I don't know if you've noticed, but they have actually been buzzing around since the first fruit trees blossomed in February. There has been a lot of press coverage about bees, especially about Colony Collapse Disorder and the critical importance of bees to California Agriculture. Haagen-Dazs even partnered with UC Davis Bee Biology Department in 2009 to create a Honey Bee Haven, an educational garden open to the public to inform people about the importance of bees to our food systems and to inspire people to use bee-supporting plants in their own gardens. We all have a roll to play in making conscious decisions to support the bee and other pollinator populations in California.
What does that have to do with pesticide applications?
I was recently asked my advice about applying a common tree insecticide drench product that contains the active ingredient imidacloprid. The homeowners association member who asked advice wanted to prevent aphid infestations before they happened by drenching in early spring as the leaves were emerging. I recommended against this. So what is the problem?
When you use these broad-spectrum killers as prevention, you set up a system that never reaches a balance of pests and predators/parasites, and you end up being completely dependent on the repeated use of chemicals while creating a garden environment devoid of healthy wildlife.
So, what do you do if you do have a serious aphid issue?
You have several choices, but you should try combining tactics for the best control. First, if you have certain plants that seem to be more highly attractive to aphids, like crape myrtles, be sure to watch for ants and control these with baits (like those containing boric acid) they take back to the nest. Ants will protect and farm the aphids making the infestations worse, but controlling them with baits is highly effective and non-toxic to non-target species.
Don't be too quick to resort to chemical sprays. In spring, the aphids will show up about two weeks earlier than the ladybugs. If you can hold on, the predators will show up and take care of the issues without the need for sprays. In the meantime, you can knock down the highest populations with hard sprays of water from a hose with a nozzle.
If you have a really serious issue of scale or aphids in trees that is causing heavy honeydew drip on cars, pavements, and other plants leading to sooty mold and unhappy people for several years in a row, then it is time to consider a treatment. It should never be applied when bee populations are noticeable in the area, and it shouldn't be used for years in a row. Usually, a properly timed application will be enough to get the problem under control in a single year, allowing the beneficial populations to resume control in subsequent years. If the issue is on shrubbery or roses, then consider using organic sprays like those derived from chrysanthemums (pyrethrins) that kill on contact but have no residual toxicity. But be forewarned that if you spray bees directly, they will also be affected.
Taking a measured approach that considers all the factors in the environment and uses a combination of methods is the best way to maintain healthy landscapes without the need for regular use of highly toxic pesticides. When we protect the bees, we protect ourselves./h3>/h3>/h3>
Fall 2020 Tree and Turf Continuing Education
I just want to share some great virtual learning opportunities this fall, some beginning next week. Most of these events will be less expensive than their pre-COVID counterparts, but most have DPR and/or ISA CEUs available. There is always something more to learn- or at least be reminded of, so take advantage of as many of these as you can.
TEACHER: UC Cooperative Extension Advisor Dr. Jim Downer
When: 5-Part series, every Friday in October starting October 2, 12:30-2:00 PM (PDT)
Where: Virtual Webinar via Zoom (links and instructions to will be emailed to registrants)
Intended Audience: Arborists (DPR & ISA Units applied for)
Registration fee: $15 per session OR a discounted $50 fee when registering for all 5 sessions.
2. ISA Z133 COURSE ON TREE SAFETY
- Introductory course on the ANSI Z133 Safety Requirements for Arboriculture Operations.
- Gives key information about the most common incidents in arboriculture operations which cause worker injuries and fatalities.
Other ISA sponsored events:
- October 7-14: Participants will have access to watch seven 15-minute, professional quality videos of research on the UCR turfgrass plots. Must be registered to gain access.
- October 15, 8:30 AM PT: Virtual webinar with presentations and Q&A; participants will receive access to the online field day booklet.
The truth is that you have to allow a certain amount of what may be harmful in order to establish a balanced system that can take care of itself. This is hard. We don't like the occasional brown leaf or aphid sighting. But if we respond to the first sign of trouble with the nuclear option like a broad-spectrum insecticide or fungicide, we kill off our friends along with our enemies. If we can take the wait-and-see approach, we will usually find that our allies will show up in time and restore a balance we can live with. We don't need a perfect landscape, we just need a healthy one.
These are 2-year trials, so the roses planted in 2018 are finished, the roses planted in 2019 are in their second year, and the roses planted late this winter in 2020 are just getting established. We have had roses here long enough now for that healthy balance to take hold. Once again this spring, as is pretty common everywhere, there was a flush of aphids that appeared as the plants were filling in with spring leaves. In mid April, I recorded the presence of these critters, though they had yet to cause any real damage.
This is a model that I have seen succeed again and again. It requires patience and patience is something we may have to teach our clients, our supervisors, and our public agencies. From a labor and financial perspective, this is the most feasible course of action. From an ecosystem perspective, it is the healthiest, most sustainable way we can show our respect for the resilient world we all share.
