Plant disease Kelvin found in Toronto ground (4-4)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

An envelope (‘found in’) of K (temperature, ‘Kelvin’) in ROOTNOT, an aangram (‘ground’) of ‘Toronto’. Root-knot is a debilitating gall on the roots of plants, caused by a parasitic root-knot nematode.