we are inundated with queries concerning pest and disease problems that are specific to this time of the year. In this article we will highlight some of the most common of these problems and offer recommendations for their control.

Look out for these problems and remember that timely controls can prevent plant losses! *** Powdery Mildew -- Roses: Powdery mildew is the most serious disease of garden grown roses. The causal agent, a fungus called Sphaerotheca, was first described in 1819, but the disease was present long before then and is known in all countries in which roses are grown.

The fungus is visible as a white powdery coating covering the leaves and stems. Younger leaves may be distorted by this fungus. The white powdery growth is comprised of fungal threads and spores. The fungal growth is superficial and can be rubbed off but the leaf beneath is discoloured.

Powdery mildew is encouraged by dry conditions around the roots and by moist air around the foliage. Powdery mildew is less a problem when the plant surface is wet. Apparently the spores do not readily germinate when films of water are present on the leaf. The fungus overwinters as stem infections and also is dormant buds.

Here are some tips on how you can protect your plants Cultural practices that will aid in controlling this fungus include pruning out and destroying infected shoots at the end of the season and raking and destroying fallen leaves from around the base of the bushes. Keep roses adequately watered, particularly during dry weather, but avoid wetting the foliage. Applying a bulky mulch will encourage soil moisture retention.

Chemical controls such as copper sulfate (Basic Copper), cupric hydroxide (Kocide, Champion, Champ, Blue Shield), thiophanate methyl (Cleary's 3336) and triforine (Funginex) are often employed to combat this disease.

*** Black Spot -- Roses: Black spot, also known as leaf blotch, leaf spot and star sooty mold is a major problem on garden grown roses. The causal fungus, Diplocarpon rosae, produces characteristic black spots 2-12 mm in diameter on the upper leaf surface. These spots are circular or irregularly shaped with feathery, radiate margins.

Unlike the fungus that causes powdery mildew, Diplocarpon spores must be immersed in water for infection to occur. Overhead watering of your rose bushes will therefore favour the development of this disease.

Cultural controls involve the removal of infected leaves during the season and all old leaves in the winter and early spring. This will reduce inoculum levels.

Black spot is chemically controlled by applications of any of the following fungicides; chlorothalonil (Daconil), copper sulfate (Basic Copper), cupric hydroxide (Kocide, Champion, Champ, Blue Shield), maneb, thiophanate methyl (Domain, Cleary's 3336) and triforine (Funginex).

*** Sclerotinia Stem Rot -- Petunia, Periwinkle, Chysanthemum, Easter Lily, Tomato, Irish Potato, Peas, Beans....: This fungus causes the plant tissues to become discoloured, brown and wet as they rot. If you squeeze the stem of a plant infected with Sclerotinia, you will find that some parts of the stem are hollow. Cutting open this stem, and carefully looking in the area around the hollowed out interior reveals one of the most tell-tale symptoms of the invasion of this fungus, the large, black sclerotia (fungal resting bodies), scattered within the hollow stems. These structures may be several millimeters long. They are a means of survival for this fungus. Within these fungal resting bodies is a compressed mass of fungal threads.

Sclerotinia rot originates from invasion by the fungal threads in the sclerotia that are resting in and on the soil. If the diseased stems are buried deeply, they will decompose, but those that are left to rot at or near the soil surface can cause infection in succeeding growing seasons when weather conditions are favourable. For this reason, it is advantageous to remove or deeply bury diseased plant parts.

Fungicides such as benomyl (Benlate) will control Sclerotinia stem rot.

*** Fusarium Dieback -- Pittosporum: You may have noticed that discrete branches of some of the pittosporum trees around the Island have died back while the remainder of the plant appears perfectly normal. The leaves on these dead branches are brownish red, hard and curled under at the edge. This disease resembles lightning damage, which leaves a plant with a scorched appearance. The fungus responsible for this dieback is called Fusarium. Fusarium resides in the soil and causes infection of some branches but not others.

Drenching the soil at the base of the pittosporum plants at the onset of the disease development with a fungicide such as Banrot will aid in controlling this disease.

*** Rhizoctonia Hard Rot -- Strawberry: Caused by the fungus Rhizoctonia, this disease appears as a hard, brown rot on the side of the berry touching the soil. This disease may occur every year despite the fact that the strawberries are grown through plastic mulch and never touch the soil! The use of benomyl (Benlate) will aid in the control of this disease.

Leather Rot -- Strawberry: Caused by the soil inhabiting fungus, Phytophthora cactorum, this disease affects the fruit at any stage of development, from blossoming to full maturity. The appearance of this disease depends on the age of the fruit. On immature fruit the affected area is brown to dark brown. Infected areas on maturing fruits appear bleached and range in colour from light lilac or purple to nearly the colour of the ripened fruit. Infected areas are tough, with only slightly softened tissues. The fruit are discoloured both internally and externally and usually have a bitter taste.

Phytophthora cactorum may exist in all strawberry plantings but only becomes a problem under warm, rainy weather conditions or cool temperatures accompanied by frequent fog and morning dew. Mulching helps to keep the fruits off the ground and minimizes rain splash of soil onto the fruits. Fungicides such as Thiram, Topsin and Rovral can be used to control this fruit rot.

TERRY LYNN THOMPSON Plant Protection Officer