- Author: Kamyar Aram
Autumn is in the air, and while it is still high season for harvest for many crops, shorter days and cooler temperatures inevitably bring to mind that winter prep tasks are not far off. And while the winter is the off-season for most crops in our region, it is definitely the on-season for cover crops. This is because, in California where irrigation water is a premium resource, we typically rely on winter rains to water cover crops. While it is ideal to make plans in advance and get the seed order in ahead of the fall rush, there is still time to think about getting a cover crop in before winter storms settle in.
What are cover crops and what are their benefits?
Cover crops include a wide range of herbaceous plants grown with the primary goal of producing biomass for the soil. They offer many opportunities to address specific soil concerns, in addition to improving and maintaining soil health, in general.
Cover crops can:
- Improve soil physical & biological functions
- Improve water infiltration
- Contribute and retain soil nitrogen
- Allow machinery earlier access to wet fields
- Suppress weeds
- Support pollinators & other beneficial insects
Water infiltration is one of the main issues that motivate growers to plant cover crops in California, as roots open new channels and feed underground life. This is especially helpful in orchards and vineyards where soil compaction is especially difficult to remedy. Cover crops can also contribute significantly to nutrient management, both in the use of nitrogen-fixing legume species, or by just foraging left-over nitrogen at the end of the season and keeping it from leaching out of the soil profile. The organic matter that cover crops contribute also improves soil structure and how much water and nutrients it can hold.
Cover crop types and their applications
Cover crops are often broadly grouped by plant types that differ in their primary benefits. For example, grasses generally produce dense stands with extensive, fine, fibrous roots that improve water infiltration and are excellent at mining nitrogen. They are more amenable to driving on at earlier growth stages, and are usually easy to mow. Legumes can actually add nitrogen to the soil through their symbiosis with bacteria that sequester nitrogen from the atmosphere. Because of their high nitrogen content, their biomass generally decomposes more quickly than other cover crops, which can mean a quicker turnaround in a tight planting schedule. Plants in the mustard family produce deep, thick tap roots that open up the soil, and their flowers are favorites of pollinators and other beneficial insects, but if allowed to mature, their sturdy stems may take more work to chop and more time to decompose.
These different types can be used singly or in combinations. There are mixes that incorporate all three types to "hedge bets" against conditions that might disfavor one or another type, and to take advantage of the way that they can complement one another. Many seed companies have developed their own mixes with characteristics to serve specific needs and circumstances.
2022 Orchard Cover Crop Trial
Cover cropping can be as much art as science, if not more so, which means that experience and experiment are essential. To this end, in the fall of 2022, I teamed up with Tom Johnson of Kamprath Seed and a local walnut grower to test out some different cover crops with the hope to improve water infiltration in the orchard. Our trial included a winter triticale, a hybrid grass known for abundant root production without too much aboveground growth, a mustard “pollinator blend” that included a mix of mustard and radish types, and Kamprath Seed's walnut mix, which includes a full complement of grasses, mustards, and legumes. The grower added a forage, spring triticale, which has more of an upright growth, adding a second triticale type for comparison. It turned out to be a lucky year to have cover crops in the orchard, as it was an exceptionally wet winter, putting many fields feet underwater, especially where infiltration was poor. Overall, all of the cover crop types established rather well in most of the planted rows, though there was a great deal of variation throughout the orchard, showing how conditions can affect the crop. Nevertheless, the walnut mix (with legumes, mustard, and grasses) consistently produced the highest total biomass, even in places where the mustard mix and straight triticale came up somewhat thin (see chart below). This highlights the advantages of diversity, but as Tom pointed out during our spring field day for the trial, results may vary considerably from year to year, and each type or blend will have advantages and disadvantages. You can learn more about the trial and the qualities of different cover crops in a video version of the field day on my YouTube channel.
