant or self fertile. Self fertile cultivars still need to be pollenized but insects don’t have to bring in pollen from a different tree. Plan to grow fruit trees on a trellis system and outfit it with a clear rain shield about half the year, from leaf fall to petal fall. Consider growing more small fruits such as strawberries and raspberries which may also benefit from rain shields. Take advantage of south or southwest facing walls for reflective heat. Investigate high tunnels made from 20 ft PVC hoops and polyethylene sheeting. Finally, think about relocating to property which slopes to the southwest and has full sun exposure.
Last year saw several all time weather records broken, none of them good. Let’s hope for better conditions this year!
