28 May 1999

Blights about, so dont delay initial sprays

WITH potato blight already reported in early crops growers are warned not to delay their initial blight sprays.

"The timeliness of the first four or five applications is very important in a high pressure season," says Peter Tayler, technical services manager at Cyanamid. "At this stage optimum spray timing is more important than choice of product."

Reflecting a re-positioning of blight fungicide Invader (dimethomorph + mancozeb) Mr Tayler says many growers could switch to using the non-phenylamide product in the early stages of a blight programme.

"It is not as systemic as some blight products, but it does move in the xylem, so it will travel upwards from the stem to the leaves. And it offers excellent stem blight control, which is important in preventing the development of tuber blight. SAC work indicates that the early sprays are key in preventing stem blight."

Phenylamide fungicides remain a very useful element of a blight control strategy, he agrees. But Invader has a place where resistance to phenylamides is known to exist.

"In a low-risk situation, mancozeb or fluazinam will give good protection early on. But medium to high-risk situations are better dealt with by Invader."

The widespread use of blight sensitive varieties, together with a mild winter and wet, humid conditions are all favouring blight development this year, Mr Tayler adds.

"The last two seasons have reminded us of the value of early applications. Growers who managed to get five or six sprays on in June last year got ahead of the disease and kept it out of crops. But those who missed their chance early on were struggling in July."

Spending more on blight control will be worthwhile this season, he believes. "ADAS and SAC work shows a robust blight programme raises margins by £3412/ha. But this figure can be increased by £586-£1100 simply by using more appropriate products." &#42