Below is an article from The Weed's News.
By the beginning of the irrigation season, the entire root zone is usually wetted by winter rainfall. Under low volume irrigation during the irrigation season only fifty percent or less of the root zone is wetted with each irrigation on most soil types. Soils with slow infiltration do not allow enough water to penetrate into the root zone to meet the plant’s water requirement. During an irrigation the water puddles while the soil beneath remains dry. Less than ten percent of the soil in the root zone may be wetted during an irrigation when water infiltration is a problem. Water storage in such a small volume of soil may amount to only two to three days of evapotranspiration. The tree may be under stress even though the amount of applied water exceeds the amount lost by evapotranspiration (ET). An infiltration problem is often associated with irrigation water low in salt and/or soils with inherently slow infiltration rates. Soil particles contain sites occupied by electrically charged ions such as calcium, sodium, and magnesium. In an optimum situation, a sufficiently high percentage of these sites are occupied by calcium which results in an aggregating or clumping effect among soil particles allowing water to penetrate. When the percentage of sites occupied by calcium is low and sodium predominates there is a repelling or dispersion of particles and water penetration is reduced. With increasing numbers of the exchange sites occupied by sodium ions the soil particles swell and repel each other creating a dispersion or loss of aggregation resulting in single particles. As this happens the porosity (or pore space) is reduced and the ability of water to enter is reduced. On the other hand as the exchange sites become more occupied by calcium the particles move closer together and aggregate or clump resulting in an increase in pore space. Therefore, soils that have a high percentage of the exchange sites occupied by sodium ions are dispersed and deflocculated and resist the entry of water while those with a high percentage of calcium ions are flocculated and favor water infiltration. With the use of low salt water over time, such as snow melt water, calcium may be removed from the soil particles exchange sites and these sites may then become occupied by another ion such as sodium.
Research addressing this problem of low infiltration was conducted in citrus under low volume irrigation by University of California researchers Peacock, Pehrson and Wildman. The soils type, at the experimental site of mature navel oranges, was a San Joaquin sandy loam characterized by a low infiltration rate. Canal water with a low salt content was used for irrigation. The trees were irrigated with a drip system every week day. Treatments began in June when soils typically begin to exhibit a reduced infiltration rate and were continued until mid-August but measurements continued until September. Simple devices for measuring the infiltration rate, called infiltrometers, were made from 12 inch PVC pipe and installed in the orchard. Chemical treatments and water were applied and rates of water infiltration were measured within these infiltrometers. Gypsum was applied weekly to the soil surface to maintain a slight excess continually on the soil surface and watered in resulting in gypsum application with each irrigation. Calcium nitrate and CAN-17 were each injected into the irrigation water. Calcium nitrate was introduced into the irrigation water at the rate of ten pounds per acre per irrigation. Calcium nitrate was applied daily, biweekly and in a single application. CAN -17 was applied daily, biweekly and in a single application. With these injections into the irrigation water, calcium was being introduced into the water at the rate of 3 milliequivalents per liter. Adding calcium continuously to irrigation water doubled infiltration rates over that of untreated low-salt water. It took 2-3 weeks before a treatment difference could be measured. However, the occasional additions of calcium nitrate or CAN-17 were not effective in maintaining infiltration rates. There were concerns that nitrogen application from these treatments could result in the nitrogen level in the tree being in excess of the tree’s nutritional requirements. Following this research equipment was made available on a commercial basis for regulated injection of materials into low volume irrigation systems.
Case Studies of LBAM and EGVM: Community Perceptions of Emergency Responses to Invasive Species in California
I encourage readers of this blog to peruse the attached file, written by Margareta Lelea, a post-graduate researcher at UC Davis, with Frank Zalom, Jim Greishop and Jennifer Sedell. This study, funded by a Cooperative Agreement between the USDA (United States Department of Agriculture) and UC Davis, is a comparison of the emergency responses on the part of the USDA and CDFA (California Department of Agriculture) to the light brown apple moth (LBAM) and European grapevine moth (EGVM).
The experience of the LBAM emergency response was negative for many people on the Central coast of California. Seemingly dead set on the eradication of LBAM no matter what the cost, the USDA and the CDFA brooked very little community input as they attempted to put into place a program of aerial pheromone application accompanied by a quarantine regime composed of intrusive field inspections, disruption of farm business operations and costly field closures.
In contrast, the regulatory experience of EGVM emergency response was more positive for many (including me), and was a program which found its success in the working relationships between local regulatory officials, locally based USDA officials and agents (many of whom were already here for the LBAM program), UC Cooperative Extension and a diversity of other groups including growers and pest managers.
As one can draw from reading this report, that these two programs should have really different outcomes currently should then not be surprising.
The hugely unpopular LBAM emergency response program has had its budget virtually eliminated through the representative political process and has garnered a real distrust of the USDA and CDFA by the affected communities, which to some extent continues to this day.
LBAM continues to flourish on the Central Coast, although it still doesn’t cause a lot damage besides not being anything that can’t be managed easily with environmentally sensible methods. Nevertheless, LBAM still affects trade in a big way, the current situation being a threatened closure of our Canadian and Mexican export markets for berries or broccoli should LBAM arrive there in any shipment of either of these commodities.
