Weed size and post-emergence herbicide efficacy

Weed management is essential during the establishment phase of orchards to improve the survival of newly transplanted nursery stock. In commercially bearing systems, weeds must be controlled in order to increase irrigation efficiency, provide equipment access, and ensure that fruits can be harvested effectively and economically. Furthermore, non-managed weeds may support populations of insect, vertebrate, and pathogenic pests that can significantly reduce tree health over time.

Weed control strategies may not always be 100% effective and escapes can occur for numerous reasons. Situations leading to herbicide failure include: improper herbicide selection or inappropriate timing of chemical applications, unfavorable weather conditions at the time of treatment, reduced herbicide activity due to poor water quality, and the development of herbicide resistance in the target weed population, among others. Plant size can also affect weed control; the efficacy of post-emergence herbicides is often diminished when products are applied to large/mature plants (Figure 1).

Figure 1. Ineffective management of large weeds in a plum orchard with a contact herbicide. Reduced control is attributed to poor herbicide coverage and subsequent plant regrowth.

 

As an example: weed scientists at the University of California, Davis, recently undertook studies to describe how the control of hairy fleabane (Conyza bonariensis), a close relative of marestail/horseweed (Conyza canadensis), differed with respect to plant size at the time of herbicide application. Treatments included: glyphosate (Roundup WeatherMax at 3.5pt/A), glufosinate (Rely 280 at 3 pt/A), paraquat (Gramoxone Inteon at 3pt/A), and saflufenacil (Treevix at 1 oz/A) applied at one of three different growth stages: small rosette (4- to 5-leaf, < 1 inch height), large rosette (15- to 20-leaf, < 7 inches in height), and bolting (> 20 leaves, 7 inches in height).

Greater than 90% control of hairy fleabane was achieved when plants were treated with glyphosate, regardless of size at the time of application (Table 1). Glyphosate is a systemic herbicide that it is translocated within treated plants; it eventually accumulates at meristems and inhibits the production of aromatic amino acids (tryptophan, tyrosine, and phenylalanine) that are needed for protein synthesis. Conversely, the efficacy of glufosinate, paraquat, and saflufenacil decreased when hairy fleabane plants began to bolt (Table 1). Unlike glyphosate, these active ingredients exhibit no or limited mobility in treated plants; as a consequence, herbicide-induced injury is limited to the tissues that come into contact with the spray solution. In the case of larger plants, the outermost portions of the canopy can act as a shield for the innermost leaves, stems, and buds, which may continue growing. Additionally, contact herbicides will not impact underground tissues (roots, rhizomes, bulbs, etc.), which also support plant regrowth.

Table 1. Hairy fleabane control with glyphosate (Roundup WeatherMax at 3.5pt/A), glufosinate (Rely 280 at 3 pt/A), paraquat (Gramoxone Inteon at 3pt/A), and saflufenacil (Treevix at 1 oz/A) as affected by plant size at the time of application.

 

Still, it isn’t sufficient to focus on in-season weed control as the sole metric of efficacy. Plants that escape treatment may reach reproductive maturity and produce viable seeds. These seeds are the foundation for weed problems in future years. As a consequence, weed escapes necessitate that growers engage in additional management practices that may have been unplanned and that add to the cost of crop production. Increased seedbank/in-field weed densities could also facilitate the development of herbicide resistance. When weed infestations are heavy, the probability of selecting for resistance can be high, even if the mutation rate that leads to the development of resistance is low.

There are several steps that growers can take to maximize weed control with post-emergence herbicides, including timing applications to treat weeds while they are small and tender. Additional strategies include: selecting the appropriate herbicides to control target weed species and applying them at appropriate rates, minimizing off-target movement due to rain and wind, calibrating spray equipment, properly, and using adjuvants, effectively, to ensure coverage and penetration. To minimize the potential for herbicide resistance, growers should diversify their chemical, cultural, and physical weed control strategies as much as is environmentally and economically possible.

Any mention of herbicides in this blog does not constitute a professional recommendation by the author or her employers.

What’s with those different herbicide names?!?

