- Author: Ryan Hill
- Author: Marcelo Moretti
Introduction:
Pollinator insects are essential to produce many economically and nutritionally important crops grown in the western USA. These crops include blueberries, almonds, sunflowers, cucurbits, and many others. Almond pollination in California plays a vital role in the apiary industry, driving beekeepers to haul huge numbers of bee colonies to California for the few weeks in late winter when almonds bloom. Bees are selective of the pollen and nectar they forage, and diverse floral resources can allow bees to forage according to their nutritional needs (Leponiemi et al. 2023). Planting pollinator habitat in natural areas, gardens, and agricultural land is one method of supporting bee health. Irrigated agricultural land in the western USA can be an excellent resource for bees during the dry summer when flowers are rarer. However, the resident weeds in these settings are often not of high nutritional quality for hungry pollinators. To make matters worse, pollinator habitat in agricultural fields can be choked out by competition from weeds. Our control plots from these studies (Figure 1) demonstrate that point effectively.
Figure 1: Control plots at all three experimental sites were extremely weedy. This sometimes meant that none of the planted species could grow, as seen in the pictures above.
Objective:
The studies described here attempt to use herbicides to improve the chances for success in pollinator habitat establishment.
Methods:
Three locations in Oregon's Willamette Valley were selected for studies. Two were hazelnut orchards watered with drip irrigation, and one was a field plot set up for sprinkler irrigation. Each location received different soil preparation. The first orchard location (Corvallis) was not tilled, and soil compaction issues were present. The second orchard location (Amity) was power-harrowed, so the top two inches of soil were loosened. The third location (Lewis-Brown Research Farm) was plowed and disked.
All three locations were seeded in the fall with a set of flowering species with potential for pollinator habitat (Table 1).
Table 1: Species and seeding rates used for pollinator habitat establishment in Oregon's Willamette Valley. |
||
Common Name |
Scientific name |
Lb/Acre |
Hairy vetch |
Vicia villosa |
60 |
Lacy Phacelia |
Phacelia tanacetifolia |
12 |
California poppy |
Eschscholzia californica |
8 |
Farewell to spring |
Clarkia amoena |
2 |
Globe Gilia |
Gilia capitata |
2 |
Sweet alyssum |
Lubularia maritima |
2 |
These species were planted in rows, and herbicide treatments were applied over the top perpendicular to planting rows (Table 2). Four herbicides were applied post-emergence, and the rest were applied one day after planting (pre-emergence). Glyphosate treatments were only included in the orchard trials. Experimental plots were set up as a randomized complete block design with four replicates, and each species was treated as a separate experiment. A crop oil concentrate at 1% v/v was included for Motiff (mesotrione) and Basagran (bentazon), while a nonionic surfactant at 0.25% was included for Matrix (rimsulfuron) and Quinstar 4L (quinclorac). All post-emergent treatments (and glyphosate) included ammonium sulfate (AMsol 1% v/v).
Table 2: Trade name, active ingredient, and rate of herbicides applied to pollinator habitat species. Pre-emergent herbicides were applied at planting, and post-emergent herbicides were applied 30 days after crop emergence. |
||
Trade name |
Active Ingredient |
Rate (product/A) |
Pre-emergent treatments |
|
|
Cornerstone Plus |
Glyphosate |
3 qt |
Alion |
Indaziflam |
4 fl oz |
Trellis SC |
Isoxaben |
21 fl oz |
Devrinol 2XT |
Napropamide |
8 qt |
Chateau SW |
Flumioxazin |
6 oz |
Prowl H2O |
Pendimethalin |
6.3 pt |
Princep |
Simazine |
4 qt |
Motiff |
Mesotrione |
6 fl oz |
Post-emergent treatments |
||
Motiff |
Mesotrione |
6 fl oz |
Matrix |
Rimsulfuron |
4 oz |
Quinstar |
Quinclorac |
12.6 fl oz |
Basagran |
Bentazon |
2 pt |
In Amity, competition from perennial grasses resulted in poor stand establishment. A grass-selective herbicide (clethodim) was used, and the site was reseeded six months after the initial planting when soil conditions were appropriate.
Results and discussion:
Site differences.
Drastic differences were seen between sites. Table 3 shows how crop coverage differed between the three sites for each species.
Coverage at the Corvallis site was deficient for all species except hairy vetch.
Several species did very well at the Amity location. Phacelia in the glyphosate plots was exceptionally well established due to glyphosate's good control of perennial grasses that were not killed by the power harrow.
