MAY
2005
By
Beverly Shaw
Advanced
Master Gardener
Purdue University
|
|
Q. We've had serious problems for years with cedar apple rust, presumably
because of the abundance of red cedar trees on and near our property.
We purchased some ground a few miles away and are considering trying apples
there, hopefully far enough away from the red cedars to get away from
the rust. Now, the question: Do northern white cedars also carry the cedar
apple rust? We'd like to plant a windbreak around the west and north sides
of the other property, and we're wondering if we'd just be moving the
problem out to the new site. -- Ivan & Louise Nichols, North Vernon,
Ind.
A. Cedar apple rust relies on two hosts during its lifecycle. One is apple
(including crabapples) and the other is juniper, primarily the eastern
red cedar, southern red cedar, Rocky Mountain juniper, some prostrate
junipers and Chinese juniper. Northern white cedars are actually Thuja
occidentalis, an arborvitae, and do not enter into the cedar apple rust
cycle.
Cedar apple rust is a common fungal disease of junipers, apples and crabapples.
The fungus overwinters on junipers, forming chocolate brown galls, generally
the size of a half-dollar, on infected twigs. In early spring, bright
orange, finger-like tendrils (spore horns) emerge from the galls. The
horns have a gelatinous (jelly-like) texture, and these structures produce
the spores. Truly, they look like something from under the sea! These
galls maintain their bright color for two or three weeks, then dry and
wither.
During spring, with emergence of spore horns on the junipers, a different
type of spore is produced that infects the alternate host -- apple or
crabapple. In early summer, small yellow spots appear on the upper-leaf
surface of infected apples and crabapples. The spots rapidly enlarge,
becoming a brilliant red-orange color. In midsummer, infected apple leaves
produce spores, which, in turn, infect junipers, completing the life cycle.
The most damaging phase of the disease is on the alternate host: apples
and crabapples. Severe defoliation may occur, weakening the plant. This
disease generally does not cause significant injury to junipers. The best
method of avoiding cedar rust diseases is to use resistant plants when
installing new trees.
The rust fungi are dependent upon both the primary (juniper) and alternate
(apple, crabapple, quince or hawthorn) hosts for survival. Removal of
one or the other breaks the life cycle of the fungus, thus preventing
disease. A distance of one-quarter mile between junipers and alternate
hosts is helpful, but this is often not practical. Whenever possible,
at least avoid planting the two different host types right next to each
other.
In a light infestation, cedar apple rust can be controlled by removing
and destroying all galls from junipers in late winter.
Rust does not kill apples, crabapples or hawthorn, and generally does
not cause sufficient injury to warrant use of fungicides. If rust is a
chronic problem causing leaf drop and poor tree vigor, registered fungicides
may be used on the broadleaf host.
These fungicides are preventive and must be applied several times during
early spring to maintain a protective coating on developing leaves, twigs
and fruit. When spring weather is dry, fungicide applications are generally
not required. Read and follow label instructions regarding amounts of
fungicide method of application and safety precautions.
Registered fungicides for rust control are subject to change. For current
control recommendations, consult the Purdue Extension office in your county
or Purdue University's Plant and Pest Diagnostic Laboratory, 1155 LSPS,
West Lafayette, IN 47907, (765) 494-7071.
Q. I have a question concerning tomato plants. I have raised tomatoes
for several years. For the last few years, something starts at the bottom
of the plant and slowly works it way up, eventually killing the leaves
and stunting the plants. I suspect that rainwater splashing onto the plants
could be the problem. I have been spraying several times, but it does
not seem to help. I have been told that copper sulfate will take care
of the problem. Do you know what the problem might be and what I can do
about it? Thank you for your help. -- Bill Hole, Crawfordsville, Ind.
A. There are several possibilities. Fusarium and Verticillium wilts are
common wilt diseases of tomatoes. The first symptom is a yellowing of
the lower leaves, which then progresses upward through the plant. These
two diseases are very difficult to distinguish from each other. No chemical
control is available. Destroy infected plants as soon as possible. In
the future, choose resistant cultivars to help prevent diseases from starting.
Cultivars with resistance have the letters V or F following the cultivar
name. You might also find it necessary to rotate that garden plot out
of tomatoes for a few years.
Walnut toxicity also causes similar yellowing of foliage. Tomato plants
are particularly susceptible to juglone, a chemical given off by walnut
trees. Black walnut leaves, bark and wood chips should not be used as
mulch or compost in the garden.
Bacterial canker is an infectious disease of tomatoes that usually causes
reduced yields and premature fruit drop. It is most easily recognized
by the white blisters that occur on infected tomatoes. Symptoms can occur
on all of the above ground plant but usually appear first on older leaves.
The margins of infected leaves appear brown and scorched; they are curled
upward and inward. Borders between the brown and green areas of the leaves
are distinct. They are often separated by a thin line of yellow tissue.
Light streaks usually develop on infected stems and shoots. These streaks
eventually become darker and split, forming a shallow canker. Vascular
tissue of infected plant stems is discolored, usually yellow or tan. Interference
with water transport, which is caused by the cankers, results in wilting
of all or part of the plant.
Bacterial canker is introduced to previously uninfested areas by infected
seeds or transplants. Once established in the garden, the bacteria may
survive on infested plant residue for up to three years.
Prevention is the only acceptable strategy for control of bacterial canker;
using disease-free seeds and disease-free transplants is crucial. Once
bacterial canker becomes established, repeated application of copper compounds
may reduce the rate of disease spread but should not be considered a reliable
control measure.
Infested gardens should be rotated out of tomatoes for at least three
years. Nightshade, a weed related to tomatoes, should be controlled since
it may harbor bacteria.
Q. Six years ago, I planted some fruit trees: two pears, two plums, one
apricot, four apple. All of them were semi-dwarf. They are now 15-plus
feet tall. To this day, one of the pear trees bore fruit twice, and all
the rest never had one bloom. If you can solve my problem, I would appreciate
it, and thank you for doing so. -- Bernard Steiner, West Lafayette, Ind.
A. First, it's not unusual for dwarf trees to need up to five years before
becoming mature enough to bloom. Overfertilizing with nitrogen, a lack
of sun or improper pruning may cause a lack of blooming. Apples are borne
on short fruiting branches or spurs that grow on year-old wood. Prune
lightly, and avoid removing many of the spurs.
Once the trees are mature enough to flower and bear fruit, apples, pears,
cherries and plums generally tend to produce the best crop on wood that
is 2-3 years of age. However, peaches tend to produce best on 1-year-old
wood. So, the goal in pruning the home orchard is to keep a good amount
of the appropriate-age wood for that particular species
5-5 -05
|
