22
THECOMMERCIAL GREENHOUSEGROWER • MAY 2018
• CRO0 0ROTECTION
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the active is currently under regulatory review for Annex
II listing. David also feels that leaf hoppers are likely to
increase as a threat for ornamental growers, since there
are currently few control options apart frompyrethroids
andneonicotinoids, bothof which are largely incompatible
with IPMprotocols. “The invasionof newpests into the
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making the use of bio controls far harder,”warnsCaroline.
“For example if Stinkbug (Nezara) invades and it can
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ecosystem in the cropwill bewipedout. As deltametrin
is very persistent it will remainharmful formanyweeks.
Growers need to cleanup thoroughly at the endof the
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the longest residue freeperiodpossible.”
In the non-edible sector one of thebiggest pest
pressures comes from vineweevil, andSelchuk says
that there has been an increase in the use of IPM control
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it with conventional chemistry. “In the edibles sector,
tomato russetmite had abig impact on crops last year,”
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mainly in the south and north east of theUK. Thiswas
mainly due to an increase of importedplantmaterial
from the continent, coupledwith ideal conditions for
thepest in the spring and early summer. “Thebiggest
disease threat inprotected leafy salad crops is lettuce
fusariumwilt. Although it has beenprevalent for a number
of years, a recent outbreak of a new aggressive strain
has caused concern. Only a small number of growers in
Lancashire and Irelandhave experienced thediseasebut
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disease is a siNUifiJaU[ JVUJeYU [V [Oe iUd\s[Y` 7V^deY`
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bio-fungicides, as sporulation canoccur with the smallest
amount of leaf condensation, triggering rapid infection.
Although there are contact bio-fungicideswith activity
onpowderymildew, growers still rely on conventional
chemistry in high-risk periods.”When it comes to
controllingdiseases, adifferent approach is required
explainsDavid. “Diseases are continually evolving and
withnew strains developing that could have the ability
toovercome genetic resistance in varieties,” he says.
“That has beenwidely experiencedwithDownymildew
indigitalis and impatiens, andproven a continuous
battle inprotected lettuce for breeders to keep ahead
of Bremia. This year there have alsobeen concerns
over the incidence of Fusarium in lettuce too. “Disease
resistance has tobe considered among theprimary
factors for breeders indeveloping new varieties, and a
key element of any growers’ choice. There is a reasonable
arsenal of fungicides availability, particularly for protected
edibles.What we have seenover recent years is greater
awareness of preventative fungicideprogrammes
toprotect against initial infection.Withbetter risk
assessment, the focus on application timingwill be toget
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protected crops or under EAMU approval.”
“Most protected crops tend to have fairly limitedplant
protectionoptions available, and sogrowers rely on
a carefullymanagedbalance of agronomicpractices,
biological and chemical controls to achievemarketable
crops,” adds TimLacey, CampaignManager Horticulture
withBayer CropScience. “For example in soil-grown
protected lettuce crops, whereSclerotiniaminor can
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biological fungicide in the soil to reduce theSclerotinia
loading is very common. This is then followedby a
careful programme of foliar fungicideswhere required,
including the recently EAMU for LunaSensationwhich is
exceptionally strongon sclerotinia, botrytis andpowdery
mildew. In the large range of cropswherepowderymildew
is aproblem,manyBayer trials have shownSerenade
ASO to have a strong effect. Good application is critical
for success however, withgrowers having to ensure
very good uniform coverage of the leaf surfaceby using
appropriatewater volumes, nozzle sizes and the use of
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