Dave Zlesak has published a blackspot paper

It appears that Dave has time to do other things in addition to his rose hybridizing.


Congratulations Dave on a HortScience publication.

Link: forums2.gardenweb.com/forums/load/roses/msg1209445326242.html?5

Thanks Henry :0).

I’m excited to have that work out. It’s a follow up work on a short pub from HortScience in 2000 where we used sodium silicate in the mist water while rooting ‘Nearly Wild’ cuttings. The cuttings were mildly infected with black spot and we found that the sodium silicate helped slow the progression of the disease and allowed the cuttings to retain infected leaflets longer and ultimately root better. This recent study uses potassium silicate ( it was donated by Dyna-gro and is their product Pro-Tekt) in irrigation water to determine if the plant can take up the silicate internally and if the same benefit of slowed disease development can be found. We found that there was a slight, yet significant, reduction in blackspot with the higher treatments (100 and 150 parts per million daily applications), but that the effect wasn’t strong enough in itself for growers to be satisfied using it alone.

The next thing to try would be to spray potassium silicate onto the foliage routinely and see how effective that method is at reducing black spot development (and mildew even too). Perhaps a stronger effect would be seen than administering it in the irrigation water like what was found in the mistbench with the cuttings. Since spraying silicate over the plant would coat the leaves, the typical point of entry of the pathogen, it would ultimately be more effective. Since rain can wash off the treatment and confound a controlled experiment and we don’t have a lot of greenhouse space, we probably won’t do this follow up work. Some public rose gardens have trials where they show the public the relative disease control using a number of more organic approaches (baking soda, neem oil…). Perhaps those of you doing such studies would like to consider adding potassium silicate among your treatments. A local rose nursery owner has been spraying potassium silicate overhead on his roses since the 2000 paper came out and believes it helps a lot, but hasn’t done a controlled experiment to truly compare and prove how effective it really has been.