Tasmania’s brassica harvest spans across the year for the fresh and processing markets. The agronomy to produce the best outcomes has a lot of similarities to mainland crops, as well as a few unique considerations.

Tasmania’s broccoli and cauliflower growing regions are primarily along the northwest coast and inland to the south of Launceston. The coastal regions provide a milder environment and faster growing conditions, than inland.

Tim Walker, agronomist amongst a crop of cauliflower

Broccoli and cauliflower for fresh markets starts in early August for harvest commencing in December, through to March. Processor markets will start in January and finish in March, with harvest occurring from May through to July. Growth through the summer is typically 70-80 days, but through winter can be three to four months. Planting schedules are often three to four days apart to maintain regular market supply. Larger paddocks will be divided into different planting windows, often in the order of 3-5Ha per planting.

“In the summer when the plants grow quickly, it is important to make sure that the planting and harvesting schedule is maintained – if one planting is slower to grow and the window to market is missed it can be ploughed in,” said agronomist Tim Walker of WalkerAg Consultancy.

For most growers, cauliflowers are grown to around 1kg per head, with 20-40 tonnes per hectare for the processors, while broccoli is based on weight and yields around 6 -12 tonnes per hectare, but has a higher commercial value than cauliflower. To gain the yield, nutrients will be increased to meet plant demand.

“Strip till is the primary method over working the ground up and fertilising as it was done years ago. That method was able to do four rows at a time, plus fertiliser which led to a lot of soil compaction from the tractors.

“The advantage of strip till is that you can go into a wheat paddock or peas, where there is little trash left on the surface, strip till and top fertilise and take advantage of the nitrogen already in the soil from the peas.”

For a cauliflower crop, Tim says that a tonne of fertiliser at a ratio of 6/15/13 for N, P and K plus trace elements is enough, while for broccoli 600kgs is sufficient. Tim prefers to do a top dressing of calcium nitrates to help the seedlings recover from transplanting shock.

If weeds become a problem three to four weeks after transplanting, inter-row scarifying may be done in which case another top dressing of fertiliser is done to get into the brassica root zone. For many regions of Tasmania, the country can be quite steep and stony, so chemical control of weeds, radishes and volunteer potatoes can be the preferred method.

“Really, it is about timing for when a pre-emergent is used, particularly as they need to be washed in. If rain is forecast, great, otherwise you may need to irrigate. For the transplant, to lessen the shock on the seedling it is also better to plant into damp ground and give it another drink once it’s planted. This summer has been pretty dry, so irrigation has been used more often to keep the plants perked up.

“Uniformity is important, as it saves on labour costs with hand harvesting. Ideally, a grower will only do one or two harvest passes, if it goes to three it starts to become uneconomical. That third pass might mean that the head size has blown out and no longer meets fresh or processed specifications.

“Getting the broccoli and cauliflower off to a good even start is a major part of the success of the final harvest.”

Hand harvesting is a major cost in broccoli and cauliflower production so the move by some seed companies to develop varieties with a long stem and even height, that are more suited to machine harvesting is welcome.

Pest and diseases in Tasmanian brassicas

Tim runs an IPM program with his growers, particularly for cauliflower.

“The challenge with cauliflower is that you can’t apply a pesticide at the start of the growth and leave it. Cabbage white moth can lay eggs under the leaves, so you need to time the insecticide application before the eggs mature and hatch. A fungicide as a precaution for mildew is also recommended. Using beneficials is quite important but needs to be present while the plant is quite small, so that as the cauli grows, you don’t end up with a pest that becomes a contaminant.”

A nemesis for the industry is slugs, snails and crane fly. Tim will perimeter bait around the field to keep slugs and snails under control, particularly as strip tilling into a wheat paddock and not working the ground can increase insect pressure on young brassica seedlings. Growers need to be mindful of the withholding periods for baits.

The crane fly maggot can quickly decimate a crop, as well as become a contaminant issue at harvest and stains the cauliflower curd.

“The beneficials that are most effective are ladybirds and spiders, so keeping them going to the end is great. Seeing the webs in the early morning dew across the crop is a welcome sight, because you know they are doing their job.”

Diseases such as white blister, powdery mildew, Alternaria need to be prevented not cured according to Tim. Mixing up the active ingredients every couple of years, and not using the same one repeatedly means that the risk of developing resistance is low.

Follow the Ps of rotation

Many growers will undertake rotations across a five-to-six-year cycle with many different crops such as potatoes, carrots, onions, cereal, pyrethrum, poppies and peas.

As a rule, Tasmanian growers will have a minimum five-year rotation for brassicas. A positive outcome is that issues such as clubroot are rare, aided in part by the alkaline soils. When rotating into a potato crop, the pH will be altered to give a more acidic soil particularly to enable nutritional uptake. Poppies on the other hand need a pH of around 7.0 so lime is applied to redress the alkaline levels. A soil test every couple of years to assess the pH is recommended.

The optimum harvest conditions

“Tassie growers will stop watering ahead of harvest, so it is not too wet for pickers and equipment to get through the rows.

“With steep ground, a wet slippery row can be a safety risk, let alone covering the produce and crates with mud. Of course, if it rains it makes it tricky!”

Moisture for the cool room is welcome, as it aids in the cooling of the broccoli and extends the shelf life. Any more than 15 minutes from the field to the cool room, and the broccoli head will need to go onto ice in the truck for delivery to the cool room to maintain the freshness. Most produce will be moved to the markets the next day, but on average within two to three days. The cool room has high humidity to facilitate cooling, but also increases the risk of storage diseases.

For the processing market, cauliflowers will be harvested just as the leaves open, reducing the risk of ‘sunburn’ on the curd. The ratio of stem to head for broccoli to give a diameter between 90-160mm will determine when it is harvested.

“Hand harvesting broccoli and cauliflower is hard work. The growers and pickers in Tasmania have perfected the art to get the very best and freshest of our crops for the fresh and processed markets.”

This article first appeared in Australian Grower Winter 2024, as part of the Feature on Brassicas