Disease management/erradication
 

Hello,

I have a few orchids that show symptoms of disease, and I have a few questions related to disease management:

1) How can a disease be eradicated from the host plant? I have cut diseased leaves off and tried fungicides for some of my orchids; however, new growth forms with the same disease symptoms. Would this scenario require a systemic fungicide, and if so, what kind?

2) What is the best method of disease prevention for growing? I understand that regulating the environment plays a substantial role in the influence of disease, but I am interested in other regulation methods to prevent diseases. Should fungicides be applied preemptively, or should the root microbiome be regulated? I have seen a schedule chart for fungicides here, but I wonder if fungicide use can be minimized by encouraging beneficial microbes to colonize the plant and potting media. Any suggestions?

Thank you for your time and help,

Nicolas D. Perez

It depends on the disease...some of them are not possible to eradicate.

Photos of the affected plants would be useful. Before thinking about treating, it's important to identify the ailment first. And some of the arguments against preventive treatment:
1. What are you treating (or trying to prevent)? if you don't know, the "treatment" is likely to be ineffective at best, possibly harmful.
2. If you are trying to prevent damage from an insect or arachnid, you are likely to encourage the development of resistance.

Concentrate first on good culture. If you give your plants the conditions that they need, you will greatly reduce the chances that they become diseased. If you avoid the problem in the first place, you won't have to deal with how to solve it later.

“Diseases” may be bacterial, fungal, or viral in nature. Most of the first two may be eradicated with the use of a targeted bactericide or fungicide, but you need to know what it is, first. Viruses, for now, are incurable.

Copper compounds are systemic and kill both, for the most part, but may be tough on the plants, as well, depending upon the specific types.

As an alternative, you might consider some extra large doses of a plant probiotic, followed up with their regular application regimen.

Most disinfectants and curative “-icides” are non-specific, so kill all microbes in the plant and rhizosphere, not just pathogens.

Here are some photos of the affected plants. They are all apart of the oncidium alliance (Bratonia, aliceara, and odontoglossom) and have been quarantined from the rest of my collection. The damage visible right now is not as bad as before because I have cut off most disease plant matter but it continues to form. All of the plants diseased had black spots when purchased but the disease has increased in severity.

I have been treating my diseased orchids as having a fungal or bacterial infection; is there a way to know for sure a virus is present? I have seen testing kits but they are too pricey for me. I know that OSRV is the most common for oncidicum types but I’m not sure my orchids have the same symptoms.

Also, are all copper fungicides really systemic? I have seen some copper fungicides labeled as systemic and others as not and was wondering if there is a real difference between the labeling.

I have been using your plant probiotic for the past year and have found great success keeping my plants healthy and happy. I was also wondering if the solution only works by colonizing the rhizosphere or if can it be applied directly to the phyllosphere to reduce the impact of foliar disease (with the exception of viruses). Thank you for recommending it to me a while back

My understanding is that all copper compounds act systemically, but there’s bound to be some topical effect.

The microbes in probiotics can certainly “infect” foliage as well as roots, but we cannot overlook the properties of the leaves in question, thanks to heir physiology. I feel pretty sure that a thin-leaved coelogyne can probably absorb microorganisms better than can a mature phalaenopsis.

What jumps out at me is not the spots, but really dehydrated pseudobulbs. In fact, I don't see much in the way of good ones. That can be caused by two things: Underwatering (the medium looks pretty coarse for Oncidinae, which tend to want to be kept damp) or bad roots that can be due to overwatering in broken-down medium some time in the past.

I don't think any are diseased. I agree they are severely underwatered. I would focus on watering more. It will take months to recover from this degree of water stress.

Thank you everyone for your help, it is greatly appreciated. You have all been helping me grow orchids for the past few years, and I am so grateful for your input. I will increase watering and switch some of them to more absorbent media. Thank you once again.

I'd suggest less cutting and more watering.

In that large bark I would need to water every 2-3 days.

Ok thank you so much again. I will stop cutting leaves in the future, unless I am certain that a disease is present. Until then, I will start watering much more often.