Posts

Viruses Are Good . . . Sometimes

/1 Comment/in /by

I suspected, and recently confirmed, that my raspberry plants have the “flu.” Okay, not the flu (as in influenza), but a virus, in any case. The plants looked okay but they weren’t bearing their usual abundant crops. And the berries that they were bearing seemed a little crumbly.
The virus culprits were narrowed down to two possibilities, raspberry dwarf bushy virus and tomato ringspot virus. Either of these viruses may also bring on patterned yellowing of leaves, or not, depending on the raspberry variety, time of year, and other variables. (No, raspberry dwarf bushy virus does not make raspberries grow dwarf and bushy.)
Not that viruses are the only things that can make raspberries crumbly. Tarnished plant bug is an insect that feeds on developing flowers and fruits of raspberries and a slew of other plants. If too many druplets of a berry are eaten, the rest of the berry can’t hold together. Boron is another possibility, an

essential micronutrient, the deficiency of which also results in low yield and crumbly fruits. But . . . tarnished plant bugs were not particularly prevalent this year and sandy soils low in humus are where boron is usually lacking. Soil here on the farmden is not sandy and years and years of mulching have maintained very high levels of humus.

Weather — my usual scapegoat for everything this year — can also be responsible for crumbly raspberries, both directly and, by its effect on bees, indirectly. But . . . raspberries flower over a long period so the weather, every type of which we experienced this season, has to be let off the hook this time.
Specific virus infections can be confirmed with a antibody test called enzyme-linked immunosorbent assay, or, for short, ELISA.  Back in July, I sent separate samples of leaves from my Cuthbert and Fallgold raspberries to Agdia Labs in Elkhart, Indiana. Bummer, The variety Cuthbert was confirmed to be infected with tomato ringspot virus and Fallgold with dwarf bushy virus.
———————————————–
Once a virus infects a plant, it spreads throughout, and a plant generally cannot be cured. Still, I’m not giving up eating home-grown raspberries, and I’m not settling for crumbly ones either.
The first thing to do is get new plants. No, not plants dug up from my own raspberry patches or from generous neighbors’ or gardening friends’ patches. What’s needed are certified virus-free plants from a nursery that produces such plants.
Ideally, my new plants would go into new ground far from my old planting or wild raspberry or blackberry plants. But where am I going to find a place at the recommended 600 feet(!) “from my old planting or wild raspberry or blackberry plants?” In my neighbor’s yard?
Tomato ringspot virus is spread by dagger nematodes, and some evidence exists that thorough tillage causes dramatic drops in their numbers. Generally, I rail against tillage for a number of reasons but, hey, gardening and life are about achieving a balance. For my new raspberries, the benefits of tillage might outweigh the negatives.
Dwarf bushy virus is carried from one plant to the next via infected pollen. Preventing pollination would, of course, prevent fruits from developing. So there’s nothing that can be done to prevent eventual infection if it’s in the vicinity.
Time flies, and I realize now that my raspberry plantings are getting some age to them. Although raspberries are perennial, after about 10 years, any raspberry planting — not just mine — is bound to pick up diseases, some of which result in nothing more dramatic than a decrease in yields. The time clock is up on my plantings. I’m ordering new plants for planting in a new location in soil that will be tilled up and enriched with wood chips, leaves, or other organic material.
I’ll plan on replanting again in by the year 2023.
—————————————————
Virus diseases aren’t always to be cursed, in plants or animals. They can be beneficial.
In dwarf apple trees, for instance. Apple trees are dwarfed by being grafted onto special rootstocks that limit tree size of whatever variety is grafted upon them. (The apple fruits are the same as on full-size trees.) Dwarf trees are more efficient than large trees at converting sunlight into tasty fruits. Malling 9 apple rootstock restricts tree size to no more than about 8 feet high.
Plants can sometimes be cleared of viruses through heat treatment or by cloning whole new plants from a few cells that have not yet become infected. When Malling 9 rootstock was cleared of viruses, it lost some of its desirable dwarfing powers. (The virus-free rootstock of Malling 9 is called EMLA 9.) I’m scared of heights and like to harvest the most apples per square foot of ground, so I made my trees by grafting them on Malling 9, rather than EMLA 9, rootstock.
Looking around my yard, my eyes come to rest on the fantail willow, its branches fused together and

contorting in fanciful directions — more pretty than painful. Such fusion is called fasciation, the result, sometimes, of virus infection.

