Pest and Disease Management

Organic pest and disease management places priority on indirect control methods. Direct control methods are applied as a second priority.

Indirect Control Methods:

< Promotion of beneficial insects and plants by habitat management: organic orchard design, ecological compensation areas with hedges, nesting sites etc.;

< Soil management: Organic compost and plant slurry to improve soil structure and soil microbial activity;

< Pruning: good aeration of the orchard.

Direct Control Methods:

< Biological control: release of antagonists, natural predators and entomophagous fungi;

< Mechanical control methods;

< Organic pest and disease control products (see positive-lists of organic regulations).

Examples of pests and organic control methods

Most mites, insects and nematodes that attack citrus cause economic damage only occasional. Many pest problems in conventional citrus production are related to the almost complete elimination of natural enemies through the excessive use of synthetic pesticides. Organic growers make use of natural control agents to the maximum. Many pest problems can be controlled effectively with biological Table 4:

Citrus Pests and Organic Control Management

Pests Important to Know Biological Control Methods

ERIOPHYIDAE: • Damage results from feeding by piercing • Application of Hirsutella thompsonii, an entomophagous fungi (in many cases this fungus is naturally present);

Phyllocoptruta oleivora and sucking; • Introduction of predatory mites;

(Citrus rust mite) • Causes formed twigs, leaves and fruit;

• Mite must be observed with lens;

THRIPIDAE: (a) Cause fruit blemishes; • Introduction of predatory mites (Euseius hibisci and Anystis agilis) and the minute pirate bug;

Heliothrips (b) Orchards with ground cover have fewer thrip • In case of high infestation pressure rotenone and pyrethrum may be applied;

haemorrhoidalis problems (natural enemies in the ground litter);

(Greenhouse thrips)

ALEYRODIDAE: • Attack young flushes; • Introduction of parasite wasps (but this control is easily disturbed by ants defending the honeydew);

Dialeurodes citrifoli • Serious problem for young trees;

(Citrus white fly) • Produces honey dew that attracts ants, causes sooty mould and “dirty” sticky fruit;

APHIDIDAE: • Population increases very fast on spring • A number of predators, parasites and fungi can help to control brown citrus aphid;

Toxoptera citrisidus leaves and flushes; • Bio-control methods and agents usually help to decrease the level of a pest rather than to eradicate it;

(Brown citrus aphid) • Usually not an economic pest, but important vector of Citrus tristeza virus (CTV);

COCCIDAE: • The young scale settles on all parts of the • Parasitized by Metaphycus spp.;

Coccus hesperidum canopy, adults on twigs; • Application of ladybird beetle larvae and parasitic flies (pest species are specific and differ from (Brown soft scale) • Produce honeydew which attracts ants and location to location);

causes sooty mould;

• Natural predators – such as ladybird beetle larvae and parasite flies contribute to soft scale control;

DIASPIDIDAE: • Primarily a limb and trunk feeder; • Application of ladybird beetle and parasites;

Unaspis cirti • Soil cover provides a habitat for natural

(Snow scale) predators;

CURCULINOIDAE: • Larvae fall to the ground and infest • Application of entomophagous fungi such as Beauveria bassiana, Metarrhizium anisopliae;

Pachneus citri the root system; they attack the larval stage in the ground;

(Citrus root weevil) • Application of predators and parasites;

FORMICIDAE: • Cause severe leaf loss; • Application of Beauveria bassiana to the soil; they parasitize the fungi in the nests of the ants;

Atta spp.

(Leaf-cutting ant)

LEPIDOPTERA (ORDER): • Generally not an economic pest; • Release of several predators and parasites;

Phyllocnistis citrella • Occasional leaf or fruit damage;

(Citrus leaf miner)

TRYPETIDAE: • Adults oviposit in the immature fruit and • Mass trapping (combination of food baits with organic insecticides, such as Spionosad);

Ceratitis capitata the larvae feed and develop in the fruit pulp; • Release of the braconid parasite Diachasmimorpha tryoni and nematodes;

(Mediterranean fruit fly) • Sterile insect technology (STI) is not permitted in organic agriculture.

control methods. Generally, bio-control methods and agents usually help to decrease the level of pests rather than to eradicate them. The following table is not complete and shows just one important species for some pest families.

In some cases, preventive and bio-control measures are not sufficient and the damage by a pest or a disease may reach a level of considerable economic loss. This is when direct control measures with natural pesticides, such as pyrethrum, derris, neem, soaps, mineral and plant oil as well as mass trapping and confusion techniques may become appropriate.

Examples of Diseases and Organic Control Methods There are a large number of citrus diseases caused by bacteria, mycoplasma, fungi and viruses. Table 5 contains some important examples. The organic citrus disease management consists in a three-step system:

< Use of disease-free planting material to avoid future problems;

< Choosing rootstocks and cultivars that are tolerant or resistant to local diseases;

< Application of organic fungicides such as and copper, sulfur, clay powder and fennel oil. Cu can control several disease problems. However, it must not be forgotten that high Cu accumulations are toxic for soil microbial life and reduce the cation exchange capacity.

Table 5:

Citrus Pests and Organic Control Management

Disease Important to Know Indirect Control Direct Control

Xanthomonas • bacterial infection of fruit and leaves, • Planting windbreaking trees or headges; • Cu applications during spring flush;

campestris dissemination by wind, rain and injuries;

(Citrus canker) • Affects fruit quality and causes fruit losses;

Capnodium citri • Fungus that grows on leaf surface; • Control of honeydew producing insects • Cu applications, (Sooty mould) • Honeydew from insects promotes (Dialeurodes citrifoli, Coccus hesperidum etc.);

Sooty mould;

Mycosphaerella citri • Causes serious yield loss in humid climates; • Removal of leaf litter if natural decomposition • Applications of Cu and other fungicides oil;

(Greasy spot) • Yellow moddle on the upper and lesions is not sufficient (this practice may not be

at the lower surface; economically feasible);

• Blotchy areas on grapefruit;

Phytophthora parasitica • Causes root rot and gummosis; • Resistant and tolerant rootstocks (Trifoliata, • Good pruning practice;

and Phytophthora • Root and trunk infections decrease tree vigour Swingle, Cleopatra, Sour orange, rough • Cu applications on wounds (Bouille bordelaise

citrophthora and productivity; lemon etc.); 2% and cover with wax);

(Gummosis) • Good soil drainage;

• Careful irrigation (avoid flood irrigation and irrigation directly on the trunk);

Citrus tristeza virus • Virus is transmitted by budding and by • Avoid sour orange rootstock; • Remove infected trees;

CTV aphid vectors; • CTV-free budwood programs;

• Trees are stunted and remain small, • Control vectors like Toxoptera citrisidus;

leaf chlorosis, reduced fruit size;

Citrus blight • Probably caused by a pathogen; • Choice of tolerant rootstock (very small • Pruning or removal of infested trees;

• Transmitted by root grafts or peaces choice available);

from infected trees;

• Trees are weakened and become infected by Phytophthora;

2.1.10 Harvesting and Post Harvest