CDA for Fungicide and Insecticide Application in Vegetable and Leguminous Crops
Although there is a great deal of information reported on the
use of low volume CDA sprayers, such as the Micron ULVA+, for
insecticide treatments within large scale cash crops such as
cotton there is not so much reported on their use within other
field crops, particularly vegetables, legumes and other smallholder
horticultural crops. It is known, however, that sprayers
purchased for cotton treatment by smallholder farmers in Africa are
also used extensively on such crops. Moreover, until ten
years ago, most hand-held spinning disc sprayers were used for
ultra-low volume (ULV) application using specific oil or solvent
based formulations that had limited availability and were not
generally recommended for food crops due to increased persistence
of deposit. Moreover, until 10 years ago, most hand-held
spinning disc sprayers were used for ultra-low volume (ULV)
application using specific oil or solvent based formulations that
had limited availability and were not generally recommended for
food crops due to increased persistence of deposit.
This review aims to draw together the work available on the use of
low volume CDA spraying techniques for insecticide and fungicide
treatment of legumes and vegetable crops It includes
published scientific literature, unpublished reports (such as
in-house reports) and anecdotal reports under general crop
headings.
Vegetables
While the term vegetable is widely inclusive of a range of
horticultural crops, they may have little in common as targets for
insecticide spraying and it is unwise to rely too much from the
results of a spraying technique on one vegetable crop when
considering its use in another.
Tomatoes
Johnstone and Huntington (1975) looked at the physical aspects of
very low volume (10-15 l/ha) spraying in tomatoes and concluded
that dew played a major part in the redistribution of discrete
spray deposits. Quinn et al (1975) reports work in Nigeria in
which a range of fungicides were applied against Alternaria solani,
Fulvia fulva and Septoria lycopersici. Conventional
high volume (1121 l/ha) spraying systems and a Micron spinning disc
CDA sprayer (Micron Ulva 8) were compared with no significant
differences found between the spraying techniques. The CDA
technique used conventional fungicide formulations diluted with
water. In a continuation of this work, Quinn and Erinle
(1979) compared swath widths of 1.8 m and 3.6 m for CDA
treatments. Although the wider track spacing gave poorer
control, the same dilution of spray solution was used in each case,
thus effectively meaning that the wider spacing applied half the
dose rate of the narrow spacing. No attempt was made to
investigate the effect of track spacing alone. Quinn and Johnstone
(1979) found that VLV drift spraying at full and 2/3 chemical dose
rates were equally as effective as high volume (1000 l/ha) spraying
at full dose using Captafol (at 3 kg/ha). A hand-held Micron
spinning disc sprayer was used, producing small droplet sizes of
60-80 ?m, with a maximum swath width of 3 m is recommended.
Erinle et al (1986) used a Micron spinning disc sprayer to apply
Captafol at a rate of 2 kg in 10 l of water per hectare. Good
control was achieved using a spray pass interval of 1.5 m, with a
7-10 day interval between applications.
In a report from the FAO (1988), application of ULV formulations of
pyrethroids cypermethrin, deltamethrin and fenvalerate gave control
of Heliothis armigera using swath widths of up to 3 m. It was
noted that fenvalerate caused slight phytotoxicity.
Kisha (1986), reported good control of whitefly using the
Electrodyn ULV sprayer compared with a conventional high
volume knapsack sprayer, though this did not translate into better
control of the virus of which the pest was a vector. Potter
(1981) compared vehicle mounted CDA (using Micron Micromax
atomisers) and conventional hydraulic tractor-mounted atomisers for
control of early blight (Alternaria solani and Septoria
lycopersici) and anthracnose (Colletotrichum phomoides) and found
no significant differences between application methods. The
CDA application rate was around 47 l/ha with a relatively large
droplet size (250 ?m). Pitblado (1981) also used tractor-mounted
atomisers (though applying at the lower volume of around 22 l/ha)
for application in tomatoes of moderate to heavy foliar
growth. Fungicide was applied at 2.2 kg/ha and two speeds of
disc rotation were used (2000 and 5000 rpm - giving estimated,
though not reported, droplet sizes of around 250 ?m and 150 ?m
respectively). Improved penetration was reported at the lower
speed of rotation.
It should also be noted that air-assisted low volume CDA spraying
is widely used for treatment of tomatoes and other horticultural
crops in protected cropping situations such as glasshouses and
polytunnels. This is commonly undertaken using spray volumes
of around 15-40 l/ha, with droplet sizes of around 70-100 ?m.
