How has climate affected tart cherry tree phenology and yield in the past?
A. Freeze/cold injury to flower buds
B. Number of wet days and length of bloom (pollination)
C. Total precipitation during latter stages of previous growing season (+)
D. Leaf spot disease pressure previous growing season (-)
A. Freeze/cold injury to flower buds
The most important climate-related factor impacting tart cherry yield and production are spring freeze events. This was clearly stated and described by tart cherry growers in meetings between the growers and researchers that focused on major weather/climate variables that might influence crop yield. Early spring freeze events, preceded by warm temperatures that bring over-wintering crops out of dormancy were clearly identified as the number one issue.
As over-wintering crops come out of dormancy in the early spring, they quickly loose their resistance to cold temperatures, and the potential risk of cold injury increases rapidly. Using a derived phenological growth curves, observed minimum temperatures and cold injury observations, Pileus researchers developed a set of regressions to estimate winter injury in terms of surviving viable buds. Based on this research, the frequency and magnitude of spring freeze events appears to have not changed significantly over time, but the period of vulnerability is longer compared to 10 or 20 years ago due to warmer temperatures earlier in the spring season.
Please visit the Tart Cherry Phenology and Yield Tool to see the model results for the percent of viable buds left after cold injury for locations throughout Michigan and surrounding areas.
B. Number of wet days and length of bloom (pollination)
Wet days are less favorable for the rate of pollination during the flower/pollination stage, and subsequent yields tend to be lower. This negative correlation between precipitation, pollination, and yield was suggested by our stakeholder partners and has been identified in our research and previous studies, primarily due to unfavorable flight conditions for bees and the relatively poor pollination that results.
C. Total precipitation during latter stages of previous growing season (+)
On the other hand, a positive correlation has been found between precipitation near the end of the preceding growing season with yields the following year. While this new finding is still being investigated, the research suggests that greater total precipitation during a 30-day period prior to the first killing freeze of the fall season in the preceding growing season is correlated with either a greater number of potential buds the following season or a higher winter survival rate of those buds. Note that this mechanism has been identified by previous researchers in associating yield reductions with the presence of foliar diseases during the preceding season
Also, cloudiness tends to be associated with relatively warmer nighttime temperatures and cooler daytime temperatures. Hot and windy weather before harvest may lead to problems with fruit quality, especially soft fruit. This is difficult to pursue due to the lack of available wind data, but quality problems associated with the 2006 crop are an example of this phenomenon.
D. Leaf spot disease pressure previous growing season (-)
Many tart cherry foliar diseases are strongly associated with certain weather/climate conditions and may result in significant reductions in yield. We investigated the role of climate on the development and risk of a major foliar disease of tart cherry, cherry leaf spot (Coccomyces hiemalis) on crop yield. Fungicides must be applied during wet growing season conditions to prevent infection and spread of this disease at a significant cost to the grower. We used a an existing weather-driven algorithm for this disease developed by Dr. Alan Jones of Michigan State University that has been used operationally by the industry for disease management for more than 10 years in the Great Lakes region. We obtained a series of observed leaf spot disease incidence and severity data for an untreated orchard block near Traverse City, MI from 1986-2000 (data were provided by Dr. George Sundin of Michigan State University). The risk of leaf spot disease was simulated using hourly weather data from Traverse City, Mi for the same time frame. Overall results of the comparison were poor, with the algorithm missing many observed infestations and vice versa. Dr. Sundin indicated in subsequent consultation that the results may be related to the differences between orchards which are never treated (and have a much higher level of fungal innoculum present) and those which are treated each year. We are attempting to obtain a suitably long disease spray record from a commercial grower and setting to investigate this aspect.