- Author: Oleg Daugovish
Using organic herbicides in production fields and non-crop areas.
The forecasts call for rainy winter and that means a lot of weeds. During dry times perennial weeds tend to grow better than annual weeds, since perennial structures such as underground rhizomes or tubers can support them and give competitive advantage. Seed of annual weeds in dry soil may have been losing viability, senescing or eaten during this time, but many have remained dormant and look forward to the wet winter us much as the rest of us.
Controlling weeds ‘organically' is always an extra challenge whether you are in a certified field or in an area where synthetic herbicides are not desired. Hand-weeding, already expensive, is even a greater burden with limited labor availability, and frankly not much fun either. Of course sanitation and prevention, mechanical and cultural management are essential in organic systems. That requires time and commitment and can quickly become your not-so-favorite pastime.
Organic herbicides have traditionally been contact materials with no systemic activity. This means that they only affect tissue that they contact and do not translocate through the plant like most synthetic herbicides. Thus, good coverage is critical for these contact materials. Many years ago the first herbicides were sulfuric acid and diesel fuel, current organic materials are often acids or oils too, although a lot more benign.
Recent trials by the University of California weed scientists showed that several organic herbicides provided decent control of easy to control pigweed and nightshade when they were small. When weeds were 12 days old, a mixture of 45% clove and 45% cinnamon oil, 20%-acetic acid and d-limonene gave 61-89% control; however only d-limonene controlled 19-day old weeds and none was effective on one-month old ones. As weeds get bigger they also develop a protective cuticle that minimizes efficacy of these herbicides.
This year we conducted trials with a recently OMRI approved herbicide for row crops, trees and vines that is a mix of caprylic and capric acids. It disrupts cell membranes of plans and causes the contents to leak and plants to desiccate. It worked well at 6 to 9% by volume mixture with water and gave 90% control of little mallow and >95% of annual sowthistle compared to untreated checks. We have also tested it in organic strawberry furrows before planting the crop to prevent potential injury from drift. Furrow cultivation does not get close to the plastic mulch that covers the beds to prevent tears, so the weeds in that zone are good target for the herbicide. This fatty acid herbicide provided excellent control of common lambsquarter, reduced the growth of common purslane but didn't do much for yellow nutsedge - one of our notoriously difficult to control perennial weeds (Figure). The bigger weeds need higher rates (9% is the maximum labeled rate) and better coverage. When you have multiple layers of weed leaf canopy and diverse architecture some plants or their parts may be protected by others that intercept the deposition of the herbicide. When on target, this contact material acts fast – you can see results within 2-3 days, however, it does nothing to weed propagules in soil and has no residual activity against wind-dispersed weed seed that fly in after application. This means the control does not last and you will need additional applications or other control measures. Repeated application is not a problem in a non-crop area and is a great way to deplete your weed seedbank, but crop protection from drift, such as shielded sprayers, is necessary to avoid off target plant injury.
Figure. Weed control in strawberry furrows prior to planting with 9% by volume of fatty acid herbicide (top) and weeds in untreated check (bottom)
Of the many known varieties, they fall into three broad categories based on whether they are of the Mexican, Guatemalan or West Indian races of Persea americana, the avocado specie and the crosses that occur between these races. For example, ‘Hass' has the thick skin of the Guatemalan but turns black like a Mexican. Generally speaking, California varieties have been the result of crossing between the Mexican and Guatemalan races. West Indian race varieties are not common here because of their generally lower cold tolerance. There are lots of factors approaching the identification of an avocado and its origins, and here is a brief run down on those that need to be considered.
Is it a grafted tree, or is it a known variety with known characteristics which the tree can be compared to? Look for the change in bark texture at the base of the tree where the graft was made.
When you crush the leaf, does it have an anise smell (Mexican) or not?
Is the leaf edger smooth (Hass) or wavy (Zutano)?
Is the color of the new leaves red and turn green (Mexican) or are green (Guatemalan)?
Is it columnar (Bacon, Reed) or umbrella (Hass)?
