My heart goes out to you all for the stress that you are going through. Please know that I’ve been monitoring the situation on apple trees and stone fruit. Don’t hesitate to tell me any barriers that you face and any recommendations that you have so I can share it in planning discussions and communicate to decision makers.
Interpretation of Drought Stress
Fruit Size
Trees under drought stress will prioritize survival mechanisms over tree and fruit growth. Apple fruit are expected to have a continuous increase in their fresh and dry mass during the final two months of their growth and some of this time has been lost to water stress. Fruit size is being restricted by the drought.
How much fruit growth is restricted depends on the crop load and the water stress. I’ve measured fruit sizes of Honeycrisp 47-67 mm (1.8-2.6”), peach 40 mm (1.5”), Gala 45 mm (1.8”), and Ambrosia 44 mm (1.7”). The fruit size measurements are about 30% smaller than the sizes being reported in Ontario. Research suggests that a rain episode that interrupts a drought can lead to the greatest increase in fruit mass observed over the whole period, so there are opportunities for fruit size gains.
Curling Leaves and Wilting Canopies
The first visual canopy symptom of drought stress is curling leaves (Figure 1, top). Early this week it was common to see leaf curling on Ambrosia. Leaf curling is a plant response that reduces the surface area of the leaf exposed to the sun and minimizes water loss.
As water stress continues, the leaves can wilt (Figure 1, bottom). Wilting is the tree’s strategy to reduce their functional leaf area and by closing the pores on the leaf surface (stomata) they avoid water loss by transpiration. Apple trees on light and less than ideal soils are wilting. There are cases of wilt in pears, peaches and European plum. The leaf curling and wilting starts at the tree top and can progress down the tree. I am hopeful that if water stress is ended in trees at an early stage of leaf wilt that trees can regain their health. Leaves may not recover their functionality, but water will hydrate xylem tissues to promote tree recovery.
(Initially there were questions about leaf wilting being caused by mite pressure, but mites would not cause a widespread and uniform wilting of entire tree canopies. Also, signs of leaf bronzing would have been visible first. If you used early season preventive measures to keep mite populations low then the trees benefitted.)
Figure 1. Ambrosia leaf curling (top photos). Pear with whole tree wilting leaves (bottom left) and Gala with tree tops wilting.
Brown Leaves and Defoliation
If whole wilted trees continue to experience water stress, then the oldest leaves can dry out and fall off followed by the youngest leaves. In situations where the water stress is severe enough to cause defoliation, research has shown that trees are unlikely to survive to the following season. The dying leaves are a sign of failure of the xylem to move water from roots to leaves. I hesitate to mention this as I don’t want to cause undue stress, but I know you are seeking answers and knowledge is power when it comes to insurance claims and planning purposes. Having said that, we will not know for sure until bloom next year which trees are past the point of return. Trees on more robust soils are not wilting and are using their survival mechanisms to withstand the drought.
Rootstock Influence
There are countless variables in apple orchards (soil type, tree age, variety, rootstock etc) which in the case of a climate stress can work in our favour by contributing some resilience. Right now I'll talk rootstocks because there is research by Xu and Ediger 2021 to suggest different drought responses among the rootstocks.
(Please note that the following comments are limited because they’re based on published research with only Ambrosia and the five rootstocks G.202, G.935, M.26, M.9NIC29, and B.9. Plus, some of the work was done in the greenhouse. But regardless, there may be some helpful information to glean.)
The research reports that semi-dwarfing G.202 used the most water and had the highest water stress. This agrees with our local challenges to grow G.202 without irrigation. Our industry has also identified other drawbacks of using G.202 like delayed cropping, limited leaf area, and small fruit. As a subjective comment, it appears that the fruit on G.202 are indeed struggling with size at this time.
The large dwarfing G.935 and M.26 had stricter control of their stomata which reduced water use under stress. The rootstocks therefore contribute a drought-avoidance strategy. This is good news for our industry that is heavily reliant on M.26 because they have likely been reducing water use to avoid water loss.
The small dwarfing M.9NIC29 and B.9 had small and dense stomata that gave them a stable water status and suggested a level of tolerance to drought conditions. However, in a field setting I suspect that the smaller root system would limit water foraging abilities.
A note about peach trees:
In some of my research I’ve come across mention of peach trees and that they are more susceptible to tree death during drought than apple trees. Also, water stressed peach trees may not produce fruit the following year. It has been a very hard couple of years for peach trees…
Decision Making
Reflective mulch
My theory would be that the additional sunlight exposure would heat plant surfaces and increase transpiration and water loss, so using reflective mulch this year is discouraged. Furthermore, sunlight is not lacking this year so the benefits of improving fruit colour using reflective mulch might not be observed this year. I suspect that the greatest opportunities for using reflective mulch are during years of scarce sunlight exposure when every chance to capture sunlight matters.
Watering priorities
Watering priorities
If you have access to water, prioritize supplying newly planted trees or rescuing trees with early signs of wilting. Limited water resources should be used to prioritize tree health rather than try to improve fruit size. The best time to water is in the early morning.
Water hauling
Water hauling
Is it an option to purchase water from a water hauling company? I don’t want to get your hopes up if it is unavailable due to high demand and it may require a holding tank and delivery infrastructure. I just wanted to throw this idea out there to discuss in case somebody is wondering.
