I bought these mums less than a month ago and planted them in Miracle Grow Potting Soil. Kept them in sun for 3-4 hours and in shade for the rest. They were left in sun for a couple of days at around 90 degree F. After watering them in the evenings they appeared to recover. After a while, I saw white powdery substance on the leaves and assuming it was some kind of fungi, I sprayed Neem Oil and water mix. The powdery substance disappeared but soon all flowers turned brown and I thought that happened cause of hot temperatures. But the leaves would never feel as fresh as when I bought them. Then I noticed all flower buds browning and falling and brown spots showing up on the leaves. I also noticed small white larvae (4 in number) feeding from the plant stems and then they'd disappear below the leaves. I removed all of them and since then I have not seen any.
I have other plants too (Mint, Basil, Other Mums) potted in the same soil which seem healthy for now.
Is there anything that can be done to save this plant or should I discard this plant and the soil to prevent the infection (if any) form spreading ?
P.S - The plants are located in Seattle, WA, USA area. This year the summer has been rather brief.
