Potato Review

www.potatoreview.com POTATO REVIEW JANUARY/FEBRUARY 2021 13 COVER CROPPING Improving pest control, naturally More diverse agricultural systems tend to support higher biodiversity. is results in better resource provision for bene cial organisms which carry out ecosystem services, including natural enemies which predate on and suppress insect pest populations. More diverse agricultural systems can be achieved by increasing vegetation diversity and heterogeneity at eld, farm, and landscape scales. It’s long been recognised that aphids are preferentially attracted to light re ected from soil in blank beds and the contrasting neighbouring plants. Introducing ground cover into these situations can prevent landing strips for aphids as well as increase natural predator populations. As part of integrated pest management (IPM), it can reduce aphid-borne virus mid to late season. An example of this is drilling ower mixes in these blank beds, a practical mitigation technique for early generation - FG2 and FG3 - seed growers, with a disproportionately higher number of separation zones between the numerous seed stocks. is creates corridors throughout the crop, increasing biodiversity in a move away from a monoculture system with its high reliance on chemical controls. Corn ower, common vetch and yarrow are highly e ective in attracting natural enemies of aphids. ese are low growing plants that are the same height as potato crops. Biofumigating nematodes In recent years, biofumigation has emerged as an e ective non-chemical alternative to manage nematode pests including potato cyst nematodes (PCN). Biofumigation is the suppression of soil-borne pests, pathogens and weeds by a glucosinolate-myrosinase substrate enzyme defence mechanism present in brassica crops. In the UK, biofumigation typically involves growing brassica green manure crops. e most common biofumigant species are Indian mustard (Brassica juncea), rocket (Eruca sativa) or the partial biofumigant oil radish (Raphanus sativus). All need to be treated as crops and require careful management. If other brassicas (particularly oilseed rape or vegetable brassica) are grown in the same rotation, growers should avoid those that may result in an increase in club root. e relative performance of biofumigation can be variable and depends on a range of environmental and agronomic factors. Indian mustard speci cally requires maceration, incorporation and soil sealing. e optimum time to drill a biofumigant crop is between mid-July and mid-August, growing for eight to 14 weeks. e summer– autumn window also enables access to long day lengths and high ultraviolet (UV) radiation, which is important for the production of glucosinolates. Adequate nitrogen and sulphur nutrition is important for maximising biomass, with high concentrations of glucosinolate content. Maximum e cacy of PCN reduction for this window is usually between c.40–70%. e nature of degradation products depends on factors such as pH, substrate, availability of ferrous ions and the activity of certain protein factors. Soil pH is critically important. If the pH is below 5.6, the chemical conversion of glucosinolates will be driven towards nitriles instead of generating the biocidal isothiocyanates. Autumn-established biofumigants for overwintering have a relatively lower potential. e restriction is due to shortening days with lower UV exposure and limitations on fertiliser applications. If established by early to mid-August, however, oil radish can be grown over winter during which it releases glucosinolates speci cally from its roots. Extracellular myrosinase, linked to microorganisms and common fungi like aspergillus occurring naturally in “One of the reasons to grow cover crops – sometimes known as green manures - is to help build soil organic matter.” ➜