Ever wonder why sometimes a weed scientist will say ‘glyphosate’ and another time they will say ‘Roundup’? There’s actually a good reason for this – they are either talking generally about an active ingredient or else specifically about a formulated product.

Let’s look at ‘glyphosate’ in more detail. There are three different ways that we can refer to it:

Firstly, by its chemical name

This is the name that describes the chemical composition of an active ingredient (probably the most rarely encountered term).

i.e. N-(phosphonomethyl) glycine

 

Secondly, by its common name

A unique name given to each active ingredient.

i.e. glyphosate

 

Trade name

The name an individual manufacturer gives a formulated product (or combination of chemicals) that make up a formulated product (a.k.a. the name the herbicide is marketed under).

i.e. Roundup, Accord, Rodeo, Touchdown, Acquire, Glyphomax, and approximately 700+ others!

And now you know.

Any mention of herbicides in this blog does not constitute a professional recommendation by the author or her employers.

Technology and specialty crops

Just read this really awesome article by Helena Bottemiller Evich entitled “The Vegetable Technology Gap” at Politico.

http://www.politico.com/agenda/story/2017/03/fruits-and-vegtables-technology-000337

Some snippets that I found extremely interesting regarding the historical funding for research into fruits and vegetables:

“So-called “specialty crops”—the government’s name for the category that includes, essentially, all fruits, vegetables and nuts—received just 15 percent of the federal research budget over much of the past three decades.”

“Specialty crops remain special—just 3 percent of cropland is dedicated to growing them—though they make up roughly a quarter of the value of crops grown in the U.S. because they demand higher prices. This lopsided dynamic means that specialty crops have historically received very little federal research investment compared to their value. It also means the country simply doesn’t have a food system that supplies what we’re told to eat. In 2007, there were about 8.5 million acres of specialty crops in a sea of more than 300 million acres of everything else.”

But I’m not gonna give all the secrets of this article away. Do yourself a favor and read it to learn more about the challenges and the successes related to specialty crop production, storage, and transport.

Cheers!

 

Herbicide-related definitions

When I first started my Ph.D. in Weed Science, I encountered a strange, new language that appeared to be composed, almost entirely, of acronyms. PRE. POST. PD. Layby. PPI. AI. Etc…

You see, I didn’t grow up in, or even around, agriculture; I was born and raised in the “Coal Region” of Pennsylvania and I was infinitely more likely to see anthracite sliding down the chutes of coal trucks (into my neighbors’ basements) than I was a John Deere tractor.

So I had to learn. This blog is meant to be a primer for the (similarly) uninitiated.

Firstly, a definition to get us started.

Herbicide: To be honest, there are lots of definitions out there, and they all say just about the same thing: Herbicides are materials that are used to control or kill plants.

Herbicide label: A legal document (recognized by courts of law) describing the brand name or trade name of the product; the name and address of the manufacturer; the amount of active and inert ingredients in the container; the net contents of the container; the EPA registration and establishment numbers; whether the product is for general or restricted use; directions for use, storage and disposal; re-entry, replanting, harvesting and grazing restrictions; environmental hazards and first aid treatments.

Herbicides can be further defined in several ways based on their general mode of action (contact vs systemic), their selectivity (selective vs non selective), their timing (e.g. pre-emergence vs post-emergence) and their application strategy or placement (e.g. broadcast vs banded, soil vs foliar), in addition to other characteristics. This next section will attempt to address the multiple classifications that people may expect to encounter.

Definitions describing the placement of applications.

Soil applied: Herbicides applied to the soil that come into contact with germinating or emerging weeds or into contact with the roots of emerged weeds.

Foliar applied: Herbicides that are applied directly to the plants.

Broadcast: The application of herbicides evenly across an entire area.

Banded: The application of herbicides over a portion of the total treatable area (for example, in strips on top of a seeded row).

Directed: The application of herbicides that are targeted at a very specific area (for example, at the base of a crop plant). In certain situations, this might be referred to as a lay-by application.

Definitions describing the timing of herbicide applications.

Pre-plant (PP): Herbicides applied prior to planting. Often, this may refer to herbicides that are applied well in advance of crop planting in order to treat existing vegetation.

