Download HL01102 Abstract

HL01102 – Reducing herbicide use in row crops with targeted application
methods treating detected weeds in small patches or spots.
Aim of Initiative: To develop and demonstrate weed detection methods and novel spray
application technologies that will enable the delivery of herbicides with high spatial
precision suitable for targeted applications to control a wide range of weed species in a
range of row crops using spray characteristics appropriate to the effective use of new and
existing formulations. The work will aim to achieve high levels of weed control with the
minimum risk of crop damage and residues and with substantial reductions in herbicide
use delivering environmental benefits when compared with alternative and conventional
approaches.
Commercial and Technical Background:
EU legislation (e.g. the revision of
91/414 EEC and the Water Framework Directive) is reducing herbicide availability - the
limited range of herbicides remaining does not cover the weed spectrum encountered and
for some weed species there is, or soon will be, no means of control. There are very few
new herbicides in the pipeline even for cereals. This is a particular problem for
horticultural crops because high quality is required and growers cannot risk leaving
weeds if it could result in crop rejection and loss of income.
Mechanical weed control is now more widely practised, but there are a number of
circumstances when these methods are unsatisfactory – in wet weather, and for control of
perennial weeds and species with a strong tap root. Chopping up roots of some target
weeds such as creeping thistle exacerbates the problem. Repeated cultivations may also
have adverse effects on the environment both in terms of energy use and greenhouse
gas emmissions. Flame and steam weeding are damaging to invertebrates and consume
large amounts of energy. Hand labour has now become expensive and scarce.
Targeted application of herbicides to weeds that are difficult to control mechanically is an
attractive option potentially providing good control with minimum chemical quantities and
thus a low cost and environmental impact. Systems for guiding precision banded
applications including band spraying are commercially established although limited work
has quantified the spray distribution in narrow bands (see Lund and Jensen, 2002) and
the sharpness of the cut-off at the edge of the band. It is likely that there is scope to
improve both these performance aspects. The effectiveness of spot spraying volunteer
potatoes has been demonstrated in a recent Horticultural LINK project (HL Project
No.0183LFV). Results from this work demonstrated the feasibility of detecting volunteer
potatoes in carrot, onion and parsnip crops and treating them with a targeted total
herbicide spray. This was applied as very large droplets (circa 1000 m diameter) via a
new nozzle design to achieve levels of control typically in the range 75% to 95% and with
acceptable levels of crop loss. The proposed work seeks to further develop this approach
to achieve improved performance, include a wider range of target weeds and crops, and
to improve physical spray characteristics, particularly droplet size and velocity that can be
matched to target and formulation requirements.
The use of droplet size and velocity distributions that are similar to those of existing
techniques for applying plant protection products would then enable the use of existing
approved selective chemicals where appropriate. Where there are herbicide solutions at
present, for example a Starane/Totril mix to control volunteer potatoes in onions, or Dow
Shield (clopyralid) to control volunteer potatoes in sugar beet, a targeted spot application
would reduce overall herbicide use with advantages in reduced risks of water
contamination and costs. Where there are no solutions that are safe to the crop, spot
application of non-selective herbicide glyphosate would be an effective alternative. The
nozzle technology developed as part of the project would be relevant to the application of
chemicals in narrow bands as well as targeted spots.
The technology has relevance to almost all row crops, but to provide focus we propose to
concentrate on drilled crops that have particular weed issues including (to be prioritised
by grower groups):

Leeks and onions: black grass, oilseed rape, thistles, mugwort, mayweed, fumitory,
volunteer potatoes
 Sugar beet: weed beet (and in other crops), thistles, volunteer potatoes
The Problem/Opportunity: The problem is to develop cost effective techniques for
applying an effective dose of herbicide directly to detected weeds with minimal off target
contamination and associated crop contamination and loss. The nozzles to be developed
and employed in spot/banded applications are likely to cause less drift than conventional
sprays and together with the much reduced pesticide usage (typically < 2% for spot
application of larger weeds and <10% for patch spraying small areas of smaller weeds),
substantially reduce any potential impact on ground water contamination and water
quality. Solution of the targeted application problem would provide new opportunities for
chemical weed control in vegetables that would be competitive with existing herbicide use
strategies (band and overall application), but with a much reduced environmental impact
and hence improved sustainability.
