Cutting Revelations: Keep an eye out for trouble while you prune in spring

The plants we love take care of themselves, mostly. We put each in the right environment and it grows well, looks beautiful, and staves off problems on its own.

Sometimes things do go wrong. We keep an eye out for problems, investigate, decide which warrants our intervention, and take appropriate steps. At the very least, our remedial or prophylactic steps include keeping an eye on the situation so we will know if it becomes more serious. When we need to move one step up from simple monitoring, that step involves good sanitation -- removing suspect parts and cleaning tools.

Poor forsythia, with crown gall infections sapping its strength, marring its beauty. Poor gardener, who's learned the hard way to avoid pruning while wood is wet, and to disinfect shears between crown-galled Euonymus and everything else. This Forsythia's branch tips were infected all along the cutting line.

Poor forsythia, with crown gall infections sapping its strength, marring its beauty. Poor gardener, who's learned the hard way to avoid pruning while wood is wet, and to disinfect shears between crown-galled Euonymus and everything else. This Forsythia's branch tips were infected all along the cutting line.

Look sharp while you cut in spring

Spring pruning time is an important time to watch for new oddities as well as to check up on what caught our attention in the past. Discolored wood, odd growths and deformities can be symptoms of diseases of the wood, some of which our pruning tools might spread from limb to limb and between plants. These things stand out now while we're pruning leafless shrubs and trees or cutting into evergreens to keep the interiors well lit.

When we see something we know is trouble, we act. When we see something new and questionable, we take basic precautions, set aside samples of the wood for later investigation, and report what we found. That report is for you, here but also for ourselves. When we make notes we won't have to re-do that research next time.

Here are some things to watch for now. (Scroll down!)

Standard precautions apply

We hope you don't find anything troubling in your garden but if you do, disinfect your tools between cuts and keep samples for later study. In this quick advisory, we give you photos of some of our samples and some key words to plug into the GardenAtoZ search field, copy into a search engine or look up in the index of pest- and problem reference books.

Crown gall bacterial infection

You've probably seen it while working around evergreen Euonymus, a species quite susceptible to this disease. But did you know that crown gall bacteria (Agrobacterium tumefaciens) can infect dozens of other species?

Key words to help you learn more:

Crown gall; agrobacterium + plant species

Starter resources:

http://www.apsnet.org/edcenter/intropp/lessons/prokaryotes/Pages/CrownGall.aspx

(Wow, and we harness the beast: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC150518/)

Key precautions:

Do not prune while the wood or the weather is wet. Remove affected parts well below the gall. (Yes, sometimes that means removing the plant.) Disinfect pruning tools with peroxide or 10% bleach between cuts. Don't touch the affected parts if you can avoid it, but if you do handle galled wood wash your hands well before touching other plants.

You have probably seen the tumor-like growths from crown gall on Euonymus, but do you know to watch for them as you prune your roses, too? This rose is a loss, infected so low we can't cut it out -- as we must -- without removing the graft union.

You have probably seen the tumor-like growths from crown gall on Euonymus, but do you know to watch for them as you prune your roses, too? This rose is a loss, infected so low we can't cut it out -- as we must -- without removing the graft union.

Most people figure nothing can kill a wisteria. Crown gall weakened this wisteria so that its entire main trunk died back and had to be cut out. This is the fist-sized, galled base and portions of canes from that trunk showing in their cross section the stain of infection.

Most people figure nothing can kill a wisteria. Crown gall weakened this wisteria so that its entire main trunk died back and had to be cut out. This is the fist-sized, galled base and portions of canes from that trunk showing in their cross section the stain of infection.

Rose rosette virus

Early symptoms of this mite-spread disease are poor growth, then odd foliage, unusual thorns, then ferny bright red new growth and all the while less and less vigor.

There is no cure; once a plant is infected it's only a matter of time before it diminishes. It comes to your roses and moves among them when mites feed on an infected rose and then others.

Key words to help you learn more:

Rose rosette disease

Starter resource:

We wish we could point you to one, but for now we say search the Internet and ask at your Extension for 2016-publications. Most we've seen up until now have good information but remedial and preventive advice that's still varies widely and in our opinion is not accurate or complete. For instance, one bulletin prescribes replacing the soil where an infected rose was removed, before another can be planted. This does not track with the disease's development or transmission so it may have been included because the athor was writing early on, and being very- to overly cautious.

Key precautions:

Remove every suspicious rose. The non-native climbing multiflora rose (Rosa multiflora) is an all-too-common weed throughout North America and may be the chief disease source in an area. Controlling rose thickets in your area is an essential practice for those who want a healthy rose garden.

Will your rose insect control products help? Probably not. Mites are not insects but arachnids -- spider relatives. They are extremely difficult to control even with miticides. As of early 2016 universities and plant disease researchers are still testing effectiveness of various miticides against this relatively new problem. Keep a look out for new Extension- and botanical garden bulletins.

A: When a rose's new growth or thorns are 'way too red, get suspicious of rose rosette. B: When thorns or new shoots grow in crowded clusters, mourn that rose. C: Another symptom is thorns that are atypical, such as these tiny, raspberry-like bristles on this hybrid tea rose.

A: When a rose's new growth or thorns are 'way too red, get suspicious of rose rosette. B: When thorns or new shoots grow in crowded clusters, mourn that rose. C: Another symptom is thorns that are atypical, such as these tiny, raspberry-like bristles on this hybrid tea rose.

