Hi Don,

Volunteer Rachel here. Thanks for the picture. Were you able to see mites on your tree? Also did you see a canker, to make you suspect fungus? I am just trying to get an idea what the problem is. 

I have some additional questions, just in case those weren't the problem: was there any new landscaping done around the trees? New gravel? New trees planted nearby? New changes to your watering system? Anyone spray herbicide or weed killer nearby? It looks a bit like someone might have treated the gravel with herbicide and it washed into the grass near the boundary. Any additional information would be helpful. 

Also, can you possibly take a few more pictures, both close up of dead needles and then also maybe inspect the trunk/branches to look for damage. Then one or two more panoramic pictures of the landscape so I can see what else is nearby. 

Thanks,

Rachel

Hi Rachel,
This is a problem that I have been dealing with for twenty years, it
begins in late July - September.  The pines are forty years old.
There is no visual evidence of spider mites but I have treated them
twice this year for the mites.  Also, cannot find any cankers. The
gravel is new but the problem started a month before the gravel was
put down,  No other changes were introduced in the area were the
problem is.  Hope this pictures help... thanks again.
Don


On 8/7/21, Ask Extension <askextension> wrote:
></askextension>

Don't know if I have a fungus or spider mite problem. What product do you recommend for the treatment of fungus? Have been treating them with Bioadvanced insect disease and mite control with limited success. These plants are 30 years old. Thanks in advance for your help.

Hello Don,

This is Shelley. Today is my day to volunteer for Arapahoe County Master Gardener. I have read the exchange of messages thus far, and have looked at the pictures. Thanks for sending them!

There is the possibility that the browning of your mugo pine needles is due to winter drying. Water them during dry spells in the winter months to make them less susceptible to insect and disease problems. If this has been going on for 20 years, it sounds like the plants can handle it, but who wants unsightly browning?

In the case of spider mites, you would see silk between the needles. One test is to take a piece of plain white paper and hold it under an affected branch. Tap/shake the branch. If you have spider mites, this will dislodge some of them and you will see them as tiny specks on your paper.

Spraying the branches regularly with a hose will also control the problem by knocking off the spider mites.

I'm attaching a fact sheet on spider mites from Colorado State University. The active ingredient in Bioadvanced is imidicloprid, which is not listed as a miticide in the fact sheet. You could try one of the recommended products.

I hope this helps.

https://extension.colostate.edu/topic-areas/insects/spider-mites-5-507/