honeybees find abundant nectar in the tubular flowers of Texas sage

The bees are out.

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?

Imidacloprid is a broad-spectrum insecticide of a type known as neonicotinoids, or neonics as they are sometimes called. These insecticides are highly effective at killing sucking insects that feed on treated plants. The most recent research shows there is also a negative effect on bee survival when they eat pollen from plants treated with neonics. Not only that, but beneficial insects that feed on pests that have eaten treated plants also show lowered survival rates. That means that not only are you killing the pest, you are killing the good bugs, like ladybugs and green lacewings, that help keep pests like aphids and spider mites in control. Additionally, some parasitoid insects that lay their eggs in aphids and kill them, feed on pollen as adults and are also affected negatively. That's why we sometimes call this the nuclear option.

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.

Next, provide some diversity in your planting schemes because a wide variety of flowering plants and plant forms support a wider variety of beneficial insects that can control pests. For instance, ornamental grasses like deer grass, fountain grass, or feather reed grass provide over-wintering shelter for ladybugs, keeping them on site. 

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.

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.

1. SHADE TREE DISEASE WEBINAR SERIES (UCCE)

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. 

LINK:SHADE TREE DISEASE WEBINAR SERIES INFO & REG

 

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. 

Link: ISA Z133 TREE SAFETY COURSE 

 

Other ISA sponsored events:

FREE TREEFUND WEBINARS

POST-FIRE TREE RISK ASSESSMENT 

 

3. 2020 TURFGRASS RESEARCH FIELD DAY (UCR/UCCE)

• 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.

       LINK TO INFO/REGISTRATION/AGENDA

One of the beautiful things about conducting "NO SPRAY" plant trials is seeing just how resilient landscapes can be if you give them a chance. We are all familiar with "helicopter parents", those fussy fearful folks who hover over their children to protect them from every possible physical and emotional risk of harm. Well, I think there are way too many helicopter gardeners- hovering over their plants with a spray bottle in one hand and a granulated fungicide in the other!

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.

This became really obvious to me again this spring in our Stockton trial plots of the American Rose Trials for Sustainability at the San Joaquin County Agricultural Center. The first two years after converting grass lawns into rose trial plots we were plagued with some pretty heavy aphid and thrips damage. Because this is a NO SPRAY trial, we simply observed and recorded what we saw, which was still pretty good performance despite some leaf scarring.

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.

Two weeks later when I went back to take end of the month ratings, I spotted in all the plots at least 4 different natural enemies working diligently to clean up our pests! These included lady bugs, syrphid flies, tachinid flies and green lacewings. Was there some early leaf and flower bud damage? A bit. But with the hands-off approach, the plants have since outgrown early munching and show no significant signs of the earlier infestation.

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!

It is still confirmed over and over by research that organic mulch in the root zone of trees produces more fine roots, less compaction, and higher levels of beneficial microbial activity that contributes to the availability of necessary nutrients for tree growth.  One aspect of any organic mulch is the carbon-to-nitrogen ratio, sometimes written as C:N.  Typical chipped wood has a high C:N ratio - there is much more carbon than nitrogen - whereas something like composted steer manure has a low C:N ratio, with high levels of nitrogen.  In fact, most any fully composted green-waste is going to have a much lower C:N level than a simple chipped wood material, because microbes have already digested a good portion of the carbon and converted some of the nitrogen to a form readily available to plants.  Adding this type of material directly to the surface as a mulch application has much the same effect as adding a nitrogen fertilizer- rapid top growth to the detriment of overall tree health.

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!