These are pear and cherry slugs, and as you can see, they eat the leaves on pear and cherry trees.
The first question to ask yourself when you see these creepy looking slugs (as with all pests and diseases on our fruit trees) is, how much damage are they really doing?
One of the advantages of keeping a close eye on your trees is that you will often notice problems as soon as they occur, and can then take simple action, like squashing the slugs between a folded leaf.
In a normal season, this particular pest will go through at least two life cycles, so the more of them you squash as soon as you see them, the more you interfere with their natural life cycle and can prevent numbers building up.
Fruit trees can actually tolerate quite a bit of damage without losing function or growth – our rule of thumb with pear and cherry slug is that if a tree has lost more than 30% of its leaves, that will be our trigger to treat them, and in all our years of growing, we’ve closely monitored every year, and never had to take action against them.
Usually what we find is that if we are patient, a predator insect will come along and do our work for us, leaving behind a dry, parasitised slug as you can see on the leaf below.
So pear and cherry slug is a great example of learning how to watch our trees and learn what’s really going on, rather than assuming that if there’s a bug, there’s a problem!
If you want to find out more about the life cycle of the pear and cherry slug, and how to treat and prevent them, check out “What’s Bugging My Fruit?“.
Buds are starting to swell and seeds are beginning to germinate…a call to action in the heritage fruit tree nursery. Merv has been busy preparing the soil in the new nursery patch. Katie has been busy selling the last of the beautiful fruit trees that we grew before they come out of their winter sleep and need to be planted in the ground properly again. But now that our saved apple, quince, pear and peach seeds are starting to shoot, its all hands on deck.
This week we planted our cherry rootstock and acquired some compact apple rootstock varieties to experiment with. Along with grafting the cherries in September and budding the apples we’re hoping to experiment with creating a ‘stool bed’. Katie and I haven’t ever done a stool bed so we’re excited to learn this technique from Merv. A stool bed (from my limited understanding) is a way of trench layering a ‘mother plant’ in order to grow multiple root stock trees from a small number of ‘mothers’. This is important for cherry rootstock, which don’t grow readily from seed, and special varieties of rootstock, which you want to multiply true to type.
The plum cuttings are starting to ‘heel up’ (grow a heel/scab over them from which the roots will sprout) which means we’ll plant them out soon . The apple, peach and quince seeds are sprouting so we’ve begun to plant them out in rows. These we will grow up over summer and ‘bud’ in February with a number of different varieties for sale the following year.
We have also been cutting back the trees we budded last February, to the bud union. These trees (see pic) with different colored pipe cleaners are the plum rootstock we budded multiple varieties of plum and apricot onto. Another experiment, which so far seems to be going well…as long as we can keep track of which branch has which variety budded onto it!!
Soon it will be time to sow our green manure crop in the resting nursery patches and sow some more citrus seed in the hot house (yet another experiment). Most of the rootstock we grow, except for our experiments with cherries, citrus and small apple rootstock, we have grown ourselves. We either collect seed or take cuttings to create them, and like Merv always marvels, “it doesn’t cost you anything”! There is a lot of time and care that then goes into turning that seedling into a good fruiting tree, but Merv’s right, it doesn’t cost you anything to give it a go!
Have you heard of the “Tree of 40 Fruit” project? It’s an art project created by American artist Sam Van Aken, where he creates beautiful mega-multigrafted trees, for example a peach tree with more than 40 different varieties of peach and nectarine, for their aesthetic value. They are absolutely stunning (we can’t show you one here because we didn’t get permission to use his photos, but here’s the link to his website if you want to have a look).
Instead, here’s a photo of a multigraft tree from a recent garden consultation we did, showing the different coloured leaves of the two different varieties on the same tree.
Not as spectacular as having 40 different varieties putting on their various autumn colours, but you get the idea! Here’s another one of a multigrafted cherry showing the different coloured blossoms in spring (this photo is from Wikimedia Commons).
A multigraft is, as the name suggests, a tree that has multiple varieties grafted onto a single rootstock. So for example an apple tree with Pink Lady, Granny Smith and Fuji all on the same tree (which coincidentally, is one of the trees we have for sale this year). Multigrafts are always the same type of fruit (e.g., all apples), whereas a tree with different types of fruit on the same rootstock – say a plum, an apricot and a peach – is called a “fruit salad” tree and is quite a different animal.
The idea of a many-grafted fruit tree is not new – there are a couple of very famous examples around the world, such as this ‘family tree’ that has been grown by Paul Barnett in West Sussex, England, on which he’s grafted 250 different apple varieties (photo from the Daily Mail).
Multigrafting has been used not only as a repository of genetic material of lots of different varieties, but also as a mark of the skill of the master grafter, proving not only their grafting skills, but also their superior pruning and management skills in keeping each separate variety alive and growing, and keeping the whole tree in balance.
Which brings us neatly to the question of, should you bother?, because while multigrafts have lots of advantages, they are almost always a harder tree to manage in the garden, if you’re trying to keep the different varieties in balance with each other, and they can be daunting for a new gardener in particular.
Sometimes keeping the tree in balance doesn’t matter, for example if you’ve grafted a piece of wood of the same fruit but a different variety to act as a cross-polliniser on to your tree because it wasn’t setting a good crop of fruit. In trees like that, you’re not aiming to grow both varieties in equal proportion.
But if you’ve planted a multigraft because (for example) you have limited space but still want roughly equal amounts of an early and a late apple, then for sure it matters – there’s not a lot of point of having a multigraft Gala and Pink Lady if you get 10 boxes of Gala early in the season (when you already have plenty of plums and peaches), and then have to wait until the end of the season when you pick 2 Pink Ladys from one weakling branch!
So, how do you manage them?
The trick is to pay a lot of attention to your pruning in the first few years of the tree’s life (which we call the ‘establishment phase’). Monitor closely how well the different varieties are growing, and you may need to prune the more dominant variety back quite hard at the beginning to let the weaker side get equally established.
Of course, one of the pruning principles is that the harder you prune, the harder your tree is likely to grow, so the tree’s most likely response to hard pruning is that the dominant side will respond with even more gusto. You can minimse this bounce-back effect by pruning the tree in late summer, rather than winter.
Another trick that might help if you don’t want to continually prune is to weigh the dominant limbs down more horizontally (e.g., with a brick) so the height of the growth tip is lower than the height of the weaker side of the tree. This physical height confers an advantage onto the weaker side, and the tree is more likely to direct more energy and resources to the weaker (higher tip) limb, allowing it to catch up.
So is it worth it? Absolutely! If you’re interested in gardening and growing fruit, all of this is tremendous fun, both the grafting and pruning management. It can be a quick way to experience the age-old relationship between farmer and nature (“who’s in charge here?”), that often starts as a battle for new growers but can end with a much deeper understanding and respect for how nature works. And remember, the tussle goes on mostly in your mind – the tree will just keep being a tree.