Getting started with cover crops
If you are inspired, I think it is with good reason. Cover crops are tools with great potential and they really engage farming know-how and problem-solving muscles. As in all new things, it's always best to start small and experiment. There are many resources available for learning the basics or refining your existing knowledge about how to effectively employ and benefit from cover crops. In 2021, UCCE and the Resource Conservation District in Contra Costa County together developed Cover Cropping Opportunities in Specialty Crops, a series of recorded webinars and virtual site visits that explore the world of cover cropping from many different angles. These videos offer a wealth of information, instruction, and demonstrations from experienced practitioners and experts.
In addition, below are listed some other excellent UC resources on cover cropping:
Cover Cropping Opportunities in Specialty Crops video series by Contra Costa County Resource Conservation District and UC Cooperative Extension
Grasses, Mustards, & Legumes: An Orchard Cover Crop Field Day video featuring Tom Johnson of Kamprath Seed by UCCE Specialty Crops in the East Bay/Mt Diablo Region
Covercrops for California Agriculture UC ANR Publication Number 21471
Cover Cropping for Vegetable Production UC ANR Publication Number 3517
Cover Cropping in Vineyards: A Grower's Handbook UC ANR Publication Number 3338
Cover Crop Management in Annual Farming Systems Blog Post by UCCE Agronomy Advisor, Sarah Light
Cover Crop Best Management Practices published by the Almond Board of California in collaboration with UC Davis and UC ANR.
Cover Crops for Walnut Orchards UC ANR Publication Number 21627e
Cover Crop Selection tool by UC ANR SAREP
/span>/span>Did you know? Fruit trees can be kept under 6' tall so you can easily access the fruit. Surprisingly, although the trees are small, you will still get plenty of fruit!
UCCE Stanislaus County Master Gardeners hope to see you at a local Stanislaus County library branch to learn more.
- Tuesday, December 6, 2022 at 6:00 p.m. – Salida Library
- Monday, December 12, 2022 at 6:00 p.m. - Ceres Library
- Wednesday, December 14, 2022 at 2:30 p.m. - Patterson Library
- Wednesday, December 28, 2022 at 6:00 p.m. - Turlock Library
Backyard Orchard:Growing deciduous fruit trees is not for the faint-hearted. Trees such as apples, apricots, plums, pears, peaches, cherries, are not all pruned or managed the same way. Winter is the best time to plant a fruit tree, as you can purchase them as “bare root” fruit trees at a lower cost. You will learn how to correctly plant a bare root fruit tree, and how to prune it in the future to keep it small. This class does not include citrus, a separate class taught next spring.
Due to holidays conflicting with class dates, this class won't be offered at Riverbank, Oakdale, and Modesto Library locations.
Contact your local library branch to find out more. Missed a class you wanted to take? Watch it on our YouTube Channel! http://ucanr.edu/youtube/ucmgstanislaus
*Unfortunately, deciduous fruit trees that lose their leaves like apple, plum, pear, apricot, and cherry, have root systems that grow too large for containers. Luckily, you can plant many citrus tree varieties in containers.
- Author: Tong Zhen
- Author: Bradley Hanson
- Posted by: Gale Perez
Tong Zhen is a Ph.D. student in the Hanson Lab at UC Davis.
Non-chemical weed control usually is based on physical methods (e.g. tillage or mowing) or thermal methods such as propane flaming or steam. Electric Weed Control (EWC) is another thermal method that passes electrical current through target plants and the heat generated by electrical resistance damages plant cells. With funding from the Organic Agriculture Research and Extension Initiative (OREI), we recently initiated new research with collaborators at Oregon State University and Cornell University to evaluate an electrical weed control device in orchard and berry crops.
The EWC machine we are using was manufactured by Zasso, a Brazilian company. The EWC machine has several parts shown in Figure 1. The tractor engine locally generates the electric power, and the transformer at the back of the tractor will generate the high-frequency electric current. Our machine is configured to treat one-side of the tree row (Figure 1B). The applicator unit has two electrodes, one at the front that is positively charged and applies current to the plants and another towards the rear of the unit that touches the ground and completes the electrical circuit as the electricity exits the plant roots into the soil.
