Hello! I have a Kelvin Floodlight dinner plate variety that after about two weeks after I put it in the ground, the buds starting getting this dark brown to black spotting on it, which covers most of the face of the bud. Now that the buds have opened, they are beautiful, except the petals in certain patches are browning. The leaves and other parts of plants are not affected. Only the buds and blooms.
I have a raised bed about 2-2.5 feet high and water deeply 2x/week. I give it an extra zap of water when it is extra hot out. I live in Northern California. I have pictures at home to post if that would help. Please help. I have gone to two nurseries for help and no one has been able to provide solutions. My other two Dahilas are thriving in same bed on same water schedule. THANK YOU FOR YOUR INPUT!
From the picture of the bud's and the opened flower I'd say the damage has been done while the plants were still forming the buds, these are several things that damage the buds of Dahlias while they are still tightly closed is either some type of insect, or some type of disease that takes hold within the structure of the plant and shows up more when the flowers are fully open BUT the problem start way before that but is invisible.
The most cause of problem by insects are Greenfly, blackfly BUT chewed petals are pointing more to Earwig's these are small brown insects about half inch long or less, they have ferocious clippers at their rear end, the difficulty trying to spot them eating your plants is, they only come out from their hiding place (that's inside the buds of your Dahlias) soon as dawn breaks, they have finished feeding and get back to their hiding place before the preditors / birds etc want them for a feed.
The best way to try spot them is to get out into the garden at night with a flash light, take a small bucket of hot water, hold this under the flowers of the Dahlias and gently shake the flowers being careful to hold the flowers close the flower heads or you might snap the flowers off, OR cut one of the flowers and take them indoors and carry out the shake and search on a news paper on the kitchen table, I warn you these are fast movers.
If it is Ear-wigs that are the problem, you need to try kill or trap them, I use a small flowerpot filled with shredded paper or straw, place this filled pot onto a garden cane just a few inched above or beside the plants, this is a warm dry place these insects like to hide in and they are easier to get rid of each morning without using sprays etc, each morning you just take the boiling water outside and empty the straw or newspaper into the bucket of water and this kills the many Earwigs off or if you want speed training, try stamp on them as the race away after being disturbed.
next after these little insects damage the tight buds, when watering, the damage can allow water to enter the middle of the buds and this in turn allows diseased like Mould or rust to enter the buds, the good news is, these 2 types of things don't kill the plants BUT it does spoil the appearance, once you have mastered removing the earwigs, the problem will go as there are few other things that do this damage to Dahlias.
Aphids can be hosed or crushed or a mixture of dish washing liquid mixed to a week salution and sprayed onto the plants, be it Roses, fruit, Dahlia's this spray wont damage the plants but it prevents the aphids breeding and washes them away.
Hope this helps you out and things will soon settle down for you.
Your post was so incredibly helpful and was the gift of wisdom I was hoping for! I know I have earwigs and have planned to control them. Thank you for your advice on how too. I also have aphids, which I now know a safe way to spray my plants. I was using an insecticidal soap that was supposed to be "organic" but apparently that did not provide a long lasting or successful solution.
I love the dish soap solution.
I am going to tackle these two issues this weekend and hope for the best. I will keep you posted.
PS- the same discoloring on the buds is starting to occur on my other Dahila plant which was doing extremely well for the last two months! I hope this solves the problem before my other Dahlia's are affected. THANK YOU!
Your welcome, do take on board that these insects don't care weather they eat your most favourite plant or just nibble the edge of plants that you think you wont grow next year, they just munch away till you find the damage LOL.
Now you know there are aphids, Earwigs and possibly other bugs too, you need to treat ALL the plants with the dishwater spray and PLEASE don't think one spray with do the trick, you need to keep this spraying going till your absolutely sure they have all gone, same with the ear-Wigs, you need to place a pot filled with straw beside ALL the plants as they will just travel from one to the plant next to it, so be prepared to get some straw from PET SHOP , farm or use all the shredded paper from the office shredder or your neighbours.
there are hundreds of baby Ear-wigs about right now so maybe you will be lucky enough to find their nest,
Good luck, don't dilly dally, just get the traps set up and mix up plenty of the dish water mix as you will be needing plenty till you see the decline of those pests.