Pest behaviour
Field margins and beetle banks rather than biocides are now being employed by progressive farmers to control the wee beasties, as Tim Field explains
Acre by acre the yield is monitored as the combine swallows another year’s harvest. The data raises questions about the discrepancies in performance across the farm, triggering hypotheses on crop nutrition, soil conditions, the weather and the impact of infinite miniature beasties.
Traditionally, the latter has been addressed with regular passes by the boom of doom, spraying a concoction of biocides to halt the prevailing pests. However, with increasing limitations on the effectiveness and usage of crop-protection products, progressive farmers have begun to incorporate beneficial ecology into pest management and not depend entirely on the chemistry set.
It is often too late to adopt an ecological approach once the crop has suffered an attack, so holistic pest management is considered at the start of the growing year or, better still, at the beginning of several years of rotation, with regular reviews. Integrated pest management requires multifaceted intervention, including predation, lifecycle disruption or creation of a hostile environment to deter colonisation. It is much like the principles of species conservation only in reverse, with the ultimate aim of cutting the costs of agrichemical applications while still improving yields.
effective pest management can start with the selection of varieties, such as those emitting more parasitoid-attracting herbivore-induced plant volatiles (HIPVS). Under attack these plants emit a chemical signal (HIPV) that triggers a number of responses, including the attraction of predator allies. To be effective, the crop requires predators to call upon and thus attention turns to the assemblance of suitable habitat, such as field margins and beetle banks, and plant species selection can be important. For instance, there is an association between red fescue and colonisation by a beneficial parasitoid wasp that predates fruit fly.
Flowering plants in the margins will increase populations of beneficial hoverfly larvae, as the nectar and pollen are critical to the adult hoverfly, while semi-natural habitat with structural complexity supports ladybirds, a valuable predator of aphids. Habitat in the margins supports the ladybird’s prey species early in the year before the aphids emerge – thus the whole ladybird lifecycle is taken care of. Intercropping reduces pests and enhances natural enemy populations in-field; beyond the boundary a diverse landscape has a similar effect on the macro-scale. Once the helpful predators are colonising, the spraying of pesticides can undo all the good work so if spraying is essential, timing is critical.
cultivation techniques can have a significant bearing on pest burdens, the options giving conflicting information, particularly with variance in soil conditions and weather. reduced tillage may have countless benefits for soil management but it can increase pest problems, such as wireworm damage. Orange wheat blossom midge can be impeded by ploughing and the dense litter layer of non-inversion tillage is unhelpful with a pending slug burden, requiring removal of debris and stubble to deprive habitat. Likewise, where cereals follow grass infested with leatherjackets, ploughing from July to early August will bury herbage at the critical stage before adult craneflies emerge, disrupting the lifecycle. The timing and technique of drilling will also have a bearing on pest attack, virus transmission and the crop’s ability to recover; and invariably depends on weather conditions.
The science of pest management unveils countless contradictions in practice, from suggestions of multiple-cultivations to zerotillage; promoting or avoiding proximity of spring and winter crops; landscape homogeneity versus heterogeneity. For optimum ecological assistance, the drilling, cultivating and management techniques need to respond to the prevailing ecological conditions. The subtle nuances of entomology within farms are important but not straightforward, so essential skills are required if farms are to benefit from ecological assets. When we launched the Agricology project it was this demand for knowledge that our partners set out to fulfil.
In June, our co-founder, the GWCT’S Allerton Project, celebrated its 25th anniversary. More than 200 papers on agriculture and conservation have emerged from its farm and research base in Leicestershire, including valuable work on agro-ecological methods. However, it has been a struggle to deliver the results to practitioners or policy makers. This special occasion was therefore marked with the release of practical guidance summaries from Allerton research, including a summary on the Sustainable control of crop Pests. May the coming year’s crop be pest free and plentiful.
The ultimate aim is to cut the costs of agrichemicals while still improving yields