Lewis-Brown (LB) plots had the best crop establishment initially. However, this location had intense pressure from perennial weeds, so the initial crop establishment did not translate to superior pollinator habitat. The plots at LB where Alion was applied produced a good stand of Canada thistle (Cirsium arvense) by the end of the trial, which the bees loved.
Table 3: Crop Coverage for each species at each location is shown here. The values reported are from the treated plots with the highest coverage. |
|||||||
% Crop coverage (Best treatment) |
Site |
Vetch |
Phacelia |
Poppy |
Gilia |
Clarkia |
Lobularia |
Plowed and Disked |
Lewis-Brown Research Farm (LB) |
100 |
100 |
75 |
84 |
97 |
98 |
Power harrow |
Amity |
55 |
81 |
47 |
47 |
34 |
47 |
No tillage |
Corvallis |
89 |
11 |
28 |
0 |
15 |
0 |
Pre-emergent treatments
Pre-emergent herbicides often had inconsistent pollinator species safety; however, several combinations seemed safe. Napropamide was safe for Phacelia, Gilia, Clarkia, and Lobularia, while flumioxazin and pendimethalin were safe for poppy (Table 5). All five species only had adequate crop establishment at two of the three locations. Hairy vetch establishment was improved by simazine applications at all three locations, but crop coverage was not significantly different from the untreated control for this species (Table 5). Figure 2 shows the treatment by species combinations that were sometimes safe versus the combinations that were consistently safe for the planted species.
At the two orchard sites, glyphosate treatments were the best for Gilia, Phacelia, and poppy establishment (Table 5).
All three trials were conducted on fine soils with organic matter content ranging from 2-7% (USDA-NCSS soil survey). The safety of pre-emergent herbicides for pollinator species establishment may vary depending on soil characteristics.
Post-emergent treatments
Post-emergent (POST) applications were challenging to evaluate for safety. Weed control efficacy was inadequate, and so often, crop establishment was not good enough to confidently assess crop injury.
One exception was hairy vetch. This species exhibited good tolerance to a post-emergent application of Basagran, a result seen at all three locations. The results from two trials suggest that Clarkia tolerated POST applications of Quinstar. Not enough data were collected to conclude the other four species. See Table 4 for crop coverage data.
Conclusions
Site preparation was an essential consideration in our study. Soil compaction and perennial weed pressure must be addressed to have a successful pollinator habitat planting. It was also clear that pre-emergent herbicides can improve habitat establishment, but safety must be adequately established. This is especially true of different soil types and environments. In California's Central Valley, pendimethalin has been seen to occasionally cause injury in poppy plantings, which is in contrast with this study.
Table 4: Spring crop coverage (%) from plots treated with post-emergent herbicides one month after planting, which happened the prior October. Missing data from Phacelia and Lobularia at LB is due to crop loss from frost injury. |
|||||||
Crop coverage (%) |
|||||||
|
Corvallis |
Amity |
LB |
|
Corvallis |
Amity |
LB |
Hairy Vetch |
|
|
|
Gilia |
|
|
|
Untreated |
29 |
28 |
98 b |
Untreated |
0 |
8 |
54 b |
Mesotrione |
21 |
3 a |
0 a |
Mesotrione |
0 |
0 |
0 a |
Rimsulfuron |
18 |
1 a |
0 a |
Rimsulfuron |
0 |
4 |
78 b |
Quinclorac |
34 |
0 a |
28 a |
Quinclorac |
