Hi there,
Specs:
– full sun balcony and container garden
– large planter with three dahlia tubers that should grow around 2 ft tall
– watering every other day with drip irrigation
Issue:
One of the three rivers has stunted growth. There’s another plant next to it and It’s at least 3 x bigger
Weird dried parts on the leaves
Yellowing and dying of leaves
What is the issue I’m having and how do I remedy it?
Thank you for your help!
Ashley
Thank you for contacting the Toronto Master Gardeners.
The damage to your Dahlia looks suspiciously like an insect infestation. Below, you will find the most common culprits for this damage and a treatment option. You can find pictures of the insects online, to readily check your plants to make a definitive identification.
Aphids — a good blast of water from a hose should wash these pesky creatures off, making sure to wash leaf undersides too. You may have to repeat several times in order to get the upper hand. Introducing predatory insects such as Lady beetles will be a short term fix as they tend to fly off once their food source is depleted.
Snails & Slugs — removal by hand-picking in the evenings, when they’re active. Clear the soil surface of any debris or leaf litter. Water plants at soil level, so as not to wet the foliage. Beer, or soda, traps can also be effective. Diatomaceous Earth powder, sprinkled on the soil around the plants can be an effective deterrent.
Thrips — a forceful hose spraying several times a day will diminish the infestation. A neem oil spray will also do the job. Prune off any infested or damaged foliage, and dispose of it with the city garden waste: do not place in a home composter.
Spider mites — remove any infected leaves and the lower foliage on the plant. Horticultural oil and insecticidal soap may help if the infestation is small. Plant should be removed to prevent spread of insects.
Leaf hoppers — remove all affected leaves and wilting blooms from plant. Keep soil clear of debris. Horticultural oil can be sprayed on the undersides of leaves to help control population.
Earwigs — damage can be unsightly but is rarely fatal. Earwigs can keep aphid & mite populations in check, so are beneficial when their numbers are low. Use traps at soil level to reduce the earwig infestation.
Caterpillars — vigilant monitoring and hand picking are your best defense against these voracious eaters. Birds can also help control the population.
Of note, all the insects above will spread from one Dahlia to the next, especially if you have them all planted together in the same container. It may be wise to remove the infested one now and relocate it to another pot. Dahlias are also heavy feeders, so the two remaining plants may benefit from having more space, water and nutrients.
Any horticultural product you purchase for insect control should be used following the container instructions carefully. Also, any pruning sheers or scissors used should be sterilized between pruning plants in order to contain spread of any disease.
We hope this information is helpful.