Scientific Background: Traditional spray applications research has concentrated on
achieving a uniform spray volume distribution and high levels of target coverage across a
treated swath. Relatively little has been done to localise treatments in a way that is
necessary for spraying bands on or between crop rows beyond the development of a
range of “evenspray” nozzles. When treating small target areas, these designs suffer
from blockages due to their small elliptically-shaped orifices. In common with most
agricultural nozzles they have a wide droplet size distribution including fine droplets that
are prone to drift. Similarly, spot treatments have received little attention with research
studies based on single plant identification and the use of pulsed syringes to apply
treatments at very low operating speeds (Giles et al., 2004 in the USA and Christensen et
al., 2009 in Denmark). While this work has made some progress, the techniques used
were not relevant to full scale operation at commercial acceptable speeds. Our own
recent work (HL Project No. 0183LFV) has identified potential ways forward, but because
of limited resources, most of these have not been progressed.
Our work has been successful in developing an image analysis based weed detection
system linked to a spot spray control mechanism. This system has been developed
around the specific problem of treating volunteer potatoes within onion and carrot crops.
Discrimination of live plant material from background was on the basis of colour and a
number of criteria were used to determine if plant material was crop or weed. As
implemented during the 2009 field trials these criteria included; distance from crop row
(located using a bandpass filter), feature size (volunteer potatoes tend to be larger) and
feature shape (overall aspect ratio rather than leaf profile). Much of the technology could
be applied to the treatment of a wider range of large weeds and row crops. The existing
experimental platform will therefore form a sound foundation for the proposed work with
new image analysis development relating to improving tracking accuracy and the
identification of patches of smaller weeds building on the work of Hague et al, 2006.
Scientific Approach: The chemical application component of the proposed work will
focus on two main issues, the generation of a narrow spectrum of droplet sizes and an
ability to direct those droplets into narrow bands that can be turned on and off very rapidly
and cleanly. Agricultural hydraulic nozzles produce a spray using processes that create a
relatively wide range of droplet sizes which makes accurate targeting impossible.
In this work we will investigate use of Raleigh breakup that occurs when a coherent jet of
liquid is introduced into air. This method of droplet generation can be used to create an
inherently narrow range of droplets sizes that can potentially be improved further using
techniques such as a gas dynamic virtual nozzle, electrostatic charging or peizo electric
resonance to excite the jet at the natural breakup frequency, as used in inkjet printing.
Reliance on a jet to create droplets requires a mechanism to steer the jet so as to provide
a narrow fan-shaped spray pattern.
We will consider a number of alternative
mechanisms including electrostatics, moving coil oscilator (like a speaker), vibrating
motors (used by us in 0183LFV) and direct cam drive (used in 1960’s by “Vibrajet”). The
most promising of these will be integrated with the jet for full evaluation.
The work will also consider the extent to which the physical properties of the spray liquid
can be manipulated to modify both spray formation and droplet transport to the target. It
is known that factors such as dynamic surface tension and viscosity influence jet breakup and that different break-up mechanisms are involved with liquids that are emulsions
compared with complete solutions. The use of oils as well as water-based mixture with
different addatives will be considered together with the implications for delivering
formulated pesticide products.
For the small weed patch detection components, we will make use of earlier work in which
a vegetative index in the inter-row zone was used to estimate weed density. An evidential
reasoning based algorithm will combine that information over a sequence of images to
provide an enhanced classification. In earlier work an opportunity to improve tracking
accuracy of weed features had been identified. This will be developed and implemented
in the proposed work. This combination of techniques forms novel science that would
provide new weed sensing capabilities.
Modified detection algorithms will be produced and one or two experimental nozzle types
will be constructed in sufficient numbers to allow field trials to take place. Initial studies
will be aimed at weeds that are difficult to control mechanically and for which the options
for selective herbicide use are becoming limited due to the loss of product registrations
although the approaches developed will be relevant to a wide range of weed/crop
conditions. Performance will be assessed both in terms of engineering (accuracy, speed,
droplet size and distribution) and agronomic (weed kill and crop damage) parameters.