0 |
0 |
6 a |
Bentazon |
50 |
26 b |
94 b |
Bentazon |
0 |
7 |
47 b |
Phacelia |
|
|
|
Clarkia |
|
|
|
Untreated |
0 |
53 ab |
|
Untreated |
3 a |
0 |
83 b |
Mesotrione |
0 |
42 ab |
|
Mesotrione |
0 a |
0 |
34 b |
Rimsulfuron |
5 |
17 a |
|
Rimsulfuron |
4 ab |
0 |
55 b |
Quinclorac |
5 |
64 b |
|
Quinclorac |
15 b |
0 |
77 b |
Bentazon |
2 |
48 ab |
|
Bentazon |
6 ab |
0 |
0 a |
Poppy |
|
|
|
Lobularia |
|
|
|
Untreated |
2 |
11 |
2 |
Untreated |
0 |
0 |
|
Mesotrione |
3 |
11 |
0 |
Mesotrione |
0 |
0 |
|
Rimsulfuron |
6 |
0 |
0 |
Rimsulfuron |
0 |
0 |
|
Quinclorac |
2 |
5 |
3 |
Quinclorac |
0 |
0 |
|
Bentazon |
2 |
9 |
0 |
Bentazon |
0 |
0 |
|
Table 5: Spring crop coverage for pre-emergent herbicide treatments applied just after planting, which happened the prior October. Phacelia and Lobularia experienced winter kill at the LB location, so reported data is coverage from December for that location. |
||||||||
Crop coverage (%) |
||||||||
|
Corvallis |
Amity |
LB |
|
Corvallis |
Amity | LB | |
Hairy Vetch |
|
|
|
Gilia |
|
|
|
|
Nontreated |
29 |
28 ad |
98 b |
Nontreated |
0 |
8 a |
54 c |
|
Glyphosate |
23 |
46 bd |
|
Glyphosate |
0 |
47 b |
|
|
Indaziflam |
6 |
3 d |
79 b |
Indaziflam |
0 |
3 a |
36 bc |
|
Isoxaben |
11 |
17 ab |
83 b |
Isoxaben |
0 |
5 a |
31 ac |
|
Napropamide |
8 |
19 ab |
91 b |
Napropamide |
0 |
38 b |
56 c |
|
Flumioxazin |
5 |
36 bd |
90 b |
Flumioxazin |
0 |
18 a |
2 c |
|
Pendimethalin |
6 |
38 bd |
98 b |
Pendimethalin |
0 |
0 a |
13 ab |
|
Simazine |
34 |
55 d |
98 b |
Simazine |
0 |
44 b |
6 ab |
|
Mesotrione |
6 |
25 abc |
0 a |
Mesotrione |
0 |
3 a |
8 ab |
|
Phacelia |
|
|
|
Clarkia |
|
|
|
|
Nontreated |
0 a |
53 bc |
96 b |
Nontreated |
3 |
0 a |
83 b |
|
Glyphosate |
11 b |
92 c |
|
Glyphosate |
5 |
34 b |
|
|
Indaziflam |
0 a |
13 ab |
90 b |
Indaziflam |
0 |
0 a |
74 b |
|
Isoxaben |
0 a |
0 a |
82 b |
Isoxaben |
0 |
8 a |
88 b |
|
Napropamide |
2 a |
81 c |
98 b |
Napropamide |
0 |
25 b |
86 b |
|
Flumioxazin |
0 a |
30 ab |
57 ab |
Flumioxazin |
0 |
5 a |
20 a |
|
Pendimethalin |
0 a |
0 a |
15 a |
Pendimethalin |
0 |
2 a |
67 b |
|
Simazine |
0 a |
75 c |
56 ab |
Simazine |
0 |
30 b |
0 a |
|
Mesotrione |
2 a |
54 bc |
99 b |
Mesotrione |
0 | 0 a | 25 a | |
Poppy |
|
|
|
Lobularia |
|
|
|
|
Nontreated |
2 a |
11 |
2 a |
Nontreated |
0 |
0 a |
70 c |
|
Glyphosate |
30 b |
42 |
|
Glyphosate |
0 |
21 ab |
|
|
Indaziflam |
2 a |
8 |
8 a |
Indaziflam |
0 |
0 a |
16 ab |
|
Isoxaben |
2 a |
3 |
69 b |
Isoxaben |
0 |
0 a |
0 a |
|
Napropamide |
6 a |
14 |
0 a |
Napropamide |
0 |
47 c |
98 d |
|
Flumioxazin |
2 a |
31 |
63 bc |
Flumioxazin |
0 |
15 a |
34 b |
|
Pendimethalin |
2 a |
40 |
64 b |
Pendimethalin |
0 |
0 a |
0 a |
|
Simazine |
0 a |
46 |
28 ac |
Simazine |
0 |
44 bc |
5 a |
|
Mesotrione |
0 a |
7 |
8 a |
Mesotrione |
0 | 3 a | 3 a |
Figure 2: Crop coverage pictures from two months after planting the Lewis-Brown research farm show that the planted species (rows) tolerated several pre-emergent herbicides (columns). A black outline surrounds successful combinations seen in at least one of the other two trials. Combinations that were never seen to be successful again are surrounded by a red outline.
References:
Leponiemi, M., Freitak, D., Moreno-Torres, M. et al. (2023). Honeybees' foraging choices for nectar and pollen revealed by DNA metabarcoding. Sci Rep 13, 14753. https://doi.org/10.1038/s41598-023-42102-4
Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at the following link: http://websoilsurvey.sc.egov.usda.gov/.