The relevance of this to non-air-assisted CDA spraying in outdoor
field crops may be limited, however.
Other Vegetables
Wladyslow and Wozniac (1974?) reported the application of Mancozeb
and Maneb against onion downy mildew. They compared low
volume spraying using a hand-held Micron spinning disc sprayer (at
application volumes of 10 l/ha) with high volume knapsacks (100-600
l/ha). The low volume technique gave excellent disease
control compared with the knapsack sprayer, albeit with slight
symptoms of phytotoxicity. It was speculated that the low
volume spraying gave better deposits on the windward side of the
onion leaves which is where the incidence of infective lesions
caused by the windbourne pathogen is generally greatest.
Potter (1981, 1982) looked at the application of fungicides to
celery, comparing tractor-mounted CDA (Micron Micromax) and high
volume atomisers at spray volume of 47 and 230 l/ha
respectively. Equivalent results were obtained at full
chemical dose, while the CDA technique also gave good control at
half the recommended chemical dose rate. Comparison of
(droplet sizes around 250?m (disc speed 2000 rpm) and around
166 ?m (disc speed 3000 rpm) showed no difference in disease
control.
Kisha (1986) tested the Electrodyn ULV sprayer on eggplant for
control of jassid. Excellent control was obtained using
cypermethrin, this being markedly superior to application of the
same chemical through a knapsack sprayer at high volumes.
Owang and Matthews (1989) used a spinning disc sprayer with and
without electrostatic assistance for treatment of brussel sprouts
(as test plants) in glasshouse conditions using Bacillus
thuringiensis. The charged spray gave better distribution
than uncharged. No comparison was made with high volume
methods and the experiment was carried out under controlled
greenhouse conditions, with no pest bioassay being performed.
Legumes
There is considerable anecdotal evidence as to the successful use
of hand-held CDA sprayers purchased by smallholder farmers for use
on cotton being used for treatment of leguminous crops grown as
part of the same cropping systems, though for reasons discussed
above this is not necessarily supported by documentary
evidence. Pawar (1990) investigated the deposition efficiency
of various spraying techniques for the application of endosulphan
in a variety of tropical legumes. A hand-operated knapsack
sprayer (500 l/ha), a motorised knapsack (250 l/ha) and hand held
spinning disc CDA sprayer were compared in pigeonpea, chickpea and
groundnut. Quantitative analysis showed that the CDA sprayer
gave significantly the best insecticide recovery, though biological
efficacy was not measured.
Clayton et al (1993) carried out spray deposition trials in a range
of crops including cowpeas and groundnuts at very low volume
application rates of 10 l/ha using a spinning disc CDA sprayer
(Micron Ulva+) developed for this spraying technique and compared
this with ULV applications. Results with VLV application were
generally equivalent if not superior to ULV treatments.
Cowpea
Raheja (1976) summarises four years of insecticide trials in
Nigeria using ULV spray treatments. Various formulations were
used with results from ULV treatments proving equivalent to those
from high volume sprays. ULV treatments included both
application of oil-based formulations at 2.5 l/ha and water-based
spray solutions, containing molasses as an anti-evaporant, at 5 l
/ha. Two row (1.8 m) and four row (3.6 m) spray pass
intervals were tried and both found to be equally effective.
In general effective pest control by ULV techniques was found to
increase crop yields up to 10 times compared with untreated
controls.
Ta'ama (1990) reported the results of a five year programme on
cowpea improvement in Cameroun. Insecticide treatment using
the Electrodyn ULV sprayer applying 0.5 l /ha gave results
equivalent to conventional high volume knapsack sprayers
applying 250 - 500 l/ha. Hand-held spinning disc CDA sprayers
were also trialled and gave satisfactory control of a range of
pests including Clavigralla tomentos collis, Anoplocnemis curvipes,
Nezara viridula, Aspavia armigera and Clavigralla shadabi. It
is estimated that without adequate control measures up to 100% loss
of yield can result. In guidelines produced by this programme
Ta'ama (1990?) recommends application rates of 1.5 - 2.5 l/ha using
spray pass intervals of 3.8 - 5.2 m, with droplet sizes of 70-80 ?m
for oil-based ULV pesticide formulations. Recommended
chemicals include Permethrin, Decis, Ripcord, Sumicidin, Thiodan,
Dursban and Nuvacron.
