You Can Simply Sprinkle Water On Raspberry Leaves To Keep Spider Mites Away
Raspberry production faces persistent challenges, especially from pests like spider mites. To minimize the use of chemical pesticides, researchers from the Norwegian Institute of Bioeconomy Research (NIBIO) are exploring environmentally friendly alternatives.
One promising approach has been to simply sprinkle water on raspberry leaves to disrupt and reduce spider mite populations.
The two-spotted spider mite (Tetranychus urticae) is a small arachnid that attacks many types of plants. It primarily poses a problem in strawberries, but it significantly affects raspberries as well.
Nymphs and adults feed on the leaves, which often leads to wilting and stunted growth. They can also cause the leaves to drop too early.
“If you want to get rid of spider mites on raspberries, you either have to use biological control organisms like predatory mites or chemical pesticides,” said Nina Trandem, one of the study’s researchers.
“Fewer and fewer chemical agents are available to the growers, and neither they nor the biological control organisms always yield satisfactory results. This is why we need other good alternative methods.”
The researchers investigated whether irrigation can lower the number of spider mites in tunnel-grown raspberries. Several small chambers, each containing three raspberry plants, were set up inside the tunnel.
A sprinkler nozzle was installed above each chamber to spray the plants with water at specific times. Groups of three raspberry plants were placed outside the chambers to act as control plants. They did not get sprayed.
The researchers recorded signs of spider mite damage and documented the number of colonies on the plants. The mites tend to live on the underside of the leaves. Adults spin webs, but they are very tiny and hard to spot.
vaitekune – stock.adobe.com – illustrative purposes only – pictured above is a raspberry plant
The team observed a 40 to 50 percent reduction in spider mites on plants that were sprinkled regularly with small amounts of water compared to those that were not sprayed. Similar results were previously seen in strawberry plants.
“The effect was on par with spraying once with a miticide if we count the mites a couple of weeks after spraying. Spider mites simply don’t thrive in a moist environment,” Trandem said.
“Predatory mites, on the other hand, which are natural enemies of the spider mites, prefer a slightly humid environment. In other words, this treatment can also create favorable conditions for biological control.”
The treatment does not completely get rid of the mites—it just keeps their populations reduced enough to prevent major damage to the plants.
In addition, the spraying must be done during periods of warm weather. The water has to evaporate quickly to avoid the onset of fungal diseases like gray mold.
Other forms of water are being tested to eliminate plant pests. For one project, researchers looked into how steam can decrease fungal and pest infections using what’s called the Plant Sauna.
In the Plant Sauna, plants are exposed to steam at up to 111.2 degrees Fahrenheit for one to four hours. The results were favorable, finding that steam was effective in protecting plants from various diseases.
But when it comes to spider mites, cold water sprays are the preferred method because the pests love heat and can survive in the Plant Sauna.
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