After we assembled the EWC machine, we tested the machine in some weedy spots at the UC Davis Plant Sciences Field Facility on April 26, 2022. In each location, we tested different combinations of ground speed and transformer power setting.
We conducted the first test at a fallow field with horseweed (Erigeron canadensis) and common lambsquarters (Chenopodium album). The sizes of the weeds range from 2 to 20 inches tall. The horseweed started wilting 2 hours after the treatment, and the plants began to dry out in the following week. Figure 2A shows an obvious brown strip of dried plants 3 DAT and from Figure 2B and 2C, the treatment can injure larger plants as well.
Other thermal weed control methods can only damage the aboveground tissues; EWC, on the other hand, is reported to have some impacts on belowground tissues as electrical current passes into some portion of the roots before dissipating into the surrounding soil. In Figure 3, we can visually observe damage to horseweed taproots a few inches below the soil surface.
The second location (Figure 4) is a fallowed vegetable crop field. Although this machine is setup to run in the orchard, but it also fits in a 60-inch bed and treat the adjacent bed top. The major weeds were prostrate pigweed (Amaranthus blitoides) and field bindweed (Convolvulus arvensis).
In this field, we observed really good weed control efficacy in the first week, but several individuals of field bindweed regrew and a few new pigweed seedlings emerged by 7 DAT.
The third location was a fallow field with mature (beginning to flower) hairy fleabane (Erigeron bonariensis). We tested the combination of different voltages and driving speed again in this field and yielded a similar result we had in the first location. The treatment was effective on small plants while some of the larger individuals were severely injured but started regrowing after 7 DAT (Figure 5). According to Zasso, mature and taller weeds may require repeated treatments for full control.
The fourth location (Figure 6) was an almond orchard with a heavy population of California burclover (Medicago polymorpha). The overall control of burclover was good with EWC at this site; however, treatment effects were difficult to separate from natural senescence of the burclover since it was late April. This orchard was irrigated with micro-sprinklers and there was no damage to the plastic irrigation tubing even when directly contacted by the applicator. However, in this heavily vegetated site that had been previously mowed, there was some risk of igniting dry vegetation with electrical arcing from the applicator to the soil surface.
Weed control was quite effective on most species in these demonstrations, especially young annual plants. Initial damage to field bindweed was rapid and severe, but many of these plants were showing regrowth after 7 days. Some of the larger and more mature hairy fleabane and horseweed plants were not completely controlled with a single application of EWC at this stage. The most sensitive plants had an impressive level of injury and desiccation within a few hours of treatment while some of the larger plants took several days to show maximum levels of injury.
Our first impressions of the Zasso electrical weed control machine were fairly promising and we are excited about conducting more thorough evaluation of this non-chemical weed control approach in California perennial crops. Over the next few years, we will conduct several experiments to address several research questions:
- how does voltage level and ground speed affect EWC efficacy?
- how different soil types and soil moisture levels can affect EWC efficacy?
- how do different weed species respond to EWC at different growth stages?
- how economical are EWC approaches compared to other organic weed control methods?
If you want to see the machine working, you can check out the link for a short video: https://youtu.be/ef__tbkZvA4.
/span>
- Author: Lee Allen
- Posted by: Gale Perez
From Page 13 of the Western Farm Press (May 2022) magazine
Electric weed control takes hold in orchards
By Lee Allen (Contributing writer)
Sometimes it takes a long time for an idea to be embraced by the public. Take electric weed control, a concept first patented in 1890, yet it hadn't received much attention until a few decades ago.
“Even if current ways still work, new ways are inevitable because they may be more cost-effective or perform a task faster, easier and better,” said Marcelo Moretti, weed specialist for Oregon State University Extension.
