Consumers are demanding food grown without the use of chemical sprays. Pollinators are declining, with pesticide use being one culprit. Climate changes are causing changes in pest pressures while altering precipitation and temperature patterns. By necessity, tree fruit growers are finding new ways to adapt to the conditions – social, cultural and environmental – which are changing the way the orchard grows.
A recently released study out of Europe, “Perennial Flower Strips – A Tool for Improving Pest Control in Fruit Orchards,” focuses on the use of perennial flower strips planted between orchard rows as a means of naturally enhancing pest control and reducing insect and disease issues in tree fruit. According to the study, the flower strips not only promote habitat for beneficial insects, providing food and shelter, but also promote biodiversity of soil species by expanding habitat for spiders, ground beetles and other soil-dwelling insect predators.
These perennial strips, containing a combination of several dozen flowers, herbs and grasses, provide a variety of flowering plants all season long, reduce the amount of mowing required in the orchard and provide added sources of nectar for pollinator activity. By decreasing pest pressures and increasing pollination, organic orchards could potentially see increased yields.
The study referenced data from other research, citing evidence that aphid pressure was reduced in several previous flower strip trials. According to data from the European EcoOrchard Project, orchards with flower strips between rows had 15 percent less damage from the rosy apple aphid than did control orchards. There were also more aphid enemies present on the flowers, fruits and shoots than in the control. Diversely sown flower strips were more effective than a mowed and mulched control, or a spontaneous flower strip, in attracting beneficial orchard insects.
Weed control in the flower strips is via mowing, and three or four cuttings per year are recommended to keep the balance between habitat and weed control. Removing the plant residue if it becomes too thick is recommended. The perennial plants should be cut high enough to allow regrowth. Cutting is timed to coordinate with the growing periods of the orchard crops as well as to maintain the health of the flower strip – flowers need to be in bloom during the time of the tree fruit bloom to enhance pollination.
Flower strips should include early flowering plants to attract early season beneficials and keep early pest populations low. Continual flower bloom, by incorporating a variety of species, is needed to ensure a steady food source for desired insect populations. Any plant known to be an attractant for pest species shouldn’t be utilized. Selecting a seed mixture compatible with orchard soil conditions which provides nectar for both short- and long-tongued pollinators is another consideration.
The flower strips, situated in the drive alleys, don’t compete with the orchard trees for nutrients. Properly planted and maintained, the strips should not increase weed pressures. If pesticides or herbicides are used in the orchard, targeted products not harmful to beneficial insects should be used. Cutting the flower strips down prior to chemical applications is recommended to prevent unintended harm to the habitat and the beneficial bugs.
Other complementary measures to reduce orchard pest pressures naturally include bat boxes, wild bee nesting boxes, flower strips at orchard edges and orchard hedgerows.
As climate change impacts continue, commercial growers will have to contend with many changes. The growing degree days (GDD), on average, have increased each March since 2012 at the Penn State Fruit Research and Extension Center, resulting in early blooming of fruit trees. In 2016, the accumulation of GDD was the highest in 20 years of collecting data, said Robert Crassweller, Ph.D., professor of horticulture at Penn State.
There have been more severe weather extremes, and temperate zones have become milder. Changes in winter temperatures impact chill units, either bringing trees out of dormancy quickly or not allowing adequate chilling. Either of these may require growers to select different cultivars or utilize techniques to force chill units, such as the use of dormancy-breaking chemicals.
The Northeast, which has seen a 71 percent increase in the amount of precipitation falling during the top one percent of precipitation events since 1958, anticipates that hail and wind, along with other volatile events, will increase, impacting orchards. Increasing carbon dioxide in the atmosphere will increase photosynthesis, perhaps dramatically, resulting in more fruiting as well as more vegetative growth in orchard trees. Weed populations are also expected to increase along with rising rainfall and temperatures.
Sunburn on fruit, increased transpiration, premature ripening and decreased shelf life are some concerns as the climate heats up. Water stress – despite intense rainfall events – will become more common with increased summer temperatures and periods of drought.
“With a changing climate, there will be changes in pest populations,” Crassweller said. “Insects respond primarily to temperature. They also respond to day length and food quality.”
Increased pest generations per season, the movement of pests into new regions as temperatures change and earlier emergence means combating orchard pests will become increasingly challenging. It’s expected that disease pressure will increase as well. Powdery mildew and scab pathogens will not be killed by the cold as temperatures rise. Insects and disease pathogens will experience an enhanced genetic diversity, with genetic recombination causing the decreased efficacy of standard chemical controls.
Cultivar selection will change, with the need for different bloom times to avoid new frost patterns. Site selection will become even more important, as marginal sites will no longer be productive. Protecting trees from extreme winter events will require more diligence, including changing pruning times to protect bark from splitting events. Summer pruning will probably increase, while dormant pruning will decrease as the trees show different growth patterns.
High tunnels, shade cloths and automated irrigation systems are all tools which will become more prevalent in orchards as growers contend with erratic weather patterns and the resulting challenges. Overhead irrigation, although expensive, can enhance fruit coloring while preventing plant stress from low moisture levels, and can provide frost protection.
Climate change will impact all sectors of agriculture. As growing conditions continue to change, new approaches are needed, both to mitigate the degree of climate damage and to cope with the results of the changes.