Dahlia Disaster

[sanzfrancisco]

I love planting dahlias and watching them grow and color my otherwise dull garden.
This year, however, was not a good one. Thousands of white flies, and a major plague of powdery mildew, made for a very unsatisfactory summer.
First, if you know what I can do about the powdery mildew, I would SO appreciate some assistance. Am I correct in understanding that the spores live in the soil and can re-emerge next year? Is there something I can do to prepare the soil to avoid this? The stuff killed a number of plants, even though I used an anti fungal, potassium bicarbonate, and pruned the affected leaves and stems. It was such a bummer!
White flies seem to be impervious to some of the remedies I have tried. Even the sticky yellow paper didn't help. Advice please.
Many thanks,
janice

 

[Tetters]

Janice, it is unlikely that your dahlia tubers will be affected. It's important now to clean away any debris from around your plants, and remove at least half of the leaves (the most badly affected ones first.) Burn these, and let the rest die back to the tuber naturally.
These plants prefer a warm sunny position in an open space. The important thing to remember is hygiene, rather like cleaning up after roses have black spot. If the tubers are left over winter in the garden, it is a good idea to pile some extra earth back over the tuber for extra protection from frost. I'm sure if you follow the drill you will have a lovely show next year. Keep an eye open for whitefly, or any other aphids that attack, and wash them away with water and dish soap. Look after insects generally, and try to avoid poisons. Working against nature creates a very vicious circle. I wish you success. I love dahlias too - it's the vibrant colours.

 

[sanzfrancisco]

Janice, it is unlikely that your dahlia tubers will be affected. It's important now to clean away any debris from around your plants, and remove at least half of the leaves (the most badly affected ones first.) Burn these, and let the rest die back to the tuber naturally.
These plants prefer a warm sunny position in an open space. The important thing to remember is hygiene, rather like cleaning up after roses have black spot. If the tubers are left over winter in the garden, it is a good idea to pile some extra earth back over the tuber for extra protection from frost. I'm sure if you follow the drill you will have a lovely show next year. Keep an eye open for whitefly, or any other aphids that attack, and wash them away with water and dish soap. Look after insects generally, and try to avoid poisons. Working against nature creates a very vicious circle. I wish you success. I love dahlias too - it's the vibrant colours.

Thanks so much for your kind and thoughtful reply. I will take those steps. Cheers!

 

[Steve @ Celtic Farm]

Janice,
I'm genuinely saddened to hear about the powdery mildew and white fly challenges you faced with your dahlias. Both can be persistent garden pests, but there are solutions to address them. We grow dahlias, and mostly deal with the mildew issue, especially later in the season and find preventative measures work best.

Understanding Powdery Mildew on Dahlias Powdery mildew spores can survive the winter in plant debris and, sometimes, the soil. They become active when conditions are right, such as warm and dry days followed by cool, humid nights.

Cultural Practices to Reduce Mildew Ensure your plants have adequate space between them to allow for proper air circulation. This can minimize the humidity around the plants. When watering, aim at the soil level rather than overhead. If you do need to water from above, do it early in the day so the leaves can dry by evening.

Rotate Your Crops Consider planting your dahlias in a different location next season to reduce the risk of reinfection.

Clean Up in the Fall After the growing season ends, clear out and dispose of all infected plant debris. This can help diminish the number of spores in the area.

Boost Soil Health A healthy soil ecosystem can make plants more resilient to pests and diseases. Integrate compost or organic matter into your dahlia beds either in the fall or early spring.

 

[sanzfrancisco]

Thanks very much, Mike. I really appreciate your info and assistance. I actually do employ the suggestions you have made, but I've been growing dahlias for years, and this year has been the worst. Here in San Francisco we definitely have cool nights. (thanks fog.) but I continually clean up the debris under the plants, so I have to guess that the spores live in the soil. I am confounded by the swarms of white flies. I've never seen them like this.
Sorry it too me so long to acknowledge your message. I was visiting out of town.
Thanks again.