Biocontrol of Australian Swampweed at Rye Harbour

Barry Yates
, 10 August 2022
Biocontrol of Australian Swampweed at Rye Harbour
Aculus crassulae Credit Radmila Petanović

Australian Swampweed (Crassula helmsii) is an invasive non-native aquatic plant that dominates still and slow-flowing freshwater habitats across Britain.

This is Crassula helmsii, which can completely shade and dominate a wetland habitat.

It was first recorded at Rye Harbour Nature Reserve in 2002 at Castle Water, but has since spread through the reedbeds there, along Castle Farm ditches and even into some of the ponds and scrapes of Rye Harbour Farm. It has degraded our wetland for some of our rarest wildlife: Lesser Water Plantain, Spangled Button Beetle and breeding Lapwing, Redshank and Bittern. It grows across the damp drawdown zone and in the shallows and in the reedbeds, it shades out many of our wetland plants like Water Mint, Water Forget-me-not and Marsh Pennywort and it covers the bare damp ground loved by so many invertebrates and the birds feeding on them.

A ditch at Castle Water dominated by Crassula helmsii

But CABI is coming to the rescue - CABI is an international, inter-governmental organisation and has laboratories working on invasive species and so in 2010 a team started a search for some biocontrol agent - read the story here  The careful study has identified a small mite, Aculus crassulae to be the most suitable agent. Mite feeding causes the growing shoots of the terrestrial and emergent growth forms of Crassula helmsii to develop red galls or swellings, significantly reducing growth.

Aculus crassulae (Credit: Radmila Petanović)

Aculus crassulae on Crassula bud - the mites are the tiny projections off the bud

The exciting news is that this week staff from CABI released some of the tiny mites into a small area of Crassula at Castle Water. In there background there has been much discussion and agreement that this is the best way of improving these wetland habitats for wildlife and consents have been given by CABI, Natural England and Sussex Wildlife Trust.

The mite infected Crassula with red galls, ready for planting at Castle Water.

The CABI team planting out the Crassula with the mites.

This is the start of a long process including further introductions and monitoring that we hope will improve the health of our freshwater wetlands. In time this method can be used throughout the Rye Bay area where Crassula is locally abundant.

Henri Brocklebank – Director of Conservation at Sussex Wildlife Trust said – Crassula is a problem for so many wetland managers and the impact on our native wildlife is devastating. We very much look forward to seeing the impact of this mite over time and will be monitoring this closely. We will be sharing everything we learn from this experience with other wetland landowners.

This is one of our few Lesser Water Plantain plants just surviving being swamped by Crassula helmsii. Castle Water is the only site in East Sussex!



Leave a comment

Comments

  • Richard:

    Hello, I am part of a project in the village of Morston in north Norfolk, trying to eradicate Crassula from our village pond. I read the article about the mite and was keen to find out how the experiment was going and if there were any side effects to introducing such a creature. You’ll see from our website that we have been looking at a variety of ways to deal with the issue here – mainly excavating and burial of Crassula but are keen to find alternative solutions (if they exist) which don’t harm the environment – we have see a great increase in the amount of biodiversity since we began in 2022 and don’t want to set that back! I look forward to hearing from you.
    Rehards,
    Richard

    05 Oct 2025 09:17:00

  • Sussex Wildlife Trust:

    Unfortunately, the trial of the biocontrol agent, the gall-forming mite Aculus crassulae, has so far not proved successful, and we are considering alternative mechanical options such as physical removal and burial.

    Further information may be available by contacting CABI who are leading on the trial: Finding a biocontrol agent for Crassula - CABI.org.

    A review by Conservation Evidence found no evidence and could therefore not make an assessment of the effectiveness of using herbivores to control Crassula: Crassula helmsii: Biological control using herbivores - Conservation Evidence

