Phalaenopsis Journal Second Quarter 2014 | Page 23

color after SE treatment, but none of the tested varieties
showed improvements in yield, weight, or mineral composition. Likewise, SE treatment had no effect on grain
yield in wheat, persimmon production, strawberry or
pepper yields, pear fruit set, or tomato yield or quality.
5) Disease management
There are few reports of successful disease management
through SE application. One positive result was found in
potted cabbage seedlings, where damping-off disease was
prevented by treatment with seaweed extract. Other experiments on bacterial and fungal control have had less
success. Grain treated with SE was no more resistant to
subsequent fungal infection, but germination rates actually decreased as a result. SE treatment of strawberry fungal infection and bacterial leaf spot in tomato had only a
33% success rate, while investigations on Alternaria leaf
blight and peach leaf curl showed no effect.
6) Pest management
An early report 40 years ago suggested that seaweed extract would decrease red spider mite infestations. Nothing more has developed from that initial hypothesis, but
a number of more recent papers have documented the
nematicidal activity of some seaweed extracts. Researchers have found reduced egg production and hatching and
increased larval mortality in nematodes treated directly
with seaweed extract. Applied to greenhouse plants, seaweed extracts reduced nematode infestation of tomato
plants and citrus species, but no effect was found on these
latter plants in the field. Researchers have suggested that
plant maturity could influence effectiveness, with a greater benefit seen in younger plants compared to older, established trees in the field.
7) Environmental stress resistance
Virtually no success has been reported in this area; while
the earlier-mentioned turf work suggested SE application
improved salinity and drought tolerance, that effect does
not carry over to other plant materials. Herbaceous perennials treated with SE did not exhibit improved drought
resistance, nor did SE treatment assist in plant growth or
transplant survival of four common ornamental shrubs
and trees. In fact, untreated plants mulched with pine
bark performed better than those that received a commercial product containing “a blend of endo- and ectomycorrhizal fungi, beneficial root/soil bacteria, chelated
micronutrients and biocatalysts including humic acids,
complex carbohydrates, yucca plant extract, sea kelp and
organic N and P.” In another study, compost was found
to be more effective in drought resistance than biostimulants including seaweed extracts.

Conclusions from researchers
1) Plant selection: “…working with resistant varieties
seems to be the best solution [to disease resistance].”
2) Environmental conditions: “…soil fertility and production conditions were more important growth and
yield determinants than were foliar sprays.”
3) Management techniques: “If proper planting techniques are followed, the use of biostimulants is unwarranted.”
4) Overall assessment: “…treatments are ultimately dependent on multiple plant, soil, and environmental factors, and often have no discernible effects.” “…there appears to be little value in applying these products.”
5) Marketing: “Manufacturers’ claims for the benefits of
these products go beyond what is substantiated by the
research.” “The number of products now on the market
seems to outnumber the published papers.” These researchers’ conclusions say it all – seaweed extracts are
aggressively marketed with little regard for objective,
scientific research. There is a final concern never addressed, which is the justification for large-scale removal
of vegetation from one ecosystem (the marine kelp “forests”) for application to another (terrestrial landscapes).
The ecological impacts of increased seaweed harvesting
are currently under investigation and the possibility of
significant ecosystem damage is real. There is no argument that seaweed products are useful and valuable to
humans for the reasons discussed earlier. However, given that there are few documented benefits from applying seaweed extracts to plants, this is not a justifiable nor
sustainable practice. The marketing of such products as
“earth friendly” in this context should be repugnant to
environmentally conscious consumers.

The Bottom Line
• Seaweed extracts contain plant growth regulators
which, like traditional rooting products, can stimulate
root growth in cuttings and transplants.
• Seaweed extracts have no reliable effect on plant production or resistance to disease and environmental stress,
especially in field conditions.
• Variations in plant materials and environmental conditions are greater determinants of plant health than applications of seaweed extract.
• Seaweed extracts for landscape use represent a poor use
of natural resources, especially those from environmentally sensitive coastal ecosystems.
For more information
please visit Dr. Chalker-Scott’s web page at http://www.
theinformedgardener.com.
Phalaenopsis | Second Quarter | Volume 24 | 2014

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