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 This leads to dead areas above the blockage. Of course, if the
blockage is on the main trunk you end up with a dead tree. It is
often possible to see streaking of the wood, or a dark ring
around the center portion of the branch or trunk with
verticillium wilt, but a lab analysis is needed for definite
confirmation. There are no cures for any of these diseases at
this time. It is recommended to remove and destroy trees
severely infected with verticillium, to help prevent transfer
from root grafting. The list of trees affected by verticillium
is very large, but good quality maples are very susceptible.
There have been many affected trees this year, including maples
and ashes, as well as shrubs such as smoke bush and viburnam.
The only treatment is to water and fertilize to try and get new
growth, and new water and food carrying tissues.
We have really had twenty-plus years of stressful weather. Just
like us, trees like moderate weather. When we have extreme heat
and cold, and no moisture or a flood, the trees are stressed.
This stress makes them more susceptible to things that are
always in the environment. Try to even out some of the extremes
by watering when it is dry, fertilizing when you do the lawn (or
just fertilize the tree), and mulching to even out the soil
temperature in the root area. Remember that many diseases can be
passed with pruning equipment, so disinfect your equipment
between cuts.
The following is a recommendation from the University of
Illinois Plant Clinic: “Once a plant has succumbed to
Verticillium wilt, we recommend replanting that area with
non-susceptible species. Apple, pear, crabapple, gingko,
sycamore, walnut, willow, rhododendron and azalea, and oaks in
the white oak group are some woody plants that are considered
non-susceptible to Verticillium wilt. In addition, all conifers
are considered resistant to Verticillium wilt.”
Potato Leafhopper Damage Is Now Evident
A few weeks ago, I wrote about damage from the potato
leafhopper. The damage symptoms are now more evident on all
types of plants. Symptoms include yellow or brown “v” shaped
areas at the tips or points of leaves, possible discoloration of
leaves (evident on red maples with red leaves already), and
shrunken and distorted leaves – particularly on the youngest
leaves.
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Once symptoms are noticed, you get to ride things out. The
damage has already been done. Control of leafhoppers on trees in
particular is very difficult. You are looking at spraying on a
regular basis to cover the entire tree. Think at least every two
weeks. It is easy to see the cost of treatment would probably
outweigh the benefits. Of course, spraying a prized rose bush or
something smaller is probably something you are doing anyway.
Wilt of Vining Crops
With the growing season entering the home stretch for vining
crops such as squash, pumpkins, cucumbers, and melons, there are
few things worse than having your vines wilt suddenly. I’ve
noticed the population of the striped cucumber beetles have
exploded in the past few weeks. These beetles can be green,
black and yellow striped, or black and yellow spotted. The
importance of the beetles is not that they eat small holes in
the leaves, but that the beetles can transmit a bacterial wilt
to the plants as they eat. The first thing you see is you have a
plant that suddenly wilts on various runners, or the entire
plant. The best means of controlling this disease is a good
beetle control program. Current homeowner recommendations would
include these products with the days to harvest restrictions in
parenthesis: carbaryl (0), bifenthrin (3 days), or rotenone (1
day).
[By JOHN FULTON, COUNTY EXTENSION
DIRECTOR SERVING LOGAN, MENARD, AND SANGAMON COUNTIES]
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