- Author: Ben Faber
The latest cost of production study done on oranges came out recently.
It applies to the San Joaquin parts of the Valley for sure, but many of the assumptions are true for evergreen tree crops in general. The cost of weed control, or fertilizing are not going to be different. Pest and disease control are going to be very different if you are a navel orange grower in Bakersfield or a cherimoya grower in Santa Barbara. The key to these studies are the different issues/categories a grower should be addressing and the studies provide a framework for that study. Also it gives general costs for different inputs, such as urea and glyphosate to make a comparison to what you might be paying
- Author: Sonia Rios
Control of weeds has always been a major economic cost in subtropical fruit production because of favorable climate that allows for weed germination and year-round growth. The use of chemical weed control has increased dramatically due to labor costs, equipment costs, product costs and availability, the shift to more narrowly spaced tree rows, and installation of low volume irrigation systems that prohibit the operation of mowing or tillage equipment under the tree canopy area (Futch 2001).
However finding herbicides that are labeled for certain subtropical crops can be a bigger challenge. UC Weed Science has updated the Subtropical Crops herbicides usage chart for California growers (Fig. 1 Attachment below). It also seems that preventive programs are most frequently overlooked as a method of weed control. Preventive programs entail the use of such practices as sanitation, spot spraying, or hand labor to prevent the source of weed infestation (seed and/or vegetative) from widespread dissemination throughout a given area. By removing the undesirable weed species prior to seed development, dissemination by wind or mechanical transport on equipment can be effectively delayed.
Weed control programs will vary from location to location within the state and can even vary within a given site based upon specific conditions such as soil type, variety, method of herbicide application, and the presence of specific weed species.
Before herbicide application, growers should survey the grove and determine the stage of growth and type of weeds for that given location. Many products do not provide control of emerged species, thus requiring the application of more than one product to provide both preemergence and postemergence protection (Futch 2001). Rotation of soil-applied herbicides should also be considered to prevent the buildup of resistant annual and perennial weeds. The resistant species may not be evident initially; however, if the same herbicide and cultural program is maintained, over time their populations may build up until they infest the entire grove and become the dominant weed species (Jordan et al 1992).
Herbicide damage to foliage and fruit has also been noted when herbicides were applied under windy conditions or use of improper equipment allowed the materials to contact areas other than the weeds or soil. Please make sure to follow the label's direction and use caution.
Attached below is a chart listing herbicides registered for avocado, citrus, date, kiwi, fig and pomegranate.
Figure 1. Herbicide Registration on CA Subtropical Crops
- Author: Ben Faber
I just raked up all the leaves under the avocado and it looks so nice. PUT THEM RIGHT BACK. The avocado is shallow-rooted and really depends on the natural leaf mulch to protect its roots. In fact the roots will actually colonize the rotted leaves as if it were soil. This mulch is also a first line of defense against root rot. The decomposing leaves create a hostile environment to the microorganism that causes the disease. The mulch also helps to reduce evaporative loss of water and therefore reduces water needs. Avocado growers will actually spread mulch in cases where trees are too young to produce adequate leaf drop for mulch or in windy areas where mulch has blown away. The key to remember is that the mulch should be kept at least six inches away from the trunk to avoid collar rot which can be causes by keeping a moist mulch against the trunk.
- Author: Brad Hanson
Today I thought I'd share a recent research report on the the phenomenon of "enhanced" degradation of the herbicide simazine in citrus orchard soils. Click here for a link to the publication in the open-source journal, Air, Soil, and Water Research (Abit et al. 2012. Air Soil and Water Research 5:69-78). The lead author was a UC Davis post doctoral researcher and her coauthors include UC Davis, USDA-ARS, Fresno State, and UC Cooperative Extension folks.
This work was started several years ago in response to some questions from San Joaquin Valley orchard and vineyardists poor weed control with simazine. They suspected herbicide resistance, which is certainly a possibility given the number of weed biotypes resistant to photosystem II inhibitors reported worldwide (69 biotypes at latest count according to http://www.weedscience.org). However, when we visited some of the fields, it just didn't look like resistance or poor applications - too many species affected, good early control but poor residual performance, affected some orchards but not others, no clear application problems.
