abstract on Rose diseases

title = abstract on Rose diseases

Disease Control

Multi-Purpose Fungicide Daconil 2787? Plant Disease Control

This product is widely used for broad spectrum disease control on lawns, ornamentals and listed
fruits and vegetables. Controls many foliar diseases such as: rust, black spot, leaf spot, blights,
anthracnose and powdery mildew as listed on the label. Also controls conifer diseases and lawn
diseases such as brown patch, red thread, rust and dollar spot. Can be mixed with insecticides as
specified on the label to make a multi-purpose spray.


Powdery Mildew looks like white fuzzy powder that accumulates on leaves and stems
predominantly in spring, and again to a lesser degree in fall. It is actually a fungus that is spread by
millions of microscopic spores. It imbeds itself into tender new growth and feeds on the sap of the
plant. By the time the naked eye can see the white 'powder,' it has already invaded the plant tissue
and is feeding and reproducing at a rapid pace. As it spreads itself on the surface, it eventually kills
the cells of the plant leaf, leaving the leaf rippled and curled.

Mildew spores are everywhere in the garden - in the air, the soil, on debris and on plant surfaces -
ready to sprout when the environment is just right. Warm days (50?-80?F) and cool nights with
elevated humidity and resultant dew provide ideal conditions. Though humidity promotes fungal
growth, it grows on DRY plant surfaces, unlike blackspot which requires immersion in water for
about seven hours in order for infection to take place.

Tender new growth needs a chance to 'harden' and develop its waxy coating that provides somewhat
of a barrier to fungal growth. Therefore, the rosarian must provide protection for new spring growth
on a weekly basis.


Controlling mildew doesn't have to mean spraying the planet into oblivion. It includes plant genetics,
cultural practices and something as simple as WATER.

GENETICS: While rose hybridizers are chastised for breeding OUT fragrance, what they are trying
to accomplish is breeding IN disease resistance. For scientific reasons beyond explanation here, rose
genes don't contain both features - it's one or the other. Hence, you can expect either fragrant roses
with little disease resistance, or clean plants with little fragrance. Plants with glossy or waxy leaves
are less susceptible to mildew, as the leaf surface is harder for spores to penetrate. Rugosas naturally
possess a high degree of disease and pest resistance. Where mildew is a constant problem, the choice
in plantings can help prevent the need for extensive maintenance.

CULTURAL PRACTICE: Planting bushes with sufficient space between them and away from walls
and fences will provide good air circulation which reduces the chances for mildew.

The annual pruning event plays a major role in disease prevention. Stripping leaves from the bush at
pruning time, and cleaning up debris in the garden contribute to a cleaner environment. Dormant
spraying will at least wipe out last year's spores, leaving only this year's to contend with. Keeping the
centers of the bush open during the growing season will aid air circulation.

Avoid the use of other plant materials with high mildew susceptibility, such as euonymus and
tuberous begonias. Apply a thick layer of mulch in early spring to cover spores in the soil that may
have wintered over. WATER is perhaps the most misconceived element surrounding powdery
mildew. Many gardeners still subscribe to the belief that you should NEVER get rose foliage wet.
On the contrary, a high-pressure spray of water will remove mildew spores that haven't imbedded
themselves yet, and prevent them from germinating. Higher incidence of mildew during periods of
rain is caused by the moisture in the air and soil - increasing the humidity that promotes mildew -
not by water on the leaves. Similarly, watering early in the day will allow the soil surface to dry out
a bit before the cool night temperatures arrive, reducing humidity from moist soil.


Once powdery mildew is apparent to the eye, it can't be eradicated. It simply must be prevented.
Prevention is achieved by coating the plant tissue with something that provides a barrier to prevent
fungus from gaining a foothold and invading the plant tissue. Growth is so rapid in spring that the
leaves unfolding THIS week won't be protected by what you sprayed LAST week. This is the reason
you find application schedules of every 7-10 days on most fungicides, and the reason you must
follow that schedule.

The choice of