8 1 NATURAL PESTICIDES - 8.11 - BIOCONTROL OF PLANT DISEASES BY NON-PATHOGENIC FUNGI

 

ORGANIC FARMING COURSE AGRO-ECONOMY

8 1 NATURAL PESTICIDES - 8.11 - BIOCONTROL OF PLANT DISEASES BY NON-PATHOGENIC FUNGI

Natural enemies that kill or suppress pests or diseases are often fungi or bacteria. They are called antagonists or referred to as microbial insecticides or bio-pesticides. Some commonly used antagonistic microbes are:

Ø Bacteria such as Bacillus thuringiensis (Bt). Bt has been available as a commercial microbial insecticide since the 1960s. Different types of Bt are available for the control of caterpillars and beetles in vegetables and other agricultural crops, and for mosquito and black fly control. The bestknown biocontrol agent used in field crops is the bacteria Bacillus thuringiensis var. kurstaki and Bacillus thuringiensis. var. aizawai against diverse lepidopteran pests, and the Bacillus thuringiensis var israeliensis against mosquitoes. Bacillus thuringiensis var kurstaki is produced in local factories in different African countries (e.g. South Africa, Kenya and Mozambique) and can be used against different pests (African armyworm, African bollworm, bean armyworm, beet armyworm, cabbage webworm, cabbage moth, cabbage looper, cotton leafworm, diamondback moth, giant looper, green looper, spiny bollworm, spotted bollworm, pod borers, tomato looper).

Ø Viruses such as NPV (nuclearpolyhedrosis virus), effective for control of several cater-pillar pest species. Every insect species, however, requires a specific NPV-species. An example: The armyworm Spodoptera exigua is a major problem in shallot production in Indonesia. Since experiments showed that SeNPV (NPV specific for S. exigua) provided better control than insecticides, farmers have adopted this control method. Many farmers in West-Sumatra are now producing NPV on-farm. 

Ø Fungi that kill insects, such as Beauveria bassiana. Different strains of this fungus are commercially available. For example: strain Bb 147 is used for control of corn borers (Ostrinia nubilalis and O. furnacaiis) in maize, strain GHA is used against whitefly, thrips, aphids and mealybugs in vegetables and ornamentals. Several species of fungi can occur naturally in ecosystems. For example, aphids can be killed by a green or white coloured fungus during humid weather.

Ø Fungi that work against plant-pathogens. Some examples include: Trichoderma sp., widely used in Asia for prevention of soil-borne diseases such as damping-off and root rots in vegetables (Figure 8-10). Some Trichogramma species against the African bollworm are bred in some laboratories in Africa against lepidopteran pests and aphids.  A successful introduction of the neotropical parasitoid Apoanagyrus lopezi against the cassava mealybug (Phenacoccus manihoti) caused a satisfactory reduction of P. manihoti in most farmers’ fields in Africa. This is one of the success stories of classical biocontrol.

Ø Entomopathogenic nematodes against different weevil species (e.g. Steinernema carpocapsae, Heterorhabditis bacteriophora) and to control soil insects like cutworms (Agrotis spp.) in vegetables

 

TEXT in the picture:

 Biocontrol by Trichoderma harzianum

The fungi species Trichoderma harzianum is known to parasite important plant disease like damping off (Rhizoctonia solani)

Trichoderma species can affect plant diseases by antibiosis and competition

 In addition, Trichoderma works as a growth stimulant and improves yields and product quality 

Some products are available in Africa n countries.

 

KOZI YA KILIMO HAI KILIMO-UCHUMI

8 1 DAWA ASILI 8.11 - UDHIBITI WA UGONJWA WA MIMEA KWA KUPITIA FANGASI WASIO NA MADAWA

 

Maadui asilia wanaoua au kukandamiza wadudu au magonjwa mara nyingi ni fangasi au bakteria. Wanaitwa wapinzani au wanajulikana kama viua wadudu wadogo au viua wadudu. Baadhi ya vijidudu pinzani vinavyotumika sana ni:

 Bakteria kama vile Bacillus thuringiensis (Bt). Bt imekuwa ikipatikana kama dawa ya kibiashara ya kuua wadudu tangu miaka ya 1960. Aina tofauti za Bt zinapatikana kwa udhibiti wa viwavi na mende katika mboga na mazao mengine ya kilimo, na kwa udhibiti wa mbu na nzi weusi. Wakala wa udhibiti wa kibayolojia anayejulikana sana katika mazao ya shambani ni bakteria Bacillus thuringiensis var. kurstaki na Bacillus thuringiensis. var. aizawai dhidi ya wadudu mbalimbali wa lepidoptera, na Bacillus thuringiensis var israeliensis dhidi ya mbu. Bacillus thuringiensis var kurstaki huzalishwa katika viwanda vya ndani katika nchi mbalimbali za Afrika (k.m. Afrika Kusini, Kenya na Msumbiji) na inaweza kutumika dhidi ya wadudu mbalimbali (African armyworm, African bollworm, bean armyworm, beet armyworm, kabichi webworm, nondo ya kabichi, looper ya kabichi. , mdudu wa majani ya pamba, nondo wa diamondback, kitanzi kikubwa, kitanzi cha kijani kibichi, funza wa spiny, funza wenye madoadoa, vipekecha ganda, kitanzi cha nyanya).

 Virusi kama vile NPV (nuclearpolyhedrosis virus), yenye ufanisi katika udhibiti wa spishi kadhaa za wadudu waharibifu. Kila aina ya wadudu, hata hivyo, inahitaji spishi maalum ya NPV. Mfano: Minyoo aina ya Sodoptera exigua ni tatizo kubwa katika uzalishaji wa shaloti nchini Indonesia. Kwa kuwa majaribio yalionyesha kuwa SeNPV (NPV mahususi kwa S. exigua) ilitoa udhibiti bora zaidi kuliko viua wadudu, wakulima wametumia mbinu hii ya kudhibiti. Wakulima wengi katika Sumatra Magharibi sasa wanazalisha NPV shambani.

 Kuvu wanaoua wadudu, kama vile Beauveria bassiana. Aina tofauti za Kuvu hii zinapatikana kibiashara. Kwa mfano: aina ya Bb 147 inatumika kudhibiti vipekecha mahindi (Ostrinia nubilalis na O. furnacaiis) kwenye mahindi, aina ya GHA inatumika dhidi ya nzi weupe, vithrips, aphids na mealybugs kwenye mboga na mapambo. Aina kadhaa za fangasi zinaweza kutokea kwa asili katika mfumo wa ikolojia. Kwa mfano, aphid inaweza kuuawa na Kuvu ya rangi ya kijani au nyeupe wakati wa hali ya hewa ya unyevu.

 Kuvu wanaofanya kazi dhidi ya vimelea vya magonjwa ya mimea. Baadhi ya mifano ni pamoja na: Trichoderma sp., inayotumika sana katika Asia kwa ajili ya kuzuia magonjwa yanayoenezwa na udongo kama vile unyevunyevu na kuoza kwa mizizi kwenye mboga (Mchoro 8-10). Baadhi ya spishi za Trichogramma dhidi ya funza wa Kiafrika huzalishwa katika baadhi ya maabara barani Afrika dhidi ya wadudu waharibifu wa lepidoptera na aphids. Kuanzishwa kwa mafanikio kwa vimelea vya neotropiki Apoanagyrus lopezi dhidi ya mealybug ya muhogo (Phenacoccus manihoti) kulisababisha upungufu wa kuridhisha wa P. manihoti katika mashamba mengi ya wakulima barani Afrika. Hii ni moja ya hadithi za mafanikio za udhibiti wa kibayolojia wa kitambo.



Nematode entomopathogenic dhidi ya spishi tofauti za wadudu (k.m. Steinernema carpocapsae, Heterorhabditis bacteriophora) na kudhibiti wadudu wa udongo kama minyoo (Agrotis spp.) kwenye mboga.

TEXT katika picha: Biocontrol by Trichoderma harzianum

• Kuvu aina ya Trichoderma harzianum inajulikana kwa vimelea vya magonjwa muhimu ya mimea kama vile kunyonya maji (Rhizoctonia solani)

• Spishi za Trichoderma zinaweza kuathiri magonjwa ya mimea kwa antibiosis na ushindani

• Zaidi ya hayo, Trichoderma hufanya kazi kama kichocheo cha ukuaji na kuboresha mavuno na ubora wa bidhaa

• Baadhi ya bidhaa zinapatikana katika nchi za Afrikan