Pre-plant incorporated (PPI): Herbicides that are applied prior to planting and that are incorporated into the soil.

Pre-emergence (PRE): Herbicides that are applied prior to crop and/or weed emergence. The herbicides that are considered PRE may also be referred to as ‘residual’ herbicides meaning that they are applied to the soil where they provide ‘extended’ control of germinating or emerged weeds.

Post-emergence (POST): May also be referred to as ‘topical’ or ‘over-the-top’ herbicides. Herbicides that are applied after crop and weed emergence.

Definitions related to herbicide selectivity.

Non-selective: Synonymous with ‘broad-spectrum’; a herbicide that controls many different types of plant species.

Selective: A herbicide that is effective at controlling some species but not others (for example, mostly broadleaves or mostly grasses).

Definitions related to activity.

Contact: Herbicides that affect only the plant tissues that they come into contact with.

Systemic: Herbicides that are translocated, or moved, throughout a plant.

Site of action: The specific, biochemical site within a plant with which a herbicide directly interests. Often confused with ‘mode of action’, which references the entire sequence of events that results in plant death and injury. For more information about herbicide sites of action, see the WSSA website.

The majority of this information was gleaned from training materials developed by the WSSA. The information was kept relatively simple on purpose.

This post was originally published on the Weed Science Blog at the UC ANR website.

Weeds that sound pretty: A Valentine’s Day post

You just KNOW that some plants are considered weeds. Their common names give them away. They sound awful. Giant hogweed (Heracleum mantegazzianum). Ripgut brome (Bromus diandrus). Devil’s claw (Proboscidea lutea). Smellmelon (Cucumis melo). Itchgrass (Rottboellia cochinchinensis). Dog-strangling vine (Cyanthum rossicum).

Others…well, others seem more benign. Even sweet. For Valentine’s day I present to you nine weedy plants with lovely names. Enjoy…

1. Tree-of-Heaven (Ailanthus altissima). How celestial (Sigh…). How divine (Sigh…). How invasive (sigh…wait, what?). Tree-of-heaven is a deciduous tree, native to China, in the Simaroubaceae. It has been used, extensively, as a street tree; in fact it is the subject of A Tree Grows in Brooklyn by Betty Smith. But it suckers. A lot. And it stinks. A lot. And it spreads, rapidly, by seeds (lots and lots of seeds!) and root-sprouts. Some people living in urban areas have renamed it ‘Tree-of-Hell’.

USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner’s Sons, New York. Vol. 2: 446.

2. Baby’s breath (Gysophila paniculata). Baby’s breath?!?!? Baby’s breath?!?!? That delicate plant in the Pink family that is beloved by florists? You would have to work REALLY hard to make up a sweeter sounding name for a pest! Like ‘Fuzzy kitten herb’ or ‘Baby giraffe weed’. Or ‘Mouse ear chickweed’ (That last one is real…). But baby’s breath has become invasive in certain habitats, like Sleeping Bear Dunes in Michigan, where it escaped from gardens.

3. Amaranthus spp. The genus name is derived from two Greek words: amarantos (unfading) and anthos (flower). There it is. Unfading flower. A perfect metaphor for love, no? Well, I’ve got two words of my own for you: PALMER AMARANTH. Enough said. (To be fair, many Amaranths are used worldwide as food sources, either leaves or seeds…but my animosity isn’t directed at them.)

4. Love-apple (Solanum capsicoides). Sounds delicious, right? If you are talking about a tomato (Lycopersicon lycopersicum), sure. If you are talking about red soda apple (a.k.a. devil’s apple and cockroach berry), not so much. The fruits are toxic and have been/are being used in many countries for rodent and insect control.

5. Multiflora rose (Rosa multiflora). A ‘rose with many flowers’, how can that be bad? HA! The intentions were good when this species was being promoted in the 19th and 20th centuries (ornamental shrub, erosion control, living livestock fence, wild-life food source), but things have gone terribly wrong since then. This shrub forms dense stands that can displace native vegetation.

