What was behind Australia's potato shortage? Wet weather and hard-to-control diseases

Powdery scab disease makes potatoes look distinctly unappetising. Shutterstock

So what caused the shortage?

In the lead-up to Christmas last year, Australia had a major potato shortage^[5].

Our main growing regions in Tasmania, Victoria and South Australia were hard hit by flooding and heavy rain^[6] due to La Niña, which created conditions ripe for potato diseases to spread. Waterlogged or diseased potatoes cannot be sold.

Other issues included delays to harvesting and planting due to the weather. And the skyrocketing costs^[7] of fuel and fertiliser have forced some growers not to plant potatoes. Potatoes need a lot of fertiliser and water.

While you might associate these tubers with snack foods, in reality they’re highly nutritious^[8] and an important source of complex carbohydrates.

Read more: Potatoes deserve to be a part of the super-food family^[9]

The way we grow them is very efficient^[10]. The amount of food energy we get per hectare of potatoes is many times greater than other staples like rice and wheat.

Stored properly, potatoes can last^[11] up to eight months.

Many growers find them to be one of the most profitable crops they can grow – as long as they’re prepared to face risks such as disease.

What’s next for our potato sector?

With the major rains at an end for now, potatoes are returning to the shelves and frozen food section.

But potato lovers aren’t out of the woods yet. For producers, there are still many worries. The increasing costs of production in fertiliser and other inputs. The chance of renewed heavy rainfall. And the continual battle against soil-borne disease.

Take Tasmania’s growers, who produce almost a third^[12] (31%) of Australia’s potatoes.

Unexpectedly wet soil conditions in spring last year forced many growers to delay planting^[13] until after mid-November.

Planting after this date comes with a cost. It means that by the time the plants mature, Tasmania will be through summer and into cooler months, reducing available sunlight and growing temperatures. That can mean a lower yield.

Facing delays like this, growers often simply don’t plant a crop at all. But because of the shortages, Tasmania’s major processing companies offered a bonus^[14] to encourage a late crop to ensure factories could keep running.

The eternal fight against disease

Ever since potatoes emerged from the Andes to become a global crop, growers have battled the threat of soil-borne fungal and bacterial diseases.

Backyard gardeners may well be familiar with some of these. If you’ve ever pulled up a potato plant only to find a half-rotten tater, you’ll know the disappointment.

What keeps Australian growers up at night are diseases like powdery scab, as well as rot diseases like black leg, soft rot and pink rot.

Powdery scab is mainly a cosmetic issue, turning nice-looking potatoes into unappetising, lesion-covered blobs.

But rot is real trouble. These bacteria and fungi can destroy entire fields.

Fungal rot diseases like black foot can devastate potato crops. Shutterstock

Pink rot is heavily influenced by free water in the soil. Heavy rainfalls just before an autumn harvest have triggered major rot epidemics^[15] with significant losses to growers in three of Tasmania’s last five growing seasons.

In severe cases, growers have to abandon fields with the tubers left to rot away, while in less severe cases there’s still substantial loss of crop^[16] and lower product quality.

If we see these levels of unprecedented rainfall again – as is likely with climate changes warping weather patterns – we’re like to see more potato shortages.

So what can growers do? For pink rot and powdery scab disease, we don’t have good options. There are a few disease-resistant varieties, but their resistance comes at the cost of desirable properties like crop yield and how well they cook. Chemical controls are limited, and if we overuse them, we risk these fungi developing resistance just as bacteria do with antibiotics.

Fungi and bacteria can lie dormant for many years or stay alive on other plant species between crops. That limits how effective crop rotation is as a tool.

Cropping land proven to be pathogen free is in very short supply. Food industries which rely on potatoes are compensating for these expected losses by contracting a greater number of growers and over-planting.

But it’s not a hopeless case. We and other researchers are working on it. Recently, we made a new tool^[17] to help rapidly spot powdery scab disease in new potato varieties.

Now we’re working on ways^[18] to track changes in soil moisture and temperature against rot and powdery scab outbreaks. This, we hope, will let us predict outbreaks before they occur.

Sometimes, you don’t have to defeat a disease outright. Better prediction and containment may be enough to keep us supplied with hot chips.

Read more: What's driving the potato chip shortage and when will it pass?^[19]

Read more https://theconversation.com/what-was-behind-australias-potato-shortage-wet-weather-and-hard-to-control-diseases-205847

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