Though pruning is always called for…
Is the enemy a man or a mouse. Or more to the point is he a mouse or a vole, or a mole, or a shrew. The question may seem academic, and perhaps so to the casual backyard wanderer. But to those with an orchard the distinction is crucial.
Quite possibly the greatest scourge of the apple tree in an inch long package.
This is a large beetle whose larvae do considerable damage to fruit trees by eating and tunneling in the trunk. The damage often leads to major tree decline or death.
- Physiology : Saperda candida belongs to the cerambycid family, the broad group that encompasses the longhorned beetles. The “horns” referred to are the dramatically long antennae, often measuring as long as the body length. This adult insect is an average of 1 inch long from the base of the abdomen to the tip of the head, and may double when including those antennae. It has a brown or grayish dorsal half accented by two white lines running longitudinal the full length. The ventral portion (beneath) is a silvery white. Fine hairs cover the entire body. Antennae and legs are gray. It is an attractive creature, and quite easily spotted when in the open. When handled it becomes angry and animated with a clearly audible hissing. The mandibles are quite powerful (I had one clamped on to my fingernail and dangling, whose removal took some firm pulling). Larvae : are variable in size according to their age, but at near maturity can be as long as the adult beetle. These are a tan to white segmented creature, with a row of tiny darker dots running its length (respiratory units). The head is a deep brown and stands out from the worm like body. Jaws are sharp and black.
- Life Cycle : Early season activity depends on geographical location. The following dates are for the far northeastern areas of the US, such as Vermont and Maine.
- Adult beetle emerges in the first two weeks of June. Emergence holes are chewed through the bark and are more circular than oval, 3/16 to ¼ inch in diameter. They are often active in the foliage, feeding on leaves, twigs, and fruit. Mating occurs about a week later.
- Soon after mating, the female begins egg laying. Normally hiding during the daylight hours she can live for 40 days or longer. She chews a vertical slit in the bark of the host tree with her mandibles and lays an egg between the bark and xylem. Site of ovipositing is low on the trunk, often near the soil line. The beetle then glues the wound with a gluey substance she secretes. Egg laying can last into August.
- Eggs are 1/8 inch long and one third as wide. They are cream or white but turn brownish with age. Hatching occurs 2 to 3 weeks following laying.
- Larvae begin by feeding on tissue between the bark and sapwood. This damaging activity normally begins by September. They slowly chew deeper and deeper into the trunk in various directions. Younger larvae sometimes head lower, to beneath the soil level, but older individuals crawl higher. All activity of the larval stage is within the trunk. Their excrement is often visible as a rust/tan sawdust-like material, exuded from a hole and onto the bark.
- Larvae continue eating within the tree throughout the next growing season and growing larger. Some may remain for 4 years and do extensive damage.
- The larva begins pupation in its final year within the trunk. This occurs in late fall or early spring, with the adult emerging after one month in the pupal stage. The adult flies or crawls off to repeat the cycle.
Region and Hosts : This is primarily an insect of the Eastern US, but may occur in other areas. It is known in areas of Europe as well. Host trees include apple, pear, hawthorn, quince, amelanchier, mountain ash, cotoneaster.
Damage : Trees begin to suffer with the first bites of the larvae. The cambium is damaged along with the rest of the trees transport system. Trees with progressing damage will appear sickened, with yellowing or stunted foliage and low vigor. Suckering may occur beneath affected areas. Secondary problems include the onset of disease through wounded tissue. Advanced stages and repeated attack will lead to a brittle trunk structure, with younger trees breaking off completely. Older trees can often weather the onslaught reasonable well, but at the expense of longevity and health.
Prevention and Cure : Vigilance is important with this pest. Observation of your trees will result in success in dealing with this nuisance. These tips can help:
- Keep it clean. No grass, weeds or debris should obscure the trunk area of a 1 foot diameter. (Review the recommendations in the tree planting section on the website) The adult beetle is happy to have cover when she is laying eggs, so make the area unfriendly to her. Insects in the open are easy prey for our feathered friends. A clean area will also make it easy to spot damage on the trunk.
- Periodically look for damage or egg slits. The newly deposited egg or young larvae can easily be scraped to oblivion with the average fingernail. The real telltale sign of invasion, though is the fibrous tan exudation known as “frass”. This woody dust often spill out of the tree on its own, but sunken or discolored areas on the trunk can be gently cut open to reveal the mess.
- Go hunting. Probing ever deeper into the hole will eventually yields a speared larva. My weapon of choice is a malleable wire about 4 inches long. Bend the wire 1/16 of an inch from the tip and knick it with shears to create some barbs. This will allow the culprit to be pulled from its hiding place into the light of day. If the larva has made excess twists and turns, it may be necessary to do some serious surgery with a sharp knife to find him. Cutting into live cambium for certain is not a good thing, but will usually result in far less damage than will occur if the borer is left inside.