6. Love leaves (Arctium minus). It sounds like you could brew up a nice aphrodisiac from this species. Although parts of the plant are said to be edible, love leaves, better known as common or lesser burdock, is also listed as being toxic in many weed guides. However, burdock doesn’t make this list because of its questionable medicinal or culinary virtues, but rather for its seed. The tiny hooks on the seeds of this plant were the inspiration for velcro. Try pulling them out of the fur of a long-haired dog…

7. Heart’s ease (Polygonum persicaria). Better know as smartweed or ladysthumb. This weed can grow everywhere, it seems. Seriously. It is even found in Greenland.

USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner’s Sons, New York. Vol. 1: 668.

8. Love vine (Convolvulus arvensis). Love may keep us together, but you don’t want to be in a relationship with this plant, which is better known as field bindweed. This perennial species is listed as one of the most noxious weeds in the WORLD. It has roots that can grow to depths of >10′, it reproduces by seed and rhizomes, infrequent tillage just makes it mad, and repeated applications of herbicides are needed to suppress it. This plant also goes by the name possession vine…and you’re nobody’s property.

USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner’s Sons, New York. Vol. 3: 47.

9. Bouquet-violet (Lythrum salicaria). People love getting flowers on Valentine’s day, right? Maybe you shouldn’t send this ‘bouquet’, though, which you probably know better as purple loosestrife. This plant was introduced, intentionally, to North America as an medicinal herb, but it has since escaped from our gardens and become naturalized. Large infestations can alter water flow in streams and rivers, reduce native plant species diversity and negatively impact macrofauna, such as amphibians and waterfowl, that rely on wetlands for food and shelter.

This entry was originally posted on the UC Weed Science Blog at the UC ANR website. Any mention of herbicides in this blog does not constitute a professional recommendation by the author or her employers.

Velvetleaf and of the threat of foreign rope (and other interesting information)

Abutilon theophrasti (commonly known as velvetleaf) is a summer annual weed native to Asia. For those not familiar with the species, plants are tall (to 1-2 m) and erect with green- or purple-colored stems that branch at higher leaf axils (Warwick and Black 1988). The leaves are heart-shaped and covered in soft hairs (hence the name ‘velvetleaf’) (Warwick and Black 1988). Pale yellow- to yellow-orange-colored flowers are borne singly in the axils of leaves or in small clusters on short branches in the plant canopy (Warwick and Black 1988). Seed capsules are cup-shaped, hairy and either brown- or yellow-colored (Warwick and Black 1986, Kurokawa et al. 2003). Individual seeds are kidney-shaped and grey to black in color (Warwick and Black 1986).

 

Figure 1. The characteristic heart-shaped leaves and kidney-shaped seeds of velvetleaf (Abutilon theophrasti)

Velvetleaf, like kenaf (Hibiscus cannabinus L.), beach hibiscus (Hibiscus tiliaceus L.), roselle (Hibiscus sabdariffa L.), and other members of the Malvaceae, has been, and still is cultivated for its stem fibers, which are used in the manufacture of rope, twine, and other materials (Dempsey, 1975). Velvetleaf was domesticated in central China, where it was grown for its soft and lustrous stem fibers (Dempsey 1975). Stem tissue has been used alone to produce twine, paper, sacking, netting, and coarse cloth, or blended with silk to make satin and brocades (Dempsey 1975, Spencer 1984). It has been suggested that velvetleaf was introduced, purposely, to colonial America to serve as a fiber source for the manufacture of cordage and other necessities (Dempsey 1975, Spencer 1984).

Although velvetleaf was actively cultivated in the 1700’s, the crop was never economically successful. In the 1800’s, there was frustration with the United States Navy’s dependence on rope produced in Eastern Europe and Russia; as a consequence, farmers were asked to make better use of the plant. Don’t forget, the Navy we recognize now wasn’t the navy we had back then; the ships were wooden and relied on sails for propulsion. And sails relied on rope, lots and lots of rope. For example, USS Constitution was a three-masted frigate with masts that ranged from 173 to 220 feet in height and could require more than 4 miles of rigging. In short: our country didn’t want our military to be dependent on foreign rope!

