Rosemary hedge issues

matt_fender

Hi all, I hope everyone is keeping OK and enjoying their gardens, at least, in the current situation.

I have a worrying issue with a rosemary hedge that I planted two and a half years ago., made up of about 12 individual plants, the variety of which I don't actually remember (just bought from Homebase).

Earlier this winter, a few branches of one plant at the very end of the hedge died back quite suddenly and dramatcially - completely brown leaves. I cut these off and things seemed OK for a while, and in fact the other half of this same plant that hadn't died appeared to be doing OK as well. The hedge itself hasn't been pruned since late summer last year.

Today I have noticed that a section of the hedge nearest the dead branches that I cut out seems to be a bit poorly. Still mostly green, but with more reddish/brown leaves the closer you get to the excised area. This damage is spread across more than one plant. The tips of the affected plants appear to have stunted and curled leaves which brush off quite easily between your fingers. The rest of the hedge seems very healthy and has started growing for the season.

I have Googled about but can't seem to find a problem that fits. Frost damage doesn't seem that likely given the mild winter we had, and the localisation of the damage within the hedge - can't rule it out though, I suppose. The fact that the issue seems to be in one area but across a few plants suggests a pathogen that could be spreading, but nothing came up in the search. I guess my main concern now is should I act fast to limit spread, or leave it to see if they recover? There are some healthy looking tips amongst the affected plants.

A few pics:


Close up of some affected tips.


The whole hedge. Its kind of subtle, but the section on the right is the affected area - see how it is a little browner/thinner looking? This is more obvious up close, but I just wanted to give some context.

thanks!

amancalledgeorge

The photos didn't show up...try again @matt_fender

Dovefromabove

Click on the landscape icon and follow the instructions ... if pic doesn’t appear reduce the size 😊 

matt_fender

With pics!

Close up of problem area:



Whole hedge - suspect area is on the right. Difference is not that obvious in pic, but you might notice the right approx fifth of the hedge is a little less full/green:

Pete.8

Possibly Rosemary Beetle
Some info here may help diagnose
https://www.rhs.org.uk/advice/profile?pid=555

BobTheGardener

Looking at the tips I think I see powdery mildew, a disease which often attacks rosemary.

https://www.growveg.co.uk/guides/the-worst-enemies-of-rosemary/

matt_fender

Thanks for the suggestions chaps. @Pete.8 I couldn't see any signs of insect life on close inspection, which is not to say they aren't there. I will keep an eye. @BobTheGardener I'm not sure if there is any mildew, but there is definitely a sort of mottled look to the leaves. Here's an even closer view - note how some leaves have gone very red, as well:

BobTheGardener

Those tiny white spots could be caused by thrips which are very good at hiding from any movement they see.  Some other herbs like oregano also get that sort of damage from sap-sucking insects like thrips and leaf-hoppers.  The damage was probably done last year and the pests may have laid eggs on the plants or in the soil.  If it is a hot, dry area in the summer, it could have been spider mites.  Unfortunately, all of the above are hard to deal with, especially spider mite.

Borderline

BobTheGardener has a point. I just want to add, at the way you are growing it, I suspect it is either bacterial or fungal infection. Try to grow them in optimum conditions. 

Congested branches and soil not being exposed to the sun can make the plants grow weak. Good air-flow and planted in free draining soil. When cutting back, avoid cold or damp weather & watering overhead. You may also need to cut down on the pruning (pardon the pun) to limit reinfection for the time being. 

matt_fender

@Borderline I think conditions are pretty good where they are - they have thrived up until now. Position is unobstructed south facing, so full sun all day and on quite a gravelly bed with good drainage. I never water overhead, in fact I rarely water them at all, but of course we have had a lot of rain over winter.

I have seen quite a few nice examples of clipped rosemary hedges so I'd query whether they are too dense/congested, but I will hold back on pruning this year until any danger of frost is past and they are growing more strongly.