Pruning Begins

/8 Comments/in /by

Just because I wrote The Pruning Book doesn’t mean that I always go forth boldly, pruning shears in hand, to prune with speed and with total confidence. This realization hit me right between the eyes as I was staring at and trying to figure out what to do with a row of St. Johnswort shrubs billowing like a wave over the edge of my terrace. Any more billowing and that mass of stems would become a tsunami; the hedge had to be reduced — attractively.
The problem is that the plants are a bit big for the site. I have excuses. There are 400 species of St. Johnswort, varying in stature, and I lost the tag to my original plant from which I propagated all the others in the hedge. The soil in the planting strip used to be weedy and poor. After enclosing the strip in a wall of hypertufa (a mix of cement, peat, and perlite that ends up like volcanic rock) and topping the bed with compost, plants grew better than expected. And the St. Johnsworts were supposed to mingle and compete with potentilla plants in the bed, each showing off its sunny, yellow flowers at various times through summer and keeping the other in check. The St. Johnsworts overgrew and snuffed out the potentillas, so, lacking competition from weeds or potentilla, grew too well.
——————————————–
Lopping all St. Johnswort stems back by half or more would not be a good idea. For the rest of winter, the hedge would look hacked back (which it would have been). Hardly the graceful, if oversized, tapering, arching branches presented now. Come spring, new shoots would burst forth mostly near the pruning cuts, the ungainly result, year after year, being wild, new growth sitting atop increasingly, fat stems.
After some chin scratching, I chose a different tack. First, I shortened everything to about 18 inches. Then I shortened some of those already shortened stems to various lengths, some to as short as a couple of inches long. Simple.
For now, largish wounds do stare out from the hedge, but next year, and in years to come, such wounds will be less plentiful and less evident. This pruning’s most dramatically shortened stems will sprout just a few, lanky shoots. A greater number, but each less vigorous, shoots will sprout from stems I shorten least severely. Moderately shortened stems will sprout a moderate number of new shoots of moderate vigor, how many and how vigorous related to how much the stem was shortened.
The end result — I’m hoping — will be a hedge with shoots of various size and vigor originating at various heights within each shrub. Just like a naturally growing plant. Pruning in subsequent years should be easier.
Although this pruning sounds formulaic, it was fraught with decision-making: whether or not to cut and how much to cut, both to achieve aesthetic results now and for the future. Shrubs readily sprout new shoots naturally and following pruning, so I at least am consoled that pruning rarely harms the plant and that mistakes are soon overgrown.
————————————————————–
In contrast to pruning St. Johnswort, pruning red raspberries is a no-brainer. All you have to do is follow a 3 step recipe.
Step 1: Cut to the ground any stem that bore last summer. These stems look old, with peeling bark, and still hang on to a few remnants of fruit stalks.
Step 2: Cut down selected remaining canes. If the swathe of plants is wider than 1 foot, berries are harder to pick and, because of congestion, disease is more likely. I cut down any stems attempting escape beyond that swathe and then, within the swathe, remove enough canes so that none are closer than about 6 inches apart. Sturdiest stems are those most worth saving.
Step 3: Shorten remaining canes to about 5 feet in height. This pruning is just to keep stems from flopping around. The height could be more or less, depending on how and if plants are trellised. I leave mine longer and weave the canes together onto a trellis wire about 4 feet from the ground.