Products and Techniques for Controlling Pests on Woody Plants

Insects and mites are part and parcel of the natural landscape, and unfortunately for you and your plant life, they are voracious herbivores, meaning that their feeding habits affect the aesthetic beauty of your plants, as well as severely weakening and damaging their natural structure.

Luckily, whilst pests can be difficult to manage, by differentiating with seasonality and treatment between species of both pest and plant, some basic know-how and a few utilities, there’s much you can do to help facilitate a long and healthy life for your woodland landscape.

Due to the diversity and vastness of their classifications, woody plants are a common feature in a multitude of global ecosystems, and a popular plant to grow recreationally. Due to their equal prevalence and complexity, we’ve compiled a comprehensive list of the most common woody plant pests you have to watch out for, and a few tips and tricks of the trade to protect from a potential attack.

What are Woody Plants?

Simply put, woody plants are specified by their hard stems, with wood as the primary structural component which helps them survive above ground in the winter months. Internally, there are a few components that constitute the biological makeup of a wood plant; if you were to cut out a cross section of a trunk, or twig, you would encounter the outer and inner layers of bark, a single layer of cells called the cambium and then the wood. Bark, the outer layer, is constantly regenerating, protecting the wood on the inside, of which, a new layer is produced every year by the cambium, creating the growth ring. As the bark regenerates from the inside outwards, new bark pushing through the old to the outside, so do the new layers of wood, marking the inside rings as the oldest, and those nearer to the outside, the youngest. Analysing the rings can not only express the age of the tree but also present some information about the growth conditions for the woody plant: the wider the ring, the better the conditions were.

Although trees are the most obvious type of woody plant that springs to mind, under that umbrella classification are a number of different plant families and sub-specifications, ranging from trees to shrubs and even some, though not all, vines - all with varying characteristics between each individual plant.

But, if all woody plants share the same perennial stems, then how do we differentiate between them? Technically, whilst there might be an acceptance that certain species are trees and certain species are shrubs, which we would be able to distinguish on sight, there’s no real scientific definition that exists to separate the two. There is, however, a general rule of thumb to stratify them; generally speaking, a tree can be defined by the proportions of its trunk, one erect stem of 3 inches, or above, in diameter at a height of 4 ½ feet above the ground, and a height of 13 feet in maturity - although young trees and trees with multiple stems may miss out on this criteria. On the other hand, a shrub can be defined by several perennial stems, either erect or lying more perpendicular to the ground, with a height less than 13 feet.

Vines are the easiest to recognise, with stems that aren’t able to self-support, and therefore must lie along the ground or use other plants and objects as support.

Ladybug

How to Prevent Woody Plant Pests

Planting trees and other woody plants can be a valuable and rewarding process. However, anyone who has grown a woody plant in the past, or any plant for that matter, has, at some point, had to deal with the nuisance of pests. Unfortunately, there are a large number of potential threats to your trees and shrubs, from insects to animals, some more notorious than others.

Whilst there are some universal preventative measures necessary to ward off pests, we have detailed below some more specific methods of treatments tailored to individual pests and problems.

When cultivating woody plants, it is always important to:

  1. Remain aware: being vigilant and regularly maintaining your plants is imperative to spotting the calling cards of pests and trouble, quickly. Acting within a small window of time after the first attack can often completely save your plant from any lasting impact and future damage.
  2. Be careful to avoid drought and root damage, as these stressors can weaken your plant drastically and invite in insect infestation and disease. 

How to Protect Against Animal Pests

Animal pests are usually not as destructive as insect pests, although left unchecked they can still cause a fair amount of damage to your plants. Dependent on where your trees are situated, animal pests can range from deer to dogs, each with their own mode of impairment.

Deer

Although woody plants are not particularly a part of a deer’s diet, they will eat evergreen plants when other food is scarce, and like to browse on some deciduous trees and cedars. Deer are easily dissuaded by installing tree guards and light fencing. Similarly, larger animals like dogs can be an excellent deterrent for grazing deer, although they too can be problematic for your woody plants.

