Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: vegetation management

Cover Cropping the Coast

Save the Date!

October 31, 9am – 11am

Hansen Agricultural Research and Extension Center

287 S Briggs Rd, Santa Paula


Come gather around a cover crop demonstration for a discussion on cover crop seed selections, appropriate mixes for different cropping systems, and management issues. Other soil health topics include compost applications, Healthy Soils grant opportunities, and technical assistance availability.


This event is free and open to anyone interested in soil health. Please spread the word!


More information to follow, if you can join us please RSVP here:

citrus weeds and disc
citrus weeds and disc

Posted on Monday, September 9, 2019 at 1:06 PM

Organic Herbicides: do they work?

In recent years, several organic herbicide products have appeared on the market.  These include Weed Pharm (20% acetic 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 vegetation 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 optimum.  In a recent study, we found that weeds in the cotyledon or first true leaf stage were much easier to control than older weeds.  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).

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

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 off of grass weeds.  The Natural wet, Nu Film 17 and Nu Film P work well for both broadleaf 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 often 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.  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 production.   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.


Posted on Thursday, October 15, 2015 at 8:42 AM
  • Author: Tom Lanini
Tags: herbicides (18), organic (12), vegetation management (2), weeds (32)
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