To Fertilize or Not to Fertilize
One of the most interesting talks at the Landscape Below Ground Conference in Chicago in October was given by Daniel Herms of Davey Tree Company. His lab looked at the effects of fertilizers, growth regulators, and high and low nitrogen mulches (compost vs. chipped pallet wood) on growth, drought-tolerance, and pest and disease resistance in trees.
A general trend emerges from each experiment- when trees are given more nitrogen than is found in the native soil, extra top growth results. The question is this: is this a good thing? You may have a larger canopy, but at what price? In fact, it turns out this is not a good thing.
When top growth is produced out of proportion to root growth, you end up with a tree that is unstable in the landscape. When trees are allowed to grow at their natural pace, they will adjust and balance their canopy growth and root growth through a series of feedback mechanisms between roots and shoots. When you "juice" the canopy growth with readily available nitrogen, you get a top-heavy tree prone to toppling in wet-soil/high-wind situations. And, of course, if you have more leaves than roots, you become less tolerant of drought conditions as well, since your leaves will demand more water than your root system can provide.
Another by-product of fertilization is an abundance of lush, tender foliage that is attractive and susceptible to insect pests. In normal conditions, many plants will produce compounds that give them a degree of resistance to pest attacks, whether insects or diseases. But under the luxurious conditions produced by fertilizer applications, the plants will sacrifice producing these compounds in favor of more lush leaves. It's sort of like over-feeding them and making them fat, lazy, and prone to invaders. The result is that, at least in the species examined, trees were more prone to both insects and disease when fertilized - just the opposite of what many people believe!
The bottom line is this: if you are doing pre-plant soil preparation, adding compost and tilling it in to improve soil structure and organic matter content is a great practice that gets trees off to a good start and sets them up for longevity. After you plant, an uncomposted, chipped wood product is best for a mulch top-dressing. This product will break down slowly contributing additional organic matter at a rate that does not compete with soil microbes and doesn't add too much nitrogen to the tree's growing environment.
This is good news! You don't really need to spend any of your budget on fertilizers for your trees (and I should add that the same goes for woody shrubs), and the best mulch is the relatively inexpensive and readily available chipped wood available from any tree-trimming company or agency! Not only are you doing your landscape a load of good, you are also keeping organic waste out of the landfill!
I attended an informative conference in October that reported on the latest research results on tree root development in urban soils- the Landscape Below Ground. This was the fourth conference on this subject in the last 25 years. Much of the research seemed to confirm findings I had previously read and which have mostly been incorporated into recommendations and practice, at least in the state of California. However, it is always good to have research repeated and confirmed in a variety of scenarios and species, and there were some new and interesting findings as well. I am going to recap some of both in the next couple of posts.
The health of trees initially, especially the structure of their root system, has a significant impact on the survival rate and growth of trees after planting. Fall is an excellent time for planting trees, so pay attention to this if you are installing this season. The most important aspect of the root system (which you should inspect before planting) can be summed up in this phrase: straight roots, some of them near the surface. What trees need, and what you want is a "ladder" of roots, all of them straight or bending less than 45°. You don't want them all going straight down (diving), or the tree cannot stabilize itself in the ground. For all aspects of a healthy nursery tree, see this: Guidelines for Nursery Tree Quality.
At the nursery, a good root system can be accomplished best by one of two methods: potting up to the next size in a timely manner and shaving all roots to the point where they hit the edge at the time of potting up. This eliminates the bends before they set up in the next size. The second method is to use something called an air pot, which has perforations throughout the surface. When roots reach air, they die at the tip rather than continue to grow in a circular manner around the pot. Demand good stock and give your business to nurseries that provide it. The guidelines for growing quality trees can be found here: Quality Tree Production Strategies.
Whenever possible, rip or deep till and incorporate up to 25% organic matter to add carbon and air space for optimal root growth (more than 25% is not better). Shallow tillage has only very brief effects on trees, since roots ideally grow down past the initial 12" rather quickly. Roots grow where they can. Sounds obvious, but without oxygen and carbon dioxide exchange space, without water penetration, roots will not grow out into surrounding soil. Minimum root system means minimum canopy. If tilling cannot be done because of existing trees or other infrastructure, you can add some pore space by deep drilling holes 2' deep and 2" wide and filling with small gravel or biochar, which will maintain the space for oxygen and drainage. Additionally, sufficient space for tree roots should be planned in advance. If pavements must be installed over tree roots' eventual growth area, structural soils can significantly enhance the trees' ability to support healthy growth. To read about a project at UC Davis: UCD Parking Lot Structural Soil. For a complete guide to the first structural soil created by Cornell University researchers and to read research updates (scroll halfway down page): Urban Horticulture Institute.
Do it. Time and again research confirms the benefits of organic mulches for improvement of soil structure, water infiltration, moisture retention, temperature buffering for root health, and the health of beneficial soil microbes. The results are still out on whether the source of the mulch makes a difference, and research is ongoing to find out if mimicking the native soil litter for a particular species is more beneficial than non-specific mulch from other species.
Next week we'll discuss Fertilizing, Disease, and Tree Stability./h3>/span>/h3>/span>/h3>