Eriophyid mite infestations of wood

These members of the spider family infest new wood, casing wild, deformed or discolored growth. Their presence weakens the plant and severe, prolonged infestations can kill a shrub or young tree.

Note: These are not the same mites that transmit rose rosette virus.

In addition, keep in mind that there are hundreds of eriophyid mite species. Most are able to infest only one plant species or one plant and its close relatives. So it is unlikely that you will spread eriophyid mites between unrelated plants. You may find eriophyid mite damage on a lilac and also on a blue mist spirea but the two have no connection to each other except similar symptoms. You did not "spread" the problem from one to the other.

Key words to help you learn more:

Eriophyid + plant species

Starter resource:

http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/insects/mites/eriophyid-mites.aspx

Key precautions:

Remove all affected wood. Pruning before spring budbreak and destroying all that wood may be especially effective since many mites overwinter under the bark and in wood crevices of the host plant, emerging to lay eggs as leaves emerge. Dormant oil applied to remaining wood may help, smothering mites as they emerge.

Keep the troubled plant well watered, properly lit, well fertilized.

Hunh! What's turned the base of this lilac into a thicket of weak, tiny branches?

Hunh! What's turned the base of this lilac into a thicket of weak, tiny branches?

On this blue mist spirea (Caryopteris x clandonensis) the same symptoms, although they were generated by a different eriophyid mite.

On this blue mist spirea (Caryopteris x clandonensis) the same symptoms, although they were generated by a different eriophyid mite.

You might think at first glance that mite-affected stems have developed roots, as some branches do after a season of laying in moist, dark places. But a closer look will tell you those are NOT roots  but deformities. In a response akin to an irritated oyster producing a pearl, the infested branch grew these extensions.

You might think at first glance that mite-affected stems have developed roots, as some branches do after a season of laying in moist, dark places. But a closer look will tell you those are NOT roots but deformities. In a response akin to an irritated oyster producing a pearl, the infested branch grew these extensions.

What's key is to recognize and act to control the first, light infestation -- see the root-like projections?

What's key is to recognize and act to control the first, light infestation -- see the root-like projections?

If you think of your plants as people -- try not to! -- you may think it's cruel to cut this mite-weakened blue mist spirea to the ground in early spring. However, it's an effective way to remove overwintering mites and give this fast-growing shrub a chance to grow without heavy mite feeding.

If you think of your plants as people -- try not to! -- you may think it's cruel to cut this mite-weakened blue mist spirea to the ground in early spring. However, it's an effective way to remove overwintering mites and give this fast-growing shrub a chance to grow without heavy mite feeding.

Canker infections of wood

Canker is not a disease but a symptom, a sunken or dead spot where wood was infected, usually while young and soft. There are many fungi involved. Fortunately, several prevention strategies and remedies are effective against most.

Key words to help you learn more:

Plant name + canker

A starter resource

http://www.clemson.edu/extension/hgic/pests/plant_pests/shrubs/hgic2057.html

Key precautions:

Maintain the plant in proper light, with good air circulation, adequate water and fertilizer. Do not prune while wood or the weather is wet. Prune out infected wood, cutting well below the canker, and disinfect pruning tools between cuts.

Note: Some fungi that can infect wood can also infect foliage of that plant, causing a "leaf spot." You may apply fungicide as a preventive measure (it will protect clean foliage, will not fix existing spots) but it is probably more important to see leaf spot as a warning signal. React by improving environmental conditions and overall plant health. Infected leaves become sources of infection so thorough leaf clean up can help reduce the spread.

The canes of this Viburnum were probably infected while they were brand new, and without bark. The fungus resides there now, growing each year as the cane does, showing as football-shaped wounds. Eventually, the cumulative damage can kill the cane.

The canes of this Viburnum were probably infected while they were brand new, and without bark. The fungus resides there now, growing each year as the cane does, showing as football-shaped wounds. Eventually, the cumulative damage can kill the cane.

Argh!

Time's up for this issue's preparation. Watch our Forum for more on these last two:

Boxwood mites

What's all that dry, thin, deadwood on the interior of a boxwood?

 

Key precautions:

Better pruning to let light and air into the shrub. Don't simply shear a boxwood but cut back and thin it annually. Improve soil condition, especially aeration in the root zone. Insure the soil is moist but not soggy throughout the growing season, and apply organic slow release fertilizer regularly. Use forceful water spray to rinse the interior from time to time, as leaf feeding mites do not tolerate moisture well at all.

Please! Prune better, include thinning cuts, so even the foliage in the interior of this boxwoood can breathe!

Please! Prune better, include thinning cuts, so even the foliage in the interior of this boxwoood can breathe!

Prune for enough room to let the birds reach in and eat these insect eggs!

Prune for enough room to let the birds reach in and eat these insect eggs!

Black knot of cherry and its relatives

Looks just like its name.

Key precautions

Remove all affected wood well below the black knot. Never prune while the wood or weather is wet. Disinfect tools after each cut. Use slow release fertilizer made from as blood meal, fish meal, cottonseed meal, feather meal, bone meal and other combinations of organic materials rather than water soluble high-nitrogen fertilizer such as

Black knot infection on a chokecherry (Prunus virginiana, which despite its ugly common name is a very good tree for tough,exposed places).

Black knot infection on a chokecherry (Prunus virginiana, which despite its ugly common name is a very good tree for tough,exposed places).