Hey
@Eric Schrader any thoughts on what may be causing the blight to appear in the first place? I’ve seen you cultivate this type and was wondering if you had some insight. These are currently in about 80% pumice and 20% Akadama. They were growing so strong up until about three weeks ago. Plus I have a few pots of cuttings that have taken well but are starting to take on the brown tips on the leaves. Do you treat yours with any type of prophylactic fungicide.?
When you grow the number of plants I grow, you have to use fungicide preventatively.
In terms of Cotoneaster problems, I'm not sure what is causing yours, but here are the most common ones I'm seeing:
1. Large black bumpy Scale on the stems/shoots - they will cause branch dieback if not removed. They're pretty easily spotted, but it tends to take a few treatments to beat them back once they get going.
2. Small Scale on the mid-rib of the leaf, so far I have not seen any serious problems caused by this, but it spreads quickly and is ugly.
3. Nectria ssp. fungal canker - it causes dieback even of large bonsai branches or even full stems. There is no proven curative control, so management is through elimination of infected tissue and topical treatment. This fungus affects many of the Rose family species, which includes Apples, Hawthorne, Cotoneaster among many others. Treatment with Propiconizole sprench does seem to slow it down, but that may be just prophylactic. I've carved and removed sections of quince that were damaged. The cankers look like dead sections of bark, and tend to fall off in wet conditions.
4. Pythium and similar root pathogens - these are not species specific, but can cause weakness, dieback, or complete death if the roots stay wet too much. I don't think cotoneaster are particularly susceptible, but you never know. Because these are opportunistic, and widespread in the nursery industry you should consider every plant that you obtain a potential vector. Treat incoming plant material with a broad-spectrum knock down like Zero-Tol or even just Hydrogen Peroxide, then re-inoculate with myco and soil bacteria. Topical treatment like Zero-Tol will only kill the pathogens present in the soil, outside of the plant tissue, so if the plant is actually infected and not just a carrier, then you'll need to use a systemic fungicide in addition to the topical treatments. I rotate Subdue Maxx (Mefenoxam), Orkestra (pyraclostrobin), Banrot (Etridiazole) and RootShield Plus WP (a biological) to control root pathogens.
5. Mites can attack anything, so keep an eye out for them also. I find a simple soap spray to be the best solution, because they can't develop resistance. If you actually find mites, you'll want to treat 3-4 times at 10 day intervals to be totally sure you got them all. Cocktailing soap and a systemic can also work, but soap alone is enough if you do it right.
Good luck.