Some colleagues in Colorado and Mississippi were conducting research on faster-than-normal degradation of atrazine, a related triazine herbicide. We decided to conduct laboratory studies to determine if the poor residual performance in our orchard systems could also be due to the so-called "enhanced degradation".
First, some background. To a large degree, all herbicides degrade is soil - a complex molocule is eventually broken down into component elements; however the rate of degradation can vary greatly. The two biggest contributors to herbicide degradation are "chemical processes" that include all sorts of ways that chemical bonds are broken and "microbial processes" in which soil microorganisms use the molocule as a carbon source (ie "food"). Generally, microbial processes are the most important but are usually not specific to a particular herbicide. Sometimes, however, a microbial population with a special ability to degrade a particular herbicide (or chemically related compounds) can build up in the population and very rapidly degrade all of the herbicide. [analogy: a bowl of candy on your desk that lasts for weeks if you eat one or two per day but lasts only a few seconds when your hungry teenager and his friends show up!].
To determine if there were differences in simazine degradation rates among orchards, we collected soil from 27 citrus orchards in Tulare and Ventura counties. The orchards had a range of simazine use histories ranging from being treated every year for decades to having no simazine for at least the past 15 years.
1. In one set of experiments, we found that the soils that had not been exposed to simazine for at least 15 years degraded the herbicide much more slowly and that annual use (for the past 5 years, or longer) tended to be accociated with faster degradation.
2. In a second set of experiments, we autoclaved (heat sterilized) soil to kill any microbes present to determine if the herbicide degradation was due to microbial activity. This study showed that the degradation was almost completely due to microbial degradataion - simazine degradation was almost non-existent in autoclaved soils. Some soils have the the specialized microbial population while others do not.
The conclusions of the study were that repeated use of simazine can lead to more rapid degradation of the herbicide but that the correlation was not perfect. The correlations were better in the Tulare County sites than in the Ventura County soils. Some soils with long-term use of the herbicide continued to degrade simazine at a "normal" rate while other degraded it faster than predicted.
Overall, this is an interesting phenomenon that growers and pest control advisors should be aware of when making weed control decisions. Simazine can provide very effective and economical weed control in many situations but, as always, we recommend monitoring orchard conditions and adjusting weed control strategies accordingly.
This research was partially supported by funding from the California Citrus Research Board and USDA-ARS.
A couple of my previous posts on herbicide degradation at the UC Weed Science Blog can be found at: http://ucanr.org/blogs/blogcore/postdetail.cfm?postnum=5929 and http://ucanr.org/blogs/blogcore/postdetail.cfm?postnum=3923
- Posted By: Chris M. Webb
- Written by: W. Thomas Lanini
In recent years, several organic herbicide products have appeared on the market. These include Weed Pharm (20% ace c acid), C Cide (5% citric acid), GreenMatch (55% d limonene), Matratec (50% clove oil), WeedZap (45% clove oil + 45% cinnamon oil), and GreenMatch EX (50% lemongrass oil), among others. These products are all contact type herbicides and will damage any green vegeta on they contact, though they are safe as directed sprays against woody stems and trunks. These herbicides kill weeds that have emerged, but have no residual activity on those emerging subsequently. Additionally, these herbicides can burn back the tops of perennial weeds, but perennial weeds recover quickly.
These products are effective in controlling weeds when the weeds are small and the environmental conditions are op mum. In a recent study, we found that weeds in the cotyledon or first true leaf stage were much easier to control than older weeds (Tables 1 and 2). Broadleaf weeds were also found to be easier to control than grasses, possibly due to the location of the growing point (at or below the soil surface for grasses), or the orientation of the leaves (horizontal for most broadleaf weeds) (Tables 1 and 2).