Time Δ Debug Message - Perch Runway 3.2
1782979568.24940 [906] SELECT p.pagePath, pr.routePattern, pr.routeRegExp, p.pageTemplate, pr.routeOrder, s.settingValue AS siteOffline FROM swt_pages_staging p LEFT JOIN swt_page_routes pr ON p.pageID=pr.pageID LEFT JOIN swt_settings s ON s.settingID='siteOffline' UNION SELECT NULL AS pagePath, pr2.routePattern, pr2.routeRegExp, pr2.templatePath AS pageTemplate, pr2.routeOrder, NULL AS siteOffline FROM swt_page_routes pr2 WHERE templateID!=0 ORDER BY routeOrder ASC, pagePath ASC
1782979568.27630.0269Matched route: news/[slug:s]
1782979568.27640.0001Server address: 216.73.217.103
1782979568.27640Using master page: /templates/pages/blog/post.php
1782979568.27650Page arguments: 
Array
(
    [0] => /news/biocontrol-of-australian-swampweed-at-rye-harbour
    [s] => biocontrol-of-australian-swampweed-at-rye-harbour
    [1] => biocontrol-of-australian-swampweed-at-rye-harbour
)
1782979568.27680.0003 [1] SELECT * FROM swt_pages_staging WHERE pagePath='/news/post' LIMIT 1
1782979568.27780.0011 [86] SELECT DISTINCT settingID, settingValue FROM swt_settings WHERE userID=0
1782979568.280.0022 [1] SELECT locationID FROM swt_shop_tax_locations WHERE locationIsHome=1 LIMIT 1
1782979568.28080.0007INSERT INTO swt_shop_cart(memberID,locationID,currencyID,cartPricing,cartProperties) VALUES(NULL,'1',47,'standard','[]')
1782979568.28310.0023 [1] SELECT * FROM swt_shop_cart WHERE cartID=22512521
1782979568.28380.0008 [1] SELECT * FROM swt_shop_cart WHERE cartID=22512521
1782979568.28460.0007 [nil] SELECT * FROM swt_shop_sales WHERE saleFrom<='2026-07-02 08:06:00' AND saleTo>'2026-07-02 08:06:00' AND saleActive=1 AND saleDeleted IS NULL ORDER BY saleOrder ASC
1782979568.28620.0016 [1] SELECT SQL_CALC_FOUND_ROWS DISTINCT tbl.* FROM ( SELECT idx.itemID, main.*, idx2.indexValue as sortval FROM swt_blog_index idx JOIN swt_blog_posts main ON idx.itemID=main.postID AND idx.itemKey='postID' JOIN swt_blog_index idx2 ON idx.itemID=idx2.itemID AND idx.itemKey='postID' AND idx2.indexKey='_id' WHERE 1=1 AND ((idx.indexKey='postSlug' AND idx.indexValue='biocontrol-of-australian-swampweed-at-rye-harbour')) AND idx.itemID=idx2.itemID AND idx.itemKey=idx2.itemKey GROUP BY idx.itemID, idx2.indexValue, postID ) as tbl WHERE (postStatus='Published' AND postDateTime<='2026-07-02 08:06:00' ) GROUP BY itemID, sortval ORDER BY sortval ASC LIMIT 0, 10
1782979568.28920.003 [1] SELECT FOUND_ROWS() AS `count`
1782979568.290.0008 [1] SELECT * FROM swt_blog_posts WHERE postID=2848 AND postStatus='Published' AND postDateTime<='2026-07-02 08:06:00'
1782979568.2910.001 [13] SELECT * FROM swt_blog_sections ORDER BY sectionTitle ASC
1782979568.29190.0009 [1] SELECT * FROM swt_blogs ORDER BY blogTitle ASC
1782979568.29270.0008 [1] SELECT * FROM swt_categories WHERE catID=57 LIMIT 1
1782979568.29340.0007 [1] SELECT * FROM swt_categories WHERE catID=70 LIMIT 1
1782979568.29420.0008 [1] SELECT * FROM swt_categories WHERE catID=51 LIMIT 1
1782979568.29470.0005 [1] SELECT * FROM swt_categories WHERE catID=66 LIMIT 1
1782979568.29550.0008Using template: /templates/blog/post.html
1782979568.29580.0003 [162] SELECT catID, catPath FROM swt_categories
1782979568.2970.0012 [1] SELECT * FROM swt_blog_posts WHERE postStatus='Published' AND postDateTime<='2026-07-02 08:06:00' AND postSlug='biocontrol-of-australian-swampweed-at-rye-harbour'
1782979568.31830.0213Using template: /templates/blog/post.html
1782979568.31980.0015 [250] SELECT country, countryID FROM swt_shop_countries WHERE countryActive=1 ORDER BY country ASC
1782979568.32160.0018Using template: /templates/pages/attributes/seo.html
