Source: NASA Earth Observatory
Raspberry and blackberry consumption, collectively called “caneberries”, is at an all-time high as consumers gain awareness of the health-promoting attributes of these tasty fruits. The Pacific Northwest’s historically cooler summer climate used to provide an ideal environment for successful caneberry growth. However, the Pacific Northwest’s weather has started to shift due to climate change and this change is forecasted to continue. This shift includes increasing air temperatures. You may have even noticed we are experiencing many days with temperatures close to the hundreds (in degrees Fahrenheit) starting as early as May. Prior to recent years, this was more the exception than the standard.
Caneberries are adapted to growing in mild climates. The sudden change and increase in temperatures during the growing season has negatively affected their production. Heat stress along with high levels of UV can result in leaf scorching, shriveled berries, wilting, and white druplets. Damage like this has resulted in crop loss, reduced fruit quality, and fewer berries available in stores. It also threatens the future viability of caneberry farming and the rural livelihoods of surrounding communities.
Heat stress is a reaction by plants after persistent exposure to extreme temperatures beyond their optimum. The stress can cause physiological and morphological alterations (de Souza et al., 2012). Examples of those changes are reduced photosynthesis, carbon assimilation, and sexual reproductive success (i.e., less vegetative growth and fruit). Without any form of shade or evaporative cooling protection, this heat stress can cause reduced crop growth, establishment, yield, and even result in plant mortality under extreme situations.
Scorching of caneberry leaves is the inability of the root system to uptake sufficient water to ensure proper hydration and evaporative cooling during high-temperature extremes (Rose and Swift, 2019). Hot, drying winds can further worsen leaf scorch. When plants are not properly hydrated, leaf tissue farthest from the plant veins dehydrates first. The dehydrated tissue turns brown or black indicating that those parts of the plant have died.
Wilting is another common reaction to prolonged hot temperatures and decreased water uptake. The leaves will droop and lose their structured shape. Extreme wilting or “permanent wilting point” can result in plant death (Locher, 2022).
White druplets or sunscald are a result from solar injury and excessive heat stress (Mintenko, 2023). It causes individual druplets to turn white in color and become deflated. Fruit can also sometimes simply shrivel due to excess heat. While still edible, white druplets and shrivel lowers fruit quality and can reduce grower profitability.
Due to climate change, some of the caneberry cultivars that are currently being grown don’t contain the genes or physiological traits to withstand higher temperature environments to successfully grow. This has necessitated breeding efforts to rapidly develop and release more adapted cultivars that still meet growers other horticultural needs.
Breeding heat tolerant caneberry cultivars takes time. That’s why we must evaluate other methods like evaporative cooling, shade nets, reflective films, and priming agents for protection.
Currently, physical methods of mitigating heat are being researched to determine their economic viability and fruitfulness in protecting caneberries from heat stress. These techniques are widely used for other crops to mitigate heat and UV damage, but methods must be researched to best suit the important caneberry industry in the Pacific Northwest.
References
de Souza, M.A., Pimentel, A.J.B., and Ribeiro, G. (2012). Breeding for heat-stress tolerance. In R. Fritsche-Neto and A. Borém (Eds.), Plant breeding for abiotic stress tolerance (pp. 137-156). Springer, Berlin, Heidelberg.
Locher, L. (2022). Heat wave in the garden: How to identify and prevent heat stress in plants. In: OSU Extension Service. https://extension.oregonstate.edu/gardening/flowers-shrubs-trees/heat-wave-garden-how-identify-prevent-heat-stress-plants. Accessed 5 June 2023.
Mintenko, A. (2023). Raspberry drought and heat stress symptoms – province of Manitoba. In: Raspberry Drought and Heat Stress Symptoms. Accessed 31 May 2023.
NASA Earth Observatory (https://mynasadata.larc.nasa.gov/sites/default/files/inline-images/Pacific%20Northwest.png)
Rose, S. and Swift, C.E. (2019). Leaf Scorch – 2.911. In: Colorado State University Extension. https://extension.colostate.edu/topic-areas/yard-garden/leaf-scorch-2-911/. Accessed 5 Jun 2023