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I have two rosemary plants, one is over six months old and the other was bought from a shop about 4 weeks ago.

This is the older one I grew from seed. It was the only survivor of 5 seeds I planted roughly 6-7 months ago. It was also one of four pots partly damaged by Cane Toads and I have neglected it for roughly eight weeks now. Its leaves are very powdery, cracking and frail looking. One stem had lost all of its leaves which I pruned today. Since I started watering it the lower leaves seemed to have that nice dark green color return but now they too are starting to look bad. enter image description here

This is my newer plant and it too is getting the powdery coating on its leaves. It has grown quite a bit in the last four weeks but has had the powder for about 2 weeks now. enter image description here

EDIT

I have the new plant in an upright planter that does get lots of water so I'll be moving it to its own pot. The planter gets sun for most of the morning but by midday it is in shade from the house eves. During the coming summer they will get a lot more sun. The pots on the ground get the same amount in the morning but they also get the afternoon sun until about 4:30. The reason for the extreme moisture you can see in the pot was I had something eat a lot of my herbs so I moved to a small green house. This kept everything very moist and a fungus/mould started in quite a few pots for the week they were in there. I had already asked about the fungus earlier, and didn't think that a greenhouse would cause it too. So they are now back outside to dry and air out. (less than a day outside and my kale had 5 leaves eaten)

This is a close up of the leaves of the newer plant in the upright planter. enter image description here

This is a close up of the older plant in the pot looking very sad. enter image description here

An this is the entire herb garden early morning minus the trickle feed system that I normally have hooked up to the pots. The older rosemary plant is in the pot near the reddish pot, and the newer one is in the left hand side upright planter second bay from the top and on the right side of that pot. (there is a curry plant next to it in the middle) enter image description here

UPDATE

The milk spray has worked really well. This is the newer plant looking super healthy. enter image description here

And this is the older plant after a prune and milk spray. It hasn't grown much at all compared to the newer plant but its looking really healthy now. It does have some new leaves though. enter image description here

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  • I think experts here, maybe, would ask for a closer look at the leaf. Also, in case, you should put a close-up pic of the leaf and the underside of the leaf, too.
    – 4-K
    Commented Aug 20, 2016 at 14:35
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    Damaged by Cane Toads! There's something we don't read every day..
    – kevinskio ♦
    Commented Aug 20, 2016 at 16:45
  • Yeah, during summer here it cant get really hot. I had a misting sprinkler system that automatically watered them twice a day and the Cane Toads loved it. They made wallows in my pots and dug up my still very young plants.
    – John Petrak
    Commented Aug 21, 2016 at 7:02
  • QUIT misting and watering every day. Fungus LOVES that PLANTs don't get any benefits. Allow the plants to dry out and water according to each plant! If the pot is heavy do not water. If it is light and dry down 1/2 inch or whatever, water deeply, allow to dry before watering again!! I'd put a big fan out there to blow the air when conditions are calm. That removes the oxygen produced by the plants so that they get more co2 and aerates to prevent fungus!! You should see the leaves MOVING with the right amount of air movement. You are OVER watering, toads are enjoying.
    – stormy
    Commented Aug 21, 2016 at 21:45

2 Answers 2

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It does look like powdery mildew, but ensure they get plenty of sunlight, so if they're not in a sunny spot, move them if possible. Try the milk treatment - 1 to 3 parts cow's milk mixed in a sprayer, spray all parts of the plant, including under the leaves, until run off. Repeat after two or three days if necessary - works best in bright light or in sunlight.

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  • Hey! This milk treatment WORKS!! Bamboo, you told me 1 to 9 parts water...1 to 3??? My goodness! The season is fast approaching and I used 1:9 last year and it worked very well! This could also be the normal condition of rosemary. I see too much water!! Allow to dry out before watering again, especially with rosemary!!
    – stormy
    Commented Aug 20, 2016 at 22:53
  • @stormy, yea, 1 to 9 is what I use and is the original recommendation - however, people have been experimenting and there are people using 1, 2, 4 even 5 parts milk to water. I;m sticking to 1 to 9 myself, it works anyway!
    – Bamboo
    Commented Aug 21, 2016 at 1:00
  • I'll give that a try. But will it help my older plant?
    – John Petrak
    Commented Aug 21, 2016 at 7:04
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    Does look a bit far gone, to be honest, but worth a try - I'd cut the longer shoot back by half or down to the height of the other shoots first though
    – Bamboo
    Commented Aug 21, 2016 at 9:11
  • The milk has worked really well! Even the sick one is looking much stronger. Thanks @Bamboo.
    – John Petrak
    Commented Sep 25, 2016 at 4:29
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I think this may be powdery mildew.. does it wipe clean? Please post a good closeup pic of the leaves.

If so, before resorting to fungicides try cleaning and changing its environment.

Clean each leaf by wiping them down gently ensuring a clean green surface. Make sure the plant is in a good sun spot. If the powder returns, try a teaspoon of bicarb in 1l of water and clean again. Ensure your soil is draining properly and not incessantly moist and dark.

If its not helping you can look for a fungicide and apply it as per instructions. I believe an oil like neem can also help

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  • Wiping down the surfaces of the leaves is tenuous. This might not be powdery mildew anyway. I am seeing too much water, Jonathan, please allow to dry out before watering again deeply and no sitting in a saucer of water, get the bottom of pot off the surface to allow air beneath the pot to assist drainage! This is a desert plant. It requires some dryness and less water. Did this plant have this much white stuff on the leaves a month ago? What are your using for water? Truly, it will not hurt to use Bamboo's milk/water spray!! Even if there is no Powdery Mildew!
    – stormy
    Commented Aug 20, 2016 at 22:57
  • Yes they are small little leaves, but there is not much rosemary there. Spraying keeps it damp. If you have some time to even wipe some of the really bad spots it can help a lot.
    – JonathanC
    Commented Aug 21, 2016 at 8:22

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