It isn’t just the little guys who can take a bite out of your fruit yield. Orchard growers are attuned to the lifecycles of the insects (aphids, leafhoppers, codling moths, apple maggots, mites, stink bugs, apple tree borers and others) which cause harm to trees or fruit. The myriad microbes which cause common diseases such as black rot, crown rot, apple scab, sooty blotch, flyspeck and fire blight are targeted each season with increasing precision. But the bigger guys – birds, voles, deer, elk and bear – can also cause damage. While integrated pest management (IPM) is often used for the small, destructive pests, it can be utilized for wildlife too.
James DeDecker, Michigan State University Extension specialist, explored the topic of wildlife IPM, with a focus on fruit growers, during the 2022 Michigan Ag Ideas to Grow With Conference. Wildlife IPM is a complex topic which involves high economic stakes for both the farmers whose crops are damaged and other stakeholders, such as hunters and eco-tourists (and the industries which support them). Add in state and federal regulations on species protection, and the North American model of conservation – which is based on preservation and protection – and practicing wildlife IPM on the farm isn’t a simple task.
It’s a necessary one, however, with “yield and quality loss associated with wildlife damage on the farm” causing economic harm to fruit growers across the nation, DeDecker said.
Those economic damages are difficult to quantify, though. The loss which farmers perceive can vary greatly from the actual economic value of the loss, and data on crop loss specific to wildlife damage is not readily available. Tree fruit growers in Michigan reported songbirds as a primary wildlife concern. Voles, deer and birds such as gulls and crows also do damage, as can bears, mice and porcupines. Whether they damage the trees or the fruit directly, tackling these pests requires IPM.
“Usually IPM is in discussion of kind of more traditional pest complexes: insects, diseases, weeds,” DeDecker said. “The concepts of IPM are definitely applicable, and in some ways maybe even more important, to addressing wildlife damage specifically.”
That’s because the IPM approach takes into consideration the cost benefits of pest control and focuses on managing risks such as the effects of control on non-targeted species, environmental concerns, the value of the pest species in the overall ecosystem and maximizing control benefits. IPM involves monitoring pest levels, collecting data, focusing on prevention, establishing a damage threshold for action and using multiple tactics to deter pest activity. Chemical controls – which typically aren’t as cost-effective or productive for wildlife control – are usually a last resort in IPM.
Separate from IPM, the wildlife damage management approach considers the interaction of humans, wildlife and the environment and attempts to balance these components. Combined with the strategies of IPM, approaching wildlife damage in the orchard through the lens of a complex economic-human-environmental interaction requires focusing on many factors.
Assessing when and where the damage occurs is crucial. What is the crop being damaged? What part of the crop is damaged? When in the season is this occurring? What is the surrounding habitat? Does the damage happen during the day or at night?
Properly identifying the pest is key. Looking for tracks, scat, the time of day the damage occurs, the point in the growing season at which the damage occurs and what the damage looks like can differentiate between similar damage done by different pests.
Habitat modification, through purposeful planting of trap crops, buffer crops or forest management, could divert the pest from targeting the orchard and instead provide preferred food sources. A buffer crop or trap crap can also add pollinator habitat, enhance the environment by taking marginal lands out of crop production (which are probably not cost-effective anyhow) and keep wildlife out of the cash crop.
There are studies showing that wildlife have cultivar preferences. In apples, deer have preferred Ligol to other varieties such as Ida Red or Golden Delicious when all were equally available. But whether this preference would matter if Ida Reds were exclusively planted in an effort to deter deer isn’t known. The nutritional content (protein, carbohydrates or specific mineral contents) could also play a role in attracting or deterring wildlife feeding. Knowing why certain cultivars are targeted could provide growers with options to reduce loss. DeDecker thinks there’s a lot of opportunity in this area for further research.
Population control methods, such as hunting, can play a significant role in maintaining balance between wildlife and crop damage. In many areas, the number of hunting permits issued has decreased in recent years – and could increase the amount of wildlife damage happening on farms.
Predators are a biological population control method, and having a balance between prey and predators can reduce wildlife damage to crops. Whether introducing prey species back into their historic habitats or maintaining predator habitat to prevent loss, keeping predator/prey populations in balance is a pest control technique.
Kestrel nesting boxes have been shown to decrease the number of birds which cause fruit damage in orchards. The kestrels will kill some of the pest birds and scare others away. Kestrels can also reduce rodent populations. Installing and maintaining the nesting boxes for the migratory kestrels is a small expense in money and labor and has been shown to prevent significant crop damage.
Scare tactics such as predator effigies, water guns, noise machines, lights, air dancers and other novelties can be effective, but habituation does occur. Altering the timing of events, regularly moving the location of these systems or varying their intensity can all maximize effectiveness. Combining multiple tools provides the best defensive strategy.
Fencing is another tool to keep pests at bay. While perimeter exclusionary fencing is often the first approach, tree cages on vulnerable young trees or less extensive fencing options may do the trick, being cost-effective and eliminating a majority of pest damage.
“How bad is our problem? How much efficacy do we need? What does our budget look like? How much labor and time do we have to dedicate to maintenance?” are the questions to ask before deciding on a fencing option, DeDecker said. “Not every farm needs a 10-foot exclusion fence. You may be able to get by with something less expensive or with a lower lifespan if it’s going to meet your needs.”
There are repellents labeled for tree fruit use. Methyl anthranilate is an irritant that acts upon contact, affects all bird species and birds do not habituate to it. It is applied via fogging or spraying. Re-application is often needed. Effectiveness depend upon many factors, including weather, level of pest population, alternate food sources and the use of other control measures in conjunction with repellants.
While wildlife IPM follows the same principles as IPM for insects and microbes, it looks different. Wildlife is more visible, and the animals causing damage also provide benefits to humans and are a notable part of the landscape. Their habits and preferences are dependent on many factors – alternative food sources, habitat loss, predator populations, human interactions – that together form complex interactions and involve many stakeholders.
The loss wildlife causes to orchards isn’t insignificant, and focusing on reducing these pest pressures through the use of IPM can bring economic benefits to farmers without doing overall harm to the rest of the equation. Using IPM can mitigate the real concerns of wildlife damage.