I have a large hillside plot of pachysandra, roughly 40 x 15 feet.
Last spring it had a fungus, due to the wet weather. I treated the
disease with Daconil fungicide,
and cut the pachysandra back with hedge clippers to allow better air
pachysandra recovered, except for two sizeable patches, which are
still have not filled in.
for the first time the entire plot - not just the bare spots -
became infested with several types of common weeds, including
crabgrass, dandelions, etc.
I pulled them by hand last summer, but
I am looking for a way to kill the weeds without harming the
pachysandra. Can you recommend anything? Also, should I replant the
bare spots or will they come back on their own?
Pachysandra under a Pin Oak
A: It sounds as
though you took the proper steps to get the disease under control.
Most likely the planting was suffering from volutella blight, the
most common fungal disease that affects pachysandra. This disease
starts as discrete tan or brown spots that eventually merge together
and kill the entire leaf. You may notice concentric line patterns in
the spots that resemble a bullís-eye. Volutella will progress from
the leaves down to the stems, and as happened in your bed, large
patches of pachysandra can be killed. Management includes treatment
with a fungicide such as Daconil (chlorothalonil) and thinning the
planting to improve air circulation. It is also helpful to water
during hot, dry weather to avoid drought stress. Watering is best
done in the morning so that the foliage dries quickly. If you water
in the evening, the foliage stays wet overnight, which creates a
favorable environment for volutella to start again.
infestation that occurred during the summer probably was able to
take hold because of the bare areas and because you thinned the
patch out. Weeds have a much harder time becoming established in
dense plantings, whether a ground cover bed or a lawn.
work in a number of ways. They can be selective, which means they
only affect certain weeds without harming the desirable crop. The
herbicides used to control broadleaved weeds in lawns are selective.
You can use a selective herbicide that kills grassy weeds such as
crabgrass in ground cover beds, including Ortho Grass-B-Gon or
Ornamec (fluazifop-P-butyl). They will not harm your pachysandra,
but they will not control broadleaved weeds such as dandelions,
either. Unfortunately, the herbicides that control broadleaved weeds
will also kill pachysandra, so you probably still have to hand pull
those weeds. Non-selective herbicides kill most plant material they
contact and would not be suitable to use in a ground cover bed
except possibly in the areas that are already bare of pachysandra.
Round Up (glyphosate) and the many available glyphosate knock-offs
currently available are examples of non-selective herbicides.
Use of Herbicides
herbicides also work by preventing seed germination, or
pre-emergently. These products do not kill standing weeds or those
growing from roots or rhizomes. Once you have the bed free of weeds,
you can apply a pre-emergent herbicide to keep weed seeds from
germinating. Pendulum (pendimethalin) is labeled to control weeds
growing from seed in pachysandra. Be sure to read and follow all
label directions. For example, pendimethalin works best if watered
in after application. If not, it begins to break down on exposure to
sunlight, resulting in reduced control.
Since the bed
has not filled in since you got the disease under control, plan to
replant the bare spots this spring. Pachysandra is typically planted
on six-inch centers in staggered rows, the same way you lay bricks.
Avoid using pre-emergent herbicides in the newly planted areas until
the plants are well established.