Jackai et al (1985), summarising techniques employed for insect
pest control in African cowpea, state that "insecticides have
normally been applied with hydraulic high volumes sprayers or
spinning disc sprayers that are ultra low volume with predictably
good results ... when properly used the sprayer provides good
results in every cropping system". Similarly, Alghali (1992),
Amatobi (1949, 1995) and Jackai all report the successful use of
the Electrodyn ULV sprayer for the application of a variety of
insecticides for insecticide application on cowpeas. As the
object of the trials was not to compare spraying techniques, no
comparative data is given for the technique compared with other
spray methods. Volume application rates of (undiluted
Electrodyn ULV formulations) range from 0.5 - 0.8 l/ha with two
rows being treated with each spray pass.
Pigeonpea
Pawar (1986 and 1987) and Awadhwal and Takenaga (1987) summarise
several years of research at ICRISAT in India on the use of CDA
spraying for the control of pests of pigeonpea. In general
CDA sprayers used at 10 l/ha were more effective than high volume
knapsack sprayers or mistblowers. Attempts were made to adapt
the principle of CDA including the production and testing of a
bullock cart mounted CDA sprayer and backpack CDA sprayers using
either two or three rear-mounted spray heads. The paper
concludes that "CDAs can be successfully used by small-farm
pigeonpea growers to control the pod-borer H armigera", though it
is stressed that safety aspects and training are critical and must
be given highest consideration.
Groundnuts
Much of the available literature on CDA spraying of groundnuts
refers to work carried out in the 1980s in mechanised farming
systems (particularly the USA) using tractor-mounted spray booms
fitted with CDA Micromax atomisers e.g. Middleton (1982a, 1982b),
Samples (1984), Littrell (1984). In general CDA application
of fungicides appeared to give good control of Cercospora leaf spot
disease and was equivalent to conventional high volume
techniques.
Several publications do however refer to the use of hand-held CDA
sprayers for groundnut spraying. Mercer (1976) reports the
successful use of CDA spraying of water and oil-based sprays at
application rates of 10-15 l/ha using the fungicides
chlorothanlonil and carbendazim for the control of Cercospora in
Malawi. Some leaf scorch was observed in the chlorothalonil
treatment. A spray pass interval of 1.8 m was used.
Fowler and MacDonald (1981) describe trials carried out in Nigeria
in which ultra low volume CDA applications of the fungicides
Mancozeb, Captafol and Benomyl for control of Cercospora in
groundnuts were compared with conventional high volume
spraying. Though water based ULV application at 6 l/ha showed
slightly poorer disease control this did not translate into
significantly reduced pod yields. Also working in Nigeria,
Salako (1985) investigated the application of a range of fungicides
for disease control in groundnuts using a hand-held Micron spinning
disc sprayer. Fungicides were applied as water-based spray
mixes at volume application rates of 10 l/ha. Treatments
resulted in yield increase of 132 - 286% over unsprayed control
plots depending on the fungicide used. The paper concludes
that this application is effective for the control of groundnut
foliar diseases. Comparison was not made with high volume
spray techniques. Work carried out at ICRISAT in India
described above (Pawar 1990, Awadhwal and Takenaga 1987) also
included trials on CDA treatment of groundnuts, with CDA heads
being fitted to backpack sprayers for very low volume (15 l/ha)
treatments.
In a recent volume on pest control in groundnuts (NRI 1996) ultra
low volume application of sulphur and copper fungicide is described
as effective, while in the same publication ULV spraying is listed
as a standard technique for pesticide application in groundnuts,
though consideration of CDA spraying is restricted to oil-based
Ultra-low volume applications, failing to take into account the
development of the water-based very low volume (VLV) spraying
technique which is more useful for growers, given the restricted
availability of ULV formulations. Therberge and MacKenzie (1981?)
describe the use of advantages of fungicide application to
groundnuts using hand-held CDA sprayers in China, though no details
of techniques used nor results obtained are given.
Beans
Trials (Southern 1982) in Phaseolus bean comparing a Micron hand
held spinning disc CDA sprayer with high volume spraying using a
knapsack for fungicide treatments against bean rust were
inconclusive, indicating that there appeared to be no significant
differences between the treatments. No details on application
parameters are given, however. This contrasts with trials
carried out in Colombia on Phaseolus, comparing high volume
spraying with water-based VLV treatments using a Micron hand-held
spinning disc sprayer and the Electrodyn ULV sprayer. While
insecticide trials were inconclusive, fungicide application at very
low volume rates failed to give control of a complex of diseases
including ascochyta leaf spot, web blight and angular leaf
spot. It is speculated that this was due to poor canopy
penetration due to low windspeeds at time of spraying.
