Honest, Unambiguous
and
Updated
technical information for Stevia Industries
Farming
Extraction
Formulation
Crop Protection
Though wild Stevia is fairly resistant to major pest and diseases, and steviol glycoside itself has significant pest repellant effect, modern high yielding breeds of Stevia needs crop protection to a degree. Generally, sub-optimal growing conditions, high moisture level in soil and air, weed infestation and unbalanced nutrition are triggers for pest and disease attack. Perfect nutrition and proper agronomic management often is the first line of defence.
Stevia is reported to get infected by several fungal species, which may result into significant yield loss. Some fungal pathogens for Stevia and their diagnostic features are listed below.
Infecting Organism
Diagnostic Symptoms
Picture (click on picture to magnify)
Alternaria alternata
Light brown small circular spots that turn dark brown to grey and are circular to irregular in shape with concentric rings. Spots may coalesce forming large areas of necrosis.
Sclerotinia sclerotiorum
Wilting, chlorotic leaves, necrotic leaves at the base of the stem, and bleached stems. Symptomatic plants often have tufts of white hyphae present on stems and large, irregularly shaped 2 to 8mm black sclerotia on the base of the stem.
Sclerotium rolfsii
Yellowing and wilting of leaves, bleached stems, and eventual plant necrosis. White cord-like mycelia growth is visible at the base of stems, especially early in the morning. Mycelium is accompanied by the formation of brown sclerotia 0.5-2mm in diameter.
Septoria steviae
Shiny olive-gray foliar lesions, that are depressed and angular. Lesions often have a chlorotic halo and rapidly coalesce, turn necrotic, and leaves fall from the plant. Up to 50% of the foliage can become necrotic in severe cases.
Rhizoctonia sp.
Sunken reddish spots, gradually expand to kill the plants. Reddish-brown to brown collar rots and root rots are common in young plants. These rots inhibit normal growth and cause stunting or plants with poor vigor. Callus formation and thickening of the collar area also occurs.
Fusarium oxysporum
Wilting, chlorosis, necrosis, premature leaf drop, browning of the vascular system, stunting, and damping-off. Fusarium wilt starts out looking like vein clearing on the younger leaves and drooping of the older lower leaves, followed by stunting of the plant, yellowing of the lower leaves, defoliation, marginal necrosis and death of the plant.
Remedial measures
Cultural control
If there is any water logging in the field arrange for drainage.
Get rid of all weeds
Stop nitrogen fertilization or organic manuring until the disease is controlled.
Apply a top dressing of potash to enhance immunity.
Biological control
Profilactically use inoculants of the following
Trichoderma harzianum/viride
Ampelomyces quisqualis
Bacillus subtilis
Gliocladium catenulatum
Streptomyces lydicus
These are not very effective for curative purpose.
Organic certifiable control measures
Use any of the following
Copper oxychloride
Copper sulphate lime mixture
Chemical control
Effective chemical control agents include
Chlorothalonil
Propiconazole
Trifloxystrobin
Captan
Carbendazim
To be applied in recommended doses.
The most common insect pests of stevia and their control measures are as follows :
Insect Pest
Description
Control Measure
Cutworm
Cutworms are moth larvae that hide under litter or soil during the day, coming out in the dark to feed on plants. A larva typically attacks the stem, and consequently cuts it down; hence the name cutworm. Cutworms are not worms, biologically speaking, but caterpillars.
Biological
Use Bacillus thuringiensis var. Kurstaki inoculants either as spray or with baits.
Chemical
Soil application of Carbofuran 3G or Phorate 10G followed by an irrigation.
Aphids
White fly
Aphids are small, soft-bodied insects with long slender mouthparts that they use to pierce stems, leaves, and other tender plant parts and suck out fluids. Many aphid species are difficult to distinguish from one another; however, management of most aphid species is similar.
Whiteflyis a sap-sucking insect that is often found in thick crowds on the undersides of leaves. When infested plants are disturbed, great clouds of the winged adults fly into the air. Both nymphs and adults damage plants by sucking the juices from new growth causing stunted growth, leaf yellowing and reduced yields. Plants become weak and susceptible to disease.
Biological
Use Mineral oil + soap emulsion or Neem oil based insecticides
Chemical
Apply synthetic pyrethroids like permethrin or conventional insecticides like Imidacloprid, malathion, and acephate
Biological
Use Mineral oil + soap emulsion or Neem oil based insecticides
Ues yellow sticky traps
Chemical
Apply dichlorovos, imidacloprid or synthetic pyrethroids
Red spider mites
Red spider mites feed on the content of plant leaf cells by piercing them with their mouthparts. This results in a fine brown speckling effect on leaves where the cells have died. Adult mites also spin a fine silk webbing over leaf surfaces. With heavy infestations this can cover most of the plant
Biological
Use Mineral oil + soap emulsion or Neem oil based insecticides
Wash the plants to physically remove the nites
Chemical
Apply dicofol, dinocarp, abamectin, bifenazate, hexythiazox, or spiromesifen based spray pesticides
Thrips
Biological
Use Mineral oil + soap emulsion or Neem oil based insecticides
Ues yellow sticky traps
Chemical
Apply dichlorovos, imidacloprid or synthetic pyrethroids
Thrips are tiny, slender insects with fringed wings. They feed by puncturing the epidermal (outer) layer of host tissue and sucking out the cell contents, which results in stippling, discolored flecking, or silvering of the leaf surface. Thrips feeding is usually accompanied by black varnishlike flecks of frass (excrement)
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Precautions for pesticide application
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Wear the personal protective equipment recommended on the label.
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Use the label rate. Increasing the rate may leave high residues or harm the crop. Decreasing the rate may result in poor pest control or contribute to the development of pesticide resistance.
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Use application equipment that is calibrated, properly maintained, and adjusted for the crop being treated.
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Use and maintain tractor speed and pressure chosen during calibration.
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Shut off the spray nozzles when you turn.
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Stop the flow of granular formulations at the end of rows.
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Wear gloves to replace or clean plugged nozzles. Do not blowout a plugged nozzle or screen with your mouth. Use a soft brush or toothpick.
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Spray when human activity nearby is unlikely. For example, do not spray near a school while children are on the grounds.
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Do not work alone when handling very toxic pesticides.
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Avoid eating, drinking, smoking, and touching your face during pesticide application.
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Wash before eating, drinking, smoking or using the toilet.
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Have fresh water available for emergencies.
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Prevent pesticides from contaminating non target areas. Leave a buffer zone or untreated area. around lakes, streams, ditches and wells.
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Spray when the wind is blowing away from sensitive areas.