Kind of looks like a phosphorus deficency I believe. @garrigan62 would be the best tag 
Looks like mine a few days ago, mine needed K. There’s a lot more info about your grow needed to help yours though…water, nutes,lights,temp etc?
Really need a pic in natural light, but it looks like a calcium deficiency.
@Lildeno
First I would like to welcome you to ILGM.
I hope you join your community OK
What Is Rust Fungus?
Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales(previously also known as Uredinales). About 7800 species are known. Rusts can affect a variety of plants; leaves, stems, fruits and seeds. Rust is most commonly seen as coloured powder, composed off tiny aeciospores which land on vegetation producing pustules, or uredia, that form on the lower surfaces.
How Does It Spread Infection?
The main cause for Rust is night time temperatures being too cold with a high humidity.
Rust fungus produce asexual spores which are spread like wildfire by water, wind or bugs. Pathogenic fungi are biotrophs meaning they take the nutrients they need directly from the plants cell tissue. Once the spores settle on a plant hydrophobic interactions are formed on the plants cell surface through a process that isn’t fully understood yet the Rust fungus produces a sticky like substances which attaches the spore to the plant. Once attached to a host plant the Rust fungus spores germinate by growing a “germ tube” eventually reaching a stoma, once inside the hyphae tips flatten out to lock into cell walls. A “peg” then grows into the plants mesophyll cells its creates specialised tips “Haustorium”, they spread around cells without affecting the membranes. The plants membranes invaginate around the haustorial forming a open space. Iron & phosphrous rich neck bands connect the plant and fungi known as apoplast which prevent nutrients from reaching the plants cells, its grows until its produces new spores which is repeated every 10-14 days.
Prevention.
Currently there are 2 or 3 types of Pathogenic fungi which are resistant to sterilization. (Bleach washes, Sulphur Candles, Soapy washes etc.). One of the best preventions you can take in your grow room is to have proper temperature, ventilation and always disinfect your room after every grow. Spraying plants 1 or 2 a week with some kind of fungicide (I prefer Sulphur based) is also great since it reduces the changes of spore germination.
Cure
Its extremely hard to get rid of once you got it most fungicides with help slow it down but not kill it completely. At this time the only way to cure a plant once Rust fungi has gotten hold is with Systemic fungicide which runs through the plants cells killing any fungi it comes into contact with, which also can be bad since it will kill helpful fungi as well. Any infected plant material should be burnt or put in a garbage bin outside of the home as composting and leaving it a normal garbage will just spread the infection more.
If you think you noticed Rust fungi act right away because the more time it has to establish the harder it is to get rid oflrd
I
What Is Rust Fungus?
Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales(previously also known as Uredinales). About 7800 species are known. Rusts can affect a variety of plants; leaves, stems, fruits and seeds. Rust is most commonly seen as coloured powder, composed off tiny aeciospores which land on vegetation producing pustules, or uredia, that form on the lower surfaces.
How Does It Spread Infection?
The main cause for Rust is night time temperatures being too cold with a high humidity.
Rust fungus produce asexual spores which are spread like wildfire by water, wind or bugs. Pathogenic fungi are biotrophs meaning they take the nutrients they need directly from the plants cell tissue. Once the spores settle on a plant hydrophobic interactions are formed on the plants cell surface through a process that isn’t fully understood yet the Rust fungus produces a sticky like substances which attaches the spore to the plant. Once attached to a host plant the Rust fungus spores germinate by growing a “germ tube” eventually reaching a stoma, once inside the hyphae tips flatten out to lock into cell walls. A “peg” then grows into the plants mesophyll cells its creates specialised tips “Haustorium”, they spread around cells without affecting the membranes. The plants membranes invaginate around the haustorial forming a open space. Iron & phosphrous rich neck bands connect the plant and fungi known as apoplast which prevent nutrients from reaching the plants cells, its grows until its produces new spores which is repeated every 10-14 days.
Prevention.
Currently there are 2 or 3 types of Pathogenic fungi which are resistant to sterilization. (Bleach washes, Sulphur Candles, Soapy washes etc.). One of the best preventions you can take in your grow room is to have proper temperature, ventilation and always disinfect your room after every grow. Spraying plants 1 or 2 a week with some kind of fungicide (I prefer Sulphur based) is also great since it reduces the changes of spore germination.
Cure
Its extremely hard to get rid of once you got it most fungicides with help slow it down but not kill it completely. At this time the only way to cure a plant once Rust fungi has gotten hold is with Systemic fungicide which runs through the plants cells killing any fungi it comes into contact with, which also can be bad since it will kill helpful fungi as well. Any infected plant material should be burnt or put in a garbage bin outside of the home as composting and leaving it a normal garbage will just spread the infection more.
If you think you noticed Rust fungi act right away because the more time it has to establish the harder it is to get rid of
.
It’s a hydroponic system ,temp is usually a little higher at 82 ,that’s on a hot day but usually it stays at 79 humidity varies from 35 to 50 % humidity ,strain is white widow and on week 10 altogether but week six of flower,ph is kept at 5.5 to 6.5and this has been here for a about 2 to 3 weeks ,but buds look good and also I use tap water and it’s been a little muddy the last 2 changes and I tried filtering with a towel beatnik could but was still dirty so that’s most of the info I know of top
And also I use general hydroponics nutrients