- Author: Ryan Daugherty
I recently helped one of our local student gardens install a drip irrigation system in some raised beds. During the installation, I had to explain why we were using ½” tubing for most of our system instead of ¼”. Some believed that using the smaller tubing would give us better pressure, like putting your thumb over the mouth of a garden hose. I explained why this would actually result in less pressure and worse water distribution throughout our system. This misconception is common, so I thought I'd discuss it here.
If you think there's no way I'm about to talk physics in a garden blog, prepare to be amazed!
First, a review. Friction is the force that opposes the sliding or rolling of one solid object over another. There are a few different types of friction, but the one most relevant to our irrigation lines is kinetic friction.
Kinetic friction is the force that opposes the movement of two objects in contact while in motion. Think of it like using the brakes on a bicycle: when you pull on the brake lever, the brake pads contact the wheel, and the kinetic friction between the pads and the wheel opposes the wheel's forward motion, eventually stopping the bike. As water moves through our irrigation lines, it is in contact with the inside of the tubing. The kinetic friction between the water and the tubing surface opposes the water's forward motion, resulting in a loss of pressure. In irrigation lingo, we call this "pressure loss from friction" or just "friction loss."
If you could see a cross-section of your tubing while water was running through it, you wouldn't see a solid cylinder of water. Instead, it's more turbulent, with empty space, bubbles, and vortices. If the amount of water moving through the line remains constant and we decrease our tubing diameter, that empty space shrinks, and more water comes into contact with the sides of the tubing. More surface area of the water in contact with more surface area of the tubing generates more friction, resulting in more pressure loss.
Like tapping the brakes on a bicycle, there isn't much friction generated when it's just your thumb at the end of a garden hose. The real pressure loss comes from consistent friction over distance, like holding the brakes down until the bike stops. Multiply even a small amount of friction over any real distance, and you're looking at significant pressure loss.
In response to this, drip irrigation experts developed “rules” or guidelines for drip irrigation. For ¼” tubing, we call it the 30/30 rule: no more than 30 feet in any given run of ¼” line, drawing no more than 30 gallons per hour (GPH). More than 30 feet generates too much friction loss, and hydraulically only so much water can move through any given volume of tubing, hence 30 GPH. For ½” tubing, it's the 200/200 rule, for ¾” it's 480/480, and so on. As our system grows in length and demand, our tubing diameter has to increase accordingly.
If we don't match our system to the length and demand, we risk poor distribution uniformity. We might have to overwater or underwater one part of our garden to properly water another, leading to water waste and poor plant health. For most home landscapes, 1/2" tubing works well since we seldom run more than 200 feet on a single line.
These principles are simple but powerful, and by understanding them, you can make more thoughtful decisions in the design of your drip systems to get the most out of them.
Thanks to the generosity of the Hrdy family, we are pleased to announce that the following proposals have been selected for funding through The Daniel & Sarah Hrdy Fund for UC Cooperative Extension Research.
- Evaluation of climatic drivers of endemic and invasive citrus pest populations using grower data (Bodil Cass, Hamutahl Cohen, Sandipa Gautam, and Jay Rosenheim)
- Protecting Crops Providing Homes: The Raptor Nest Box Grower Alliance (Breanna Martinico)
Proposals were submitted by individuals or teams. Proposal reviewers ranked the 25 submissions, giving priority to outstanding proposals submitted by early to mid-career level (assistant to associate level) UC ANR academics. Projects will receive three to five years of funding, with up to $25,000 per year. Funds will next be available for proposal submission in 2025.
Brent D. Hales
Associate Vice President, Research and Cooperative Extension
- Author: Belinda Messenger-Sikes
The emerald ash borer (EAB) may be beautiful, but it is the most destructive forest pest ever seen in North America. Hundreds of millions of ash trees across 36 states and 5 Canadian provinces have been killed by this invasive insect. Fortunately, EAB has not been found in California, but it was discovered in Oregon in 2022, the first time this insect has been detected on the West Coast.
Emerald Ash Borer Awareness Week is May 20-26th of 2024. During this week, the Don't Move Firewood campaign is offering SIX webinars over the first three days (May 20, 21, 22). Webinar topics include exciting new developments in ash tree breeding and resistance, research findings on best management strategies, and important updates on management responses to EAB. Register for any or all of these free webinars at https://www.dontmovefirewood.org/eabweek2024/.
If you think you've seen the pest or ash tree damage caused by an EAB infestation, report it to your local County Agricultural Commissioner's Office or the California Department of Food and Agriculture at https://www.cdfa.ca.gov/plant/reportapest/.
