Master Gardener News Blog
By Leonard Cicerello UCCE Master Gardener
Why are my Cypress dying in my front yard? Joe B. Paso Robles
A study published in 2011 by UC Berkeley and Italian researchers may have solved a decades-long mystery behind the source of a tree-killing fungus that affected six of the world's seven continents. The pathogen, Seiridium cardinale, also known as Cypress Disease or Cypress Canker, was likely introduced from California either in the south of France or in central Italy 60 to 80 years ago. Its introduction devastated the region's iconic Italian cypress trees. Researchers found historical catalogues of large commercial nurseries in Italy and France and found records of mature Monterey cypress trees for sale during the late 1920s and 1930s. The records indicated significant imports of the California trees and their seeds during that time.
Seiridium cardinale was first identified in California's San Joaquin Valley in 1928. The fungus attacks trees in the cypress family by entering through cracks in their bark and producing toxins that wreak havoc with the flow of sap, limiting the supply of water and nutrients. The cracks in the bark could be caused by pruning cuts, boring insects, or weather damage. The spores spread by wind and water splash. Symptoms include dieback beginning from the top of the tree or branches browning and dying throughout the canopy. A branch can change color over a period of days.
You may see thin, elongated cankers on the stems and branches. These cankers cause twig and branch dieback. Most cankers are wounds, slightly sunken, with raised margins, and they may be discolored, dark brown to purple. An infected tree with cracked bark often has extensive resin that flows down the diseased branches and trunk. Once most of the canopy has turned brown, that limb or tree will almost certainly die. The whole limb or tree should be removed and properly disposed of.
The principal hosts for cypress canker are Monterey cypress, Italian cypress, Leyland cypress, Lusitania cypress, and Arizona cypress. It is best not to replant new cypress immediately following the removal of diseased trees. No specific cure exists. The best you can do is supply adequate water, minimize soil compaction, apply a thin layer of mulch, and avoid wounding the tree.
By Leslie E. Stevens UCCE Master Gardener
What's turning my rose leaves into skeletons? Kathy M. San Luis Obispo
Those raggedy, semi-transparent leaves ruining the appearance of your rose bushes are likely evidence of bristly rose slugs – the black-to-pale-green larvae of the sawfly. The younger caterpillar-like larvae skeletonize the leaf undersides, while more mature larvae finish the job by chewing large holes in the leaves.
Starting in spring, watch for the appearance of shiny black adult sawflies. These stingless wasps are so named for the female's saw-toothed egg-laying appendage. She uses these to make cuts along rose leaf edges, inserting a single egg in each pocket. Sawflies produce up to six generations annually, with the last one overwintering as pupae in the soil.
The damage rose slugs cause is not only unsightly, but the pests' leaf feeding strips the green chlorophyll from the foliage, diminishing the rose's ability to photosynthesize and potentially weakening the plant. Manage small infestations by pruning out infected leaves and picking off and killing the pests. You also can try hosing off rose slugs with a strong blast of water. Just remember to use the hose method in the early morning to allow foliage to dry before nightfall. Lingering wet foliage can introduce fungal infections such as mildew and rust.
If needed, treat heavy rose slug infestations by spraying an insecticidal soap or spinosad, making sure to coat both sides of leaves. Insecticidal soaps kill only the rose slugs it comes in direct contact with while spinosad must be injested by the insect. Therefore, it may be necessary to do subsequent applications throughout the warm growing season as long as the pests are present.
It is important to avoid using broad-spectrum insecticides to control sawflies and rose slugs, since they also indiscriminately kill the many beneficial predators such as parasitic wasps and predaceous beetles that help control the pests.
By regularly inspecting your rose bushes for pests and diseases and eliminating any problems early, you'll likely enjoy many months of healthy plants and beautiful, fragrant blooms.
By Jutta Thoerner UCCE Master Gardener
Please give me some tips on growing and harvesting avocados.
Mike P. Cambria
Our coastal climate is ideal for avocado trees with low temperatures in the 30s and 40s and highs that seldom top 80. A sandy/loamy soil is preferred since avocados need a well-drained medium soil to discourage Phytophthora, a deadly root rot disease. Expect to wait 9-15 years for your first fruit if you plant from seed; 4-6 years if you plant a young tree.
A common question is whether one should grow at least two trees - one with “A” flowers and one with “B” flowers. This is not necessary. But when both an A and B type are planted, the male and female flowers on each tree will open at precisely the right time and improve both trees' fruit set. It is reassuring to know that a single mature tree has a flower set that consists of up to 1 million flowers per year. From those 1 million flowers, 100-200 will develop into an avocado fruit. That's 1 in 10,000 flowers developing into a fruit.
