[NAFEX] Fwd: Biofumigating Apple Orchards

Lon J. Rombough lonrom at hevanet.com
Wed Apr 12 09:49:38 EDT 2006

Begin forwarded message:

From: ARS News Service <NewsService at ars.usda.gov>
Date: April 12, 2006 6:12:15 AM PDT
Subject: Biofumigating Apple Orchards
Reply-To: ARS News Service <NewsService at ars.usda.gov>

Evaluating a Natural Fumigant for Apple Orchards

ARS News Service
Agricultural Research Service, USDA
Jan Suszkiw, (301) 504-1630, jsuszkiw at ars.usda.gov
April 12, 2006
--View this report online, plus any included photos or other images, at 

Apple growers seeking to use natural substances produced by decomposing 
Brassica plants to "biofumigate" their orchards may want to first 
consider new findings by Agricultural Research Service (ARS) scientists 
in Wenatchee, Wash.

Rapeseed, mustard and other Brassica species are gaining popularity in 
Washington and California as a natural means of controlling soilborne 
pests before planting time. That's because they release a variety of 
chemical byproducts upon decomposing--particularly isothiocynates. But 
according to Mark Mazzola, mechanisms other than biofumigation are at 
work against Rhizoctonia solani, a fungal culprit behind apple replant 
disease. Mazzola is a plant pathologist with ARS' Tree Fruit Research 
Laboratory in Wenatchee.

Mazzola and collaborators want to improve the use of Brassicas in 
integrated approaches to managing replant disease, which is 
traditionally fought with chemical fumigants. In the Pacific Northwest, 
this growth-sapping affliction of young apple trees can cause 
diminished crop returns up to $40,000 per acre over 10 years.

In trials using ground-up rapeseed as a soil amendment, Mazzola 
observed that release of isothiocynates had nothing to do with 
Rhizoctonia control. Rather, the control stemmed from changes the 
rapeseed caused to the soil environment and microbes living there. Some 
flourished, while others perished.

For example, Pythium fungi -- another replant disease culprit -- and 
Streptomyces bacteria strains that produce nitric oxide both thrived. 
In plants, nitric oxide is an important signaling compound that musters 
a pest-fighting response called systemic acquired resistance. Mazzola 
theorizes that Streptomyces increases resulting from rapeseed 
amendments stimulated this resistance response in apple tree roots, 
suppressing Rhizoctonia survival long after the isothiocynates had 
disappeared from the soil.

However, Pythium increases required chemical control with mefenoxam. 
Thus, Brassica's pest control effectiveness isn't so clear-cut, 
according to Mazzola, whose studies appear in the journal Plant 

Read more about the research in the April 2006 issue of Agricultural 
Research magazine, available online at:

ARS is the U.S. Department of Agriculture's chief scientific research 

* This is one of the news reports that ARS Information distributes to 
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