No matter what is growing in your orchard – apples, stone fruit, nuts or berries – protecting that crop from pests is always a concern. The use of integrated pest management (IPM) strategies has growers thinking twice about blindly reaching for orchard sprays without first considering the life cycle of the pests and disease agents they are actively targeting, as well as the tolerance threshold for a given pest.
But IPM goes beyond spraying only when warranted and at the precise time for targeted pests. It also includes management techniques to reduce the risk of pest problems.
One such strategy is to change the way the orchard looks. Giving the orchard a makeover may not sound like a pest control approach, but it can be an effective tool for mitigating pest pressures.
Mowing and Pruning Impact
Spotted wing drosophila (SWD) has become a major concern to growers of all types of fruit. Researchers at the Northwest Michigan Horticultural Research Center have been studying how changes in the orchard environment can influence the damage done by SWD in tart cherry orchards.
Commercial tart cherry growers in Michigan have adopted the standard practices of mowing only twice per season – near Memorial Day and just prior to harvest – and of pruning trees only once every two to three years, removing just a few large branches. In 2017, orchard blocks not treated with any sprays were evaluated to determine whether more intensive pruning and mowing practices would impact SWD pressures. The pest pressures for SWD were very high in Michigan in 2017.
The research was conducted on no-spray blocks of orchard at the Research Center. Annual pruning was shown to reduce SWD populations over unpruned blocks. Mowing once every two weeks reduced SWD pest pressures too, and was beneficial in both pruned and unpruned blocks.
In order to better align beneficial mowing and pruning practices with current orchard management techniques, 2018 research was done to further compare winter pruning practices with various mowing techniques at four commercial Michigan tart cherry orchards.
Two or three sprays of pyrethroid or organophosphate insecticide were applied every seven to 10 days, starting when fruit turned yellow and through harvest, as per industry practices, to both orchard blocks that had and had not been pruned. Mowing was either done twice per year, or once every two weeks across both pruning treatments, and replicated on each of the four farms. Each treatment included a block of at least 150 trees per farm.
While the researchers did not see any statistical differences between any of the four management methods when used in combination with the standard commercial spray program, SWD pressures in 2018 were much lower in general as indicated by trap counts throughout the season than in 2017, and may have impacted results. If SWD pressures were higher during the 2018 season, the researchers hypothesized that differences would have been seen between pruning and mowing management strategies. In situations where a standard SWD spray program is in place, management changes may have less of an impact than when sprays are not used as a tool, particularly when SWD pressures are low, but further study needs to be done.
“What is the right soil biology?” Michael Phillips, author and holistic orchardist, asked – an important question when talking about orchard health. Phillips, whose Lost Nation Orchard is in New Hampshire, is an in-demand presenter at conferences, including the Practical Farmers of Iowa 2019 Winter Conference.
“When you have a diversity of plants, you will have many, many species of mycorrhizal fungi,” Phillips said. “It’s a really important piece of how the plants get their nutrients.”
Extreme diversity on the orchard floor provides habitat for beneficial insects. These different plants also network via their roots and the mycorrhizal fungi network. Fungi help plants to resist disease by tapping into a vast nutrient network.
The zone underneath the tree, to a foot or so beyond the drip line, is the area where the mycorrhizal fungi will thrive and help promote tree growth, Phillips explained. Organic matter is what feeds the fungi, and providing it to this zone is key.
“It’s on the edge of the forest where the fungal biomass is about 10 times greater than the bacterial biomass,” Phillips said. “That’s what I want to emulate in the soils where I plant fruit trees. You bring the soil ecosystem found there underneath your fruit trees.”
This environment is a lot different than that found in an herbicide strip under tree rows.
To help build the environment where mycorrhizal fungi can thrive, Phillips uses practices such as adding fungal compost to the tree rows in autumn, when feeder root growth begins again and nutrients essential for spring growth are taken up from the soil by the trees.
“Compost is not just about returning nutrients. It’s actually more about increasing the diversity of organisms in your soil,” Phillips stated. Mushrooms on the orchard floor are a good indicator of fungal activity, and a habitat which provides the soil biology fruit trees need to thrive.
Beneficial insects require some debris to overwinter. A diverse, rough understory in the tree row not only provides habitat for them, but also for spiders that can help to intercept insect pests on their way to pupate in orchard soils. Managed cover cropping, using multi-species mixes, is another method of building in-row soil health and providing the optimal habitat for biologically activated soil and tree health.
A plant’s phenolic compounds, derived from plant metabolism, act as the plant’s immune system. Plants can protect themselves from disease if the biology needed for optimal plant metabolism is in place in the orchard.
Phillips’s three acres of fruit trees, from which he sells fruit directly to those in his community, are admittedly not a vast commercial operation. While large orchard operations may not be able to adapt all of his practices to scale, the concept of soil biology promoting soil health, and the impact on fruit tree health and productivity, doesn’t change based on the scale of the operation. Building soil health has no size limit. Incorporating practices which enhance an orchard’s ability to ward off pests and diseases and optimize the trees’ own protective measures is a goal that all orchardists can achieve.
By taking the practices of IPM one step further than monitoring pest pressures and spraying accordingly, management techniques can help to create an orchard environment which works naturally to decrease the susceptibility to pests. An orchard makeover might just be the next step in combating pest and disease concerns, and optimizing productivity.