- Some folks elect to inject a pesticide into the hole. There are organically approved substances such as pyrethrum or spinosad that may have effect, but beetles by their very nature are a tough bunch.
- Preventives. – Coating the trunk with a whitewash may offer some protection. Although a latex paint is commonly used, a more natural approach is to make a slurry of clay and apply that. Some folks (like us) have even added thickening or abrasive agents like sand or spackle. If it is thick enough, it will deter them. There are a few problems with the method, though. First, trees do engage in some respiration through their bark and covering it too thickly can prevent this. Second, it will become more difficult to notice borer activity, such as sunken areas. Make sure you do a thorough search of the tree and destroy all larva before sealing. The good news is that frass will show up nicely when a new larva moves in. White washes have the added bonus of minimizing southwest injury (sunscald).
-Closing off the lower trunk with screening may kind of, maybe, lessen the chance of attack. The idea is to have in place a cylinder of screen about 2 inches from the trunk, buried below the soil level, and wrapped tight at the upper end. The portion that contacts trunk must be protected with a soft material like cloth or foam, and periodically checked for disease or borer damage. Physical barriers like this, and coatings as well, often only change the location of borer entry. Although it is easier to deal with eradicating it from a higher physical position, it will not usually keep the tree from being attacked. They will often lay eggs beneath the material where guards touch bark.
Again, persistence is key here. By checking the base of the tree several times a year and digging out the culprit as soon as he is discovered is the way to go. Many commercial orchards use a soil drench of insecticide which works systemically to kill borer larva, in addition to aerial sprays to combat adults. We do not support these methods due not only to organic regulations, but in terms of the health of the orchard and its inhabitants…like me.
1. Location, location, location. Very few trees will do well in wet muck, atop ledge (close to surface stone), or in a cold hollow. The ideal position is on a slight hillside so cool air can run past your planting- it must have an outflow. Hillside also means water drainage. Spring flooding is usually ok, but should drain by the time growth begins in earnest or root death will ensue. Drain tile or trenching can help with water issues, and clearing air outflow by taking down trees and such can remedy that issue. Extremely dense hardpan soils and shallow ledge, however, cannot be corrected without excavation or blasting. The good news is there is usually a good spot to be had in close proximity, the subterranean world is often just as varied as the world on top. Aspect (think compass direction) isn’t as important, unless you are trying to influence blossom timing (ie- delaying early bloomers) or heating (ie- ripening grapes). Despite all these words, we all have to deal with the land we have and do the best with what we’ve got.
2. Soils. Look up any species and its soil preferences and you’ll find it would like a nice bed of something like “sandy loam”, or “rich loam” or somesuch. So, if you are one of the 1% of folks on this planet with this underfoot, you are in perfect shape. For the rest of us, we will have to make due. Any, and I mean any, soil can be made to grow food. Whether the amending process makes practical sense is entirely up to you to decide.( Look deeper at soil improvement coaching in the Research section of the website. Most important is to find spots in your landscape that will require the least labor and cost, bearing in mind a diversity of soil types may simply mean finding the right species for each area.
3. Dig that hole. A good shovel is all you really need, but a mattock/grubbing hoe will make short work of heavy sods and stubborn tree roots. Loosen the soil, then shovel it. It will prove easier and will also break the debris up so you can use it for backfill. Make the hole big enough to accommodate roots without bending them, but don’t overdo it. An overly expansive hole means a soft and fluffy perimeter, which can lead to poor anchorage. You want the tree to anchor its roots in firm soil in the near future.
4. Ammendments. Here too you want not to overdo things. Compost (which does not mean uncomposted manures) is always a good start, especially on soils low in organic matter. Phosphorus in the planting hole is also important as it is important for root development, does not move as easily through the soil in topdressings, and normally takes time to be made available to plants. General fertilizers are ok in the hole but often not advantageous. Anything containing nitrogen should be used only in plantings made before mid-summer or winter injury from succulent growth is likely. Furthermore, most nitrogen sources will produce injury to roots with direct contact.
5. Check over the tree. After removing the tree from the bag, pot or wrapping, check for roots that are injured or are that were circling and distorted. Spring or earlier summer planted trees will deal with root pruning and general root manipulation (ie- tugging, unwrapping and root ball loosening) better than late season planting. In this case prune away dead or decaying roots, and allow for distorted roots to be directed once in the hole. Fall planted trees, however will be less stressed if left alone. These should have their root ball left intact and unpruned or manipulated if the root system appears healthy.