Organic herbicides only kill contacted tissue; thus, good coverage is essential. In test comparing various spray volumes and product concentrations, we found that high concentrations at low spray volumes (20% concentration in 35 gallons per acre) were less effective than lower concentrations at high spray volumes (10% concentration in 70 gallons per acre). Applying these materials through a green sprayer (only living plants are treated), can reduce the amount of material and the overall cost (http://www.ntechindustries.com/weedseeker-home.html). Adding an organically acceptable adjuvant has resulted in improved control. Among the organic adjuvants tested thus far, Natural wet, Nu Film P, Nu Film 17, and Silwet ECO spreader have performed the best. The Silwet ECO spreader is an organic silicone adjuvant which works very well on most broadleaf weeds, but tends to roll o of grass weeds. The Natural wet, Nu Film 17 and Nu Film P work well for both broad leaf and grass weeds. Although the recommended rates of these adjuvants is 0.25 % v/v, we have found that increasing the adjuvant concentration up to 1% v/v o en leads to improved weed control, possibly due to better coverage. Work continues in this area, as manufacturers continue to develop more organic adjuvants. Because organic herbicides lack residual activity, repeat applications will be needed to control new flushes of weeds.
Temperature and sunlight have both been suggested as factors affecting organic herbicide efficacy. In several field studies, we have observed that organic herbicides work better when temperatures are above 75F. Weed Pharm (acetic acid) is the exception, working well at temperatures as low as 55F. Sunlight has also been suggested as an important factor for effective weed control. Anecdotal reports indicate that control is better in full sunlight. However, in a greenhouse test using shade cloth to block 70% of the light, it was found that weed control with WeedZap improved in shaded conditions (Table 3). The greenhouse temperature was around 80F. It may be that under warm temperatures, sunlight is less of a factor.
Organic herbicides are expensive at this time and may not be affordable for commercial crop producti on. Because these materials lack residual activity, repeat applications will be needed to control perennial weeds or new flushes of weed seedlings. Finally, approval by one's organic certifier should also be checked in advance as use of such alternative herbicides is not cleared by all agencies.
Review tables below...
(Table 1. Broadleaf (pigweed and black nightshade) weed control (% control at 15 days a er treatment), when treated 12, 19, or 26 days after emergence.
Weed |
age |
||
|
12 Days old |
19 days old |
26 days old |
GreenMatch Ex 15% |
89 |
11 |
0 |
GreenMatch 15% |
83 |
96 |
17 |
Matran 15% |
88 |
28 |
0 |
Ace c acid 20% |
61 |
11 |
17 |
WeedZap 10% |
100 |
33 |
38 |
Untreated |
0 |
0 |
0 |
Table 2. Grass (Barnyardgrass and crabgrass) weed control (% control at 15 days after treatment), when treated 12, 19, or 26 days after emergence.
Weed |
age |
||
|
12 Days old |
19 days old |
26 days old |
GreenMatch Ex 15% |
25 |
19 |
8 |
GreenMatch 15% |
42 |
42 |
0 |
Matran 15% |
25 |
17 |
0 |
Ace c acid 20% |
25 |
0 |
0 |
WeedZap 10% |
0 |
11 |
0 |
Untreated |
0 |
0 |
0 |
Table 3. Weed control with WeedZap (10% v/v) in relation to adjuvant, spray volumne and light levels. Plants grown in the greenhouse in either open conditions or under shade cloth, which reduced light by 70%. |
|
||||
Pigweed control (%) |
Mustard control (%) |
|
|||
|
Sun |
Shade |
Sun |
Shade |
|
WeedZap + 0.1%v/v Eco Silwet (10 gpa) |
31.7 |
93.3 |
26.7 |
35.0 |
|
WeedZap + 0.5%v/v Eco Silwet (10 gpa) |
31.7 |
48.3 |
43.3 |
71.7 |
|
WeedZap + 0.5%v/v Natural Wet (70 gpa) |
26.7 |
94.7 |
26.7 |
30.0 |
|
Untreated |
0.0 |
0.0 |
0.0 |
0.0 |
|
LSD.05* |
5.7 |
11.5 |
|
|
* Values for comparing any two means. Pigweed and mustard were each analyzed separately.