Phytophthora causes damping off, root and collar rot in nurseries. Plants affected in nursery beds develop chlorotic symptoms, stunted in growth and with poorly developed root system. In severe infection, stem at ground level shows rotting. Phytophthora causes foot rot, root rot, crown rot, gummosis, leaf fall and brown rot diseases in well-grown orchards. Foot rot lesions develop as high as 60 cm from the ground level on the trunk and may extend below the soil on crown roots as crown rot. On scraping the dead bark of the lesion, a brown, discolored, slippery area can be seen. Such active lesions start oozing gum, which can be seen on the trunk as brownish black oozing known as gummosis. In dry season, the dead bark becomes firm, breaks away from healthy bark, curls and splits. In severe cases, when foot and significant portion of root system is damaged, the large branches of the same side of the affected plant are killed due to the rot of conducting tissues near the bark. Usually the disease is confined to feeder roots and remains unnoticed by the growers. Dull chlorotic foliage is.the first symptom of such affected plants where mid rib, main lateral veins and bands of leaf tissue bordering them become yellow leaving rest of the leaf normal in colour. Such vein chlorosis is often confused with nitrogen deficiency. The diseased plants thus have comparatively fewer fibrous roots than healthy plants. In severe cases, where regeneration of feeder root does not cope with the rate of destruction, the affected plant will show starvation, less canopy volume with naked branches, die back and slow decline symptoms. In continuously wet weather conditions for about 24 hrs or more. Phytophthora splashes along with raindrops to low hanging fruits and causes a typical brown rot of fruits and leaf fall. Foot and root rot cause severe moisture stress in the plants and result either in erratic bearing and yield loss or such plants bear heavily and collapse when fruits are still on the plant.

Heavy and poor drained soil, excessive irrigation, use of susceptible rootstock and, prolonged contact of water with tree trunk exacerbate the diseases and buildup of inoculum. The major source of disease spread is infested citrus nurseries. In citrus nurseries,

1. use of susceptible root stock,
2. flood irrigation and flat bed system
3. retention of water for longer period in beds,
4. low budding,
5. repeated use of same land for nursery raising,
6. location of nurseries near old orchards and
7. regular contamination through soil and irrigation water are the predisposing factors for Phytophthora diseases.

In citrus nurseries and orchards, 5-350 propagules/cc of soil was recorded in majority of samples.

1. Use of resistant rootstocks,
2. Appropriate cultural practices and
3. Use of chemicals.

Being soil borne nature, once Phytophthora enters in a nursery or orchard, it becomes an endemic problem and difficult to eradicate. 'Prevention is better than cure' should be followed strictly. Plant should be selected from Phytophthora free certified nurseries and with high budding (above 9" ht.).

While planting, care should be taken to keep bud union as high as possible so that irrigation water should not touch the scion. Soil should be kept well drained and flood irrigation and stagnation of water for longer period in the basin should be avoided. Injuries to trunk and root system by farm operation should also be avoided.

Since the pathogen is soil borne, its complete eradication becomes difficult in field nurseries but modified cultural practices can keep diseases under control. For example:

1. Seeds should be treated with fungicides before sowing.
2. Seeds should be sown in trays or in raised nursery beds where water can not stand for longer period and nursery beds should be fumigated before seed sowing.
3. Nursery should be away from the citrus orchards
4. To avoid contamination, nursery operation equipment should be separate from the orchard equipment.
5. Introduction of soil and other materials infested with the pathogens should not be allowed.

Use of fungicides can mitigate the problem up to a great extent but can not eradicate it. Copper fungicides are used as foliar spray, drenching of basins and as trunk paste to control Phytophthora diseases. Copper fungicides are effective in controlling foot and root rot and gummosis of citrus provided they should be used at correct time. Generally citrus growers in Central India apply Bordeaux paste in winter season after harvest of the crop because of their two convenient reasons.

1. after harvest they have money as well as time to do this operation and
2. for their notion that paste washes out due to showers in monsoon if applied before monsoon.

In this way the whole purpose of using bordeaux paste is defeated and it gives mere cosmetic effect rather prophylactic or curative when applied in winter. Bordeaux paste should always be applied before onset of monsoon on tree trunk as prophylactic measure. Foot rot or gummosis affected portions should be scraped out with sharp knife taking care not to damage the wood before application of bordeaux paste. Availability of systemic fungicides like matalaxyl and fosetyl-al has given the citrus growers additional and more effective options for the control of Phytophthora diseases. Due to systemic in nature and long term persistence in plant system, the foliar spray and drench treatment or pasting the affected trunk can save labour and time consuming operations like opening of root system and surgery of the affected parts for the control of disease with copper fungicides.

Before application of metalaxyl or fosetyl-al fungicides, one should be sure about the involvement of Phytophthora in the disease. The soil and plant samples should be got tested for the disease because these fungicides are specific in their action only against Phytophthora and related fungi and also higher in their cost, thus the effectiveness of these fungicides sometimes may be misunderstood in case of their application to other problems.

In order to develop eco-friendly management of Phytophthora diseases, screening of bio-control agents against citrus Phytophthora has become a vital research aspect and is being worked out all over the world.