Whether it was brought here intentionally or not, it is safe to say that velvetleaf has become an established pest. As of January 2017, the USDA PLANTS database indicated that the species can be found in the 48 contiguous states and 9 Canadian provinces.

Now for the boring stuff.

Not all velvetleaf is created equal; it looks as though crop and weedy biotypes exist and differ in their growth and development. Describing the defining characteristics  separating the crop and the weedy forms will help us understand responses to selective pressure in velvetleaf and crop-weed evolution in general.

Scientists have shown that a substantial amount of variability exists among velvetleaf accessions with respect to physical appearance, flowering phenology, and capsule color. In 2003, while working in John Cardina’s lab (Ohio State), I  conducted a study to characterize the morphological and phenological variation present in velvetleaf accessions from Asia, Japan, India, Europe, Eastern Africa and North America. Velvetleaf seeds (80 accessions from 21 countries) were obtained from Dr. R.N. Andersen (USDA-ARS, retired) and the U.S. National Plant Germplasm System (NPGS) (NPGS samples used in our study were originally collected by the N.I. Vavilov Institute of Plant Industry between 1916 and 1940. Kurokawa et al. 2003). Replicate samples from each accession (a minimum of 5 to 7 plants, each derived from a different parent) were grown in a greenhouse at the Ohio Agricultural Research and Development Center (OARDC) in Wooster, OH. A total of 586 plants from 77 accessions were evaluated. Some of the attributes that were described included: stem height (mm) at 4, 7 and 10 weeks; number of days from sowing to flowering; stem height (mm) at flowering; duration of flowering (days); number of days from sowing to harvest; final height (cm) at harvest; number of nodes at harvest; number of capsules (seed pods) per plant at harvest; and capsule color.

Figure 2. and example of the differing colored capsules (yellow and black) observed in the velavetleaf accessions.

Results from our study indicate that accessions producing yellow-colored capsules differed significantly from those possessing brown-colored capsules. In general, plants with yellow seedpods were:

1) taller,

2) flowered later and for a shorter period of time,

3) and produced fewer seedpods per plant as compared to plants producing brown capsules.

Figure 3. Some of the morphological and phenological differences between velevetleaf biotypes producing yellow and brown capsules.

Our results are in agreement with Kurokawa et al. (2003) who reported that the NPGS accessions could be divided into two forms (“crop” and “weedy”) based on a comparison of their morphological and phenological characteristics. According to Kurokawa et al.(2003), crop forms (which were primarily collected from Africa, Asia and India) are:

1) possessed yellow-colored seed capsules,

2) were taller at all observation dates,

3) were minimally branched, and

4) had a longer vegetative phase than their weedy counterparts.

Figure 4. Our multivariate analyses demonstrating the collective morphological and phenological separation between the crop and weedy biotypes.

Weedy accessions (which were typical of Europe and the US) were shorter, more branched, and produced greater numbers of non-dormant seeds in brown seedpods (Kurokawa et al. 2003). The differences among the crop and weedy forms suggests that they have been subjected to different selection pressures. An upright, minimally branched form of velvetleaf would allow for the easier harvest of stem fibers (Kurokawa et al. 2003). Velvetleaf appears to be determinant with respect to growth; an increase in the duration of the vegetative phase would result in greater stem height, which is directly related to fiber yield (Kurokawa et al. 2003). A rapid transition between the vegetative and reproductive phases could be an advantage for the weedy velvetleaf, as this allows for increased reproduction potential (Baker 1974, Patterson 1985). Increased branching  is associated with increased capsule production because velvetleaf flowers are produced on short branches that develop from leaf axils in the canopy of the plant (Warwick and Black 1988). Kurokawa et al. 2003) speculated that the yellow capsule color, which is a recessive trait, may have served as a tool for preventing genetic contamination from the weedy forms.

Baker, H.G. 1974. The evolution of weeds. Annual Review of Ecology and Systematics 5:1-24.

Dempsey, J.M. 1975. Fiber Crops. University of Florida Press. Gainsville Florida

Kurokawa, S., N. Shimizu, S. Uozumi, and Y. Yoshimura. 2003a. Intra-specific variation in morphological characteristics and growth habitat of newly and accidentally introduced velvetleaf (Abutilon theophrasti Medic.) into Japan. Weed Biology and Management 3:28-36.