In contrast, EGVM has been eradicated following its brief appearance in Santa Cruz County in 2011 and its numbers have been dramatically lowered in other infested areas such as Napa, Sonoma and the Central Valley.
The attached paper does a first class job in outlining and comparing LBAM and EGVM emergency responses and shows us what we and the regulatory agencies can learn from these two experiences to guide us in the future.
Some key takeaways from the paper:
1- Agencies lose credibility and trust from communities when they undertake actions against the will of the people. This the USDA and CDFA did in spades on the LBAM emergency response, pushing ahead while initially ignoring many community concerns about their activities and creating a perception of an abuse of science and government power.
2- Agencies gain credibility and trust through a willingness to engage and effect change, which includes responding to the needs of the communities and the environment and adapting new information from science as appropriate. This was clearly the case with EGVM, as USDA and CDFA agents (many of whom were also involved in LBAM programs) worked together with local regulators, UC Cooperative Extension and growers to arrive at a workable, successful solution to the issue.
3- Aerial spray programs must be enacted only with the support of affected communities.
I guess what I think about after reading through this report is how did the LBAM emergency response go so awry? Most of the USDA and CDFA people involved in the response are very competent, decent people who truly want to serve the public and the agricultural industry in the best possible way.
Have these agencies become bureaucracies, who, to quote the philosopher Ludwig von Mises, “are no longer eager to deal with each case to the best of their abilities; they are no longer anxious to find the most appropriate solution for every problem” and whose “main concern is to comply with the rules and regulations, no matter whether they are reasonable or contrary to what was intended."? I would today answer in the negative, because even if the USDA and CDFA started out behaving as the bureaucracies described by von Mises, they both seem to have learned from their experience and turned the corner pretty promptly. Indeed, that both seemed to undergo pretty well a paradigm shift in their approach on the EGVM emergency response just a few years later after the difficult start on LBAM is a testament to their ability to learn and evolve to best serve the publics who have entrusted them to keep invasive pests out of California.
Kudos to a really thought provoking and illuminating report by Dr. Lelea and her colleagues about two signal invasive pest responses. A must read for entomologists, regulators and pest managers on the Central Coast.
Cover crop growing in cotton and tomato residues.
Here's an article from the UCCE San Joaquin County Field Notes newsletter (May 2013.)
Controlled Burn. Fire is the best option for controlling medusahead. Since it is a late-season grass, our desirable grasses have already set seed and the seeds are on the surface of the ground, ready to germinate in the fall, while medusahead is still actively growing and green. A quick moving grass fire can control medusahead while not harming the seeds that have already dropped. Timing for a controlled burn typically should be early to mid-May, after the desirable grasses have started to turn brown and drop seeds and while Medusahead is still green and has not dropped seeds. Obtaining burn permits may be difficult.
Targeted Grazing. Medusahead has a short window of opportunity where grazing can have an impact. Typically in our area that window falls from April 15th to May 1st and corresponds to the period in development just before seed heads emerge. After the seed heads emerge, livestock typically will not graze it. Management practices that can increase animal concentration in areas with high medusahead can all work. We have created small pastures where we can increase the stocking density to 0.8 AUM/acre (an AUM is a 1000 lb. animal for a month), effectively creating pressure so all plants are grazed equally. Using 125lb supplement tubs, we created localized concentration areas and saw an effect up to about a 50-yard radius out from the supplement tub. Using this method, the supplement tub would have to be moved from one patch of medusahead to the next to see large-scale results.
Herbicide. Since Roundup is non-selective, we used it at three different timing levels to find a combination where we can allow for the longest grazing period and still control medusahead. Our late spring (early April) timing accomplished this. Recently Milestone has been used early in the year to selectively control medusahead and broadleaves, especially yellow starthistle. Timing is early fall and the higher the rate of Milestone applied, the better control was found to be, with roughly 89% control at 14 oz./acre compared to 59% control at 7 oz./acre. The label states “Spot treatments may be applied at an equivalent broadcast rate of up to 0.22 lb. acid equivalent (14 fl oz. of Milestone) per acre per annual growing season; however, not more than 50% of an acre may be treated at that rate.” So in addition to the cost of treatment, the label does not allow more than small patches to be treated at this high rate annually.
Mechanical. Mowing is another option and will allow for a three week window of opportunity, a week longer than grazing. We had success mowing plots in the Dunnigan Hills area and saw a substantial decrease in medusahead along with an increase in filaree, rose clover and annual ryegrass, desirable forages. Before mowing consider the amount and size of rocks in the area.
Fertilizer. One of our more recent projects has been to look at how nitrogen fertilization can change forage composition. In a drought year, fertilization resulted in a roughly 50% decrease in medusahead while annual ryegrass and bur clover increased. This year, we have added to the project, with a fall and spring treatment timing as well as two different rates of nitrogen. Results are promising so far that we should see a decrease in medusahead in the spring-fertilized plots, regardless of rate. These plots are grazed, and the reduction is due in part to competition since more desirable forages are using up the soil moisture, and by attracting livestock to the fertilized area. We are analyzing the percent crude protein between all of the plots. Our thought is that the extra nitrogen is increasing the crude protein in all of the forages and making medusahead more palatable at the critical period of grazing, right before it develops a seed head.
If you have medusahead on your ranch, especially if you find a new infestation, it is important to try a management practice that can help you reduce it and hopefully eradicate it before it becomes well established.