Yellowing Grass

[Hysteresis]

Hi Gardeners,
I have a cosmetic problem with my lawns that I am sure some knowledgable gardener will have seen before and Know the solution.
My lawns are not bowling green turf but the normal turf purchased for domestic lawns similar to all of the turf suppliers.
The turf was laid 7 years ago and I tend them well, feeding with general fertiliser twice yearly after which the grass grows quickly and very green and attracts comments from neighbours as to how nice they look.
After about two months growth, I start to get individual blades of grass turning Yellow. Lack of nutrients I conclude, but the odd thing with this yellowing is that whilst cutting using a petrol rotary machine, I notices a Yellow Powder deposit all over the grass box, internally and externally. The Powder looks Identical in colour and consistency to Turmeric (the culinary spice). What ever can this be and what is its cause?

 

[westwood187]

If your grass blades are covered in an orange powder, and the reddish-brown lesions underneath don't rub off, you've got rust. The fungi to blame are usually active during humid weather (70�-to-75� F). Grasses under stress from nitrogen deficiencies, moisture shortages or close mowing are most susceptible. Solution: Rust develops slowly, so in many cases frequent mowing, adequate water and an application of a high-nitrogen fertilizer can stop the problem. Frequent mowing can help control the problem too. However, if the disease is severe, I'd treat affected areas with a chlorothalonil fungicide.

 

[Hysteresis]

Thanks Westwood187.
Have you any suggestions as to a branded Name for the treatment chlorothalonil fungicide . I will certainly try it.