Q.
I cut out the leaves with the large black spots and lesions on my agave. There are a few leaves with fairly small
black dots speckling all over the underside (too many to cut out), should I cut
off the entire leaf? Additionally, there is another photo showing the edge of
the leaf that’s kind of perforated – is this age or some kind of
bug/mite/disease?
 |
| Agave with black spots |
A. I think this is a fungal disease that favors higher humidity than we
normally have in the desert. The disease was caused and spread by the rain and
wind that we had earlier. You don’t want that fungal disease spreading to the
mainstem. To prevent that, you can apply a common landscape fungicide to the
cactus if you think there is going to be a repeat of the rain and wind. Watch
your weather app. If your weather app says the rain is returning, apply the
landscape fungicide. In the meantime prune out any black spots that you see in
the stems.
I would sanitize between any cuts to eliminate those black spots
that you make. Use 70% ethyl alcohol to sanitize a knife or pruning shears.
Both the fungicide during wet weather and cutting out the black spots will help
eliminate problems.
Octopus agave originates in the Sonoran Desert of Mexico and Arizona. Make sure
you’re not watering too often. Get it off of the irrigation controller and hand
water with a hose. If you using a hose, water these plants five times a year;
three or four times during the summer. Water with a hose three or four times
each time you water these plants to get the water 12 to 18 inches deep as it
gets bigger. Otherwise the water will only get three or 4 inches deep if you
water them only once. Once you establish how often to water, don’t deviate from that except for the seasons. The number of minutes stays the same. How many times you water each month changes…that’s all.
The leaves of agave won’t totally die back to the stem when part of their leaf
is cut. It will just sit there, usually edged with brown where it has been cut.
If it doesn’t look “funnier” and out of balance, I would suggest removing the
leaves entirely. Your call.
 |
| It is up to you if cutting the leaves of agave is acceptable or not. Some people don’t mind. Others do. |
Remember that fungicides prevent
fungal diseases from getting worse. Right now, the humidity is above 15% so I
don’t expect diseases to get any worse unless the plant is in poor health. I
would recommend “dusting” the leaves with a fungicide dust to prevent the
spread of those black spots that you are talking about.
https://edis.ifas.ufl.edu/publication/PP154
Most fungicides are liquid now and not a
dust. Dusts were more popular 50 years ago. If the fungicide exists as a spray, it is a different formulation from a
dust. Read the directions. An alternative to dusts is to spray over the black spots as “insurance” to keep the
disease from spreading if the weather or plant health changes. If it rains
again, reapply the fungicide within 24 hours after it stops raining.