Is the mature tree big (Hass) or under 20 feet in height (Holiday, Littlecado, Gwen)?
Is the fruit round (Nabal), pear shaped (Fuerte), thin necked (Pinkerton) or broad shouldered (Lamb-Hass)
Is it thick skinned (Guatemalan) or thin skinned (Mexican)?
Is it green when ripe (Guatemalan) or black (Mexican)?
Is it big (more than 16 ounces; Daily 11 is 5 pounds) or small (Mexicola is 5 ounces)?
When is fruit maturity; winter, spring, summer or fall?
The combination of all these factors go into describing a variety and distinguishes it from other varieties. When varieties have mixed parentage, they will take on those characteristics of each parent, so often the lines of either Mexican or Guatemalan get blurred.
Hot off the presses
Years of drought, and a stressed tree are a perfect set up for navel oranges and fruit splitting.
The days have turned cooler and suddenly out of nowhere there is rain. That wonderful stuff comes down and all seems right with the world, but then you notice the navel fruit are splitting. Rats! No, a dehydrated fruit that has taken on more water than its skin can take in and the fruit splits. This is called an abiotic disease. Not really a disease but a problem brought on by environmental conditions.
Fruit splitting is a long-standing problem in most areas where navel oranges are grown. In some years, the number of split fruit is high; in other years it is low. Splitting in navel oranges usually occurs on green fruit between September and November. In some years, splitting may also occur in Valencia oranges but it is less of a problem than in navel oranges.
Several factors contribute to fruit splitting. Studies indicate that changes in weather including temperature, relative humidity and wind may have more effect on fruit splitting than anything else. The amount of water in a citrus tree changes due to weather conditions and this causes the fruit to shrink and swell as water is lost or gained. If the water content changes too much or too rapidly the rind may split. In navel oranges the split usually occurs near the navel, which is a weak point in the rind.
Proper irrigation and other cultural practices can help reduce fruit splitting. Maintaining adequate but not excessive soil moisture is very important. A large area of soil around a tree should be watered since roots normally grow somewhat beyond the edge of the canopy. Wet the soil to a depth of at least 2 feet then allow it to become somewhat dry in the top few inches before irrigating again. Applying a layer of coarse organic mulch under a tree beginning at least a foot from the trunk can help conserve soil moisture and encourage feeder roots to grow closer to the surface.
If trees are fertilized, apply the correct amount of plant food and water thoroughly after it is applied. If the soil is dry, first irrigate, then apply fertilizer and irrigate again.
Meet the Buyer: An L.A. Produce Market Tour for Los Angeles Growers and Food Advocates
Do you want to find new channels for selling your produce and make connections with produce buyers? Join us on a one day tour of produce distributors in the L.A. area where you will meet with senior buyers and leaders at these distribution companies committed to building their local base of suppliers:
Santa Monica Farmers' Market - our early start will allow for a special behind-the-scenes market tour to learn about the vibrant business-to-business transactions occuring there every week.
Space Exploration Technologies - meet the culinary team feeding the folks at the frontier of space exploration seasonally-inspired menus, much of it sourced from farms nearby.
Whole Food Distribution Center - talk with buyers committed to small, local and organic producers at the new state-of-the-art distribution facility and enjoy a yummy lunch.
Heath & Lejeune - learn the art of distributing orgranic produce from a seasoned buyer / seller.
These high-level buyers are positioned to appreciate your farm and products—whether organic, local, family-owned, sustainably grown, or high quality specialty crops. You'll gain an understanding of what it takes to work with them, have a chance to network with other farmers, and learn tips on how to tell a compelling story about your farm and its products that will expand your sales opportunities. This tour will be valuable for ANY farmer who wants to learn more about different distribution channels for their products, as well as for healthy food advocates and policy makers who want to have a better understanding of what small farms need to do in order to connect with willing buyers.
Space is limited; advance registration is required. Please reserve your space by December 4th, 2015. Lunch and snacks will be provided. There is no charge for this tour thanks to our generous sponsors.
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