Strawberries (Fragaria spp)How well established is this crop?
This crop has been grown commercially in the region for over 10 years. Commercial returns, current growers and some level of regional based research is available to help those new to this industry.Background
What New Zealand summer would be complete without the taste of fresh strawberries? They are no doubt the best known and most widely purchased berry crop in this country. The main issue being faced by the industry at the moment is the phasing out of the use of methyl bromide. Growers have used this to fumigate soil between crops of strawberries to destroy any weed seeds insect pests or fungal pathogens in the soil. Unfortunately this product is also affects the ozone layer and its use is being phased out all over the world. Other means of soil sterilisation such as steam are now available. Crop rotations are also important.Winter Chilling and Frosts
Both strawberry plants and the fruit are susceptible to frosts. If growing in a frost prone area, make sure these are able to be controlled with wind machines or overhead irrigation.Rainfall and Irrigation
Irrigation is essential to grow strawberries successfully, because the plastic mulch prevents rain getting into the root zone of the crop. Because of the fungal problems associated with overhead irrigation most growers put dripper tape under the plastic mulch when the beds are being formed. These raised beds also help drain away excess water from the rooting zone.Wind
Even though strawberries grow very low to the ground they still benefit from some wind protection. Shelter reduces the chance of bruising on the fruit and reduces the drying effects of wind over the summer period.
Most blocks rely on natural tree shelters. A good rule of thumb when designing shelter is to multiply the final height of the shelter by 5. Use that measurement as the distance you position your shelters apart. For example, when using shelter trees that are 10m high you will need shelters 10m x 5 = every 50m. Some consultants are recommending a multiplier of 10 for crops but with a low growing valuable plant such as this, a more conservative approach is advised.
Strawberries require a well drained soil. Without it the plants are very susceptible to root rots. Most growers place the plants on raised beds to further drain soil around the rooting zone.Fertility
Strawberries require reasonable levels of soil fertility as they tend to be cropped quite hard. Soil tests before the crop is planted beneath the polythene (see weed control section) will quickly identify any deficiencies whcih can be easily corrected with the addition of fertilisers. Foliage tests during the season can also be used within corrections being applied using liquid foliar feeds. Companies such as Hills Laboratories have a datasheet with the recommended soil and leaf nutrient levels for this crop. See the ‘Contacts’ section at the end of this datasheet.Weed Control
Weeds are controlled in strawberry blocks with the use of black polythene mulches. These are put on the soil surface using bed forming machines towed behind tractors. Holes are then cut in the plastic and the young strawberry plants placed in the soil.
Mulches (synthetic or natural) and hand pulling are the only way of controlling weeds in strawberry crops. Herbicides can be used to control runners but caution is advised.
Most modern varieties of strawberries are treated as an annual and there are a large number of them. Most produce a single crop each year but a few can produce two crops. You need to decide which sector of the market you are aiming your crop at before choosing a suitable variety.
Market sectors and varieties for each include
2. Local Fresh.
4. Pick your own.
Strawberries suffer from a range of insect and disease pathogens, the severity of which is driven by the environmental conditions the crop is grown in. The disease Botrytis is by far the worst problem facing the crop. It affects the roots, leaves and fruit, especially near harvest. Insect pests on the crop include slugs, leafrollers, aphids, two spotted spider mite and cyclamen mite. Most commercial growers use a spray program to control these pests.
The other major problem for strawberry crops is bird predation. Birds are attractive to any fruit that is red and will quickly work through a strawberry patch as it nears harvest. Bird scarers, shooting or large tents/nets have been used with success in the past.
Most strawberry blocks consist of long rows of plants approximately 1m apart. This allows for easy foot access to each individual plant. Every 10 rows or so, a wider row allows for machinery access. This is to get a tractor and a boom mounted spray unit into the block. Plants are usually placed every 20cm within the row.General Management
After ground preparation and planting is complete, the key thing to watch for with strawberries is the development of fungal diseases. Regular monitoring by walking through the blocks is recommended. Early intervention with fungal problems is crucial. As harvest approaches getting enough labour to pick the crop can be a challenge especially if you are located some distance from a town. Irrigation is also key during this period. During harvest, the plants may need to be picked over every few days depending on temperature and market requirements. If growing annual crops the water is turned off after harvest and the plants pulled form the soil when they die off.
The harvesting stage of strawberries depends on the final market destination. For example export fruit need a good shelf life as they need to be sent to overseas markets. This means picking them when they are slightly less ripe than you would for a crop that is meant for the local supermarket. The key thing when harvesting strawberries is to leave the fruit on the plant for as long as you possibly can before harvest. This will allow for natural ripening and makes for a better tasting berry.Equipment
Because most commercial blocks of strawberries are planted on a reasonably large scale a tractor is required along with spray units. Most of the rest of the work is done by hand and labour requirements are high.Returns
Returns depend on which market sector you are growing the fruit for
4. Pick your own.
If you are thinking of growing strawberries, talk to some local growers or contact the following organisations.
For soil fertility information contact
Strawberry and NZ Berryfruit Propagators Ltd
11 Grenville Street
Ph 04 569 8263