Hello,

It looks like it could be a needle blight, Mugo pine are susceptible to Dothistroma needle blight. The tips brown first and it goes from the lower canopy up and starts from the older needles out. However I do not see any dark colored banding on the needles which is a good indicator of Dothistroma; there are some good pictures of the banding at this site: https://plantpathology.ca.uky.edu/files/ppfs-or-w-25.pdf. If you cannot find any banding like in those pictures (check the green needles too for signs of banding), then I would think it is something going on with the soil/roots. If it were sun, or winter desiccation I would except to see symptoms on the the upper canopy as well and see it starting on the new growth. Issues with the roots usually start from the bottom and from the old growth out, like you are seeing. Also if there is a problem with the roots, this would also cause overall thinning / decrease in fullness you are seeing. Issues with roots can be difficult to pinpoint. Could the area where the Mugo pine is browning gotten more compacted, or is it more damp or dry, or is there some sort of barrier the roots are hitting? Could this one have gotten planted too deep? I would first check if the soil in the area is more compacted or wetter than the soil where the healthy Mugos are at, you can use a long screw driver to see how easily it goes into the soil & how deep at the different locations. You can also use the screw driver to check for structural roots near the surface, if you can't find any large roots in the top few inches of soil that is a sign it was planted too deep. I would start by checking these things first, if you do not find any differences and the trees doing poorly are not very close to the healthy trees you might want to get a soil test comparing the two areas as well. Thank you for using Ask An Expert!

Hi Denyse-  Thanks so much for your reply. I don't see the banding on the green parts like in the link you shared. Just a browning beginning from tip working back to the branch. The browning of a needle moves rapidly and only takes about 5-7 days for a needle to go from green to brown and fall off. The browning issue became noticeable less than one month ago, and progressed rapidly effecting 5 of the Mugos. A few more data points for consideration: a) The effected Mugos are all North facing and were covered in a lot of snow until early May (located in Keystone, Colorado). They might have had some extra snow piled on them from snow removal efforts in late Spring. b) they had significant dead needle and aspen leaves thatching covering the low parts of the branches (doesn't look like was not cleared out in the fall). c) When i cleared the dead needle and leave material out there was some white (mold-like) substance under the needles close to the lower branches that entered the soil. photos attached. d) the Mugos are into a rock retaining wall, but should have decent drainage and root growth options, but must get a lot of moisture as there is a lot moss growing near them.  e) the Mugos effected are the ones that seem to get less daily sun, and might soil at base is not evaporating very quickly. f) the mugos effected range from small/  young (~4 years) to old / large (~14 years). Thanks again! 

Thank you for all the information and pictures, that is very helpful! It looks like the tree had needles browning on all sides, not just on one side? Is it possible the snow that was piled against them had salt mixed in it? Or is there anyway they caught some spray drift?Otherwise, I am thinking it might be Dothistroma or another needle blight fungus. It looks like there are black spots on the dead needle material which might be the fungus fruiting structures, the fruiting structures develop on the needles after the needles have died. Also symptoms of Dothistroma can develop fairly quickly - within 2-3 weeks of start of symptoms - and the needles drop in the spring / early summer. I would keep all the needles dropped cleaned up and discarded throughout the summer and fall. You can also apply a copper fungicide once all the new needles have grown to their full length (early to mid-summer, so about now should be good). Timing for the copper fungicide is once just before buds open in the spring and once early to mid-summer. Mugos like moist but well-drained soil but it sounds like that is what they are receiving. I am not completely sure what kind of mold that is but I do not think it is what is causing the symptoms, white mold (Sclerotinia stem rot) is major problem for herbaceous plants but not woody plants.  

Hi Denyse-  Thanks again for the reply.  The browning and needle dropping has continued and unfortunately now spread to other healthy mugos, even after clearing all old needles and leaves from the base. 

I was able to order a Copper Fungicide (photo attached).  Do you have recommendations on how much I should dilute it?  Is there a proper way to apply it to the Mugos?  Should I treat all Mugos, or just the ones that are browning?

PS) I also read that Neem Oil can be helpful to control Fungus.  Should I consider applying it too?  If so, any suggestion on use?

Hello,

I'm so sorry I missed your last response!! Follow the dilution and application instructions on the label (the label on the back should peel back and have instructions for dilution based on different plants/diseases). You should treat all the Mugos, the fungicide won't treat affected needles but it will protect new needles from infection. Neem oil (and horticultural oil) can help prevent powdery mildews but I do not think it is very effective on other types of fungi. Also next year I would consider using the copper fungicide again in the spring (especially if it is a cool, wet spring) just before the buds open and again mid-summer to protect them in case there are still infected needles in the canopy or infected fallen needles.  

Thanks Denyse. I gave all Mugos one application of the Copper Fungicide 1.5 weeks ago, and figured I would do a second application this weekend.  I'll hold off on the neem.  I've continued to see more browning of new needles and drop, but I assume that is because these are the needles that were infected last year and the fungicide can't help them? Any reason not to apply a second time? When do you expect the browning to stop? Should I not see browning next year? Will the lower needles that fell, regrow?  

Thanks again!

Hello!

No reason not to apply a second time. Yes any needles that were already infected will continue to brown. The needles that dropped will regrow and if there are any infected needles that stay on the tree or drop and are missed in clean-up then there is a possibility that you will see browning again next year. I would use the fungicide again next year to prevent any new needles / old needles that weren't infected from becoming infected since it is very easy to miss a few dropped needles or some infected needles might remain on the tree. The browning should stop when the fungus has completed its life cycle on all the needles that were infected. 

Thanks again Denyse.  How often should I be cleaning the needles?  There have been a ton of dropped ones unfortunately and now I am seeing the browning happing to other Mugos (I suspect the fungus was carried by the rain/wind and spread across the entire property).  Some of the Mugos are 50% yellow now.  Do you have an idea what time of year, the cycle will end and no more needles will brown/drop?  What time of year next year should do the first spray? Is there a time of year this year, that I should stop spraying? 

The fungus is not active in temperatures below 40F so once the temperature is below that during the day there would not be any reason to spray. The fungus takes a year to complete its life cycle from the initial infection so without know when needles were infected it is hard to say when the cycle will end. Next year you will want to do the first spray before buds open in the spring, so probably sometime in May and then do a second spray after the new needles have reached their full length (early to mid-summer).