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.
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!)
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.
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?
Crown gall; agrobacterium + plant species
(Wow, and we harness the beast: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC150518/)
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.
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.
Rose rosette disease
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.
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.
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.
Eriophyid + plant species
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.
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.
Plant name + canker
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.
What's all that dry, thin, deadwood on the interior of a boxwood?
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.
Looks just like its name.
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