John Ball of Agrovista was expecting Comet 200 (pyraclostrobin) to control the main diseases in his maize trials last year, but perhaps what he wasn’t expecting was the measurable physiological (AgCelence) benefits of this fungicide on the crop.
Last year was a low disease year for eyespot and Northern Leaf blight. Brown rust came in at a low level too. All these diseases take out green leaf area, reducing the crop’s ability to photosynthesise and hence reducing the tonnage of the crop, explains John. “Leaf diseases also affect the starch levels in the crop, which is important to growers.”
He says that the strobilurin fungicide Comet 200 acts preventatively in maize and it is a well-known and highly effective active ingredient. “It is also known to have positive physiological effects and last year when diseases were low in maize this was very obvious. Treated crop yields were up by 5% (around 2.5 t/ha) and there were measurably fewer double cobs. The untreated had 20% double cobbing and the Comet 200 treated had just 7%. Starch levels were up, too. Double cobbing is usually a consequence of stress and it adversely affects silage quality, so the pyraclostrobin was definitely helping here. We wanted to look at chlorophyll levels as greening is another classic benefit of Comet 200 in other crops, but there aren’t any specific calculations for maize at the moment.”
Agronomy Manager for BASF, Tom Scanlon reports that Comet 200 now has a full label recommendation for use in forage and grain maize crops. “The new label approval replaces the previous EAMU and is applicable for this season. The label recommendation is for the control of maize eyespot and moderate control of Northern corn leaf blight. The label also carries statements that support the physiological benefits that John Ball has seen.”
The relevant label statements are ‘In maize a grain yield response may be obtained in the absence of visual disease’ and ‘Comet 200 can maintain the total greenness of the crop towards the end of the growing season’,(which helps maximise yield without impacting on how quickly the plant reaches optimal dry matter.)
Tom Scanlon explains that eyespot (Kabatiella zeae) is the main disease problem in maize, along with Northern Leaf blight (which was Helminthosporium but is now known as Setosphaeria turcica). “Eyespot, not related to the disease in cereals, thrives when it is cold and wet with high air humidity and is spread from maize trash. The disease spreads rapidly throughout the plant if conditions are conducive and prevention is not taken. It is also important to note that many varieties do not have strong resilience to eyespot bred into them.”
Eyespot tends to attack maize early, from the 8th leaf onwards, with symptoms appearing much later on. It is seen as small colourless spots with brownish-red centres and yellow halos on the leaves. The leaf dries out from the bottom. By reducing the green leaf area that is able to photosynthesise, the disease can cause significant losses.
Where it is drier and warmer, Northern leaf blight can be more important. Its symptoms are spindle-shaped oblong lesions, parallel to the leaf veins. These lesions eventually coalesce to destroy the entire leaf. High yield losses can occur with early infections. “You sometimes get rusts, too, but Comet 200 controls all three diseases. It also provides important physiological extras, which easily pays for the strobilurin treatment even in absence of disease. Comet 200 is definitely providing the worthwhile extras! We will be repeating the trials this year, looking at different application timings and on a larger scale,” says Agrovista’s John Ball.
Fungicide application should be early enough to provide protection against diseases and with the aim of covering the plant, which at the time of treatment can be 1.5 metres high. A good water volume of 200-300 l/ha is needed, he says.