1782979568.32190.0003 [1] SELECT regionID, regionTemplate, regionPage, regionRev AS rev FROM swt_content_regions WHERE regionKey='Banner image' AND (regionPage='/news/post' OR regionPage='*')
1782979568.32290.001 [nil] SELECT * FROM ( SELECT idx.itemID, c.regionID, idx.pageID, c.itemJSON, idx2.indexValue as sortval FROM swt_content_index idx JOIN swt_content_items c ON idx.itemID=c.itemID AND idx.itemRev=c.itemRev AND idx.regionID=c.regionID JOIN swt_content_index idx2 ON idx.itemID=idx2.itemID AND idx.itemRev=idx2.itemRev AND idx2.indexKey='_order' WHERE ((idx.regionID=104 AND idx.itemRev=0)) AND idx.itemID=idx2.itemID AND idx.itemRev=idx2.itemRev ) as tbl GROUP BY itemID, pageID, itemJSON, sortval, regionID ORDER BY sortval ASC
1782979568.32410.0012 [82] SELECT * FROM swt_pages_staging WHERE pageNew=0 AND pageHidden=0 AND pageDepth >=0 AND pageDepth<=2 ORDER BY pageTreePosition ASC
1782979568.32740.0033 [1] SELECT pageTreePosition FROM swt_pages_staging WHERE pagePath='/news/post' LIMIT 1
1782979568.3280.0007 [2] SELECT pageID FROM swt_pages_staging WHERE pageTreePosition IN ('000-006-001', '000-006', '000') ORDER BY pageTreePosition DESC
1782979568.33020.0022Using template: /templates/navigation/ps_nav_template.html
1782979568.33030.0001 [6] Using template: /templates/navigation/ps_nav_template_children.html
1782979568.33140.0011 [4] Using template: /templates/navigation/ps_nav_template_children.html
1782979568.3320.0006 [29] Using template: /templates/navigation/ps_nav_template_children.html
1782979568.33550.0035 [10] Using template: /templates/navigation/ps_nav_template_children.html
1782979568.33680.0013 [7] Using template: /templates/navigation/ps_nav_template_children.html
1782979568.33770.0009 [9] Using template: /templates/navigation/ps_nav_template_children.html
1782979568.34060.0029 [1] SELECT pageTreePosition FROM swt_pages_staging WHERE pagePath='/news/post' OR pageSortPath='/news/post' LIMIT 1
1782979568.34160.001 [1] SELECT * FROM swt_pages_staging WHERE pageHidden=0 AND pageNew=0 AND pageTreePosition IN ('000-006-001', '000-006', '000') ORDER BY pageTreePosition
1782979568.34420.0026 [1] Using template: /templates/navigation/breadcrumbs.html
1782979568.34470.0005Using template: /templates/blog/post.html
1782979568.3450.0003 [1] SELECT * FROM swt_blog_authors WHERE authorID='6' LIMIT 1
1782979568.34580.0007Using template: /templates/blog/author.html
1782979568.34620.0004 [1] SELECT SQL_CALC_FOUND_ROWS DISTINCT tbl.* FROM ( SELECT idx.itemID, main.*, idx2.indexValue as sortval FROM swt_blog_index idx JOIN swt_blog_posts main ON idx.itemID=main.postID AND idx.itemKey='postID' JOIN swt_blog_index idx2 ON idx.itemID=idx2.itemID AND idx.itemKey='postID' AND idx2.indexKey='_id' WHERE 1=1 AND ((idx.indexKey='postSlug' AND idx.indexValue='biocontrol-of-australian-swampweed-at-rye-harbour')) AND idx.itemID=idx2.itemID AND idx.itemKey=idx2.itemKey GROUP BY idx.itemID, idx2.indexValue, postID ) as tbl WHERE (postStatus='Published' AND postDateTime<='2026-07-02 08:06:00' ) GROUP BY itemID, sortval ORDER BY sortval ASC LIMIT 0, 1
1782979568.34860.0025 [1] SELECT FOUND_ROWS() AS `count`
1782979568.34930.0006 [1] Using template: /templates/blog/post.html
1782979568.35280.0036Using template: /templates/blog/comment_form.html
1782979568.35430.0014 [1] SELECT * FROM swt_blog_comments WHERE 1=1 AND postID=2848 AND commentStatus='LIVE' ORDER BY FIELD(webmentionType, 'like', 'repost', 'comment', NULL) ASC, commentDateTime ASC
1782979568.40650.0522 [1] Using template: /templates/blog/comment.html
1782979568.40720.0007Using template: /templates/blog/post.html
