Biobest offers complete leafminer control strategy

Biocontrol options to control leafminer include two well-known natural enemies Diglyphus isaea and Dacnusa sibirica. “Biobest’s UK team has developed valuable experience in tomato on how to use these two parasitic wasps in a robust combination strategy. As leafminer pressure increases in tomato crops in the Netherlands, France and other Western European countries, more growers are adopting this highly effective control strategy, taking advantage of Biobest’s advice and broad product offering” says Biobest’s Product Manager for Macrobials, Yann Jacques.

Several species of Lyriomyza genus occur in commercial crops: most importantly the tomato leafminer (Lyriomyza bryoniae), the serpentine leafminer (L. trifolii) and the pea leafminer (L. huidobrensis). Leafminer has become a serious pest in European tomatoes. The main issue is the damage done by larvae tunneling through the leaf. These mines reduce the plants’ photosynthetic capabilities, slow down the production of flowers and ultimately affect fruit yield. Leafminer is particularly damaging for sweet tomato varieties where it develops faster. Leafminers also cause serious problems in cut flower crops. In ornamentals such as Chrysanthemum and Gerbera, the plant punctures made by adults feeding directly on the plant are a particular problem.

Phil Walker, General Manager of Biobest UK: ”In UK tomato crops we have developed quite some expertise using a combination of two complementary parasitic wasps - Diglyphus isaea and Dacnusa sibirica. We were able to develop robust strategies, capitalizing on the complementarity between the biological characteristics of these two parasitic wasps.”

Yann Jacques explains: “Effective early in the season, Dacnusa comes in first to manage and slow down the pest build up. To identify when to start introductions we recommend yellow Bug-Scan sticky traps to detect adults, plus regular inspection of the crop to look for the tell-tale stings.

Dacnusa has a very high search capacity and, hence, can already establish at very low pest densities. Dacnusa is an endoparasite. It lays eggs directly in leafminer larvae tunneling through the leaf. Dacnusa females looking to oviposit distinguish non-parasitised from parasitised leafminer larvae. Dacnusa is very well adapted to early season conditions, less to conditions prevailing later in the season or in the south. That is where Diglyphus has complementary strengths.

Diglyphus, explains Yann, is an ecto-parasite. “The female punctures a leafminer larva to paralyse it, before depositing an egg next to it. “Diglyphus not only parasitizes leafminer larvae, it also host feeds on young larvae. Capable of fast population build up, this wasp can rapidly gain control of a rising leafminer population.”

“Timing of Diglyphus-System introductions is vital and should start once a certain threshold has been exceeded. The threshold depends on specific conditions and can best be set in discussion with your Biobest advisor. Careful monitoring is crucial for the success of this strategy.