Kurokawa, S., N. Shimizu, S. Uozumi, and Y. Yoshimura. 2003b. ISSR variation in a worldwide collection of velvetleaf (Abutilon theophrasti) and the genetic background of weedy strains mingled in grains imported into Japan. Weed Biology and Management 3:179-183.

Patterson, D.T. 1985. Comparative ecophysiology of weeds and crops: Pages. 101–130. In S. O. Duke, ed. Weed Ecophysiology. Volume. 1 Reproduction and Ecophysiology. CRC Press. Boca Raton, FL.

Spencer, N. R 1984. Velvetleaf, Abutilon theophrasti (Malvaceae), history and economic impact in the United States. Econ. Bot. 38: 407-416.

Warwick, S.I. and L.D. Black. 1986. Genecological variation in recently established populations of Abutilontheophrasti (velvetleaf). Canadian Journal of Botany 64:1631- 1643.

Warwick, S.I., and L.D. Black. 1988. The biology of Canadian weeds. 90. Abutilon theophrasti. Canadian Journal of Plant Science 68:1069-1085.

This post is an updated version of a blog contribution originally published at the UCANR WeedRIC website.

The timing of POST herbicides on field bindweed suppression

Field bindweed (Convolvulus arvensis L.), a deep-rooted and drought tolerant perennial (DeGennaro and Weller 1984; Frazier 1943a, 1943b, 1943c; Sharma and Singh 2007; Shrestha et al. 2007; Swan and Chancellor 1976; Weaver and Riley 1982; Wiese and Lavake 1986; Yerkes and Weller 1996). Although bindweed seedlings are relatively easy to manage using physical and chemical control strategies, established plants with extensive root systems are relatively tolerant to most management practices. For example, perennial bindweed control with tillage and cultivation is made more difficult by the weed’s significant below-ground nutrient reserves and regenerative capacity (Derscheid et al. 1970; Frazier 1943a, 1943b, 1943c; Swan 1980; Swan and Chancellor 1976; Weaver and Riley 1982). Infrequent mechanical cultivation may also facilitate plant spread by dispersing root fragments. Post-emergence herbicides are also important tools for managing perennial weed infestations. However, the efficacy of some products can vary, sometimes depending on application date. Wiese and Lavake (1986) demonstrated that field bindweed suppression could be affected by the seasonal timing of herbicide applications; a summary of 22 trials found that ‘the best control [of field bindweed] with glyphosate…came at any time of the year when bindweed was growing vigorously’ (Table 1).  Similar results have been reported by other authors (Dall’Armellina and Zimdahl 1989; Knezevic et al. 2009; Westra et al. 1992) who have also suggested that bindweed vigor can impact weed control success.

In 2016, we conducted a study at the University of California (Davis campus) research farm in Davis, CA, to characterize bindweed control by some post-emergence herbicides  with a specific emphasis on describing how seasonal timings may affect suppression. Glyphosate (as Roundup Powermax at 1 and 2 qt/A), rimsulfuron (as Matrix at 2 oz/A), halosulfuron (as Sandea at 2 oz/A), glufosinate (Rely at 3 pt/A), paraquat (Gramoxone Inteon at 3 pt/A) and saflufenacil (Treevix at 1 oz/A) were applied to emerged bindweed using a CO₂-pressurized back pack sprayer set to deliver at 30 GPA on either 18 May, 2016 (defined as APR-MAY, to newly emerging vines, vegetative growth only) or 30 June, 2016 (defined as JUNE-JUNLY, to vigorous vegetative growth and flower production). Vine cover (% of plot area covered with vines), the percent (%) of vines that were flowering, and the vigor of the vines (vigor as rated on a scale between 1 and 5, where 1 = less vigorous and 5 = more vigorous) was evaluated between 18 May and 13 August, 2016. The study was terminated on 13 August because the bindweed vines were becoming infested with powdery mildew.

