Q/A #26 - Nepenthes with Fungus or Cold Damage?

January 26, 2023

Q/A #26 - Nepenthes with Fungus or Cold Damage?

Recently some of my Nepenthes that I grow indoors, particularly my Nepenthes ventricosa, have developed rust spots and other sorts of fungal infections in the leaves. I was wondering if these rust spots and the other funguses effect my plants health and if the funguses will spread to my other plants. Also, could it just be the old age of the leaves? It seems like the older leaves are the ones that have contracted the fungal infections. 

My temperatures have been pretty low lately. 65-69°F (18-20°C) days and around 54°F (13°C) nights. For the led lighting I use a Feit 60 watt grow light which I’ve had great results with in my other plants. I water when the top of the soil feels barely moist. 

( Submitted in January 2019.)

This doesn't look like fungus, but cold damage. I had Jacob look at the photos as well, and he said the same thing. Fungal infections or rust spots look very different than what's in your photos.

N. ventricosa should have day temperatures in the 70's (22-24°C), and lows in the 60's (16°C). Your temperatures are on the cool side, and we normally see this type of damage when a plant is exposed to temperatures freezing temperatures for a few hours. It can also happen when plants are exposed to temperatures in the 40s (10°C) for several days.

Your temperatures are not alarming, but it's pretty clear your plants are not liking it. Is it possible there is a draft in that location? Or has the heat been turned off for a while, such as a power outage? Or maybe the powerbar for your heater tripped during the night at some point? Those are factors to consider.

Find a way to increase the day temperature above 70°F (21°C) for about 12 hours each day.

In retrospect, a fungal infection is possible. There is an opportunistic fungus that occurs at lower temperatures, or if the soil is too wet. Unfortunately, a fungicide will have only minimal effect if the growing conditions remain the same. The only cure is prevention by getting the daytime temperatures above 70°F (21°C) for 12 hours. The existing leaves are permanently damage, but new growth should appear normal after that. 

Submitted in January 2019. The original question and response have been edited for publication.
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