The fight against weeds and pests in the vineyard has evolved considerably over the past few years, with clean planting material at the forefront of this battle. While prevention is better than cure, not everyone is in the enviable position to have a clean vineyard to start with. By Bernard Mocke
This article offers but a mere glimpse into the fascinating and complicated field of vineyard weed and pest control. It’s clear that both traditional and alternative weed and pest control methods can successfully be incorporated in vineyards, but that an integrated approach is necessary.
The various pests and diseases viticulturists face are generally successfully combated with chemicals. With the rare exception of leafroll virus, various chemicals used on a rotational basis not only keep most pests and diseases at bay, but also restrict their ability to build up a tolerance to pesticides. Chemical spraying has come a long way and techniques now exist that lower spraying volume, which ultimately reduce not only pollution, but also the consumption of fuel, water and time. But many producers are shying away from traditional pest and weed control, organic producers being among them. While not all these alternative pest control methods are allowed in organic farming, they hold a certain appeal for many.
Alternative methods such as biofumigation against weeds and nematodes, steaming of weeds and biological control (biocontrol) can be very effective, but there are positives and negatives. Traditional methods of weed and pest control typically involve spraying chemicals or leaving bait in vineyards. It stands to reason these chemicals may affect harmless organisms in the process. There’s also the possibility that residues of the chemicals used may be left on plants and grapes and in the soil and groundwater.
But before turning your back on traditional weed and pest management methods, it’s worth considering why they’re still widely used. Petrie De Kock of BASF shared his thoughts on the advantages of these traditional control measures.
“When it comes to weeds, chemicals act very quickly, usually within a day or two,” he says. “Biological methods take time because populations and resistance in the treated plant have to build up. Where chemicals are employed against weeds, only two or three applications during the season are necessary compared with biological control measures, which typically have to be applied every second week. The cost of going biological is thus greater and also leads to greater soil compaction, higher fuel consumption and more carbon emissions.
“When it comes to insects and fungi, which cause various vineyard maladies, your choice of chemical substances is limited if you go the biological route. Some of the so-called biological agents are also not effective or have limited efficacy. Just because a substance is organically certified it doesn’t mean it’s effective by default.
“It’s important to realise no agent, chemical or biological, will compensate for poor vineyard management. You need eyes in the vineyard to look for potential problems – this is the first step towards proper disease and pest management. If a sudden outbreak or epidemic is imminent, immediate action can and must be taken. And this is where swift-acting chemicals are more effective than their biological counterparts.”
With proper management, alternative weed and pest control measures can however be extremely beneficial. And unlike chemical products, biological products have no negative impact on the environment or humans and no poisonous residues remain on vines or grapes. These benefits definitely make organic farming a hot topic.
Organic farming, including the use of biological weed and pest control methods, has grown considerably, says Dr Strauss Ferreira of Agro Organics. “There has been a 60% increase in organic or biological viticulture since 2005. I’ve also seen a big increase in organic vegetable farming.”
But it’s not all been plain sailing. “The manner and timing of biological product application in vineyards is critical. For instance, the control of downy and powdery mildew during wet conditions requires weekly product application or directly after rain. During extended wet spells the products must be used in combination with copper to control downy mildew.”
What are some of the biological products and how are they employed in the vineyard? Strauss says fungi are often used against both insects and other fungi. One example of a parasitic fungi widely used in biological control is Trichoderma spp. This fungus parasitises vineyard pathogenic fungi such as Phytophthora cinnamomi, Pythium spp and Plasmopara viticola (downy mildew) or controls them through the excretion of antibiotic compounds. Powdery mildew can be controlled with Ampelomyces quisqualis, which is an obligate parasite of powdery mildew. Various harmful insects can be controlled by using Beauveria bassiana, which can be used in combination with neem oil against Planococcus ficus, Plangia graminea, Frankliniella occidentalis), Phlyctinus callosus and Helicoverpa armigera.
Biofumigation is supplementary to traditional weed and pest management and is becoming increasingly popular in South Africa. Cover crops form an essential part of an integrated approach towards weed and pest management. Cover crops that display biofumigation properties are environmentally friendly and form part of a cover cropping approach that has an impact on the financial sustainability of the grape producer. These cover crops, typically of the Brassicaceae family, have supressing effects on plant-parasitic nematodes when applied as green manure. The supressing effect also extends to other soil-borne diseases and weeds and is the result of certain volatile compounds that are released during the maceration and incorporation of green manures. In the case of Brassica crops one of the biologically active compounds that is released in the soil is isothiocyanate (ITC). This is released during the interaction between glucosinolate (GSL) and the enzyme myrosinase after maceration of the plant cells.
Niel Kruger of InteliGro shared some of this thoughts on biofumigation. “The concept of biofumigation involves a thorough understanding of the different aspects that can influence the process. Aspects such as the Brassica species (different species have different types and concentrations of GSL in the plant cells), biomass production, plant rupturing/maceration process, soil pH, soil water and the incorporation process are some of the important factors that must be considered for effective biofumigation. It is also important to understand that the aim of biofumigation is the implementation of a cultural practice as part of an integrated approach to manage plant parasitic nematodes and other problems over the longer term. The impact of the cover crop host status for certain plant-parasitic nematodes/diseases (poor host, maintenance crop, good host) as well as the positive effect of the incorporated green manure on the soil microbiological activity must also be considered when looking at biofumigation crops as part of a cover cropping rotation programme.”
Organic farmers can benefit from the various alternative weed and pest control methods, but a thorough understanding of the products and their limitations is necessary. The same goes for those going the chemical route, with the added responsibility of environmental stewardship also an important factor.
Soos gepubliseer in die Augustus-uitgawe van Wynland-tydskrif.