Bindweed cover, vigor, and reproductive potential changed, dramatically, throughout the course of the study, even in the absence of herbicides (Figures 1 and 2). The percent area of the non-treated plots covered in field bindweed on 13 May was 38%; cover increased to 78% on 14 June and then fell to 21% on 13 August. The percentage of bindweed vines producing flowers exhibited a similar trend; flowering was greatest on 1 and 14 June (50 to 53%) and lowest on 18 May and 13 August. Plant vigor ranged from 3 to 4 between 18 May and 14 June and then fell to below 2. Changes in bindweed cover, flowering and vigor were attributed to the effects of abiotic and biotic stresses, namely high temperatures, limited soil moisture, and a powdery mildew infestation.

Results show that the APR-MAY herbicide applications provided almost no control of field bindweed as compared to JUNE-JULY treatments (Table 2). Cover was expressed as a percent of the 0 WAT rating for each herbicide application in order to compare the APR-MAY and JUNE-JULY spray dates at the same points in time (relative to the treatment) (Table 2). With a few exceptions, field bindweed cover increased (relative to the 0 WAT rating) for all herbicides applied at the APR-MAY timing between 2 (1 June) and 6 (30 June) WAT. Although some of the APR-MAY herbicide treatments may have reduced vine cover relative to the untreated check, the plot area covered with bindweed vines still increased over time (Table 2). This suggests that the herbicides were able to injure field bindweed but not able to suppress growth, entirely.

In contrast to the APR-MAY timing, field bindweed cover decreased between ~2 (19 July) and 6 (13 August) WAT for the JUNE-JULY sprays for all of the herbicide treatments plus the untreated check (Table 2). As was discussed previously, high temperatures, limited soil moisture, and a powdery mildew infestation helped to facilitate vine senescence. That being said, vine cover was more reduced in the Roundup Powermax, Rely, Treevix, and Gramoxone treatments as compared to the check, the Matric and the Sandea treatments.

The disparity in control between the APR-MAY and JUNE-JULY sprays dates is likely related to (1) the amount of aboveground biomass available at the time of treatment to capture the applied herbicides and (2) the strength of the rhizome as either a sink or a source of carbohydrates. During the spring (APR-MAY), bindweed rhizomes act as strong sources of nutrients as underground buds are released from dormancy and new vine growth occurs. The JUNE-JULY application was made when vine growth was extensive and the rhizomes were transitioning from being a sink for carbohydrates to becoming a source. These results are are being used to develop additional research trials to describe how and why the suppression of field bindweed can vary seasonally. Summarized raw data is presented at the end of the post.

 

De Gennaro, FP and SC Weller. 1984. Weed Science 32:525-528.

Dall’Armellina, AA and RL Zimdahl. 1989. Weed Sci 37: 314-318.

Derscheid, LA et al.1970. Weed Science 18:590-596

Frazier, JC. 1943a. Plant Physiology 18:167-184.

Frazier, JC. 1943b. Plant Physiology 18:315-323.

Frazier, JC. 1943c. Botanical Gazette 104:417-425.

Knezevic, SZ et al. 2009. Weed Technology 23-507-512.

Sharma, SD and M Singh. 2007. Hort Science 42:1221-1226.

Shrestha, A et al. 2007. Journal of Sustainable Agriculture 31:91-112.

Swan, DG and RJ Chancellor. 1976. Weed Science 24:306–308.

Weaver, SE and WR Riley. 1982. Canadian Journal of Plant Science 62:461–472.

Westra, P et al. 1992. Weed Technology 6:949-95.

Wiese, AF and DE Lavake. 1986. Weed Science 34:77-80.

Yerkes, D and SC Weller. 1996. Weed Technology 10:565–569.

 

The mention of any herbicide in this blog post does not constitute an official recommendation by the author or her employers.

Have yourself a very weedy Christmas…

It’s that time of year again. Time for egg-nog, time for gingerbread cookies, time for stringing outdoor lights that have become tangled up into a massive, intractable knot, and time for decorating the home and hearth with weeds.

What? Weeds?

Yes, weeds. That includes Christmas favorites of mistletoe, ivy, and poinsettia.

