Date: Sun, 2 May 1999 22:19:06 EDT From: CMDodd@aol.com To: cp@opus.hpl.hp.com Message-Id: <aabcdefg1519$foo@default> Subject: Nepenthes pests, diseases and nutrition
Dear Nepenthophiles,
I was asked to do a follow up on pests and diseases of Nepenthes so here
goes:
We are lucky in growing Nepenthes for as plants go they seem to have
relatively few disease or pest problems. Probably the most common pathogen
problem I have encountered is Cercospora fungi. This is a systemic fungus
that lives internally within the plant. How it enters is not known,
certainly spores are found in the air and may enter the plant after
germinating on a drop of water atop a leaf. They could also be spread by
insects or mechanical means (shears, scissors, etc.). What is known is that
this disease or something like it is probably pan-tropical. Bruce Sutton has
reported seeing the worst case he had ever seen in a plant of N. stenophlla
on Mt. Kinabalu, so as you can see it is not confined to cultivation.
Cercospora shows up as reddish or purplish blotches on the leaf blade of
the plants. It does not generally show up on the pitcher or stem. It may be
mild and barely noticeable or in some cases so bad that it is fatal if left
untreated. Some plants are affected more than others. Hairy species like N.
stenophylla and veitchii seem readily attacked, but so do burbidgea, rajah,
bellii, and truncata. Fortunately this is easily treatable. There is a
systemic fungicide, Clearies 3336 Flowable, that will kill the fungus, and it
has so far proven to be harmless to all CP, orchids, aroids, and even
sphagnum at recommended doses. It is available through V.J. Grower's Supply,
Apopka, FL (407) 886-5555. As with any new batch of chemicals try a 2 X or
4 X test on a plant you can spare like an N. alata. So far I have found no
problems with the fungicide. One the fungi is eliminated you can often see a
dramatic jump in the leaf size of the plant, sometimes twice as large as
before, showing what damage and loss of vigor is caused to the plant. This
is not a once for all cure however, the fungus can re-infect your plants in
the future.
Other fungi that may cause problems are damp-off which can wipe out an
entire flat of seedlings. The best prevention is to sterilize seedling soil
and instead of sowing all the seed in a large flat, sow several batches in
different containers. Another fungi that you may see is Sooty-mold. This is
not supposed to be a pathogen. It is most often seen where you have a scale
infestation and the droppings of the scale insects (which are full of sugar)
cause growths of this flaky black fungi where they fall on leaves of the
plants. Since this fungus loves sugar it is also no surprise that you can
find it growing on the sugar glands and pitchers of Nepenthes and it makes
them look really nasty. N. bicalcarata and reinwardtiana are favorite
targets. Trimming off the badly covered plant parts is best as it is
difficult to control. It is more nuisance than pathogenic from what I can
tell.
Pests come in many forms. Carefully watching cats and toddlers that
enter your greenhouse can save you hours of grief! More serious are rodents.
I live near a river and have had the unpleasant experience of going into my
greenhouse at night and seeing rats that had chewed a hole in a corner of the
greenhouse running to and fro on the plant hanging bars. Decon will take
care of them but remember to keep it from those cats and toddlers!!
Sometimes the natural pests controls take over. More than once I have been
watering my plants and come eye to eye with a black snake (Coluber
constrictor) wrapped around my Nepenthes! Unlike the Ausi variety, these are
not venomous but they can scare the heck out of you when you aren't expecting
them and they have a bad temper when cornered. A grower in Miami found a
more dangerous Cottonmouth in his greenhouse. Could be worse, could be
cobras.