Dogs

Dogs tend to be more of an issue for shrubs than trees, as they often urinate on the smaller shrubs causing burning leaves, or attempt to dig them up. Similar to deer, putting up fencing or protections should mitigate the issue, although due to shrub’s stockier shape, it may be better to tack up free standing tree guard mesh, in order to preserve the shape of your plant.

Mice and Rabbits

Mice and rabbits can leave a similar destructive trail to deer, chewing the ends off of deciduous trees and shrubs and girdling the stems of trees and shrubs, chewing off the bark so the sap can't rise properly in the spring. Putting down repellent or shrubbery and tree fencing can minimise issues from these animals. Likewise, if mice are becoming a particular problem, laying down mouse traps may be a more efficient way of dealing with the infestation.

Caterpillar

How to Prevent Insect Pests

With the potential to cause serious damage to your woody plants, insects can be an insidious and troubling pest. Some pests target specific woody plants, however, the following is a roundup of the most common and most universal species.

Aphids

The most common of the insect pests, these fleshy-bodied green or yellow insects attack young shoots and the foliage of trees and shrubs, causing distortion and stunting growth. They infest the shoots and leaves of plants, leaving them blackened, blistered and sticky, and symptoms may continue even after the pests have left.

Although preventing aphids entirely from settling on your plant may be impossible, the best way to ensure they do little damage and don’t return is to remain vigilant and spray your plants with a stream of water from a hose pipe every two or three days to knock the aphids off. Similarly, using an organic aphid spray (made with either garlic or soapy water) will help to neutralise the already present threat, without damaging your plant.

Other tactics include planting an aphid discouraging companion plant, such as chives, onions or mint, alongside the plants you would like to protect, or releasing ladybirds directly into the aphid population.

Caterpillars

Equally as frequent as the aphid, caterpillars are voracious and will eat the leaves of most trees and shrubs. The larvae of butterflies and moths, caterpillars may start out as the smaller leaf miner, detailed below, or skeletonizer, until they are large enough to eat entire leaves.

Whilst birds and environmental conditions act as a natural control for caterpillars, the best human control is to manually pick them off or use a BTK (Bacillus thuringiensis var. kurstaki) spray.

Leaf Miner

As stated above leafminers are larvae, although not specifically moth and butterfly larvae, that feed on the inside of the leaf, causing blisters or tunnels which kill the tissue of the leaf. Leaf miners aren’t fussy and will affect most woody and garden plants. Noticeable by the browning or yellowing of the leaf as it decays, the best way to tackle leafminers is to regularly check your plants and manually pick off, or squash, the larvae.

Slugs and Snails

Slugs and snails are a persistent pest, using their tongues to eat holes in the leaves, stems and flowers of other plants, and are especially fond of seedlings and other soft growth. Unfortunately, the damage is not just limited to ground level, and as excellent climbers, they can attack your plant at height.

Whilst easily spotted by their telltale trail, the ubiquitousness of snails and slugs means that some damage must be tolerated, however, there are a few measures you can take to prevent slugs and snails from damaging your plants. 

  • Encourage predators such as toads and hedgehogs
  • Place traps, scooped-out half orange or melon skins, cut side down near vulnerable plants, or jars part-filled with beer and sunk into the soil. Check and empty these regularly
  • Make barriers of moisture absorbent materials, like tapes or matting impregnated with copper salts, around plants
  • On damp evenings or mornings, manually pick out the slugs and snails from your garden, and dispose of them in a well-distanced waste patch

If you’ve followed our steps above and are still worried about the health of your woody plants, it is possible they might have one of the multitudes of tree diseases detailed in our previous blog article.

For more information on products which can help you keep your plants and trees free from pests, check out our extensive range of products in our landscaping supplies section.