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- Author: Ryan Daugherty
It's a common frustration that anyone with a garden or landscape can relate to. I think that the temptation to apply undiluted herbicide stems from a widely held belief that the language on the label about human safety, environmental hazards, and the mixing instructions are just veiled regulatory activism designed to water down an effective product, sacrificing potency in service of some ulterior green agenda.
If you're like my friend and the conventional concerns aren't persuasive in the face of your weed woes, you may find it more persuasive (like he did) to know how declining to mix herbicides can actually make them a less effective tool in your quest for weed vengeance.
Misapplication Can Be a Waste of Your Time and Money
Herbicides can be broken up into several different categories, but two big ones are contact vs. systemic. A contact herbicide damages only the parts of the plant that it touches. Systemic herbicides translocate, meaning they move throughout the plant and poison the entire plant regardless of the point of contact.
Many well-known, home-use, brand-name weed killers sold at your garden center are systemic herbicides. When you use an excessive dose of systemic herbicide, it can damage the conductive tissue at the point of contact. This means that the material doesn't get translocated effectively and ends up working more like a contact herbicide, burning the parts of the plant it came into contact with and leaving others healthy and able to regrow. Systemics typically cost more than contact herbicides, making your cost per application higher.
Using systemics undiluted (and thus using more product) means that your cost per application is even higher than that. If you didn't mix your herbicide, you may not get the control that you need, and perhaps worse, you will have paid a premium to do it! This wastes your time and money. Don't do it to yourself. (And it's not legal and could be unsafe to you or animals.)
Microbial Breakdown
Some herbicides boast longer control for weeks or months. In the pesticide industry, this is called “residual action” or “pre-emergent action” in the weed control game: an herbicide that continues to work for a period of time after the application to ward off future weed incursions. Several things affect an herbicide's residual action, but one of the big ones is microbial breakdown.
Soil microbes are microscopic life forms like bacteria, fungi, protozoa, etc., that live in the soil. They break down all kinds of materials in the soil into their basic parts for use in their own growth and development, with different microbes being better adapted to breaking down one kind of material or another. Those materials include herbicides, which is great news because it means that herbicides don't hang around in our soils forever. However, it can be bad news when we abuse herbicides.
When we over-apply our herbicide either through dosage or application frequency, we could create a microbial imbalance in the soil. We kill some species of microbes vulnerable to the material while encouraging the population of others that are adapted to thrive on breaking down that specific material. In addition to the implications for the health of your soils, this imbalance also means that our residual herbicides are actually shorter-lived as they come into contact with a super population of soil microbes that break it down more rapidly. This is called “enhanced microbial degradation,” where pesticides are broken down more rapidly than they would be under normal conditions, even within a few hours. Like systemics, residual/pre-emergent herbicides typically come at a premium price, and your money can be wasted if your applications start becoming dinner time for a booming population of hungry microbes.
It will also mean that you won't get the longer-lasting control that you wanted and paid for, making breakout weeds and headaches more likely.
Spray Adjuvants
When you buy an herbicide, you aren't just paying for the active ingredient(s); you're also getting what they call the adjuvant package. Adjuvants are materials added to the herbicide formulation not necessarily to make the poison more poisonous, but to enhance the act of applying the herbicide itself.
If you were an herbicide manufacturer and you had a product that would work great if it didn't just bead up on the plant's surface, you would add an adjuvant to reduce the surface tension of the product. If it is too thin and runs off the plant before it can deliver the material, then there's an adjuvant for that too. Does it break down and become inert at certain soil or water pH levels? Does it gum up sprayers? Does it foam? Are the droplets too fine and prone to drift? Adjuvants have you covered. There's an adjuvant for nearly any application.
When manufacturers formulate their adjuvant packages, they do so with the assumption that you will follow the mixing instructions on the label. The adjuvants are designed to work best at the concentrations listed. Some of them are even activated by mixing them with a solvent like water or oil. If you apply the herbicide without mixing, then the active ingredient may not be delivered, or its mode of action hindered, all because you thought you knew how to use the product better than the people who designed and tested it.
Manufacturers want their products to work and to make you a satisfied customer willing to repeat your business. The label is how manufacturers communicate to their customers how to use their product for best results. When herbicides are used judiciously and responsibly, they can be powerful tools, especially when integrated with other weed management practices such as mulching, hoeing, and sensible irrigation practices. But don't skip the label!
Failure to follow label guidelines can lead to unintended consequences not just for the environment but for your busy schedule and your wallet as well.
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