Scale and thrips are the most serious insect pests. Both have piercing
mouthparts that take sap from the plants and weaken them. I have rarely had
mealy-bugs attack Nepenthes even though I have found them on orchids and
aroids right next to the plants. Even root-mealies that attack Sarracenia
don't seem to bother them. Likewise aphids (greenfly) do not seem to like
Nepenthes. Scale may be difficult to see until it is in epidemic proportions
as it hides in leaf axils. I have seen Florida Red Scale on Nepenthes, as
well as a few unidentified species and these can usually be killed with a
systemic insecticide. By far the worst is Snow Scale. This appears as 1 mm
long white rods in groups. It starts in leaf axils and on the lower surfaces
of leaves. By the time it is noticed it may be in huge colonies and is very
damaging to plants. It occurs on palms, hollies and other greenhouse and
outdoor vegetation and I have see it as far north as Maryland. It is very
difficult to get rid of. The best method is to use a round of pesticides
like Cygon 2E (systemic), followed by Diazinon or Malathion (contact)
followed by Cygon again, each about 10 days apart. The reason is that scale
has a shield covered feeding stage when attached and a colonizing 'crawler'
stage that does not feed. Using both a systemic and a contact insecticide
will kill both stages.
Some scales are spread by and tended by ants that feed on their sugar
droppings and if you see ants in your greenhouse, and/or Sooty-mold you may
have scale.
Thrips are small spear-tip shaped insects that may be black, green or
silvery. They are slow moving, tend to feed on the underside of leaves and do
great damage. Just recently I discoved a colony that had attacked several N.
sanguinea and khasiana and done considerable damage. The damage shows up as
silvery patches, or in the case of my N. sanguina the entire underside of the
leaves were silver. The thrips has sucked out all the chlorophyll from the
undersides of the leaves, the top of the leaves looked perfectly healthy, so
they can do a lot of damage before they are noticed. Fortunately, they are
easily killed with a contact insecticide like Malathion.
A word about pesticides. All I can say is that they need to be used
correctly, only when needed and with all due safety precautions. Natural
controlls are fine, but they almost never completely kill off pests.
Horticultural oil mixed with horticultural insecticidal soap is good for spot
treatment. The problem in a greenhouse is that you may have an epidemic
before you notice it and you have to get it under controll as soon as
possible. Always follow the label, dosage, and any bodily protection. If
you don't know if a particular product will work on Nepenthes, try it on a
spare plant. Cygon is fairly toxic and can be absorbed through the skin, it
will defoliate Ficus at normal doses. It will also kill all sucking insects
and mites effectively. Treat it accordingly.
Viruses are an unknown with Nepenthes as far as I know. I grow three
varigated Nepenthes and know of two others. There is some thought that this
is caused by viruses so care should be taken when using shears from one plant
to another. There are also other theories on varigation that are not
pathogenic in origin.
For snails, roaches, earwigs, etc. a few tree frogs, Anolis lizards, a
Tokay Gecko and a toad or two will help your bug-eating vines in keeping
their numbers down in the greenhouse as well as making it a more interesting
place. Before purchasing anything too pricey, consider that I had a N. x
Dyeriana and a N. truncata devour two 8" Jamaican Anoles Bruce Bednar had let
loose in my greenhouse. I found them by the smell! Also Tokays bite!
Nutritional problems, neither pests nor disease, may show up in
Nepenthes. Yellowing in bright light may be nitrogen deficiency and a very
lighy soil drench of something like Peter's 20-20-20 (1/4 strength) may
help, but some plants (like N. lowii) may be damaged by fertilizer
application to the roots. NEVER put Osmocote into the pitchers!! If you
don't believe me try it! There is something to pitcher feeding insects to
the plants, after all they were designed to take nutrients this way. The
best way to do this is to buy crickets at a bait or reptile shop, freeze them
and then thaw as needed and drop a few into each pitcher. Do not put them
into newly opened pitchers as it may damage or kill the pitcher. I did this
to a N. lowii upper trap and was bummed when it blackened and died! Do not
over-stuff with crickets or you may do the same thing, remember a few is
enough. If the plant has pitchers too small to feed, rip the lid off the
trap and insert a cricket leg. Gross I know, but it will cause growth in
your plants.
Lastly liquid micro-nutients may help. On plants that are having
problems that can't be attributed to soil problems, water problems, or
disease, I use a citrus minor element liquid and something for fruit trees
should be available in most areas. Try it on a test plant.
Good growing to all and watch out for those snakes and geckos.
Cliff
This archive was generated by hypermail 2b30 : Tue Jan 02 2001 - 17:31:57 PST