1782979568.40740.0002 [1] SELECT * FROM swt_blog_authors WHERE authorID='6' LIMIT 1
1782979568.40830.0009 [1] SELECT pageID, pageParentID, pageDepth, pageTreePosition FROM swt_pages_staging WHERE pagePath='/what-we-do' OR pageSortPath='/what-we-do' LIMIT 1
1782979568.4090.0007 [1] SELECT pageID, pageParentID, pageDepth, pageTreePosition FROM swt_pages_staging WHERE pageTreePosition='000-002' LIMIT 1
1782979568.410.001 [7] SELECT * FROM swt_pages_staging WHERE pageNew=0 AND pageHidden=0 AND pageTreePosition LIKE '000-002%' AND pageDepth >=1 AND pageDepth<=2 ORDER BY pageTreePosition ASC
1782979568.41230.0023 [1] SELECT pageTreePosition FROM swt_pages_staging WHERE pagePath='/news/post' LIMIT 1
1782979568.4130.0006 [2] SELECT pageID FROM swt_pages_staging WHERE pageTreePosition IN ('000-006-001', '000-006', '000') ORDER BY pageTreePosition DESC
1782979568.41530.0024 [6] Using template: /templates/navigation/footer-nav.html
1782979568.41620.0009 [1] SELECT pageID, pageParentID, pageDepth, pageTreePosition FROM swt_pages_staging WHERE pagePath='/make-a-difference' OR pageSortPath='/make-a-difference' LIMIT 1
1782979568.41690.0007 [1] SELECT pageID, pageParentID, pageDepth, pageTreePosition FROM swt_pages_staging WHERE pageTreePosition='000-005' LIMIT 1
1782979568.41750.0006 [38] SELECT * FROM swt_pages_staging WHERE pageNew=0 AND pageHidden=0 AND pageTreePosition LIKE '000-005%' ORDER BY pageTreePosition ASC
1782979568.42030.0028 [1] SELECT pageTreePosition FROM swt_pages_staging WHERE pagePath='/news/post' LIMIT 1
1782979568.4210.0007 [2] SELECT pageID FROM swt_pages_staging WHERE pageTreePosition IN ('000-006-001', '000-006', '000') ORDER BY pageTreePosition DESC
1782979568.42360.0026 [10] Using template: /templates/navigation/footer-nav.html
1782979568.42770.0041 [1] SELECT pageID, pageParentID, pageDepth, pageTreePosition FROM swt_pages_staging WHERE pagePath='/visit' OR pageSortPath='/visit' LIMIT 1
1782979568.42860.0009 [1] SELECT pageID, pageParentID, pageDepth, pageTreePosition FROM swt_pages_staging WHERE pageTreePosition='000-004' LIMIT 1
1782979568.42920.0006 [30] SELECT * FROM swt_pages_staging WHERE pageNew=0 AND pageHidden=0 AND pageTreePosition LIKE '000-004%' AND pageDepth >=1 AND pageDepth<=2 ORDER BY pageTreePosition ASC
1782979568.4320.0027 [1] SELECT pageTreePosition FROM swt_pages_staging WHERE pagePath='/news/post' LIMIT 1
1782979568.43270.0007 [2] SELECT pageID FROM swt_pages_staging WHERE pageTreePosition IN ('000-006-001', '000-006', '000') ORDER BY pageTreePosition DESC
1782979568.43550.0028 [29] Using template: /templates/navigation/footer-nav.html
1782979568.43780.0023 [1] SELECT pageID, pageParentID, pageDepth, pageTreePosition FROM swt_pages_staging WHERE pagePath='/make-a-difference' OR pageSortPath='/make-a-difference' LIMIT 1
1782979568.43870.0009 [1] SELECT pageID, pageParentID, pageDepth, pageTreePosition FROM swt_pages_staging WHERE pageTreePosition='000-005' LIMIT 1
1782979568.43950.0008 [11] SELECT * FROM swt_pages_staging WHERE pageNew=0 AND pageHidden=0 AND pageTreePosition LIKE '000-005%' AND pageDepth >=1 AND pageDepth<=2 ORDER BY pageTreePosition ASC
1782979568.44240.003 [1] SELECT pageTreePosition FROM swt_pages_staging WHERE pagePath='/news/post' LIMIT 1
1782979568.44330.0009 [2] SELECT pageID FROM swt_pages_staging WHERE pageTreePosition IN ('000-006-001', '000-006', '000') ORDER BY pageTreePosition DESC
1782979568.44550.0022 [10] Using template: /templates/navigation/footer-nav.html
1782979568.44740.0019Request time: 0.1995
1782979568.44740Process time: 0.1993
1782979568.44740Memory: 1.6582