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International Society for Infectious Diseases <http://www.isid.org>
Date: Fri 23 Apr 2010
Source: FarmingUK [edited]
<http://www.farminguk.com/news/Keep-one-step-ahead-of-Chocolate-Spot-this-season_18027.html>
Growers of winter [faba] beans are being warned that they must keep well ahead of chocolate spot this season, with signs that the disease is already present at high levels.
Anthony Biddle, PGRO [Processors and Growers Research Organisation]
confirms: "We are definitely seeing more signs of the disease in winter beans than we have done for many years, and also at an earlier growth stage. This is most likely due to the hard winter making the crop more susceptible to disease. To protect yield potential it is essential that a protectant spray is applied before the disease is established."
Dr Biddle has been assessing the performance of a range of fungicides against both chocolate spot (_Botrytis cinerea_ and _B. fabae_) and rust (_Uromyces fabae_) in beans. He advises that the 1st application should occur at early flowering stage, the 2nd 4 weeks later. "The 1st spray is usually targeted just at chocolate spot, the 2nd at both chocolate spot and rusts."
According to Jonathan Ball, BASF Pulses, growers should be gearing up to start their fungicide programme. "Chocolate spot can escalate to epidemic proportions if it is warm and wet. If it stays warm, rusts could become a problem later on in June [2010]," he says. "Chocolate spot is not an easy disease to control and resistance issues need to be considered, which is why it is useful to integrate fungicides with different modes of action. With resistance management in mind, fungicides from different cross-resistance groups should be alternated."
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[Chocolate spot caused by the fungus _Botrytis fabae_ or the more virulent _B. cinerea_ is an important disease of faba bean (_Vicia faba_; also called broad bean, horse bean, Windsor bean, field bean, winter bean) and other leguminous crops. For example, it is one of the most destructive diseases of pulses in tropical African regions.
_B. fabae_ is prevalent throughout the season, while _B. cinerea_ affects crops intermittently and is usually confined to flowering time.
Symptoms start as brown spots on lower leaves, and this is considered the 'non-aggressive' phase thought to have little effect on crop yield. However, if warm, humid conditions persist for several days, the disease will spread quickly and be termed 'aggressive' with symptoms of leaf blight, defoliation, and loss of flowers and pods.
Stems can weaken and collapse, and flowers and pods may also develop lesions although affected seeds are still edible. A plant toxin produced by the pathogens is thought to be responsible for the damage to the host tissue.
A strong relationship exists between disease incidence and seed yield, with an average of 3 percent yield loss per percent of crop infection for _B. c._ and 0.5 percent loss per percent of _B. f._ infection. Disease management includes cultural and phytosanitary measures (such as burning of plant residue at the end of cropping, wide spacing of plants, limiting the amounts of nitrogenous fertilisers, crop rotation), use of clean seed, control of volunteer plants, and fungicides. Host cultivars with varying levels of tolerance are being developed.
It appears from the report above that bean rust is not present at this time, but the fungicide treatments recommended for chocolate spot will nevertheless serve as prevention for possible rust development later in the season.
Maps of UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif> and <http://healthmap.org/r/01es>
Pictures
Chocolate spot on faba bean leaves:
<http://www.inra.fr/internet/Produits/HYP3/images/6030610.jpg>
Symptoms on whole faba bean plant:
<http://www.inra.fr/internet/Produits/HYP3/images/6030616.jpg>
Links
Information on chocolate spot of faba beans:
<http://www.winter-beans.co.uk/all-about-winter-beans/disease/chocolate-spot>,
<http://www.inra.fr/internet/Produits/HYP3/pathogene/6botfab.htm>, and <http://www.dgsgardening.btinternet.co.uk/chocolate.htm>
Diseases of faba bean (including choc spot and rust):
<http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm7810>
_B. fabae_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=264556>
_B. cinerea_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=217312>
Phylogeny of genus _Botrytis_:
<http://mbe.oxfordjournals.org/cgi/content/full/msi020?ijkey=42Y3fBaCgcqCM&keytype=ref>
PGRO (UK centre for applied research on temperate peas, beans & lupins):
<http://www.pgro.org/>. - Mod.DHA]
[see also:
2007
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Fungal diseases, wheat & pulses - Australia (SA) 20070821.2729]
Topics
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