6. Set the tree. A few spades of soft backfill and some of the ammendments should go in the hole first, followed by the tree in question. Nestle the tree in and continue filling the hole with the loosened backfill, etc. , while making sure the roots have good soil contact by periodically tamping. When the hole is filled, give it a good long drink. A 3-5 foot tree would like a 5 gallon pail. After the water settles, stamp the soil down well. If you are in a dry area, or have very sandy soil, a slight depression will help collect more water on rainy days. Firming the soil makes sure that there is good soil to root contact, and prevents large air pockets from drying roots out.
7. Stake it. Trees on standard rootstocks usually only need the support for the first year or two. Metal stakes go in easiest, but can be 3 times the price of a good ol’ cedar, oak or locust post. Large diameter wood posts are also far more sturdy. Two posts and support wires are often used. (Run the rope or wire through a piece of garden hose where it touches the tree, or use fabric to prevent rubbing damage). We normally use a single post, but you should pound the post into the hole (for close proximity to the trunk). If you attempt the single post after planting you are likely to smash it into your nicely planted tree roots. With either method, the tree should be tied loosely enough to allow it to sway and develop some trunk strength.
8. Place your trunk guard. A tree without a guard on the trunk will become a rodent’s next meal. Conceivable anything a mouse or vole can’t chew through will fit the bill. Hardware cloth is high on the list for toughness and longevity, and although pricier than screen it is cheaper in the long run. Metal window screen is fine, but some rust quickly and its can be absorbed into the growing trunk if it is wrapped tightly. Mesh plastic guards work ok, but plastics photodegrade eventually, and are less likely to be available at the local store. We do not advise the use of the common white spiral guards for several reasons. Firstly, they will quickly shatter under the influence of weather or string trimmer. Secondly, they take special skill to get the guard tight enough to keep critters out- which incidentally is their purpose. Finally, there have been a fair amount of reports of (and our experience with) trunk glazing, winter damage, and burr knots. Ideally a guard would be placed as a closed cylinder around the trunk without touching. It’ll go from soil level (or a bit deeper) and upward as high as it will go. A foot or so is often enough to deter voles and mice, but the higher the better, especially in colder areas since these little guys sometimes run atop the snow and nibble from the new heights. That said, most rodents will crawl lower, at the soil/snow interface and chew below.
9. Further protection. Those of you who live in areas with deer or moose pressure will need to protect new trees from heavy browsing and racking damage. If you have the ability to do so, a stong 8 or 9 foot fence is the best. It should be strong enough to take an animal that size trying to crash into it either accidentally or on purpose. Woven or welded metal fences are nice, 12 gauge or better. The plastic deer fences I have observed are nearly worthless. There may be some better ones out there but I have seen many torn to pieces the first season. The actual fence can be as low as 4 feet, provided you apply a continuous line of wire above it every foot or less so the animal cannot jump over. This too needs to be of sufficient gauge to withstand a leaping creature, 12 gauge being about the minimum, and wound (cables) are often better. For those on a budget that have only the occasion tree, a little corral of 4 posts and a 5’ tall fence will probably do just fine. Our original small planting used just that, and we never had any trouble. The corral should be too small a space for them to jump in, and too wide for them to reach the branches with their naughty little teeth. Do the best you can. Browsing will not kill it, but it is not what your young tree wants either. Smaller unit fencing like this also keeps out the bunnies which can also damage trees. We have heavy pressure of snowshoe hare here for instance, and cute as they are can do a real number on lower branches.
10. Keep it clear. A circular area about a foot in diameter should remain clear of clutter. This means organic mulches, weeds, and especially sod (aka perennial grasses). This means a clean cultivated area, or better yet a 2-3 inch layer of stone (¼ to 1 inch diameter). The cleared area allows the trunk to remain dryer and healthier. It also prevents any unnecessary competition in a tree’s young years. Organic mulches, like hay or wood chips will allow rodents a nest right up and cozy to the trunk, which we do not want. Also, these types of mulches are in the act of decaying, and that can be detrimental when in such close proximity to the bark. The benefits of the stone mulch are that it suppresses competing growth in the area while keeping the soil moist. It can also help to anchor the bottom portion of our tree guard. Stone mulch in cold areas will become a concrete like mass come winter and impenetrable to digging critters like voles. A clear area about the trunk will also make for a clean path of sight when looking for damage and insect or disease issues. Apple tree borer activity, for instance, is easily spotted.