As a very rough calculation, if you wanted to water a row area of 3 ft x 1000 ft (3000 sq ft), every 1-inch depth of water would require about 1,869 gallons (3000 sq ft x 1 inch x 0.623 gallons/sq ft/inch). At prices starting around $125 for 1000 gallons, it would cost around $233 for 1 inch water depth on the 3000 sq ft area. The actual area covered will depend on your water delivery method. The watering would need to be repeated every 2 to 4 weeks during drought.
One inch of water will typically penetrate the soil to a depth of 6-12 inches depending on soil type. Verify that the 1-inch of water supplied reached at least 6 inches deep by digging a small cross section with a shovel at two hours after application. This strategy only makes sense to supply water to trees that are showing early signs of leaf wilting at the top of the canopy.
Mulching
As a very rough calculation, if you wanted to water a row area of 3 ft x 1000 ft (3000 sq ft), every 1-inch depth of water would require about 1,869 gallons (3000 sq ft x 1 inch x 0.623 gallons/sq ft/inch). At prices starting around $125 for 1000 gallons, it would cost around $233 for 1 inch water depth on the 3000 sq ft area. The actual area covered will depend on your water delivery method. The watering would need to be repeated every 2 to 4 weeks during drought.
One inch of water will typically penetrate the soil to a depth of 6-12 inches depending on soil type. Verify that the 1-inch of water supplied reached at least 6 inches deep by digging a small cross section with a shovel at two hours after application. This strategy only makes sense to supply water to trees that are showing early signs of leaf wilting at the top of the canopy.
Mulching
Organic mulch can help to retain soil moisture but if the soil doesn’t have moisture when the mulch is applied, the mulch will have little effect.
Summer pruning
Summer pruning
Summer pruning is a complicated decision that may have tradeoffs. An article by Cornell states that summer pruning or hedging can reduce leaf area during drought. Removing young, exposed leaves can reduce transpiration and reduce water stress. Summer pruning is unlikely to improve fruit growth but may help with tree water status. However, I suspect that the summer pruning strategy is only helpful in trees that are not yet wilting. Pruning forces the trees to expend energy to mend wounds and that can be an additional stress to an already stressed tree.
Fruit removal
Fruit removal
Research shows that tree water stress is influenced by crop load. For example, heavy fruit thinning of peaches can improve the water status of the tree to protect tree health. As a subjective observation, trees carrying less crop load this year appear less water stressed (Figure 2).
If you are currently hand thinning trees that have healthy leaves, remove more fruit to help increase the size of the remaining fruit. In situations of high drought stress and no access to water, consider removing fruit to mitigate the water stress on long-term tree health. However, if leaf wilting has already occurred, removing the fruit is unlikely to help.
Figure 2. Side by side trees of Honeycrisp with trees in their 'on' year on the left and the 'off' year on the right. The water stress seemed more severe where trees were carrying a crop.
Leaf tissue sampling
Leaf samples can be taken anytime after terminal bud set. If we were to get a heavy rain that causes regrowth, wait again for the shoots to stop growing.
Soil sampling
Soil sampling
Wait to take soil samples because the soil is too dry. Typically, early August is the best time to sample but if the soil is unusually dry then it can be difficult to extract the full 6” sample depth. You’ll get a better sample if you wait for a rain (>10 mm) to moisten the topsoil.
References:
Additional Considerations
- Contact crop insurance, and take photos and records. Take photos of which tree rows and orchard sections are wilting so that if there are issues in the future you can relate it back to this drought incident. If you take a photo with your phone there is a GPS tag marking the approximate location.
- Be careful with any equipment capable of causing sparks and have a fire extinguisher ready when operating equipment just in case.
- Apple maggot flies are emerging from the dry ground and are flying, according to our trap captures. Continue to spray for apple maggot as you normally would. Poor apple maggot control in one year can lead to resident populations of pupae in the orchard soil and high pressure for the following four years.
- Be prepared for flash floods in the event of the next heavy rain. Inspect drainage.
- The Nova Scotia Federation of Agriculture has created a drought webpage with resources available here: https://nsfa-fane.ca/drought/
- Please reach out to each other and stay connected to friends, family, and other important supports. Whenever you can find the time, I hope you enjoy a simple pleasure like a cold treat and recognize your hard work because I sure do. This is not to underplay the situation but to encourage you to take moments to recoup.
- Please know that the folks at Perennia are considering how best we can support you now and in the future. We are open to your suggestions.
References:
- Girona, J., Mata, M., Campo, J.d. et al. Apple trees’ behavior to a single-season megadrought stress. Irrig Sci 43, 871–886 (2025). https://doi.org/10.1007/s00271-025-01017-w
- Goldhamer, D.A. 2003. Managing irrigation in fruit and nut trees during drought. https://www.lawr.ucdavis.edu/managing-irrigation-fruit-and-nut-trees-during-drought
- Lackso, A.N. Robinson, T.L. Gonzalez, L. Miranda Sazo, M. 2022. Practical implications of early and mid summer water stress on tree growth, cropping and physiology. https://rvpadmin.cce.cornell.edu/uploads/doc_1082.pdf
- OMAFRA. 2024. https://www.ontario.ca/page/weather-risks-strategies-mitigate-risk-insufficient-moisture
- Xu, H.; Ediger, D. Rootstocks with Different Vigor Influenced Scion–Water Relations and Stress Responses in AmbrosiaTM Apple Trees (Malus Domestica var. Ambrosia). Plants 2021, 10, 614. https://doi.org/10.3390/plants10040614
