As much as we all detest thrip , there are , candidly , worse problem to have . And it ’s name is Leafminer . These fly cause just about the slimy price we see in floriculture(Fig . 1 ) , and they have incredible pesticide - resistance capabilities . irruption seem to go in cycles , andI’ve had quite a few gerbera and momma crops make out across my desk with leafminerthis retiring 2 weeks .
This post coverschemical options(BawHawHawHa!!!Oh … Sorry … I ’ll get myself under control condition now ) andnon - chemicaloptions for leafminer , as well ashow their ascendancy go into the expectant picturein greenhouse IPM curriculum .
The Critter:
Several species of leafminers can attack glasshouse crops ( both vegetable and cosmetic ) , butall species are similar in terms of biology , damage , and control .
To find leafminer oncards or tape , attend for small black flies(2 - 3 mm ; a little diminished than a fungus gnat , but “ huskier”)with a yellow marker ( Figs . 2&3).Their feeler are barely seeable .
However , you ’re much more probable tonotice leafminer damage first , before you ever see them on cards . terms includesstippling(i.e.female vaporize ovipositing in , or feed in from leaves;Fig . 4 ) andmines created by the larvae feedingbetween the foliage epidermis layers(Fig . 1 ) .
Fig. 1. Leaf mines on gerbera leaves.
In later summer , the leafminer living cycle is quick : at 30C , it ’s only 14 days from egg to grownup , imply there will bemultiple , overlapping generations , and multiple life history stage present(making it intemperately to manage ) .
Additionally , at warm temperature , larvae can go through all 3 instars in 1 workweek – making bigger and long mines on leaves as they go . This means you could go from a clean harvest to a to a great extent damage one very quickly . For more elaborate information onleafminer biology , clickhere .
Chemical Control:
Time to sit down and grab a stiff drink if you ’ve get leafminer already , because the news program on the chemical front ai n’t good .
presently register pesticide – include Pounce / Ambush ( permethrin ) for adult and Avid ( abamectin ) , Citation ( cyromazine ) and Orthene ( acephate ) for larvae – are unable , most probably due to electric resistance . ( This is from first - hand experience in several operations this summertime ) . Even pesticide for other insects that you ’d think might cultivate tangentially for leafminer adults do n’t ( I ’m looking at you , DDVP ) .
Greenhouse vegetablegrowers have it slightly easier , since products containing relatively new systemic insecticides ( i.e. chlorantraniliprole or cyantraniliprole ) still show decent larval mastery . But , given leafminer ’s underground history , these are plausibly only going last for 2 - 3 sprays per mental process . Even our U.S. friends , with what seems like their plethora of pesticides , do n’t really have any good products(see the latest IR4 reporthere ) – which means we do n’t have any good pesticides coming down the pipeline , either.(Insert audible sigh here ) .
Fig. 2. An adult leafminer. Notice the characteristic yellow dot on the thorax and yellow markings between the eyes. Photo by S. Jandricic.
If you ’re adamant about trying pesticides for leafminer command , then batch ofyellow sticky cards for monitoring are a must . Without a microscope , it ’s difficult to distinguish old , empty minesfrom new ones . But glutinous card put up after a spray appropriate you to see if grownup leafminer are still come out from treated plants(see Fig . 5 ) .
Other Control Tactics:
So if you ca n’t spray the heck out of it , what CAN you do in the typeface of a leaminer infestation?Here ’s the direction plan as I see it .
STEP 3 : publish Parasitic Wasps . Diglyphus isaeareally IS your front line defence against leafminer . It ’s a very effective biocontrol agent , able to parasitize learminer larvae through the leaf .
The only caveat is thatDiglyphusis EXTREMELY sensible to pesticide residues . mean you ca n’t release it until about6 - 8 hebdomad after your last pesticide app .
Fig. 3. Adult leaminer from the side appears “hunchbacked”, and yellow markings are still visible. Photo by S. Jandricic.
The Big Picture:
unconstipated releases ofDiglyphus are the most successful strategy we have for controlling ongoing populations of leafminer(e.g . in gerbera and cut Chrysanthemum morifolium , where the crop continues year round ) . However , Diglyphus can be well pink out by chemical substance , and pesticide residues make it hard to easily re - introduce . Therefore , pest direction conclusion for ALL OTHER PESTS should be made with this in mind . Before you spray for a a sudden thrips or whitefly outbreak , consider the short - and farseeing - term repercussions on your leafminer programme , so you do n’t end up with a bigger trouble on your hands in a few weeks that has NO pesticide control choice .
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Fig. 4. Leaf stippling caused by leaf miner.
Fig.5. Different flying pests caught on sticky card in an Ontario greenhouse. Photo by S. Jandricic.
Diglyphus isaea on a yellow sticky card.
The egg of Diglyphus (circled in red) on the side of a leafminer larva.
