Know the risks of growing crops cooler

Energy has been, and will continue to be, at the forefront of growers’ minds in 2022. Soaring costs across supply chains are squeezing already-tight margins and, in many cases, bringing into question the viability and profitability of growing a crop. 

We’ve seen these pressures right across the horticultural spectrum, from protected edibles to ornamentals, with many growers reducing their overall number of crops or pulling back on investment in areas such as research and development.  

The rising costs of energy means that many different businesses are looking to grow crops cooler. This can be an effective way to reduce energy bills; however, growers should be aware that it can also lead to a range of pest and disease issues. In the long run, these may result in significant extra costs for crop protection inputs, or significant loss of revenue due to a drop in yield and/or quality. 

Here, we look at how to minimise energy usage, and address the risks of growing at lower temperatures.

Keeping energy costs down 

We often talk about the importance of setting a firm base for an integrated pest management (IPM) programme that is grounded on a combination of effective practices. The same principle rings true here, too, in that there are a number of ways to reduce energy usage. 

Growers should, for example, ensure all repairs to structures are made in a timely manner, to prevent unnecessary heat loss. Similarly, they should ensure that staff are closing doors behind themselves to keep heat in; and, in some cases, ensure those doors are on the latch to prevent reopening. And they should also insulate particularly sensitive areas, such as propagation units.

Risks of overwatering and root rot

If growing at lower temperatures, there is reduced transpirational force pulling water through the plant. This effectively means that your crop will require less water. If your irrigation programme isn’t adjusted to reflect these changes, this will likely lead to overwatering. The excess water will create a saturated environment in the root zone, potentially resulting in root rot disease.

These risks can be mitigated through precision irrigation techniques; for example, using sensors to measure key metrics such as vapour-pressure deficit (VPD) and volumetric water content (VWC), and setting targets when irrigating to ensure consistent results.

Poor nutrient uptake and translocation

As the transpirational force is lower at cooler temperatures, crops tend to exhibit less (or slower) active growth. Meanwhile, growers might also find that nutrients are less well translocated around their plants – something that may present in deficiency symptoms such as yellowing leaf tips. Poor nutrition can lead to a less resilient crop that will be more prone to pest or disease infection.

Disease risks and crop protection inputs

As we have seen, running a crop cooler can lead to root rot disease, or damping off. Growers may find there is also an increase in the incidence and duration of leaf wetness, which means a greater risk of crop diseases such as Botrytis or downy mildew. These diseases will ultimately need controlling. However, if your crop is being grown at particularly low temperatures, some biofungicides may not be viable, meaning that more conventional chemicals will need to be applied. In some crops, this may present issues with residues.  

An increase in root rot disease is likely to be followed by an increase in fungus gnat populations. Control of fungus gnats is often biological, so again, growers may face a situation in which their usual controls are not effective because conditions are simply too cool.

Key considerations for cooler cultivation

Despite the potential for increased pests and diseases, it is still tempting to run the crop cooler. If doing so, growers must take steps to reduce the risk of diseases developing through proper irrigation management. They should remember that biological controls and biopesticides may not perform as well in cooler environments. 

And they should also keep in mind that, if active growth is reduced due to cooler conditions, systemic chemistry may be affected – which, again, may result in poorer control than growers were expecting.