He addressed managing herbicide resistance with electric weed control. “Technology on many fronts is evolving so fast,” he said. “Perhaps EWC wasn't economically viable a couple of decades ago, but it could be today. Look at robots, for example. We're seeing increased mechanization everywhere.”
Weed resistance to agricultural herbicides is increasing. “We can delay that pushback, but the chemical we have previously used to control weeds can now have a non-chemical companion tool,” he said.
Calling herbicide resistance “a serious problem in both organic and conventionally grown crops” — in this case, tree nuts — Moretti believes thermal weed control via a tractor equipped with a generator, a transformer and an operator could save the day. And the operator may be superfluous with an autonomous tractor.
“EWC control appears to last longer because it kills weeds at the roots,” he said. “With mowing, you see regrowth in a week or two, and if there's a rainfall, all the weeds come back even quicker.”
While specifically researching weeds among hazelnut orchards in Oregon, “our findings could become a poster child for the entire tree nut industry,” Moretti said. “If EWC is safe enough for hazelnuts with their low-to-ground suckers, it's not hard to extrapolate to almonds, walnuts, pecans and pistachios, involving millions of acres plagued by weeds.”
CALIFORNIA CONNECTION
The Almond Board of California and the University of California, Davis, have already begun collaborating.
“I think the California tree nut industry would be a prime market for an EWC application because it is such a large portrait with flat ground and not a lot of debris that could be fuel for a fire,” Moretti said. “In a nut orchard, we could use larger tractors than we would use in vineyards.”
Moretti cited increasing interest in the concept. “More and more folks are looking at this as we find better ways to deal with human safety and cost reduction,” he said, adding it's a tool that will last multiple seasons with proper maintenance.
In an organic production weed control study using 5,000 to 12,000 volts on a 75-hp tractor, excellent efficacy was found with both annual and perennial weeds. “We're seeing better results than we expected with a tractor moving at 1½ mph through rye grass in a hazelnut orchard at a rough cost of $40 an acre, comparable to herbicide application costs,” he said. “EWC appears to be something that could be a gamechanger on chemical-resistant weeds.”
Original source: Page 13 of the Western Farm Press (May 2022) magazine
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- Author: Don Bollinger
December is a slow month in The Orchard, but there are still a couple of things going on, both related to the start of winter. First up, we have had several nights of frost as well as ice on the birdbaths. That means the citrus and avocado trees are at risk. Local weather forecasts have been calling for temperatures as low as 35 degrees. Our microclimate at MCP tends to be a few degrees cooler, with the coldest air in the valley sinking into the park. Still air and clear nights are always the coldest conditions.
Sure enough, the tender young shoots on the citrus and avocado trees have been damaged by the cold. We expected this. We could have protected these young trees; the Sacramento Master Gardeners have a great post titled Frost and Protection for Sensitive Plants that discusses ways to manage frost. We guessed (correctly) that it would not be cold enough to damage the trees. If you look at the pictures, you will see that only the tender new leaves are damaged. Unless we get even colder nights this winter, these trees will grow just fine in the Spring, with no long-term ill effects. If we see forecasts below 32 degrees, we will scramble to protect the youngest citrus and avocado trees. Last winter, our trees were OK with no protection. More mature trees (like our 3-year-olds) can survive several more degrees of cold without severe damage. But be careful. Santa Clara Valley is not always safe for citrus and avocados. There will be rare nights cold enough to kill these trees!
The cold has also finally caused the peach trees to lose their leaves. That means we can now spray for peach leaf curl. The University of California has an excellent Pest Note on Peach Leaf Curl that discusses how to manage it. Following those guidelines, we applied a copper fungicide from a hose-end sprayer until the spray was dripping from the branches. We will probably spray once more, just as the buds begin to swell but before the leaves appear.
Next up, pruning, in January and February.
Photos:
- - Top right: citrus frost damage
- - Bottom left: avocado frost damage