My dahlias are dying

[Lotus1023]

I have some dahlias growing in a large pot with marigolds. For the past couple of weeks they have been getting yellowy grey leaves. There is some new growth but it goes grey quite quickly. When I water them the water runs out very quickly. The soil seems quite moist though. I've cut them back as they die off. Are they just drying out in our hot Summer or is it something else? I've attached some photos so you can see what they look like.

 

[Chuck]

I have some dahlias growing in a large pot with marigolds. For the past couple of weeks they have been getting yellowy grey leaves. There is some new growth but it goes grey quite quickly. When I water them the water runs out very quickly. The soil seems quite moist though. I've cut them back as they die off. Are they just drying out in our hot Summer or is it something else? I've attached some photos so you can see what they look like.

Looks like spider mites to me. In fact you can see what looks like a web in the picture

 

[Becky]

Welcome to the forum @Lotus1023

I think Chuck is probably right, it looks like spider mites. You should cut back all affected areas, and be careful when you dispose of the cuttings so that the mites don't spread to other plants. Neem oil is a good treatment too.