Fusarium Ear Blight
Fusarium Ear Blight
Introduction
Fusarium ear blight (FEB) can be caused by a combination of different fungal species, which can vary in their prevalence and relative proportions on the ear from year to year. There are seven different fungi which can cause FEB. However, in the past 3 years the dominant species have been Fusarium culmorum, F. graminearum, F. poae and Microdochium nivale.
Ear Blight species Mycotoxin produced
F. graminearum DON, NIV, ZON
F. culmorum DON, NIV, ZON
F. avenaceum Enniatins, Moniliformin, Beauvericin
F. poae HT-2 Toxin, T2 Toxin, NIV
F. langsethiae HT-2 Toxin, T2 Toxin, DAS
M. nivale and majus none produced
Fusarium graminearum and F. culmorum produce the DON (deoxynivalenol) and ZON (zearalenone) mycotoxins, for which strict European guidelines are set for levels in grain. Fusarium poae produces HT-2 and T2 toxins, for which legislation is being considered.
Microdochium nivale is also included in this disease complex but it does not produce mycotoxins, but it does results in seed infections which reduce seed germination and seedling vigour.
Pathogen
Fungus
Hosts
Wheat, barley, oats, rye, triticale, maize (grain and forage) and grasses
Symptoms
There are 4 typical field symptoms of FEB
1. ‘Poae-like lesion’ on floret
2. Bleaching of individual spikelet
3. Bleaching of individual spikelet and enhanced senescence of spikelet above
4. Fully developed Ear Blight symptom
Field symtoms are often combinations of all three.Inadidtion, severe Microdochium infections can end up looking like true Fusarium infections as seen in the difficult epidemic of 2012
Development
Seed infection is the primary source of infection on crops of wheat but the disease can also arise from crop debris in the soil. As the crop develops spores can be splashed onto newly opened leaves from the canopy below. Fusarium can also move into crops from cereal volunteers.
Favourable Factors
Each species of FEB has slightly different temperature optima, but general risk factors are :
Warm dry springs induce spore production on crop debris
Rainfall in June splashes spores onto ears
Infection occurs mainly during flowering under warm humid conditions
High rainfall/humidity through summer allows infection to spread, particularly once crop the ripens
When the crop ears have emerged cool, wet weather provides suitable conditions for prolonged flowering and subsequently an increased risk of infection into the vulnerable grain sites via the stamens.
Importance
The common focus for suppressing ear blight infections is mycotoxin reduction. If these enter the foodchain they can be toxic to both animals and humans and strict levels of impurities in foodstuffs have been limited under EU regulations.
The ear bleaching species Fusarium graminearum and F. culmorum can reduce yield by up to 30%, since a single spikelet infection will prevent nutrient and water flow to uninfected spikelets above it. This results in extensive grain shrivelling.
The non-mycotoxin former Microdochium nivale, commonly found in association with true Fusarium species, can also impact yield by up to 10%.
Single spikelet infections do not restrict upwards nutrient and water flow, which is why yield penalties are generally smaller. However , in very severe infections such as seen in 2012, multiple infection of single spikelets can give risk to what looks like a fully developed Fusarium infection which is when the established disease restricts the flow of nutrients and water which impacts the developing grain sites above.
Control
Crop rotation
Varietal tolerance as indicated in the recommended list
Fungicidal seed treatment
Reduction of early season inoculum with suitable choice of fungicides at the T1 and T2 timing
Fungicide product choice: e.g. differential effect on FEB fungi and how this can increase mycotoxin contamination (weak or selectively active fungicides).
Application timing is critical as this is when the ear is most susceptible to infection and ear fungicides need to be applied at early – mid flowering and ideally just prior to a rainfall event
Effective dose rate of Fusarium active fungicide. Many are insufficiently active at less than 75-100% label dose to ensure effective suppression
Grain and forage maize can be an important source of Fusarium inoculum for following crops of wheat.
Fusarium on the leaf (Photo G. Bubb)
Field shot (Photo N. Adam)
Severe field infection, Callow July 2012. c.v. Cougar 98% Microdochium nivale (FERA analysis) (Photo G. Bubb)
Fusarium discolouration (Photo G. Bubb)
Fusarium culmorum
Fusarium poae (Photo B. Giles)
Close up of fusarium culmorum
