Attacksof alternaria have already started to hit potato crops, at the same time asblight outbreaks have reached record levels for early season infection. Growersare advised to quickly assess infection risks, and bring forward treatmenttimings to prevent decimating green leaf loss.
Syngenta field technical manager, Stephen Williams,warns the continuing warm and changeable weather has increased the risk of alternaria (Early Blight)development. Outbreaks of the disease have already been observed, from thewest of England right across to Norfolk.
The risk of attack increases where conditions arehot and dry, if the crop is under nutrient or drought stress, or where there isa history of alternaria on thefarm.
In many instances all these risk could beconspiring together this season. Furthermore, a high proportion of currentvarieties have some level of susceptibility to the disease, he advised.
Alternariais best controlled with an Amphore Plus protectant programme, timed before theend of flowering. However, this season Mr Williams advocates growers may needto consider starting treatments earlier in high-risk situations.
AmphorePlus can be applied three times per season, either as a block or alternating inthe blight programme on a seven to 10 day interval, to see the crop safelythrough the high-risk conditions, he said.
Mr Williams pointed out that in addition to proven alternariacontrol, Amphore Plus also includes the highest level of blight protection,equivalent to a full-rate application of Revus. With the large number ofblight outbreaks already reported this season there is an inherently highpotential of further spread, especially in irrigated crops.
Reverting to seriously weaker blight fungicidesthat are perceived to have some effect on alternaria, such as mancozeb, wouldexpose crops to far greater risk of damaging disease infection, he added. The good news isthat with Amphore Plus there is no need for growers to compromise on theall-important blight protection when looking to control Alternaria too.