During heat wave periods, actual exterior temperatures can go up to 35 ºC in certain regions in Quebec. Tough conditions for agricultural workers and that have a negative impact on biological control agents. So, how is your biological control going?
Biological control agents – when heat strikes
It is shown by the plants around us, heat means accelerated growth. Generaly, when temperatures are between 20 and 28°C, it is a good growth window. Most biological control agents perform well under these conditions.
They are not the only ones, your pests too. For this reason, the use of a preventive control is favored before this critical period. The pest’s reproduction accelerates, the females become more fertile, the development period shortens and we must put in more beneficial insects and mites to overcome them.
When it’s too hot
When the temperature gets around 30°C, we can notice that certain biological control agents are less effective. The pest population continues to grow and is now harder to control.
So, if these conditions are present for a short period of time (1 or 2 days), the insects and mites will hide from the sun and try to find some shade, under leaves or in the ground substrate for example.
But when the situation persists, the insects, mites and nematodes start to be affected. The constant heat causes a drop in activity, a decrease in the number of eggs and above all, an increase in the mortality rate. Fortunately, above 30°C, pest reproduction (aphids, thrips, whiteflies and spider mites) start to slow down and mortality increases.
What to do in heat waves
- Choose biological control agents that is more tolerant to heat (ex : Amblyseius swirskii , Neoseiulus fallacis and Stethorus punctillum);
- Promote shadehouses installation;
- Mist the crops to help your predators hydrate;
- Introduce at the end of the day or in the morning;
- Introduce your biological control agent in the shade if possible (ex: put the trichogramma cards/ Encarsia formosa under the leaves);
- If you cannot introduce them for the moment (full sun, mid day, etc.), keep your agents fresh and contact your representative to know the conservation conditions of your agents;
- After the heat wave, reintroduce a small quantity of biological control agent to maintain a good population.
Good news for trichogramma
During the 2018 season, we informed our client of the potential danger of an actual temperature above 33°C for trichogramma based treatments (Tricho-Gard , Tricho-Maïs, Tricho-Poivron, etc.). We advised to delay the introduction for a couple of days or to place the cards in the shade, under foliage or in fuller rows.
Mylène St-Onge, scientific director of the insect division, wanted to test the impact of this heat wave on the emergence of trichogramma. Tuesday, July 3rd 2018, when the temperature rose close to 31°C, she installed the trichogramma cards under the shade, in a diverse market field. Thursday, July 5th 2018, the actual temperature climbed up to 34°C. Even in this extreme heat, the emergence rate was above 80% «It is really good considering the circumstances! » says Mylène.