11. Maintain a mulch around your new tree. What this constitutes is a ring of material beginning from the outer edge of your stone mulch/soil circle and extending at least to the dripline (to where the branches extend). The contents of your mulch will depend on what you have access to. Deciduous trees like fruit bearers will appreciate hardwood tree debris like bark and chips, the older the better. (See other Research entries on the website) Hay, straw, compost, and anything else that will rot are good choices. Several inches thick is a nice start, but don’t be too stingy, all this will become beautiful compost as we lay more mulch down year upon year. Mulching will moderate soil temperature swings, preserve soil moisture and feed our tree in a healthy, gradual fashion. It will also help to suppress excess sod and weed growth which could compete with the tree for water and nutrients. A mulch can look can look as tidy as a golf course or as messy as my son’s room, but it will all lead to the same purpose. We like to lay a fresh coat of hay beneath the trees just before harvest, which allows the fruits to fall into this “pillow” and keep them from bruising. Also makes the perfect recline to munch a crispy apple on.
12. Visiting. Like grandma, your tree will be happy if you visit frequently, and be a bit scornful if neglected. Mulching, for instance will insure against the average drought, but be wise enough to water it if times between rains starts to stretch. A 5 gallon pail once a week isn’t too much trouble and can make a big difference to a young tree. A regular program of observation, nutrition and care will be ongoing, but it really isn’t too terribly difficult. What is important is that you notice if your tree needs a hand. There is an old saying that the best fertilizer is a farmer’s footprints… and it is about the best advice this farmer can give you.
The state of Alaska is experimenting with a high tunnel system to address cold temperature conditions. Pictures and more can be seen at http://www.uaf.edu/ces/ah/fruit-tree-trials/
Late season nutrition, fall pruning and late season weather conditions can greatly influence the cold hardiness of fruit trees and bushes…..
Perhaps the worst plague of the tree fruit grower….
With regard to apples there is a decent selection for most locales. The coldest spots, however will find it necessary to seek out the toughest of the lot. Among them are Dolgo crab, Ranetka crab and Siberian crab.
Siberian, malus baccata, is likely the most cold hardy. It has had some criticism in Alaska as being a bit slow in growth (too much so for some folks) but may be oart if the reason for its high survival rate. There are reported issues with compatibility in some variety combinations. There is anecdotal evidence that cultivars with crab in their ancestry are less likely have rejection. ..
..more to come..
Scab may be reduced in the orchard through leaf fall management. Leaf litter should be ground up or composted to facilitate breakdown.
Growers in northern climates should be aware of the considerations of rootstock hardiness.
Although most folks make good decisions regarding the variety, one needs to pay attention to the rootstock as well. The aerial portion of your apple tree for instance, will suffer more disease, dieback, and the like. If the rootstock fails due to being out of its zone for hardiness, the tree will just drop dead.
Even the most cold hardy of rootstocks are really only cold hardy down to around 19 degrees F. Since soil will insulate somewhat, even bare soil in winter will afford it some protection. Geothermal heat additionally will leak to the area for further aid. The real helping hand when temps get into subzero zones is through snow cover. This is why areas like the northern plains of the US and the Canadian prairies are the real test areas in most years. When wind strips bare the soil and temperatures plummet to -40F and beyond you had better hope you were smart enough to choose the toughest roots of the lot. Now, damage doesn’t always mean death, and plants can sometimes recover from assaults like this, but they often don’t. Furthermore, damage can be hard to assess since it is, well, underground. Often the only indication is that our trees aren’t doing so well, which can sometimes be even more frustrating than having them get on with it and die. So, choose wisely. we are in the process of giving as much info on this site so you can make a good choice for yourself, and when there is choice we always graft to the hardiest we can so there is less you have to think about.
The apple genome has been sequenced and revealed 57,000 genes in malus domestica. Considerable since the human genome contains only around 30,000. It comprises 17 chromosomes compared with the 7-9 typical in other Rosaceae family members. It is also double the number of chromosomes in the ancestral apple. A 5 country 18 institution effort produced the find, which has already fleshed out 992 genes involved in disease resistance in the fruit. It also confirms malus sieverseii as the true ancester to our domesticated apple. The information will be useful in reducing the time, effort and expense involved in standard breeding systems, whether or not it is used in a program of genetic modification. It has also been shown to clear up confusion on the origins and dispersal of the malus species, as in the possibility of the native american apples being a direct link to the ancestral species of asia. (There are suggestions of coming across the Bering land bridge with the native peoples who also carry a genetic link to ancient asian peoples.) Though it is likely that advances such as this will lead to the development of plantlife which will become proprietory and profit driven, it still stands as a great human intellectual feat worthy of respect. Let us hope it will be used to more easily feed people in need, and to expand our culture and understanding above all else.
The original article was first released in the journal Nature Genetics.