Attention To Detail Can Help
Increase Raspberry Yields

Presented to the Ontario Berry Growers Association Conference, Jan 14, 2004.

Raspberries are notorious for not reaching their yield potential. Yields vary tremendously from farm to farm and from year to year. Researchers estimate less than 20% of the potential yield is actually realized. Figure 1 provides a possible scenario of what happens to the rest.

There are many production practices that affect raspberry productivity and yield. This discussion will focus on three other areas where attention to detail is important: microclimate and irrigation, pruning, and pest management. Trellising is another important management practice and will be discussed in a future article.

Microclimate and irrigation

"Warm roots, cool shoots" simplistically describes the conditions raspberries like for optimum growth. When air temperatures are too warm, ( i.e. > 25C), photosynthesis slows dramatically. However, raspberry roots appear to grow better in warm soils. Growers can use black plastic mulch over the raspberry row in the planting year to warm the soil. This mulch helps to conserve soil moisture, control weeds, and encourage strong root development. After the first year, the benefits of plastic mulch are reduced, because of shading. As the plastic breaks apart, primocanes are able to grow up and fill the row. Straw mulch is not as useful for raspberries, partly because it keeps the soil cool, and partly because damp conditions around the crown can encourage Phytophthora infection. .

Windbreaks are important around a raspberry planting. Plants in windy sites have shorter canes and smaller foliage. Fruit can be easily damaged by wind. However, last year we saw the worst winter injury near windbreaks and hedgerows. Plan your windbreak so it breaks the wind but doesn't prevent cold air drainage out of the planting. There should be about 50% barrier and 50% airspace in a good windbreak.

Generally, berries benefit 9 years out of 10 from irrigation. Trickle irrigation is preferred to overhead irrigation, because overhead irrigation spreads diseases. Raspberry roots typically extend 45-120 cm deep. Most water is taken from the top 10 cm. If the soil in this area dries out, the lower roots cannot increase water uptake to make up the difference. Growers should monitor soil moisture on a regular basis to provide just the right amount. An inch of water/week is only a guideline for irrigation amounts. The actual water needs go up or down depending on the soil type, weather conditions and stage of crop growth. The most critical time for irrigation in raspberries is from pre-bloom through the green fruit period. Primocanes, fruit and roots are all competing for resources at this time.

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Pruning

In a typical planting, where rows are 8-9 feet apart, prune out raspberry canes in late winter or early spring to approximately 10-15 canes per m of row. Where rows are further apart, cane numbers should be increased. (See Table 1). Over the whole area, the optimum cane number is about 6-8 canes per square meter.

Cut back the fruiting cane tips to a convenient height for picking. Be sure to cut off dried up fruiting clusters from the tips of Nova and Prelude.

Use a mower for your summer pruning. Keep unnecessary primocanes mowed off from the row edges. The earlier these shoots are removed the better.

After harvest, old fruiting canes should be removed from the row. We used to think that this job should be done as soon as possible after harvest. However we now know that nitrogen and other nutrients are transported out of fruiting canes after harvest, back to the crown. There is also anecdotal evidence that, in a marginal year, winter injury can be worse on varieties pruned right after harvest. On winter sensitive varieties you should probably delay pruning out the fruiting canes until the plants are dormant.

Finally, make sure that canes are pruned close to the ground. Do not leave long pruning stubs. Several insects overwinter in the lower portion of fruiting canes, and careful pruning can help control these pests. Also, old cane stubs are a source of spores for some diseases.

Pest management

Four cane diseases are common in Ontario. These include cane blight, cane botrytis, spur blight and anthracnose. The fungicides labeled for cane diseases in raspberries tend to be older products, with only moderate efficacy. Therefore, it is especially important that they are applied at the right timing and rate.

Lime sulphur should be applied between bud break and 1/4 inch green. This fungicide works on the overwintering fungus as it starts to grow. Application too early is not as effective. Application too late can cause leaf burn.

Ferbam is another product used for cane disease control. Apply it to protect new growth, both primocanes and laterals, before bloom. After bloom, we do not have many fungicides labeled for cane diseases. However, using Captan or Maestro for Botrytis control during the bloom through green fruit stage will also control spur blight. Several new fungicides are in the minor-use registration system.

Controlling cane disease is very important. Winter injury can be much more serious in plantings with significant levels of cane diseases.

Another pest that can cause harvest losses is two-spotted spider mite. Outbreaks of this pest are more likely after multiple insecticide applications, or in hot dry weather. Autumn Britten is very susceptible to two-spotted spider mite, and this cultivar should be monitored carefully for mites. In Ontario, raspberry growers have four miticides to choose from. Only Kelthane and Apollo can be used before harvest. The other two products, Pyramite and Agrimek, are for post-harvest only, and not very useful for fall-bearing raspberries.

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Figure 1. Hypothetical model of potential raspberry yield.

Related Links

• OMAFRA Berry Index Page
• Berry Bulletin Agriphone
  

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