Mistletoe (Phoradendrom spp., Arceuthobium spp., Viscum spp.): Mistletoes are evergreen, flowering plants that parasitize other plants to acquire water and nutrients. Mistletoes can, collectively, infest many different species of trees, including: oaks, alders, birches, box elder, zelkova, cottonwood, walnut, some conifers, etc…and are most easily observed after the deciduous trees have lost their leaves. The seeds of many mistletoe species are dispersed by birds who feast on the berries. In fact, the name ‘mistletoe’ is likely derived from the Anglo-Saxon words ‘mistel’ (dung) and ‘tan’ (twig), which appropriately describes the role of birds in the spread of these plants.

Although severe infestations can weaken trees, intensive mistletoe management (by removing infected branches or trees) isn’t commonly undertaken unless a sensitive orchard species or historical tree is threatened. Homeowners can slow the growth and development of mistletoe by pruning back live tissue in parasitized trees; where mistletoe is a regular problem, landowners should consider planting species that appear to be resistant, such as crape myrtle, ginkgo, and sycamore. For more information about mistletoe management, visit the UC-IPM website.

Mistletoe has been interwoven into numerous myths, worldwide. Pliny the Elder wrote that mistletoe held on to the life of an oak tree when it went dormant in the winter. Many European ethic groups hung mistletoe around homes and barns to scare away witches and demons, while others thought that it promoted fertility. The tradition of kissing under a mistletoe sprig is also shrouded in legend. In one Norse tale, Frigga’s son, Baldr, was killed by an arrow crafted from mistletoe (or else a sword named Mistletoe, depends on your source); following his death, Frigga set forth a declaration that the plant could no longer be made into a weapon and that she would kiss people who walked underneath it, instead. For more information about mistletoe myths see here.

Ivy (Hedera helix): English ivy is a perennial, climbing vine that was introduced to North America by European colonists in the 1700’s. Much prized as an easy-to-grow groundcover (it thrives under both sun and shade conditions), it has become a horticultural staple. Unfortunately, English ivy has escaped cultivation and can be found infesting many public and private lands. Despite it’s (positive) cultural association with universities (think: ivy vines growing resplendently up red brick walls), the species can be quite a nuisance; the sticky ‘glue’ on the tendrils can cause unsightly damage to buildings and walls. Ivy can be controlled by repeatedly pruning the vines back to the ground or through the application of systemic herbicides.

Ivy, because of its’ clinging nature, has been described as representing the soul’s dependence on God; because it is an evergreen, it is also believed to symbolize eternal life. Of course, numerous myths also associate ivy with drunkenness (because it was the symbol of Bacchus and Dionysus, the Roman and Greek gods of wine, respectively), death (because it often grew in cemetaries), and the battle of the sexes (along with holly, another holiday plant).

Poinsettia (Euphorbia pulcherrima): The brilliant and beautiful poinsettia that graces many a house in December is native to Mexico, where it is called the ‘flor de la noche buena’. According to a charming (but urban?) legend, Pepita, a poor Mexican child, had nothing to offer in church on the 25th of December but bouquet of scraggly weeds; looking up through her tears, she was stunned to discover that her humble offering had turned crimson on alter. The poinsettia’s prominence in modern Christmas celebrations was facilitated by Joel Poinsett (see the connection here?), an ambassador to Mexico, who brought the plant to the United States in the 1820’s. Poinsettia is grown, commercially, in CA and the UC IPM website has a pest management guide for the floriculture industry to prevent/control disease in production systems.

The cultivated poinsettia does have an especially weedy cousin, though, that is a problem in some crops, especially peanut and soybean, in the Southern US. Wild poinsettia (Euphorbia heterophylla) is a summer annual that is capable of germinating under extreme conditions (such as pH (2.5-10) and burial depth (up to 6 inches deep)) and can grow up to five feet tall. According to weedscience.org, as of 2014, wild poinsettia has developed resistance to three classes of herbicides: ALS-inhibitors, PSII-inhibitors and PPO-inhibitors, with all of the biotypes occurring in South America.

Happy Holidays.

This post was originally published at the UC Weed Science blog. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16125

Mention of any herbicides does not equal an official recommendation.

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