Crop protection in the Orchard of the Future

A changing strategy for a changing world. By Marinda Louw Coetzee.

Crop protection is changing due to increasingly stringent market requirements for ethical fruit production, as well as due to changes in orchard structure and ecology. The Orchard of the Future focuses on increased yields, and greater labour and water-use efficiency, but also on effective pest and disease management.

The drive to reduce synthetic inputs

In May 2020, the European Commission adopted a Farm-to-Fork strategy which intends to address sustainability and equity in food systems. The goals of the strategy include reducing the use of chemical pesticides by 50%, and reducing nutrient pollution resulting from the use of fertilisers by 50%.

The Farm-to-Fork strategy has important implications for trading partners. The European Union will assess environmental concerns when considering requests for import tolerances of pesticides. These concerns include issues such as the decline of pollinators and the bio-accumulation of toxins.

Effective crop protection and post-harvest decay control are threatened by new restrictions on chemicals, leading to a shrinking range of available products. For example, mancozeb, a fungicide, is likely to lose its European Union approval, which would mean that it cannot be used on fruit exported to Europe. Producers are left with few effective substitutes.

“South Africa is not only under pressure relating from EU requirements — it’s a global trend,” says Hugh Campbell, general manager of Hortgro Technical. “A focus of the Orchard of the Future is to produce marketable fruit with less synthetic chemicals.”

Coping with new canopy structures

“The biggest challenge of pest control in the Orchard of the Future is the application of pest-control products. Current equipment is not ideally suited to high-density plantings,” states Bekker Wessels, managing director of ProCrop.

However, high-density plantings have much more spray-friendly canopies than conventional orchards, according to Dr Gideon van Zyl, technical consultant at ProCrop. “It’s different in terms of depth, height, foliar density, and complexity, yet the principle of canopy-adapted application still stands.”

Trees in a high-density orchard are smaller and narrower than those in conventional orchards. This enables a producer to spray at higher forward speeds and lower air momentum, and to use less water. More effective spraying saves time, which allows growers more flexibility to manage disease and other pressures.

Nozzle selection should still be determined by the canopy shape and water volume. “Tower sprays with good horizontal cross-flow shortens the distance that the droplets travel, which improves penetration and deposition,” says Van Zyl.

The trend of planting trees under nets complicates matters by varying the orchard microclimate. “Spraying under fixed nets is in principle similar to spraying outside,” says Wessels, “but fixed nets create a softer, less UV-intense microclimate, with the possible result of higher powdery-mildew infection pressure.”

Matthew Addison, crop-protection programme manager at Hortgro Science, thinks that

the application of pest control under draped netting may be more management intensive. “Under draped nets, spray penetration is difficult to manage, and fruit-fly baits have to penetrate through the nets after aerial release.”

From the ground up

Weed control is a challenge in any orchard. Herbicides containing glyphosate may be replaced by management practices, including the use of mulches and cover crops to reduce weed emergence and growth. Mulch also helps retain soil moisture, and improves soil structure over time.

“The use of mulch and cover crops to improve orchard floor ecology is an important aspect of integrated orchard floor management, especially relevant under netting,” says Addison. Cover crops can be planted to suppress weed growth, and then flattened to form a layer of mulch — a concept known as green mulch.

Cover crops also increase biodiversity in the orchard, which in turn leads to an increase in natural predators. “We have found that, in these systems, some pests are suppressed. An example is the use of mulches and the suppression of woolly apple aphid. These natural biological systems have produced better results in pest control than the mass release of biopredators.”

The use of mulch has increased across the industry, confirms Wessels. “Mulch can help reduce defects such as stem-end cracking, which is caused by moisture stress. In addition, the use of compost and mulch has a positive effect on soil biology, which contributes to the suppression of soil-borne pathogens and nematodes. A healthier root zone contributes to healthier growth, and a healthy tree has a greater tolerance of pests.”

Wessels points out that biological control products are another alternative to chemical pesticides. “Entomopathogens, such as viruses for bollworm, false codling moth and codling moth, and egg parasitoids, are effective biological pest-control agents.”

Right from the start

Replant disease is a problem when establishing new orchards on old sites. “There is a need to move away from fumigation as a standard practice to control apple replant disease,” says Campbell. Soil preparation that includes the addition of organic material such as compost is seen as an important part of replant control in the Orchard of the Future.

Rootstocks that are resistant or tolerant to replant disease, pests, and soil-borne pathogens can significantly reduce tree losses and improve orchard performance while minimising the need for chemical intervention. Hortgro is funding various research projects aimed at screening rootstocks for disease resistance and tolerance.

Introducing disease resistance or tolerance into the genetic make-up of a cultivar could offer a novel solution to chemical disease control. “Apple scab is a major challenge due to wet springs in the Western Cape, and the chemicals needed to combat this limit the organic production of apples,” says Campbell. “Some of the new scab-resistant cultivars show promise, but the fruit must be able to compete with commercial cultivars for appearance and taste.”

The availability of quality nursery trees is crucial to the success of the Orchard of the Future, and a focus of Hortgro’s research and development strategy for 2020–2024.

“The Orchard of the Future demands the planting of clean trees on the right soils,” concludes Campbell. “New technologies, including tissue culture and containerised nursery trees growing in sterile media, provide the opportunity to deliver tested clean trees to the orchard.”

Image: No-spray crop protection with straw mulch and stem-bands.

Supplied by Anna Mouton.