Greasy Spot Mycosphaerella citri

Greasy Spot Mycosphaerella citri

Description

Symptoms first appear as yellow mottling on the lower leaf surface. Later hypha growth within leaf tissue causes cellular swelling resulting in blister formation on the lower leaf surface.

Effects

High levels of leaf infection can result in leaf drop and overtime reduced tree vigour. Fruit staining / rind blotch is infrequent.

Cultural management options

Removing or burying infected leaf litter (within 4 weeks of a significant leaf drop) will help lower disease inoculum.

Modifying tree architecture (skirting and thinning out upper branches) so that trees readily dry out after rain events will help to reduce frequency and severity of infection.

Cultural practices will not give adequate control in wet regions.

Chemical management options

Foliar sprays of Copper (Oxide / Oxychloride) is the primary method used for managing the disease.

Petroleum Summer Oil sprays at 1% could be considered as a substitute for copper if concerns existed over copper contamination in waterways. Summer oil is not directly fungicidal but reduces penetration by the fungus and delays development of symptoms.

Timing of applications

Infection and development of greasy spot is slow making timing relatively flexible.

A single summer application of copper in mid January should provide adequate control in most areas.

Two applications could be needed in high disease orchards e.g. December and again in February or around one month after spring and summer growth flushes have matured.

Cautions

· Summer oil is likely to have an adverse effect on colour in tropical regions when used later in the season (after December in the Southern hemisphere)

· Summer oil should not be used on trees with poor health

· Summer oil should not be used if trees are under moisture or other environmental stress’s

· Copper sprays can cause fruit blemishes if applied at low pH or under slow drying conditions.

· Copper can enhance or blacken existing scars caused by wind / insects particularly when used in a serial spray program or at heavy rates. (Copper Oxychloride and Hydroxide forms appear to be more of an issue in this regard than Oxide forms)

· Long term, repetitive copper sprays may lead to toxic soil accumulation

· Excess copper accumulation can be phytotoxic to citrus trees where soil pH drops below 6.5

Дата добавления: 2015-11-05