Black Knot, is a disease commonly found on plums and Prunus species. The fungus causes the plant to produce unusual galls which eventually grow to girdle twigs and branches, restricting water supply and killing portions of the canopy. It is spread to other plants via wind and water.
Control
Manage the disease by carefully pruning away the affected tissue. Use sterile pruning tools to make a cut roughly 4 to 6 inches past the lowest point of symptoms on the branch. After cutting the branch, sterilize the tools again by dipping them in a 10% bleach solution (1 part bleach, 9 parts water -> e.g. 1/2 cup bleach, 4 & 1/2 cups water). You should also spray a bit of this bleach solution on the cut wound on the tree. Repeat this process until all theblackgrowth has been removed. Burn the branches and do not compost them. Prune during dry weather to prevent the spread of the disease. This can be done in the fall and winter if the fruit is still growing on affected branches. The client may need to repeat this process every winter for the rest of the tree’s life or until symptoms no longer appear.
Check out this handy pruning guide and refresher from our Sustainable Landscaping and Nursery IPM Educators. This was written for professionals, and is also applicable to home gardeners just getting started with the basics of pruning. It includes links to other resources for continued learning as well!
– Identify the purpose of each pruning job. (Table 2)
– The amount of living plant material that can be re-moved at one time depends on the age and level of establishment of the plant (Table 3).
– Dead, broken, or diseased plant material can be pruned at any time of the year.
– To rejuvenate multi-stemmed shrubs, remove one or more of the oldest stems at the base each year to stimulate new shoots to arise from the base of the plant. Many flowering shrubs bloom more prolifically on younger, 2 to 3-year-old wood. Shrubs that respond well to having some of the 3+ year-old stems removed include forsythia, weigela, deutzia, mock orange and beauty bush.
– Newly established hedges should be pruned early in the growing season to promote the desired growth and density. More established hedges may be kept vigorous and dense by thinning out older branches, which will encourage new growth.”
Black knot of plum and cherry, caused by the fungus Apiosporina morbosa, may be overlooked during the growing season when the leaves are hiding the galls, but this time of year they are hard to miss, especially when they are as abundant as they are on the tree in the photo below.
This is a serious disease of these trees and can eventually kill susceptible varieties. Management options include sanitation, resistant varieties and properly timed fungicides.
Where manageable, prune out all galls during the dormant season and dispose of them off-site, burn or bury them. This is because even removed galls may still produce spores that can cause new infections. Prune 6″ below the visible edge of the gall because the fungus can be invading the wood in that area prior to gall development.
This disease can affect both orchard and ornamental varieties of plum and cherry but some of the tart cherries are less susceptible. Native wild cherries are hosts of the disease and provide a reservoir of inoculum for orchards and ornamentals. It’s helpful to remove those nearby where possible. For new plum plantings (fruiting/orchard), ‘President’ is highly resistant. Moderately resistant options include ‘Methley’, ‘Milton’, ‘Early Italian’, ‘Brodshaw’, ‘Fellenberg’, ‘Shiro’, ‘Santa Rosa’ and ‘Formosa’. ‘Shropshire’ and ‘Stanley’ are considered quite susceptible.
Here’s how disease develops: Infections occur in the spring on new growth from spores produced on the surface of 2+ year old galls. Spores are produced and spread during rainy weather and shoots must remain wet for a period of time for the spores to germinate and initiate an infection. Infections can occur at temperatures of 50°F or higher when water is present for the required period of time. Over the course of the first summer, a small greenish brown swelling develops. By the end of the second summer, the gall or knot becomes hard, rough and black. These galls begin producing spores the following spring. Galls expand in size each year until the branch is girdled (killed all the way around) and then they die. Once a twig or shoot is girdled, the portion beyond the gall can’t get any water or nutrients and dies as a result. Sometimes, larger branches and trunks can become infected, presumably through wounds.
What if you have a susceptible tree and want to prevent this disease? If you know you have a source of infection (hosts with galls nearby, either wild or on a neighboring property) and you’ve had some infections, keep up with the monitoring and pruning, fertilize and water as necessary to prevent stress, and use preventive fungicides, such as lime sulfur during dormancy (organic option) or chlorothalonil or others labeled for this disease. Other than lime sulfur, applications should be made as directed on the label beginning at bud swell and until new terminal growth ceases.
The hydrangea in front of my house is just a bunch of bare sticks in the winter, screaming to be cut down. It looks like quite a leafless eyesore after losing foliage in the fall. During the winter the local chickadees use it as a perch beneath the hanging bird feeder. The avian flocks do not mind its ugliness. I don’t mind it either knowing the flower buds are on those naked sticks, waiting for the coming spring and summer to bloom. There are five different types of hydrangeas. Some bloom on old wood and some on new wood.
My hydrangea is a Hydrangea macrophylla or Bigleaf Hydrangea. The ones that bloom on old wood carry the next year’s flower buds on the barren sticks, through the fall, winter and next spring. If these are pruned during the fall, winter or spring, the flower buds will be removed. The plant will grow new stems and leaves from the base of the plants, but these stalks will NOT contain flower buds, therefore no flowers that year. The flower buds are produced and set after the plant flowers in June and July but before fall. Any pruning should be done as the flowers fade during the summer to avoid cutting off the buds. I remember to prune Hydrangea macrophylla when I cut flowers for a vase to bring inside. Sometimes our winters are just too cold for the tender over-wintering buds, killing the buds, resulting in no flowers the following summer even if pruned correctly.
Hydrangea macrophyllasare divided into two groups, Hortesia and Lacecap. Hortensias have big ball flower forms. Lacecaps have a somewhat flat top shaped flower. These bloom on old wood, prune after flowering but before August 1st.
Hydrangea quercifolia, commonly called Oakleaf Hydrangea also blooms on old wood. Prune after flowering. If terminal buds are killed during winter, no flowers will be produce. Should be protected in zone 5.
Two other common hydrangea bloom on new wood, wood produce from the plant during the same year. These are Hydrangea paniculatagrandiflora, commonly called Panicle or PG Hydrangea and Hydrangea arborescens, commonly called Smooth Hydrangea. These can be pruned in late fall, winter or early spring. The flower buds will be produced on the new wood produced in spring.
Hydrangea paniculata, Panicle Hydrangea. Prune in early spring.
Hydrangea arborescens, Smooth Hydrangea blooms on new wood. Prune in winter or early spring.
Ten Tips for the May Gardener:
1. If you want to get a head start on the season, plant container gardens and be ready to bring them indoors on cold nights.
2. When transplanting annuals and vegetables, be gentle with the root ball. These plants have small root masses that are easily damaged.
3. Now is the time to divide groundcovers such as ajuga and pachysandra to create new beds or enlarge existing ones.
4. After lilacs finish flowering, prune off old blossoms.
5. When re-seeding parts of your lawn, rope those areas off with stakes and string to keep kids and pets off.
6. Weed around the bases of trees and shrubs and apply a 2 to 3 inch layer of mulch.
7. To help control weeds consider using landscape fabric. Unlike black plastic, it is porous and lets air and water reach plant roots.
8. Think about starting a compost pile with lawn clippings, vegetables scraps and leaves.
9. Now is a good time to lay soaker hoses in flower and shrub gardens.
10. Late-blooming perennials, such as asters and mums, can be divided in spring.
