Anthracnose on Rose

Anthracnose is a fungal disease which shows up on roses as black small, circular spots with distinct and clear-cut edges. As the spots enlarge, the centre dries out and becomes grey. The centre may eventually fall out to give a shot-hole appearance. The leaves may yellow, but not to the same extent as in black spot disease of roses. Defoliation is not as serious either. Spots can occur on stems and flowers rarely. Spores are spread by wind and is worse in cool, humid conditions. Rosa Multiflora,  used as rootstock is commonly affected. 

Control is by improving air circulation around the plants and ensuring they receive sun almost all day long. Chemical control includes copper oxychloride spray or zineb sprays which are used to also target black spot. 

Reference : McMaugh, pg. 219

Disease 3 - Rust on Rosa and Fuchsia

Above photo showing rust on the undersurface of fuchsia leaf from Botanic Gardens

Above is a close up of rust fruiting bodies through a hand lens. Fungus within the leaf produces stalks with spores on the end, with the continued growth of these stalks bursting the epidermis of the leaf in that area. The masses of spores are then blown about by the wind. 

Below are photos showing what rust looks like on both sides of rose leaf.

Rust is a collection of fungal diseases that refers to the orange-brown spore masses which are produced on affected plants. There are a large number of different fungal rust species which all lead to the presence of rust disease on susceptible plants. 

Host Range : ornamentals, fruit, vegetables, field crops and weeds. Generally a particular species of rust can attack only certain host species, but there are some special species of fungal rust that can attack different genera. 

Symptoms : Leaves, stems and fruit can be attacked. 

On leaves, the upper surface becomes speckled with small yellow patches which can coalesce. On the under surface there are corresponding orange-brown or rusty spots. In heavy infection there may be premature defoliation and serious weakening of plant. 

A few rusts stimulate plants cells to grow into gall-like structures (eg. acacia)

Disease Cycle : Rust can overwinter as thick walled spores on infected plants, on debris from infected plants, within the soil and on seed. Wind can blow the spores onto new hosts. Can also be spread from water splash from infected host plants. Generally speaking, most rusts favour high humidity, but vary in their preference for temperature. 

Control : 

cultural : avoid planting too thickly, avoid overhead irrigation in rusts that favour moist conditions, use resistant varieties (although this can cause emergence of new strains), do not vegetatively propagate from diseased plants or use seed from these plants, remove and burn diseased plants and prunings, control susceptible weed species.

chemical : copper or sulphur-based sprays (sulphur based can cause scorch on some plants in temperatures over 30 degrees celsius ). Most widely used fungicide is mancozeb. 

Reference : Kerruish, G-36

                     McMaugh, pg. 277

Disorder 1 - Fasciation in Dodonaea

This is an example of fasciation involving the flowering parts of this Dodonaea shrub found on the TAFE campus. 

Fasciation is a condition of plant growth in which the apical meristem (or growing tip - an area of undifferentiated plant cells found in buds and tips of roots, its main function to initiate growth in young plants at the tips of roots and shoots) becomes elongated perpendicular to the direction of growth. Normally, growth is focused around a singular point and produces cylindrical growth. In fasciated plants, the area of growth is flattened, fan shaped, ribbon-like or generally highly contorted. This can involve stem, root, fruit or flowerhead. 

Causes include a genetic mutation in the cells, bacterial infection, mite or insect attack, chemical or mechanical damage. Usually it is benign and can be left alone if tolerated. Pruning affected areas may or may not remove the condition in that area of the plant.

Reference : Wikipedia  

 

Vegetative propagation of Lavandula stoechas

In this propagation activity, I took semi-hard wood cuttings from Spanish lavender bushes growing in the production area at TAFE. Summer to autumn is an ideal time to take semi-hard wood cuttings. 

Propagation material was collected from the field and taken back to the shed to be washed in a diluted 1% ammonia solution to reduce the chance of disease (Damping off is common fungal disease of seedlings if good hygiene practises when sowing have not been observed). Lavender did not need to be transported in wet newspaper. 

After filling and lightly firming a punnet with the propagation mix, I selected side shoot cuttings of about 10cm in length, being careful to cut horizontally at the base of the cutting below the nodal growth. Nodes are points of high growth activity and contain tissue that can readily differentiate into root growth for example depending on conditions. 

Each cutting was dabbed into a petri dish containing a gel rooting hormone. Once all cuttings had been treated in this way, they could be placed sequentially in the growing media starting from the back of the punnet and working in rows to the front. A dibbler was used to make a small space for the cutting to fit in such a way that it would not easily fall after being watered, but being mindful to not have leaves touching the growing media that would otherwise encourage fungal growth. 

The punnet was watered and then place in the misting house on a layer of sand. The misting system keeps cuttings cool and limits excess transpiration which is a major reason for propagation failure. Low punnets do have a higher water table but the sand layer they are placed on assists in drawing down excess moisture in the growing media by capillary action.

Hygiene practises observed : washing down table tops and cleaning secateurs with 1% methylated spirits, sterilising punnets, using pasteurised sand in propagation mix, using healthy, strong disease free material, washing cuttings in 1% bleach solution.

Tar Spot on Callistemon Pallidus

This noted on a group walk around TAFE campus

Tar Spot is a fungal disease which from the literature on line seems to particularly target Acer species. Here it is infecting Callistemon pallidus. Causes raised black spots on upper and lower leaf surface. Rarely affects the overall health of a tree, but can be widespread and aesthetically displeasing. In severe infections, can cause quite marked early leaf drop in deciduous trees like the maples. Often first starts in early summer as yellow spots which gradually gain black colour within their centres, with the black spots gradually enlarging. 

The fungus overwinters on leaves that are left on ground and by spring, the spots split and release the needle-like spores which can be carried by wind to infect the nearest host.

General control can be achieved by raking and composting fallen leaves in deciduous trees. Fungicides not recommended as a cost-effective form of treatment.

Reference :  Cornell University factsheet online

Magnesium deficiency - azaleas

Mg deficiency first shows up on older leaves. Leaves begin to yellow near the midrib and the yellowness enlarges until the only green remaining is near the tip and near the base of the leaf, giving it a characteristic V shape. Mg is a constituent of chlorophyll and the plant transfers Mg from old leaves to new leaves - thus new leaves remain green in mild cases. Mg is also moved to developing fruit, but leaf fall and crop size reduction can result in severe Mg deficiency. Problem is more likely on acidic soils, but can occur on alkaline soils as well. Can be corrected by spreading epsom salts (Mg SO4) around under plant and watering in or by dissolving in water and spraying onto foliage. 

Infectious variegation - camellia

Probably a virus that causes variable discolouration commonly on camellia spp. - small yellow marks here and there on leaves, groups of yellow marks or yellow leaf margins. It is uncommon for more than a few leaves to show this abnormality. The plant grows and flowers normally. Remove leaves showing symptoms if they are bothering, but symptoms will develop on other leaves from time to time.