Ideal temperatures for fruit set is 65-75 degrees F. Often pea or walnut sized fruit will drop off the tree. This is normal and no cause for alarm. The tree is self-thinning and will only keep the fruit that it is able to bear. Sometimes smaller cuke size fruit will remain and they are okay to harvest. A regular watering and fertilizing schedule will insure that most of the fruit grows to size.
When to pick avocados: look for a change in color on the fruit. A dull, less shiny color, or brown specks are a good indicator that the fruit is mature. Pick a large fruit and allow it to ripen to softness on your kitchen counter. If it does not shrivel or get rubbery, and it has good flavor when you taste it, note the date for future harvest. Now you can pick the fruit as you want to use it, allowing for 1-3 weeks ripening time off the tree. Many avocadoes varietals can hang on the tree for up to 8 months (Hass, for example) making this particular tree a perfect space-saving storage system.
Winterizing the Garden
By Jackie Woods UCCE Master Gardener
The temperatures are dropping, the vegetable garden is waning and thankfully, we actually had our first decent fall rain. All of this can only mean one thing: It's time to put the garden to bed for the winter! Lucky for the Central Coast, our winters are fairly mild but there are still chores that can be done to ensure that plants have a great start come spring.
A good task to start with is clean-up. Remove fallen leaves, spent vegetable plants and pull up finished annuals. Cut back perennials, prune roses and pull any weeds. What to do with all those bare areas in flower beds? Apply mulch! Mulch helps the ground retain moisture, creates a welcome environment for earthworms and helps keep weeds to a minimum. Newly mulched gardens are aesthetically pleasing to look at and gives the garden a tidy, groomed appearance.
Fall is a good time to consider adding new bare root plants into the garden before spring arrives. Fruit trees and roses are generally available for late winter/early spring planting. If bulbs are a mainstay in your garden, split them if needed and replant. Bulbs are a wonderful addition to any garden and can be planted directly in the ground or put in decorative pots. Narcissus, crocus, daffodils and iris, just to name a few, are common bulbs that can be found at any nursery or can even be purchased online.
If there are any lawns still out there, don't forget they need fall and winter TLC, too! Fertilize in the fall and again before spring for a healthy green turf. Protect potted succulents by placing them closer to the house or store them in the greenhouse. There is one more task to consider doing during the fall and winter and that tends to be the most fun chore of all: kick back and browse all the seed catalogs while waiting for spring to arrive!
Still need some inspiration? Join the UC Master Gardeners for a free Advice to Grow By workshop on “Winterizing Your Garden” on Saturday, November 19th from 10:00AM – 12:00PM at the Garden of the Seven Sisters located at 2156 Sierra Way in San Luis Obispo.
Living Christmas Trees
By Andrea Peck UCCE Master Gardener
I'd like to have a living tree for the holidays, how do I care for it? R. Rudolph, San Simeon
Although the Christmas tree, a symbol of holiday cheer, has been a common sight in American homes for less than a century, the tradition of decorating the home with “greenery” has been around for thousands of years. Used as a reminder that abundance will resume in Spring or simply as a decorative touch that brings solace during the cold, color-wanting months of winter, many cultures throughout the world continue this joyful custom. Modern times bring novel variations and a living Christmas tree is one such choice for the eco-conscious who want to enjoy their tree for years to come.
When purchasing a living tree choose appropriately. Norway spruce, Colorado spruce, Douglas fir and noble fir, are generally sold in local nurseries. If you are going to plant the tree in your garden, be aware of its future height, width, pruning and irrigation needs. Many evergreens grow quite large care must be taken to find a location that allows roots and branches to grow unfettered by nearby concrete, overhead power lines and underground utilities. A smaller tree, even a pruned bush, such as the oft seen rosemary plant, are good options for those with a smaller yard. On the other hand, you may prefer to keep your tree in a container and bring it back inside next year.
While the holidays are in full swing, it is best if the tree is kept indoors for a short period of time 7-10 days. During its indoor visit, the tree should be kept adequately moist and not be allowed to dry out. Additionally, do not place the tree in a drafty area or near heating vents. After the holidays, bring your tree outside. In order to avoid undue stress on the tree, put it in a shed or garage during the night for a few days. Dig a hole twice the size of the root ball and amend as necessary. Water in thoroughly and celebrate!